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Journal of Animal Science - Animal Physiology

Growth and reproductive development of male piglets are more vulnerable to midgestation maternal stress than that of female piglets12

 

This article in JAS

  1. Vol. 92 No. 2, p. 530-548
     
    Received: June 02, 2013
    Accepted: Dec 16, 2013
    Published: November 24, 2014


    3 Corresponding author(s): lauriem@vet.upenn.edu
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doi:10.2527/jas.2013-6773
  1. L. A. Mack 3,
  2. D. C. Lay Jr.,
  3. S. D. Eicher,
  4. A. K. Johnson,
  5. B. T. Richert* and
  6. E. A. Pajor§
  1. Department of Animal Sciences, Purdue University, West Lafayette, IN 47907
    USDA-Agricultural Research Service, Livestock Behavior Research Unit, West Lafayette, IN 47907
    Department of Animal Science, Iowa State University, Ames, IA 50011
    Department of Production Animal Health, University of Calgary, Calgary, AB, CA T2N IN4

Abstract

In many mammalian species, prenatal stress masculinizes female and feminizes male offspring impairing their reproductive capacity. Regrouping gestating sows is a common, stressful production practice, but its impact on the developing pigs of the sow is not fully known. This study examined the effects of regrouping gestating sows and the administration of exogenous glucocorticoids on the growth and external reproductive morphology of pigs. At 37.2 ± 0.26 d of gestation, 6 cohorts of 18 sows (N = 108) were placed in 1 of 3 treatments: socially stable (Stable), hydrocortisone acetate (HCA), or mixed (Mixed). The HCA sows were administered 70 mg HCA, a synthetic glucocorticoid, twice daily during the 21 d experimental period. Each Mixed sow was penned with 2 companion sows (Companion) and regrouped on d 7 and 14 with 2 different Companion sows in a new pen. Stable and HCA sows were penned in treatment groups of 3 sows. Sow social rank was assessed weekly during feeding. After the 21 d experimental period, all sows were housed in gestation stalls for the duration of pregnancy. During the 21 d, Companion sows gained more weight than HCA and Mixed sows (P < 0.05) with Stable sows intermediate. High ranked sows gained more weight than middle and low ranked sows (P < 0.05). Mixed sows had greater head lesion scores than Stable and HCA sows (P < 0.05) with Companion sows intermediate. Head lesions increased with lower social rank (P < 0.001). Sow treatment did not affect farrowing rate, litter size, or sex ratio (P > 0.10). Social rank also had no effect on farrowing rate (P > 0.10), but affected total litter size (P = 0.03). High ranked sows bore and weaned more live females than low ranked sows (P < 0.05), in part due to differential preweaning mortality among female pigs (P = 0.01). Only male pigs were affected by sow treatment. Preweaning mortality was higher among male pigs from HCA than from Mixed sows (P = 0.04) with other treatments intermediate. Despite no weight differences in the preweaning period, at 160 d of age males from HCA sows weighed more than males from Stable sows (P = 0.01) with other treatments intermediate. Males born to Companion sows had longer relative anogenital distances, a marker of fetal testosterone exposure, than males from Mixed sows (P = 0.03) with other treatments intermediate. The prenatal environment affected the pigs in a sex-specific manner altering the growth and reproductive morphology of the males more than that of the females.



INTRODUCTION

Regrouping gestating sows increases aggression and glucocorticoid (GC) synthesis which exposes the fetal pigs to stress. The aggression may be lasting (Tsuma et al., 1996b; Arey and Edwards, 1998) and impair feeding of low ranked sows (Kongsted, 2005), especially if competitively fed. Such prenatal stress can alter reproductive development of fetal rodents and sheep. In male rodents, it reduces testes weight (Mairesse et al., 2007), fertility (Crump and Chevins, 1989), and mounting behavior (Rhees and Fleming, 1981). Comparably, female rodents may have lighter uteri (Marchlewska-Koj et al., 2003), delayed puberty (Baker et al., 2009), and conceive less (Herrenkohl, 1979). In sheep, maternal undernutrition can reduce development of the testes (Bielli et al., 2002) and lamb yield (Long et al., 2010). Rodent study results suggest maternal GC may suppress fetal androgen synthesis in male progeny (Ward and Weisz, 1984; von Holst, 1998), whereas increases in maternal androgens may alter female progeny (vom Saal et al., 1990).

The effects of prenatal stress on swine reproductive development are not as well elucidated. Maternal gestational stress and housing can alter female pigs’ puberty (O’Gorman et al., 2007; Estienne and Harper, 2010) and reduce ovarian follicles (Ashworth et al., 2011) and litter size (Jarvis et al., 2006). In male pigs, it can reduce anogenital distance (Lay et al., 2008), a biomarker for fetal androgen exposure during sexual differentiation, and postnatal reproductive hormone concentrations (Ashworth et al., 2011).

This research examined the effects of maternal stress due to GC administration, regrouping, and social rank on sow health and physiology and the external reproductive morphology, growth, and mortality of developing pigs. In addition to anogenital distance, fetal androgen exposure may also alter gilt teat development and impact nursing capacity (Drickamer et al., 1999).


MATERIALS AND METHODS

Procedures in this experiment were approved by the Purdue Animal Care and Use Committee (PACUC Number 09–065) and researchers and caretakers were qualified by PACUC for swine handling and techniques.

Treatments

The experiment used 3 sow treatments: socially stable (Stable), hydrocortisone acetate (HCA), and mixed (Mixed). A fourth set of sows served as companions (Companion) to the Mixed sows. All data except for endocrine analyses were collected from Companion sows in addition to treatment sows. For ease of communication, subsequent uses of the term ‘treatment’ will refer to all 4 groups of sows. Sows in the HCA treatment received 70 mg HCA (0.24 to 0.54 mg kg-1, CO-138, Spectrum Chemicals and Laboratory Products, Gardena, CA) in gelatin capsules (VWR, Radnor, PA) twice daily between 0600 h and 0700 h and 1600 h and 1700 h during the 21 d experimental period. At the same times, Stable, Mixed, and Companion sows received a placebo capsule containing 70 mg glucose (D-glucose, Sigma-Aldrich, St. Louis, MO) in place of the HCA. Each capsule was embedded in a cookie (Daddy Ray’s Strawberry Bars, Moscow Mills, CO) and hand fed to the sows. Hydrocortisone acetate, a synthetic GC, was used to model increased cortisol production induced by stress based on the findings of Kranendonk et al. (2005) who determined 0.30 to 0.37 mg kg-1 HCA increased gestating sow cortisol concentrations in magnitude comparably to a psychological stressor.

All the experimental pens were created in the morning on ED 0 of sows that had not been previously housed together during the current pregnancy. Stable and HCA sows were penned in groups of 3 by treatment; each Mixed sow was penned with 2 Companion sows. The first capsules, containing either HCA or glucose, were administered in the afternoon on ED 0. From experimental day (ED) 0 until 7, Stable, Mixed, and Companion sows were treated identically. On ED 7 and 14 following blood collection and HCA administration, each Mixed sow was moved into a new pen containing 2 unfamiliar Companion sows. At the end of the experimental period, each Mixed sow had been housed for 7 d in 3 different pens which resulted in exposure to 6 different Companion sows. The Companion sows were kept together, 2 per pen, and did not move, but received a new Mixed sow in their pens on ED 7 and 14. Stable and HCA sows remained in their initial pen throughout the experimental period.

Sow Social Rank

During regular feeding on ED 4, 11, and 18, social rank was determined by live observation. A researcher evaluated the social interactions to determine whether a given sow was dominant or subordinate in each dyadic relationship. Within each dyad, the dominant sow exhibited predominantly aggressive and feed defensive behaviors, whereas the subordinate sow predominantly exhibited avoidance behaviors (Table 1). The highest ( = 1), middle ( = 2), and lowest ( = 3) ranked sows were dominant in both, 1, and no dyadic relationships, respectively. No circular triads were observed. For the purposes of analysis, the sows’ average rank score was used and assigned based on bins of < 1.67 “high rank”, 1.67 to 2.4 “middle rank”, and > 2.4 “low rank.” The standard deviations of individual social rank scores were analyzed to assess social stability.


