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Journal of Animal Science - Animal Physiology

Effects of maternal nutrient restriction followed by realimentation during early and midgestation on beef cows. I. Maternal performance and organ weights at different stages of gestation12

 

This article in JAS

  1. Vol. 92 No. 2, p. 520-529
     
    Received: Aug 13, 2013
    Accepted: Nov 24, 2013
    Published: November 24, 2014


    4 Corresponding author(s): Kim.Vonnahme@ndsu.edu
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doi:10.2527/jas.2013-7017
  1. L. E. Camacho,
  2. C. O. Lemley33,
  3. M. L. Van Emon,
  4. J. S. Caton,
  5. K. C. Swanson and
  6. K. A. Vonnahme 4
  1. Department of Animal Sciences, North Dakota State University, Fargo 58108

Abstract

The objectives were to evaluate the effects of nutrient restriction during early to midgestation followed by realimentation on maternal performance and organ mass in pregnant beef cows. On d 30 of pregnancy, multiparous, nonlactating cows (initial BW = 620.5 ± 11.3 kg and BCS = 5.1 ± 0.1) were assigned to 1 of 3 dietary treatments: control (CON; 100% NRC; n = 18) and restricted (RES; 60% NRC; n = 30). On d 85, cows were slaughtered (CON, n = 6; R, n = 6), remained on control (CC; n = 12) and restricted (RR; n = 12), or were realimented to control (RC; n = 11). On d 140, cows were slaughtered (CC, n = 6; RR, n = 6; RC, n = 5), remained on control (CCC, n = 6; RCC, n = 5), or were realimented to control (RRC, n = 6). On d 254, all remaining cows were slaughtered. Cows were weighed before slaughter and all maternal organs were dissected and weighed. The diet consisted of grass hay to meet 100 or 60% NEm recommendations for fetal growth and to meet or exceed recommendations for other nutrients. At d 85 slaughters, BW and empty BW (EBW) were not affected (P ≥ 0.84) by maternal nutrition. However back fat was decreased (P = 0.05) in RES vs. CON cows. Large intestine and abomasum mass were increased (P ≤ 0.05) in RES cows vs. CON. At d 140, BW was decreased (P = 0.05) and EBW tended to be decreased (P = 0.10) in RRC cows vs. CCC and RCC being intermediate. Liver mass was decreased (P = 0.02) in RR vs. CC with RC being intermediate. Ruminal mass was decreased (P = 0.003) in RR vs. CC and RC cows. At d 254, BW and EBW were similar (P ≥ 0.78) across treatments. We observed partial changes in maternal weight and organ masses due to different lengths of maternal nutrient restriction followed by realimentation. It appears that the dam undergoes some adaptations during an early to midgestation nutrient restriction and becomes more efficient in the utilization of nutrients after being realimented and as gestation advances.



INTRODUCTION

Beef cows are commonly managed in grazing systems where forage quality varies according to regional growing conditions. Forage quality or availability is often poor, affecting nutritional and physiological status of the animal (Funston et al., 2010). During this period of reduced nutrient availability, the dam will undergo a series of metabolic and physiologic adaptations to protect some of her body stores from depletion and to supply nutrients to the growing conceptus, which has increased demands as gestation advances (Rosso and Streeter, 1979). Proper placental development allows for regulation of nutrient metabolism and supports fetal growth while still maintaining maternal homeostasis through hormone secretion and nutrient transferring capabilities (Reynolds and Redmer, 1995; King, 2000). Energy expenditure from liver and gastrointestinal tract accounts for close to 50% of the total energy utilized by ruminants (Ferrell, 1988). Previous research in mature cows has demonstrated an adaptation in energy utilization during nutrient restriction and realimentation (nonpregnant cows; Freetly and Nienaber, 1998; pregnant cows; Freetly et al., 2008). Meyer et al. (2010) reported that visceral organ masses were responsive to both nutrient restriction during early to midgestation and realimentation in mid to late gestation in beef cows. However, little is known about changes in maternal organ mass during different lengths of nutrient restriction or the effect of realimentation, particularly during early to midgestation. Therefore, we hypothesized that maternal organs in pregnant beef cows would be responsive to nutrient restriction from early to midgestation and changes would remain even after nutrient realimentation. Our objectives were to evaluate the effects of nutrient restriction during early to midgestation followed by realimentation on maternal BW, BW change, BCS, and organ mass in pregnant beef cows.