View Full Table | Close Full ViewTable 1.

Behaviors used to assess dyadic social relationships between sows

 
Category Behavior Description
Dominant
Feed restriction Sow defends feed and prevents other sow from eating
Bite Sow’s open mouth forcefully contacts other sow
Head knock Sow’s closed mouth forcefully contacts other sow
Bite threat With the mouth open or closed, sow thrusts head in the direction of other sow, often performed at a distance
Chase Sow rapidly follows fleeing sow
Subordinate
Retreat Sow flees from other sow
Keeps head averted Sow’s face is kept turned away from the other sow; eye contact is avoided
Turn head away Sow turns face away from other sow, often accompanied by lowering head
Lowering head Sow lowers head, usually to or below shoulder height
Stand behind Sow stands to the rear of other sow’s shoulders while eating

Animals and Housing

Six breeding cohorts composed of 18 gestating Landrace × Yorkshire pigs (N = 108) that ranged from nulliparous to parity 6 (mean = 1.90 ± 0.14), referred to inclusively as sows, were used. From breeding until ED 0, sows were housed either in individual stalls or small groups. One week before treatment commencement (gestational day [GD] 27.19 ± 0.26) sows were confirmed pregnant via real-time ultrasound, balanced by housing, and assigned to their treatments. Additionally, the Stable, HCA, and Mixed treatments were balanced by parity. However, to reduce the risk of injury and excessive stress for Mixed sows, Companion sows were selected to be of equivalent or lower parity than their Mixed pen mates. This resulted in the Companion sows having a numerically lower, but not significantly different, mean parity than the other treatments. During the intervening week, sows from all treatments were trained to eat hand-fed cookies and did so consistently within 5 d of initial training.

The experimental barn contained 6 pens (Fig. 1) with 1 Stable pen, 1 HCA pen, 3 Mixed pens, and 1 pen that alternated between Stable and HCA by breeding cohort. Each pen had partially slatted concrete flooring and provided 1.5 m2/sow. Sows had ad libitum access to water via a nipple drinker in each pen. Once per day, sows were floor fed approximately 2.3 kg of a gestational diet composed of 56 to 66% corn, 8 to 10% soybean meal, and 20 to 30% dried distillers’ grains with solubles which provided 3330 kcal ME kg-1, 0.50% true ileal digestible lysine, 0.80% Ca, and 0.40% available P. On ED 21, sows were moved into gestation stalls where they remained until being moved to farrowing stalls at approximately 1 wk before parturition. In the farrowing facility, sows were fed approximately 2.5 kg of a lactational diet once daily before farrowing and the same diet ad libitum after farrowing. The lactational diet was composed of 57 to 61% corn, 24% soybean meal, and 7.5 to 10% dried distillers’ grains with solubles which provided 3400 kcal ME kg-1, 0.85% true ileal digestible lysine, 0.90% Ca, and 0.50% available P.

Figure 1.
Figure 1.

Sample pen layout. Sows in Stable and hydrocortisone acetate (HCA) treatments were penned by treatment and remained together through the 21 d experimental period. Each Mixed pen had 2 companion sows (Companion, indicated by the darker color) that did not relocate and 1 sow in the mixed treatment (Mixed) that moved to a new Mixed pen on experimental d 7 and 14. See online version for figure in color.

 

Surgical castration of male piglets was performed at 3 d of age by the researchers. All other piglet processing, which included ear notching, tail docking, teeth clipping, and an iron injection, was performed by the farm staff at 2.45 ± 0.18 d of age following the standard farm protocol. To model commercial practices, all piglet processing was conducted without the use of anesthesia or analgesia. Piglets were weaned at 18.73 ± 0.30 d of age.

Gestational Sow Measures

Health Measures.

Sow BW was recorded on ED 0 (baseline), ED 21, 2 d after farrowing, and at weaning. Skin lesions were evaluated on ED -1 (baseline), 4, 11, and 18 using a 6-point scale (Table 2) adapted from Hodgkiss et al. (1998) and Arey (1999). Seven body regions, 1) head, neck, and shoulders; 2) body and udder; 3) rump, tail, and vulva; 4) upper leg; 5) hock, knee, and pasterns; 6) hooves and toes; and 7) dewclaws, were independently scored for a total possible score of 35.


View Full Table | Close Full ViewTable 2.

Skin lesion scores1,2

 
Score Description
0 Normal
1 Reddening or callus
2 < 10 scratches and no cuts3
3 ≥ 10 scratches, < 5 cuts, 1 superficial wound, or 1 abscess
4 ≥ 5 cuts, 1 deep wound, > 1 superficial wound, or > 1 abscess
5 ≥ 10 cuts or ≥ 5 wounds
2If lesions in one region met the criteria for more than 1 score, the greater of the 2 scores was assigned.
3A scratch had unbroken skin, a cut had broken skin < 2 cm in width and a wound had broken skin ≥ 2 cm in width.

Endocrine Measures.

At 0700 h on ED -1 (baseline), 1, 7, and 14 blood was collected from sows in the 3 treatment groups by jugular venipuncture into two 13 × 75 mm, 4.0 mL draw lithium heparin venous blood collection tubes (Becton Dickinson, Franklin Lake, NJ) for plasma cortisol and progesterone analyses. Increased progesterone concentrations have been observed in swine in response to exogenous GC (Schneider et al., 2004; Brussow et al., 2005) and feed restriction (Razdan et al., 2004) which may have androgenic, or conversely, anti-androgenic effects of developing offspring (Cohen-Bendahan et al., 2005). On these days, HCA administration was delayed until after the collection. Blood was stored on ice before plasma separation by centrifugation at 1800 × g for 15 min at –4°C (Sorvall RC 3B Plus centrifuge, Thermo-Fisher, Asheville, NC). Plasma was stored at –80°C until analysis.

Plasma cortisol concentration was determined using duplicate samples according to the manufacturer’s instructions (CA1529 Clinical Assays GammaCoat Cortisol 125I RIA Kit, Diasorin, Stillwater, MN). The kit had a sensitivity of 5.79 nmol/L and was previously validated for use with swine plasma (Haussmann et al., 2000). The intra- and interassay coefficients of variation were 9.5% and 8.1%, respectively.

Plasma samples were assayed in duplicate for progesterone concentration using a commercial kit (TKTT1 Coat-A-Count Progesterone, Siemens, Tarrytown, NY) with a sensitivity of 0.06 nmol/L that was previously validated for swine plasma (Mao and Foxcroft, 1998). Serial dilutions were performed in duplicate to establish linearity and the appropriate sample dilution of 75 μL Zero Calibrator Matrix (Siemens) to 25-μL sample. The remainder of the assay was performed according to manufacturer’s directions. The intra- and interassay coefficients of variation were 15.7% and 2.7%, respectively.

Sow Productivity and Piglet Measures

The gestation length and farrowing rate (number farrowed/number pregnant at GD 27 × 100) within each cohort were calculated. The numbers of pigs born, liveborn, stillborn and mummies, weaned, and males and females at birth and weaning; the testes weight of the males at 3 d of age; and the number of teats elevated above the abdominal surface of both sexes at 3 d of age were recorded. Sex ratio was calculated as the number of males/number of females. Preweaning mortality equaled the percentage of liveborn pigs that died before weaning. At birth, male anogenital distance, between the anus and the urethral opening, was measured with a tape measure while holding the pig on its back with its legs outstretched. Female anogenital distance was measured between the anus and genital papilla using calipers (Mitutoyo 500–196–20 Absolute Digimatic Calipers, Aurora, IL). The researchers collecting piglet measurements were familiar with the experimental design, but were effectually blind to treatment at the time of the measurements. Relative anogenital distance (ANO) equaled the anogenital distance, mm/pig BW, kg. Relative testis weight equaled the mean testis weight, g/pig BW, kg.

Pig BW was recorded at birth; at 3, 7, and 14 d of age; at weaning; and at 160 ± 0.37 d of age. The average daily gain (ADG) was calculated as: (final BW, kg– initial BW, kg)/time interval, d × 1,000, for all time intervals between weight recordings. If litters had pigs cross-fostered onto the sow or removed from the sow, data from the litter were used for day of birth measures, number of teats, and testes weight only.

Statistical Analysis

The data were analyzed with a multilevel mixed model (SAS 9.2, SAS Inst. Inc., Cary, NC) and are presented as least squares means ± SE unless otherwise stated. To normalize the distribution and equalize the variances of residuals, the number of stillborn pigs and cortisol and progesterone concentrations were square root transformed and the percentage of pigs stillborn, the preweaning mortality of the litter, and the female pig preweaning mortality data were angularly transformed. The least square means ± SE of untransformed data are shown to aid interpretation. All analyses included the fixed effects of treatment and sow rank and their interaction except for social stability which only included treatment. Covariates included in the model were number of pigs born for gestation length and mortality, number of females in the litter for male ANO and relative testis weight, number of males in the litter for female ANO and teat number, and baseline data (ED -1) for sow BW, lesion scores, and plasma hormone concentrations. Random effects included replication and pen nested in replication. The group option on the random statement allowed the covariance parameters to differ among groups. The groups, determined by the treatment’s amount of sow regrouping, were 1) Stable and HCA, 2) Mixed, and 3) Companion. Hormone concentrations also included time and its interactions as fixed effects with correlations over time modeled by R-side random effects (SAS Inst. Inc.; Schabenberger, 2005) with sow nested in rank by treatment by replication as the subject. Hierarchical linear modeling (nesting) was used to correct the error term and control for Type I error inflation due to pseudoreplication (Hurlbert, 1984; St-Pierre, 2007; Picquelle and Mier, 2011). The denominator degrees of freedom were approximated using the Kenward-Roger method recommended for unbalanced data (Kenward and Roger, 1997; Littell et al., 2006). Simple effects of significant interactions were used to examine the effect of one independent variable within a level of the second independent variable. The Tukey-Kramer adjustment was used to reduce experiment-wise error when multiple comparisons were made (Hayter, 1984). Spearman rank correlations were determined between sow BW, parity, and social rank. Statistical significance was set at P < 0.05 with a trend between 0.05 ≤ P ≤ 0.10.


RESULTS

Gestational Sow Measures

Health Measure: Parity and BW

(Table 3). There were no differences in sow parity or baseline BW among treatments. There was also no relationship between a sow’s social rank and baseline BW. In contrast, parity influenced social rank; high ranked sows tended to be higher parity than middle ranked (P = 0.07) and were higher parity than low ranked (P = 0.007) sows. However, baseline BW and parity were more strongly positively correlated to each other (rs = 0.75, P < 0.001) than either were with social rank (BW: rs = 0.21, P = 0.04; parity: rs = 0.31, P = 0.002). Companion sows changed rank more than HCA sows (P = 0.03) with rank change among Stable and Mixed sows intermediate to the other treatments.


View Full Table | Close Full ViewTable 3.

Sow social rank stability and BW by treatment and social rank1

 
Item Treatment2 P-value Social rank3
HCA Stable Mixed Companion High Middle Low P-value
Parity 1.9 ± 0.3 1.8 ± 0.3 2.2 ± 0.4 1.3 ± 0.3 0.15 2.4 ± 0.3a,x 1.7 ± 0.3y 1.4 ± 0.3b,y 0.009
Rank stability4 0.18 ± 0.08b 0.45 ± 0.08a,b 0.51 ± 0.11a,b 0.55 ± 0.07a 0.05
BW, kg
ED5 0 205.5 ± 5.6 200.0 ± 5.6 200.9 ± 7.8 184.8 ± 6.6 0.12 207.8 ± 5.2 193.4 ± 5.5 192.3 ± 6.7 0.09
ED 21 208.0 ± 5.5 207.1 ± 5.5 199.9 ± 8.0 195.6 ± 6.5 0.37 218.1 ± 5.4a 197.3 ± 5.5b 192.6 ± 6.7b 0.004
2 d post-farrowing 235.6 ± 6.1 234.1 ± 6.1 226.5 ± 8.1 216.6 ± 6.9 0.10 237.7 ± 5.8x 222.6 ± 5.9y 224.2 ± 7.0x,y 0.09
Weaning 218.9 ± 5.8 218.4 ± 5.8 216.5 ± 7.8 205.3 ± 6.5 0.27 222.9 ± 2.6 211.9 ± 5.6 209.5 ± 6.8 0.15
Δ BW, ED 0 to 21 2.6 ± 1.4b,c 6.8 ± 1.4a,b 0.2 ± 1.8c,d 10.6 ± 1.5a < 0.001 11.1 ± 1.2a 3.9 ± 1.2b 0.1 ± 1.5b < 0.001
Δ BW, lactation -16.6 ± 6.7 -16.3 ± 3.7 -11.7 ± 3.7 -10.6 ± 3.4 0.40 -13.6 ± 3.0 -12.0 ± 3.0 -15.8 ± 3.4 0.51
a–dLeast square means ± SE within the same row and main effect with different superscripts are different (P < 0.05).
x,yLeast square means ± SE within the same row and main effect with different superscripts tend to be different (0.05 ≤ P ≤ 0.10).
1The analyses used 27 HCA, 27 Stable, 18 Mixed, and 35 Companion sows and 41 high, 41 middle, and 25 low ranked sows.
2HCA = received 70 mg hydrocortisone acetate (HCA) twice daily; Stable = control group; Mixed = moved to new pen weekly; Companion = received a new pen mate weekly.
3Social rank was identified during feeding. High rank = sow dominant in both dyadic relationships; middle rank = sow dominant in 1 dyadic relationship; low rank = sow subordinate in both dyadic relationships (Table 1).
4Rank stability is the standard deviation of the social rank scores. Lower numbers indicate greater stability.
5ED = experimental day.

Sow weight gain during the experimental period exhibited a treatment by social rank interaction (P = 0.01; Fig. 2). High ranked HCA (P < 0.001), Stable (P = 0.003), Mixed (P = 0.05) sows gained more weight than low ranked sows of the same treatment, but among Companion sows the social ranks did not gain weight differentially. Additionally, high ranked HCA (P = 0.03) and Stable (P = 0.002) sows gained more weight than middle ranked sows of their treatment. Within the low ranked sows, Companion (P < 0.001) and Stable (P = 0.02) sows gained more weight than Mixed sows. Low ranked Companion sows also gained more weight than low ranked HCA sows (P < 0.001). Overall, Companion sows gained more weight than HCA (P = 0.002) and Mixed (P < 0.001) sows and Stable (P = 0.02) sows gained more weight than Mixed sows (Table 3). Also, high ranked sows gained more weight than middle (P < 0.001) or low (P < 0.001) ranked sows overall (Table 3). Sow BW did not differ between treatments on any day, but did differ by social rank (Table 3). High ranked sows weighed more at the end of the experimental period than middle (P = 0.02) and low (P = 0.01) ranked sows and tended to weigh more after farrowing than middle ranked sows (P = 0.10). Weight loss during lactation showed a treatment by social rank interaction (P = 0.04), but neither the main effect of treatment nor social rank differed (Table 3). Low ranked Mixed sows lost more weight than Companion sows (P = 0.05) of the same rank. Litter size also affected lactational weight loss with weight loss increasing with litter size (P = 0.01, data not shown).

Figure 2.
Figure 2.

Sow BW gain (least square means ± SE) during the experimental period. Sows in the hydrocortisone acetate (HCA) received 70 mg HCA twice daily; Stable sows were controls; Mixed sows were moved to a new pen weekly; and Companion sows received a new pen mate weekly. High rank sows were dominant to both pen mates; middle ranked sows were dominant to 1 pen mate; and low ranked sows were subordinate to both pen mates. The analysis used 27 HCA, 27 Stable, 18 Mixed, and 35 Companion sows and 41 high, 41 middle, and 25 low ranked sows. Sow BW gain differed (P < 0.05) among social ranks (a,b) within a single treatment and among treatments (x,y) within a single social rank that do not share a letter. See online version for figure in color.

 

Health Measures: Skin lesions.