MATERIALS AND METHODS

All procedures involving animals were approved by the North Dakota State University (NDSU) Animal Care and Use Committee (number A10001).

Animals, Diets, and Breeding

A total of 54 nonlactating, multiparous crossbred beef cows (initial BW = 620.5 ± 11.3 kg and BCS = 5.1 ± 0.1) predominately of Angus breeding were synchronized using a Select Synch plus progesterone insert (CIDR; Pfizer Animal Health, New York, NY) and fixed-time AI (TAI) protocol. At the NDSU Beef Research and Teaching Unit (Fargo, ND), cows were assigned to 1 of 6 breeding groups (n = 4 to 11 cows per breeding group with all treatments being represented in each breeding group) with breeding dates ranging from July 13 to October 24, 2011. Cows received GnRH (100 μg as 2 mL of Factrel intramuscular injection [i.m.]; Fort Dodge Animal Health, Fort Dodge, IA) and a CIDR on d 0. On d 7 CIDR devices were removed, and cows were given an intramuscular injection of PGF2α (25 mg as 5 mL of Lutalyse; Pharmacia and Upjohn Co., Kalamazoo, MI). Estrotect Heat Detectors (Rockway Inc., Spring Valley, WI) were used to monitor estrous behavior at least twice daily at 0700 and 1900 h for a minimum of 72 h. Artificial insemination was performed 12 h after the first detected estrus (Gonzalez et al., 1985). All cows were bred using semen from one Angus bull (Select Sires, Plain City, OH). Cows not detected in estrus after 72 h received a second GnRH injection and TAI was performed. Cows were fed a hay-based diet during the prebreeding period. Inseminated cows were transported to the Animal Nutrition and Physiology Center (ANPC; Fargo, ND; temperature controlled building) within 3 d postinsemination. From arrival at ANPC until confirmed pregnant, cows were grouped in pens (4.87 m2; n = 4 to 5/pen) and trained to use the Calan gate feeding system (American Calan, Northwood, New Hampsire). At this time, all cows were fed chopped grass/legume hay (8.0% CP, 69.2% NDF, 41.5% ADF, and 57.9% TDN [DM basis]; containing predominately cool season grasses with small amounts of alfalfa) to pass a 15.24-cm screen and a mineral and vitamin supplement (details provided below) to meet NEm recommendations and fetal growth and to meet or exceed recommendations for MP, minerals, and vitamins (NRC, 2000) until pregnancy was confirmed. Hay NEm concentration was predicted using equations described by Weiss (1992) and NRC (2000). Water was available for ad libitum intake.

On d 27 and 28 postinsemination, pregnancy was confirmed via transrectal ultrasonography (500-SSV; Aloka, Tokyo, Japan) using a linear transducer probe (5 MHz). Nonpregnant cows restarted the same breeding protocol; cows were only subjected to AI twice during the experiment; if not pregnant after the second AI, cows were not used for the experiment. On d 30 of pregnancy, cows were randomly assigned to dietary treatments (n = 4 to 5/pen with greater than 1 dietary treatment per pen): control (CON; 100% NRC; n = 18; Fig. 1) and nutrient restriction (RES; 60% NRC; n = 30). On d 85 cows were slaughtered (CON, n = 6; RES, n = 6), remained on control (CC; n = 12) and restricted (RR; n = 12) treatments, or were realimented to control (RC; n = 11). On d 140 cows were slaughtered (CC, n = 6; RR, n = 6; RC, n = 5), remained on control (CCC; n = 6; RCC; n = 5), or were realimented to control (RRC; n = 6). On d 254 all remaining cows were slaughtered (CCC, n = 6; RCC, n = 5; RRC, n = 6). An animal from the RC group was removed from the study due to early embryonic loss and a second cow was removed from the RCC group due to a twin pregnancy.

Figure 1.
Figure 1.

Diagram of experimental design. Multiparous, nonlactating beef cows were bred and fed similar diets until d 30 of gestation. On d 30 of pregnancy, cows were randomly assigned to dietary treatments: control (CON; 100% NRC; n = 18) and nutrient restriction (RES; 60% NRC; n = 30). On d 85 cows were either slaughtered (CON, n = 6; RES, n = 6) or remained on control (CC; n = 12) or restricted (RR; n = 12) or were realimented to control (RC; n = 11). On d 140 cows were ether slaughtered (CC, n = 6; RR, n = 6; RC, n = 5) or remained on control (CCC; n = 6; RCC; n = 5) or realimented to control (RRC; n = 6). On d 254 all remaining cows were slaughtered. An animal from the RC group was removed from the study because early embryonic loss and a second cow was removed from RCC group because the presence of twins. Diets consisted of grass hay and mineral and vitamin supplement at either 100% NRC recommendations for NE for maintenance and fetal growth (NRC, 2000). Nutrient restricted cows received 60% of the same control diet.