Overall, head area lesions were affected by treatment (P = 0.008; Fig. 3a) such that Mixed sows had greater lesions scores than HCA and Stable sows with Companion sows intermediate to but not different than the other treatments. Social rank also affected head lesions (P < 0.001; Fig. 3b). Low ranked sows had greater scores overall than either middle or high ranked sows and middle ranked sows also had greater scores than high ranked sows. Additionally head lesions varied over time (P < 0.001) such that scores were greater on ED 11 than 4 (P = 0.04), but lower on ED 18 then either previous day (P < 0.001).

Figure 3.
Figure 3.

Head and body area lesions (least square means ± SE) by sow treatment (a, c respectively) and social rank (b, d respectively). Lesions were scored from 0 (least) to 5 (worst; Table 2). Experimental day -1 results were used as a covariate in the analyses. Sows in the hydrocortisone acetate (HCA) received 70 mg HCA twice daily; Stable sows were controls; Mixed sows were moved to a new pen weekly; and Companion sows received a new pen mate weekly. High rank sows were dominant to both pen mates; middle ranked sows were dominant to 1 pen mate; and low ranked sows were subordinate to both pen mates. The analyses used 27 HCA, 27 Stable, 18 Mixed, and 35 Companion sows and 41 high, 41 middle, and 25 low ranked sows. (d) Social ranks that do not share a letter had different (P < 0.05) body lesion scores on the days indicated. See online version for figure in color.

 

Body lesions had a treatment by time interaction (P = 0.01; Fig. 3c) in which there was no difference between treatments on ED 4 or 11, but on ED, 18 Mixed sows tended to have greater scores than HCA sows (P = 0.05) and had greater scores than Stable sows (P = 0.02) with Companion sows’ scores between those of Mixed and HCA sows. There was no overall effect of treatment on body lesions (P = 0.06), but there was of time (P = 0.007) so that scores decreased between ED 11 and 18 (P = 0.005). There was also a rank by time interaction (P = 0.03; Fig. 3d) in which the social ranks did not differ on ED 4 (P = 0.70), but on ED 11 (P = 0.02) and 18 (P < 0.001) low ranked sows had higher scores than high ranked with middle ranked sows intermediate. Overall, social rank (P = 0.02) affected body lesions so that low ranked sows had greater scores than high ranked sows (P = 0.04).

Rump area lesions (Table 4) did not differ between treatments or social rank overall, but showed a social rank by time interaction (P = 0.03). On ED 11, lesion scores were greater among low than high ranked sows (P = 0.02) with middle ranked sows intermediate but not different than the other ranks, whereas on all other days the social ranks did not differ. Overall rump area lesion scores changed over time (P < 0.001) having been lower on ED 4 than either ED 11 (P < 0.001) or 18 (P = 0.005) and higher on ED 18 than 11 (P < 0.001).


View Full Table | Close Full ViewTable 4.

Sow skin lesions1 by treatment and social rank2

 
Body region5 Treatment3 P-value Social rank4 P-value
HCA Stable Mixed Companion High Middle Low
Rump 3.35 ± 0.20 3.36 ± 0.16 3.70 ± 0.20 3.52 ± 0.19 0.35 3.27 ± 0.15 3.52 ± 0.17 3.66 ± 0.20 0.12
Upper leg 2.72 ± 0.16 2.68 ± 0.14 3.10 ± 0.10 3.08 ± 0.15 0.08 2.61 ± 0.09b 3.02 ± 0.10a 3.05 ± 0.13a < 0.001
Lower leg 2.37 ± 0.20 2.45 ± 0.18 2.66 ± 0.20 2.27 ± 0.16 0.40 2.31 ± 0.14 2.54 ± 0.16 2.47 ± 0.17 0.40
Hoof and toe 2.33 ± 0.16 2.49 ± 0.16 2.32 ± 0.15 2.50 ± 0.15 0.35 2.28 ± 0.13b 2.39 ± 0.13a,b 2.56 ± 0.14a 0.06
Dewclaw 2.14 ± 0.14 2.21 ± 0.12 2.13 ± 0.16 2.11 ± 0.16 0.96 2.04 ± 0.13 2.29 ± 0.04 2.18 ± 0.12 0.61
a,bLeast square means ± SE within the same row and main effect with different superscripts are different (P < 0.05).
1Higher lesions scores indicate more lesions and more severe lesions on a scale from 0 to 5 (Table 2).
2The analyses used 27 HCA, 27 Stable, 18 Mixed, and 35 Companion sows and 41 high, 41 middle, and 25 low ranked sows.
3HCA = received 70 mg hydrocortisone acetate (HCA) twice daily; Stable = control group; Mixed = moved to new pen weekly; Companion = received a new pen mate weekly.
4Social rank was identified during feeding. High rank = sow dominant in both dyadic relationships; middle rank = sow dominant in 1 dyadic relationship; low rank = sow subordinate in both dyadic relationships (Table 1).
5Rump lesions = rump, tail, and vulva and lower leg = hock, knee, and pasterns.

Upper leg lesion scores (Table 4) exhibited a treatment by social rank interaction (P = 0.01). Low (P = 0.02) and middle (P < 0.001) ranked Mixed sows had greater scores than high ranked Mixed sows, but there was no difference between social ranks in the other treatments. This created an overall difference in social rank. There was no overall difference among treatments for upper leg lesions. Time (P = 0.04) also influenced upper leg lesions such that scores were greater on ED 4 than 18 (P = 0.03) with ED 11 intermediate to and not different from the other days. Unlike any other body region, lower leg lesions (Table 4) were not affected by treatment, social rank, or time (P = 0.51).

Hoof and toe lesions (Table 4) also were not affected by treatment, but tended to differ by social rank such that low ranked sows had greater lesion scores than high ranked (P = 0.05) with middle ranked sows intermediate to but not different than the other ranks. They also changed over time (P < 0.001) with sows having had higher lesion scores on ED 11 than 4 (P < 0.001) or 18 (P = 0.02). Dewclaw lesions (Table 4) were not affected by treatment or social rank, but were by time (P < 0.001). Again scores were greater on ED 11 than 4 (P < 0.001) or 18 (P = 0.01).

Endocrine Measures.

The plasma cortisol concentration exhibited a treatment by time interaction (P = 0.004; Fig. 4a) that resulted from HCA sow concentrations having been greater than the other treatments on ED 1 (P < 0.001), tending to be greater on ED 7 (Stable: P = 0.08; Mixed: P = 0.07), but no longer being different on ED 14. This caused an overall effect on both treatment (P < 0.001) and time (P < 0.001). Social rank did not affect cortisol concentration (P = 0.25; Fig. 4b). Plasma progesterone concentration was not affected by treatment (P = 0.47; Fig. 4c) or time (P = 0.32), but was altered by social rank (P = 0.02; Fig. 4d). High ranked sows had higher progesterone concentrations than middle ranked sows and tended to have higher concentrations than low ranked sows.

Figure 4.
Figure 4.

Plasma cortisol and progesterone (P4) concentrations (least square means ± SE) by sow treatment (a and c respectively) and social rank (b and d respectively). Experimental day -1 results were used as a covariate in the analyses. Sows in the hydrocortisone acetate (HCA) received 70 mg HCA twice daily; Stable sows were controls; Mixed sows were moved to a new pen weekly; and Companion sows received a new pen mate weekly. High rank sows were dominant to both pen mates; middle ranked sows were dominant to 1 pen mate; and low ranked sows were subordinate to both pen mates. The analyses used 23 HCA, 25 Stable, and 16 Mixed sows and 25 high, 23 middle, and 16 low ranked sows. (a) Treatments that do not share a letter had different cortisol concentrations (P < 0.05) on the day indicated. See online version for figure in color.

 

Sow Productivity and Piglet Measures

The farrowing rate did not differ by treatment (P = 0.83) or social rank (P = 0.75). The mean farrowing rates of the sows in each treatment were HCA: 94.44 ± 13.61%, Stable: 94.44 ± 13.61%, Mixed: 88.89 ± 17.21%, and Companion: 97.22 ± 6.80%. The average farrowing rate of high, middle, and low ranked sows were 97.62 ± 5.83%, 94.58 ± 8.72%, and 92.50 ± 5.24% respectively (data not shown). Gestation length (Table 5) did not differ by treatment, but tended to differ by social rank such that high ranked sows tended to have longer gestational periods than low ranked sows (P = 0.09).


View Full Table | Close Full ViewTable 5.

Sow productivity and piglet measures by sow treatment and social rank1

 
Item Treatment2 P-value Social rank3 P-value
HCA Stable Mixed Companion high middle low
Gest length4, d 116.3 ± 0.2 116.3 ± 0.2 115.6 ± 0.5 115.6 ± 0.3 0.13 116.5 ± 0.3x 115.8 ± 0.3x,y 115.6 ± 0.3y 0.08
total no. born 10.74 ± 0.97 10.88 ± 0.95 10.58 ± 0.78 11.85 ± 0.76 0.74 12.39 ± 0.50x 10.35 ± 0.58y 10.30 ± 0.72y 0.03
Sex ratio5 1.38 ± 0.16 1.20 ± 0.16 1.12 ± 0.20 1.28 ± 0.14 0.80 1.02 ± 0.13 1.36 ± 0.14 1.35 ± 0.18 0.22
No. liveborn 9.65 ± 1.41 10.04 ± 1.30 9.88 ± 0.80 11.26 ± 0.83 0.70 11.26 ± 0.56 9.70 ± 0.68 9.67 ± 0.75 0.17
Sex ratio 1.42 ± 0.18 1.11 ± 0.17 0.98 ± 0.17 1.36 ± 0.13 0.23 0.98 ± 0.13 1.27 ± 0.13 1.40 ± 0.18 0.13
No. weaned 9.07 ± 0.64 8.53 ± 0.59 8.87 ± 0.70 9.67 ± 0.52 0.60 9.98 ± 0.45 8.69 ± 0.48 8.43 ± 0.64 0.11
Sex ratio 1.48 ± 0.22 1.32 ± 0.20 1.20 ± 0.26 1.67 ± 0.19 0.52 0.95 ± 0.17b 1.35 ± 0.18a,b 1.95 ± 0.23a 0.01
Born dead6, % 5.99 ± 1.76 5.78 ± 1.73 9.48 ± 3.45 6.14 ± 2.25 0.78 6.97 ± 1.93 7.64 ± 2.07 5.93 ± 2.44 0.88
a,bLeast square means ± SE within the same row and main effect with different superscripts are different (P < 0.05).
x,yLeast square means ± SE within the same row and main effect with different superscripts tend to be different (0.05 ≤ P ≤ 0.10).
1The analyses used 25 HCA, 26 Stable, 15 Mixed, and 35 Companion sows and 40 high, 40 middle, and 21 low ranked sows.
2HCA = received 70 mg hydrocortisone acetate (HCA) twice daily; Stable = control group; Mixed = moved to new pen weekly; Companion = received a new pen mate weekly.
3Social rank was identified during feeding. High rank = sow dominant in both dyadic relationships; middle rank = sow dominant in 1 dyadic relationship; low rank = sow subordinate in both dyadic relationships (Table 1).
4Gest length = gestation length.
5Sex ratio = number of males/number of females.
6Includes stillborn pigs and mummies.

The numbers of pigs born, liveborn, and weaned were not affected by sow treatment (Table 5). The number of males born, which included both live- and stillborn pigs, tended to differ by treatment (P = 0.09; Fig. 5a). Mixed sows were the only treatment sows that bore numerically fewer males than females and they tended to have had fewer males than Companion sows. However, there was no difference in the number of liveborn males (P = 0.19; Fig. 5c) or males weaned (P = 0.25; Fig. 5e) among treatments. Sow treatment did not affect the numbers of female pigs born (P = 0.85; Fig. 5a), liveborn (P = 0.83; Fig. 5c), or weaned (P = 0.56; Fig. 5e). Sow treatment also had no effect on the sex ratio of pigs born, liveborn, or weaned (Table 5). Neither the number of stillborn pigs and mummies (P = 0.92, data not shown) nor their percentage in the litter (Table 5) was associated with sow treatment.

Figure 5.
Figure 5.

Numbers of total, liveborn, and weaned male and female pigs (least square means ± SE) by sow treatment (a,c, and e respectively) and social rank (b, d, and e respectively). Sows in the hydrocortisone acetate (HCA) received 70 mg HCA twice daily; Stable sows were controls; Mixed sows were moved to a new pen weekly; and Companion sows received a new pen mate weekly. High rank sows were dominant to both pen mates; middle ranked sows were dominant to 1 pen mate; and low ranked sows were subordinate to both pen mates. The analyses used 25 HCA, 26 Stable, 15 Mixed, and 35 Companion sows and 40 high, 40 middle, and 21 low ranked sows. See online version for figure in color.

 

High ranked sows tended to farrow more piglets than middle ranked (P = 0.06) or low ranked (P = 0.09) sows, but social rank did not affect the numbers of piglets liveborn or weaned (Table 5). Social rank did not influence the number of males born (P = 0.58; Fig. 5b), liveborn (P = 0.75; Fig. 5d), or weaned (P = 0.84; Fig. 5f). In contrast, social rank was associated with the number of female pigs born (Fig. 5). High ranked sows tended to farrow more female pigs (P = 0.07; Fig. 5b), bore more liveborn females (P = 0.04; Fig. 5d), and weaned more female pigs (P = 0.01; Fig. 5f) than low ranked sows. High ranked sows also tended to wean more females pigs than middle ranked sows (P = 0.07). The sex ratio did not differ by social rank for the numbers of pigs born or liveborn (P = 0.13), but did for pigs weaned (Table 5). High ranked sows had a lower male:female ratio than low ranked sows (P = 0.006) with sex ratios from middle ranked sows intermediate to but not different than the other ranks. Like sow treatment, the number of stillborn pigs and mummies (P = 0.61, data not shown) and their percentage in the litter (Table 5) was not associated with sow social rank.

Overall preweaning mortality was not affected by treatment (P = 0.88; Fig. 6a), but tended to differ by social rank (P = 0.10; Fig. 6b) such that pig mortality tended to be greater among low than high ranked sows (P = 0.09). The overall tendency for mortality to differ by dominance was attributable to female mortality which differed by social rank (P = 0.01) such that female piglet mortality was greater among low than high ranked sows with middle ranked sows intermediate but not different than the other social ranks. Female piglet mortality was not affected by sow treatment (P = 0.35). In contrast, male piglet mortality differed among treatments (P = 0.02). Male pigs from HCA sows had a higher percentage of preweaning mortality than males from Mixed and Stable sows. Social rank did not affect the mortality of male pigs (P = 0.75).

Figure 6.
Figure 6.

Percentage of preweaning mortality (least square means = ± SE) of male and female piglets by sow treatment (a) and social rank (b). Sows in the hydrocortisone acetate (HCA) received 70 mg HCA twice daily; Stable sows were controls; Mixed sows were moved to a new pen weekly; and Companion sows received a new pen mate weekly. High rank sows were dominant to both pen mates; middle ranked sows were dominant to 1 pen mate; and low ranked sows were subordinate to both pen mates. The analyses used 23 HCA, 26 Stable, 15 Mixed, and 35 Companion sows and 39 high, 40 middle, and 20 low ranked sows. See online version for figure in color.

 

Male piglet birth weight (Table 6) tended to differ by treatment such that males born to Mixed sows tended to weigh more than males born to Companion sows (P = 0.07). On d 3 also, male pig weight tended to be affected by treatment, but no pair of treatments differed. On d 7, 14, and at weaning there were no differences in male pig weights among treatments. But surprisingly, at 160 d of age male pig weight was affected by treatment such that males from HCA sows weighed more than males from Stable sows (P = 0.01). The ADG (Table 6) of male pigs differed with treatment from birth until d 3 with males from Stable sows gaining weight faster (P = 0.01) and males from HCA sows tending to gain weight faster (P = 0.09) than male pigs from Companion sows. There was no effect of treatment on male pig ADG in any subsequent time period. Sow social rank did not affect male piglet weight or ADG in any time period (data not shown). Neither a sow’s treatment nor social rank affected the weight or ADG of female pigs at any time point (Table 6).


View Full Table | Close Full ViewTable 6.

Body weight and ADG of male and female piglets by sow treatment1

 
Item3 Treatment2
HCA Stable Mixed Companion P-value
BW, kg ADG, g/d BW, kg ADG, g/d BW, kg ADG, g/d BW, kg ADG, g/d BW ADG
Birth 1.49 ± 0.04x,y
1.46 ± 0.04
1.54 ± 0.04x,y
1.50 ± 0.04
1.68 ± 0.08x
1.61 ± 0.08
1.42 ± 0.06y
1.38 ± 0.06
0.09
0.18
145.9 ± 15.8x
139.1 ± 17.7
166.5 ± 17.1a
147.8 ±18.1
132.5 ± 11.4a,b,x
157.4 ± 16.9
98.1 ± 11.5b,y
116.3 ± 17.1
0.02
0.40
d 3 1.8 ± 0.1
1.8 ± 0.1
1.9 ± 0.1
1.8 ± 0.1
1.9 ± 0.1
1.9 ± 0.1
1.7 ± 0.1
1.7 ± 0.1
0.09
0.66
181.7 ± 22.9
182.9 ± 18.2
180.9 ± 23.6
203.5 ± 18.4
192.0 ± 22.4
192.1 ± 28.2
186.3 ± 18.3
203.4 ± 14.2
0.99
0.82
d 7 2.5 ± 0.1
2.4 ± 0.1
2.6 ± 0.1
2.7 ± 0.1
2.7 ± 0.1
2.7 ± 0.2
2.5 ± 0.2
2.5 ± 0.1
0.48
0.33
271.2 ± 21.0
263.4 ± 13.7
236.1 ± 21.6
241.6 ± 14.2
259.3 ± 19.1
283.4 ± 17.2
246.5 ± 15.5
244.8 ± 10.1
0.67
0.22
d 14 4.5 ± 0.3
4.2 ± 0.2
4.3 ± 0.3
4.5 ± 0.2
4.6 ± 0.3
4.6 ± 0.3
4.1 ± 0.3
4.1 ± 0.2
0.70
0.19
236.8 ± 47.4
257.9 ± 16.5
292.2 ± 48.6
243.7 ± 17.2
267.2 ± 24.1
278.7 ± 22.7
239.9 ± 28.3
238.3 ± 14.3
0.81
0.49
Wean 5.6 ± 0.2
5.4 ± 0.2
5.7 ± 0.2
5.8 ± 0.2
5.9 ± 0.4
6.2 ± 0.4
5.8 ± 0.4
5.7 ± 0.2
0.92
0.42
686.5 ± 15.2
623.2 ± 16.5
634.7 ± 15.9
594.8 ± 16.85
660.8 ± 11.4
648.5 ± 19.1
655.1 ± 15.4
633.8 ± 13.1
0.17
0.20
d 160 105.5 ± 2.2a
96.6 ± 4.7
94.5 ± 2.5b
84.6 ± 4.7
100.0 ± 2.0a,b
89.4 ± 8.1
105.2 ± 3.8a,b
96.2 ± 1.8
0.02
0.26
a,bLeast square means ± SE in the same row with different superscripts are different (P < 0.05).
x,yLeast square means ± SE in the same row with different superscripts tend to be different (0.05 ≤ P ≤ 0.10).
1The analyses used 25 HCA, 23 Stable, 13 Mixed, and 33 Companion sows.
2HCA = received 70 mg hydrocortisone acetate (HCA) twice daily; Stable = control group; Mixed = moved to new pen weekly; Companion = received a new pen mate weekly.
3Body weights and ADG of the male piglets are listed above those of the female piglets.

The ANO (Table 7) of the male pigs differed by treatment and with the number of females in the litter (P < 0.001), but not the sow’s social rank. Male piglets born to Companion sows had longer ANO than males from Mixed sows (P = 0.03) and tended to have a longer ANO than males from Stable sows (P = 0.06). Surprisingly, having more female littermates was associated with lengthened male ANO which equaled: 81.32 mm + 1.96 mm × number of female littermates. In female pigs, ANO was not associated with either sow treatment or social rank, but female ANO increased with more male littermates (P = 0.02) such that female ANO equaled: 3.89 mm + 0.079 mm × number of male littermates.


View Full Table | Close Full ViewTable 7.

Reproductive morphology of male and female piglets by sow treatment and social rank1

 
Item Treatment2 P-value Social rank3 P-value
HCA Stable Mixed Companion High Middle Low
ANO4, mm/kg
Male 94.15 ± 1.60a,b 90.06 ± 1.50b,y 86.30 ± 3.08b,y 98.18 ± 2.49a,x 0.02 90.61 ± 1.87 92.11 ± 1.92 93.88 ± 2.46 0.59
Female 4.30 ± 0.11 4.45 ± 0.11 4.27 ± 0.23 4.35 ± 0.21 0.69 4.35 ± 0.15 4.31 ± 0.15 4.37 ± 0.19 0.96
Number teats
Male 14.49 ± 0.19 14.17 ± 0.19 14.28 ± 0.25 13.95 ± 0.20 0.24 14.52 ± 0.15 14.14 ± 0.15 14.01 ± 0.20 0.08
Female 14.47 ± 0.17 14.18 ± 0.17 14.25 ± 0.16 14.09 ± 0.14 0.41 14.31 ± 0.12 14.38 ± 0.12 14.05 ± 0.16 0.26
Rel testis wt5 × 10-3 0.93 ± 0.04 0.89 ± 0.04 0.97 ± 0.07 0.91 ± 0.03 0.78 0.92 ± 0.04 0.92 ± 0.04 0.93 ± 0.04 0.98
a,bLeast square means ± SE in the same row with different superscripts are different (P < 0.05).
x,yLeast square means ± SE in the same row with different superscripts tend to be different (0.05 ≤ P ≤ 0.10).
1The analyses used 25 HCA, 26 Stable, 15 Mixed, and 35 Companion sows and 40 high, 40 middle, and 21 low ranked sows.
2HCA = received 70 mg hydrocortisone acetate (HCA) twice daily; Stable = control group; Mixed = moved to new pen weekly; Companion = received a new pen mate weekly.
3Social rank was identified during feeding. High rank = sow dominant in both dyadic relationships; middle rank = sow dominant in 1 dyadic relationship; low rank = sow subordinate in both dyadic relationships (Table 1).
4ANO = relative anogenital distance calculated as anogenital distance, mm/pig BW, kg.
5Rel testis wt = relative testis weight calculated as mean testis weight, g/pig BW, kg.

Neither sow treatment nor social rank affected the number of teats on male or female pigs (Table 7). The relative testis weight (Table 7) was unaffected by sow treatment or social rank, but was altered by the number of female littermates. Much like ANO, more female littermates was associated with increased relative testis weight which equaled: 0.00081 + 0.00002 × number of female littermates.


DISCUSSION

In rodents, there is abundant evidence that prenatal stress can cause androgynous changes in both male and female offspring structurally (Zielinski et al., 1991; Marchlewska-Koj et al., 2003), physiologically (Ward and Weisz, 1980; 1984; Kaiser et al., 2003), and behaviorally (Ward, 1972; Sachser and Kaiser, 1996; Kaiser et al., 2003). The evidence strongly supports maternal GC effect some of the changes in male offspring (Ward and Weisz, 1984; Mairesse et al., 2007), but their culpability for changes in female offspring is less clear (Kaiser and Sachser, 2005). We predicted that the male offspring of sows given HCA would be feminized compared to the offspring of Stable sows, whereas the female offspring would be masculinized. Additionally we thought the stress of regrouping would increase sow cortisol concentrations resulting in the Mixed sow offspring, and to a lesser degree the Companion sow offspring, being similar to HCA sow offspring.

However, the results of this experiment were rather surprising. As expected, the prenatal stress acted in a sex-specific manner as only the males were affected by the treatments. But contrary to our prediction that Mixed and Stable offspring would be the most different from each other, it was the Mixed and Companion sow offspring were the least like each other. Although we did not obtain cortisol concentration data from Companion sows, the total cortisol concentrations of the Stable and Mixed sows were not different from each other and as the regrouping stress applied to the Companion sows was intermediate between that of the Stable and Mixed treatments it is unlikely that their cortisol concentrations differed. As the cortisol concentrations of the HCA sows was elevated compared with the other treatments, yet most of the outcomes of their offspring were intermediate to the Mixed and Companion offspring outcomes, it is unlikely that changes in total cortisol concentration in the sows was the primary mediator of the prenatal changes. However, this hypothesis needs to be more fully examined in the future by measuring the Companion sows, assessing the ratio of bound to free cortisol, and collecting at multiple time points through the day and week.

Administration of HCA successfully raised the plasma cortisol concentrations of the sows; however it did not serve as a good model for regrouping stress. Cortisol concentration of the HCA sows was significantly higher than the other treatments only in the first week of the treatment. Because the sows were administered HCA between 1600 and 1700 h and blood collection occurred approximately 14 h later, in the later weeks HCA administration may have resulted in an unobserved, shorter duration cortisol increase. When sows were given 60 mg of HCA twice daily, their plasma cortisol concentrations remained elevated for approximately 5 h after administration (Kranendonk et al., 2005). The declining cortisol concentrations observed in this study, presumably as negative feedback decreased endogenous cortisol release, are similar to salivary cortisol concentrations observed when sows were given 60 mg HCA for several weeks (Kranendonk et al., 2005; 2006), but they differ from the plasma cortisol concentrations reported from the same study which were lower in sows that were administered HCA than control sows (Kranendonk et al., 2005). Therefore HCA may be better suited to model an acute than a chronic stressor.

At the end of the experimental period, skin lesions on the upper body, which result from aggression (McGlone, 1985; Turner et al., 2006), were greater on Mixed sows than HCA and Stable sows. Because aggression results in physiological indicators of stress (Arey and Edwards, 1998) including increased heart rate (Marchant et al., 1995), cortisol concentrations (Tsuma et al., 1996b), and catecholamines (Fernandez et al., 1994) which are further elevated in the loser (Mendl et al., 1992; Marchant et al., 1995; Ruis et al., 2001), the lesions provide evidence that the Mixed treatment was stressful. As predicted, lesions on Companion sows were intermediary to the other treatments. Mixed sows gained the least weight and their pen mates, the Companion sows, gained the most weight during the experimental period. Repeatedly, Mixed sows were observed being displaced during meals especially within 72 h after regrouping. Because the groups were not stable, feed competition was likely greater in the Mixed pens than the other pens which may have resulted in Mixed sows reducing their feed intake and subsequently losing weight. This suggests that in addition to the stress derived from aggression, the piglets born to Mixed sows experienced the consequences of lower maternal nutrition.

In swine, social stress is multifactorial and includes both aggression to establish social hierarchy (Fraser, 1984; Arey, 1999; Strawford et al., 2008) and also competition over resources such as feed and resting space (Fraser, 1984; Estevez et al., 2007; Strawford et al., 2008). In addition to directly elevating total GC concentration, social stress may also increase prenatal exposure to GC in a less direct manner. By altering the proportion of biologically unavailable bound GC to biologically active free GC, the GC available to interact with the developing fetus may shift even in the absence of a change in total GC. Newly mixed horses into an established herd exhibit decreased corticosteroid binding globulin (CBG) binding capacity and increased free cortisol without altering total cortisol concentration (Alexander and Irvine, 1998). Decreased CBG binding capacity has also been observed in pregnant nulliparous swine exposed to heat and crowding stressors (Kattesh et al., 1980), but mixing did not affect CBG concentration of pregnant nulliparous swine (Tsuma et al., 1996b). Additionally, maternal feed restriction in gestating rats decreased CBG concentration (Lesage et al., 2001); however maternal feed restriction during early gestation did not affect CBG concentration in swine (Tsuma et al., 1996a). Besides changing CBG function, maternal feed restriction in rats can decrease the activity of placental 11β-hydroxysteroid dehydrogenase type 2 (11β HSD2), an enzyme that converts biological active GC to a non-active metabolite, thereby increasing the developing rats exposure to maternal GC (Lesage et al., 2001). Similar effects are seen in swine in which both low and high protein maternal diets decrease 11β HSD2 mRNA expression in the fetuses (Kanitz et al., 2012). Because our research study examined the overall effects of social stress, and not the individual components, all hypotheses made about the mechanisms of actions need to be tested.

When the data from male and female piglets were combined for analysis, sow treatment had no effect on any litter or piglet characteristic. This is in accordance with previous research results showing that during midgestation neither the authentic stressors of rough handling (Lay et al., 2008) and mixing (Jarvis et al., 2006; Rutherford et al., 2009), nor the artificial stressors ACTH (Haussmann et al., 2000; Schneider et al., 2004; Brussow et al., 2005; Kanitz et al., 2006; Otten et al., 2007) and HCA (Kranendonk et al., 2006) affected gestation length (Haussmann et al., 2000; Jarvis et al., 2006; Kanitz et al., 2006; Kranendonk et al., 2006; Otten et al., 2007; Lay et al., 2008), litter size (Haussmann et al., 2000; Schneider et al., 2004; Brussow et al., 2005; Kanitz et al., 2006; Kranendonk et al., 2006; Otten et al., 2007; Lay et al., 2008; Rutherford et al., 2009), or number of stillborn pigs (Haussmann et al., 2000; Jarvis et al., 2006; Kranendonk et al., 2006; Otten et al., 2007; Lay et al., 2008).

However when the sexes were analyzed separately, sex differences in response to sow treatment were revealed. Sow treatment had no effect on the female piglets, whereas the male piglets exhibited modest differences as a result of the sow gestational environment. Fewer male pigs tended to be born to Mixed sows than Companion sows although sex ratio did not differ. Previous research examining midgestation GC administration (Kranendonk et al., 2006; Lay et al., 2008) did not find differences in litter sex structure, thus our results are more likely attributable to components of social stress other than cortisol concentration. However, these results are unlike those from previous research on the effects of midgestation social stress that observed no difference in sex ratio (Jarvis et al., 2006). The current study used sows from parity 0 to 6 whose litter sex ratios were numerically, but not significantly, biased toward males, whereas the previous research study used only nulliparous sows whose litter sex ratios were numerically biased toward females. The sex ratios seen in the Jarvis et al. study (2006) are atypical as most swine research indicates a small numerical bias toward males (Fernández-Llario et al., 1999; Górecki, 2003; Servanty et al., 2007; Razmaite and Kerziene, 2009; Baxter et al., 2012). The differing results may be attributable to sow parity as greater maternal age has been associated with an increase in the proportion of male offspring in both birds (Blank and Nolan, 1983) and mammals (Côté and Festa-Bianchet, 2001).

The Trivers-Willard hypothesis predicts a female will adjust the sex ratio of her litter via differential male mortality to reduce the male to female ratio if maternal condition deteriorates (Trivers and Willard, 1973). Our results support this hypothesis and suggest changes to maternal nutrition may have affected the number of male pigs born. Mixed sows, that gained the least weight, tended to have fewer male offspring than Companion sows, that gained the most weight, during the experimental period. Both the weight gain and the number of male piglets born to the Stable and HCA sows were intermediate between those of the Companion and Mixed sows. In swine, 40 to 60% of the ova released are lost prenatally with 5 to 50% of the losses occurring after GD 30 (Foxcroft et al., 2006) which provides opportunity for differential mortality during mid- and late gestation.

Despite meeting model predictions, our results differ from other swine studies that examined the effects of maternal condition on litter sex ratio. Feed restriction of the sow during the previous lactation biased the litter toward males (Vinsky et al., 2006; Oliver et al., 2011) and lifelong nutritional deprivation increased the proportion of males born to third parity sows (Yang et al., 1989; Mendl et al., 1995). There are 3 critical ways in which those studies differ from this one. The other studies included dietary manipulations before the sows were pregnant, therefore the sex ratio differences may have resulted from differential conception rates of male and female piglets, whereas our differences occurred after conception thus requiring a different mechanism (Grant, 2007). Additionally, the differences in maternal nutrition were large and long-lasting in those studies, whereas in this one, they were short-lived and apparently small. Although the sows gained weight differentially, their absolute BW were never different. However, because we did not measure feed intake, the quantitative differences in maternal nutrition cannot be assessed. Lastly, in this study the nutritional change was only one component of the regrouping stress and multiple aspects of the stressor may have been involved in the litter sex structure alteration.

The birth weight of male piglets from Mixed sows tended to be greater than that from Companion sows which was especially surprising as reduced sow weight gain was associated with greater piglet weight. Reduced sow gain coupled with increased piglet weight has been observed previously in sows administered ACTH during late gestation (Otten et al., 2007) and in those offspring weight differences were maintained until 21 d of age. However in this study, reduced maternal nutrition, rather than maternal GC, likely increased the birth weight of male piglets of Mixed sows. In sheep, early and midgestation maternal nutrient restriction increases the adiposity of neonates, especially if followed by full rations in the remainder of gestation (Symonds et al., 2004). In this study, the greater maternal GC concentration of HCA sows increased BW of male piglets compared to those from Stable sows at 160 d of age. Maternal HCA administration has been associated with reduced piglet weight before weaning followed by increased backfat thickness at slaughter (Kranendonk et al., 2006). Taken together, the results suggest that in swine increased maternal GC has long term effects on offspring metabolism, but that the onset of the change does not appear until sometime after weaning. Fetal programming of metabolic changes is linked with adult disease. In swine, low natural birth weight is associated with glucose intolerance, insulin resistance, and increased backfat as adults in a sex-specific manner (Poore and Fowden, 2002; 2004a,b). And in humans both maternal nutrient restriction and increased gestational GC concentration with resultant low birth weight have been implicated in adult obesity, diabetes, and other metabolic disorders (Cottrell and Ozanne, 2008; Morrison et al., 2010; Harris and Seckl, 2011).

Preweaning mortality was greater among the male offspring of HCA sows than the male offspring of Mixed and Stable sows. Neither maternal HCA nor ACTH treatments have shown an unequivocal effect on piglet vitality or mortality (Haussmann et al., 2000; Kranendonk et al., 2006; Otten et al., 2007; Davis, 2010). Like the results from this study, previous studies have not observed an association between social stress and increased mortality (Jarvis et al., 2006; Kranendonk et al., 2008; Couret et al., 2009a,b). In contrast, late gestation restraint stress often results in greater morbidity and mortality (Otten et al., 2000; Otten et al., 2001; Tuchscherer et al., 2002; Kanitz et al., 2003). Paralleling these results maternal social stress has few negative effects on offspring immune function (Couret et al., 2009a,b). In fact, late gestation social stress increased lymphocyte proliferation in response to mitogens (Couret et al., 2009a,b). In contrast, maternal restraint stress may impair offspring immune function. Among other changes, offspring have exhibited decreased lymphocyte proliferation (Otten et al., 2000; Tuchscherer et al., 2002; Otten et al., 2007) and serum IgG concentrations (Otten et al., 2000; Tuchscherer et al., 2002). Preweaning mortality of male pigs may be associated with impaired ability to obtain colostrum which reduces homeothermy and can result in delayed gut closure and may increase risk of pathogenesis (Baxter et al., 2011). Whether maternal stress further impairs nursing behavior and contributes to greater male mortality needs to be further examined; however neither latency to first udder contact or milk intake were reduced by maternal ACTH administration (Otten et al., 2007).

Increased anogenital distance in both males and females results from greater testosterone concentration during differentiation of the external genitalia which begins near GD 30 in swine (Klonisch et al., 2004). In human men, reduced anogenital distance is associated with reduced fertility and may be associated with cryptorchidism (Hsieh et al., 2008; Eisenberg et al., 2011) and reduced semen quality (Mendiola et al., 2011). In this study, ANO was longer in the males from Companion sows than males from Mixed sows and tended to be longer in the males from Companion sows than males from Stable sows. The males born to HCA sows were not different than the male from Stable sows; therefore, once again, effects of maternal social stress other than total cortisol appear to have been the causative agent. Because the male piglets from both Mixed and Stable offspring had shorter ANO than the male piglets from Companion sows, it is possible that increased maternal nutrition increased fetal testosterone and thereby increased ANO and not that maternal nutrient restriction or other consequences of social stress impaired testosterone secretion.

In contrast to these results, ACTH injections from GD 42 to 77 reduced anogenital distance in male pigs (Lay et al., 2008) which supports the hypothesis that the ANO lengthening observed in this study was not due to increased GC concentration. Previous research by Ashworth et al. (2011) demonstrated that midgestation maternal social stress can influence postnatal testosterone concentration and testicular steroidogenic enzyme expression. However, midgestation maternal heat stress and crowding did not affect testosterone concentrations of pubertal boars (Kattesh et al., 1979). In sheep, maternal undernutrition can increase fetal testosterone concentration and steroidogenic enzyme expression in male fetuses (Rae et al., 2002). Although those results are in the opposite direction as our results, it provides evidence that maternal nutrition affects reproductive development of male ungulates. Additionally, maternal undernutrition and maternal overnutrition often have similar consequences for the offspring (Ford and Long, 2012).

Most surprising was that male ANO and relative testis weight were increased when the number of female littermates increased. Male anogenital distance and testis weight are unaffected by intrauterine position (Rohde Parfet et al., 1990) which indirectly supports the finding that the increases are related to the number of females in the litter rather than their positions. In swine, unlike most other mammals, increasing the number of female piglets may decrease estrogen concentrations in the uterine environment which may result in increased masculinization of male piglets. Testes of both immature and adult boars produce higher concentrations of estrogens than is typical of male mammals and the plasma estrogen concentrations of boars is actually greater than that of gilts (Booth, 1983; Raeside et al., 1993; Bazer et al., 2001). Reducing endogenous estrogen production by the testes during postnatal Sertoli cell proliferation results in more Sertoli cells, larger testes, and improved sperm quality (Berger et al., 2008; 2012). A similar mechanism may exist prenatally. Sertoli cells undergo differentiation and proliferation from GD 30 until birth (van Vorstenbosch et al., 1984; McCoard et al., 2002). Placental tissue and fluids of female fetal pigs contain lower concentrations of estrogens than those of male fetuses (Choong and Raeside, 1974; Tarraf and Knight, 1995) and female fetuses begin gonadal production of estrogens later in prenatal development than male pig fetuses (Parma et al., 1999; McCoard et al., 2002). The combination of these factors could reduce the quantity of estrogens leaked into the surrounding environment during sexual differentiation. Sertoli cell proliferation and testes size may increase in response to lower estrogen exposure. Thus an increase in the number of female littermates could increase testes weight.

In addition to relative testis weight, ANO was lengthened with more female littermates which suggests having more female littermates increased testosterone concentration. In vitro, reducing estrogen concentrations in immature porcine Leydig cells increases their testosterone production (At-Taras et al., 2008). Therefore like testes weight, reducing exposure to estrogens produced by the male fetuses may have resulted in increased masculinization. However, none of this has yet been tested and whether these processes occur prenatally is currently unknown.

Sow social rank influenced a few characteristics of the sow and her offspring. High ranked sows were heavier and had fewer lesions than middle and low ranked sows at the end of the experimental period which provides evidence that high rank was less stressful than middle or low rank. Although plasma cortisol concentrations did not differ among social ranks, high ranked sows had greater plasma progesterone concentrations than middle ranked and tended to have greater concentrations than low ranked sows. Progesterone release from more corpora lutea likely contributed to the concentration differences between the ranks (Edgerton et al., 1971; Webel et al., 1975) as high ranked sows tended to have larger litters and presumably more corpora lutea. Unlike the effect of sow condition on offspring sex, the effect of social rank on sex ratio is the opposite of Trivers-Willard hypothesis (Trivers and Willard, 1973) based predictions because by the time of weaning low ranked sows had a greater proportion of males than females. But it is in alignment with the variation previously seen in pig litters (Meikle et al., 1993; Mendl et al., 1995; Vinsky et al., 2006). It is interesting to note that social rank had the greatest effect on female offspring, whereas sow treatment had the greatest effect on male offspring.

The prenatal environment did influence piglet development. Most important was the strong evidence of differential prenatal effects on the male and female piglets. Although sex differences in response to prenatal stress have been found previously in swine, researchers often pool male and female offspring if the traits being examined are not obviously sex related and thus may fail to observe sex differences in response. Additionally, these results provide evidence that acutely elevated cortisol concentrations can have long term effects on the growth of offspring and support the possibility that maternal nutrition may alter reproductive function of male offspring.

 

References

Footnotes


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