 

The control diet consisted of grass hay (Table 1) fed to meet 100% NE recommendations for maintenance and fetal growth (NRC, 2000) and to meet or exceed MP, mineral, and vitamin recommendations. Nutrient restricted cows received 60% of the same control hay diet. Cows were individually fed once daily in a Calan gate system at 1000 h and had free access to water. The mineral and vitamin supplement (Trouw Dairy VTM with Optimins; Trouw Nutrition International, Highland, IL; 10% Ca, 5% Mg, 5% K, 2.7% Mn, 2.7% Zn, 1,565,610 IU/kg vitamin A, 158,371 IU/kg vitamin D3, and 2,715 IU/kg vitamin E) was top-dressed 3 times per week at a rate of 0.18% of hay DMI to meet or exceed mineral and vitamin requirements relative to dietary NE intake (NRC, 2000). Cows were weighed weekly at approximately 0800 h throughout the experiment. Initial and final BW were taken on 2 consecutive days. Dietary intake was adjusted relative to BW weekly and to NE requirements for the specific period of gestation (average requirements for periods from d 30 to 85, d 86 to 140, 141 to 197, and d 198 to 254).


View Full Table | Close Full ViewTable 1.

Nutrient analysis of grass/legume1 hay

 
Item DM basis, %
Ash 11.8
CP 8.1
NDF 69.2
ADF 41.5
1Containing predominately cool season grasses with small amounts of alfalfa.

Body Condition Score and Carcass Ultrasonography

Body condition score was obtained using a 1 to 9 scale (with 1 = emaciated and 9 = obese; Wagner et al., 1988) by 4 trained technicians on d 30, 57, 83, 112, 138, 167, 195, and 254 of gestation and their scores were averaged. Carcass ultrasonography measurements were also taken on d 30, 57, 83, 112, 138, 167, 195, and 254 of gestation. Briefly, at the 12th rib and rump, hair was clipped (<1.27 cm), vegetable oil was applied to the area where the probe was placed, and measurements for back fat thickness at the 12th rib, LM area at the 12th rib, and rump fat thickness were determined using a model 500-SSV ultrasound machine (Aloka) with a 5 MHz linear transducer probe.

Slaughter Procedure and Tissue Collection

Cows were weighed the day before and the morning of slaughter to obtain a 2 d average live BW (d 85, 140, and 254 ± 2 d SD). All weights were obtained before morning feeding and cows were not fed on the morning of slaughter. Cows were transported from ANPC to the NDSU Meat Laboratory approximately 30 min before slaughter. No more than 2 cows were slaughtered per day due to Meat Laboratory capacity and time constraints of sample collection (slaughters ranged from November 2011 until April 2012). On the day of slaughter, cows were stunned with a captive bolt and exsanguinated. The gravid uterus was immediately removed and weighed, and then the hide was removed and cows were eviscerated. A total viscera weight (including digestive tract contents) was then obtained. The liver, spleen, and pancreas were dissected from the mesentery and associated tissues and were weighed. The digestive tract was stripped of fat and digesta, and the stomach complex and small and large intestines were dissected and weighed. The stomach complex was then divided into the reticulum, rumen, omasum, and abomasum, and each component was weighed. The heart, lungs, kidneys, perirenal fat, and adrenals were dissected from the carcass and weighed. Carcass weight was obtained. The carcass was split at the 12th and 13th rib, and LM muscle area (ribeye area [REA]) was determined using a USDA beef measuring grid. A fat thickness measurement was made at a point three-fourths of the way up the length of the LM from the split chine bone. Average LM area and fat thickness was determined from both left and right sides of each carcass to determine an average.

Calculations

Percentage of BW change was calculated as final BW – initial BW divided by initial BW times 100, in which initial BW was BW at d 30 of gestation. Initial BW was an average of a 2 d weight. Digesta weight was calculated by difference (total full viscera weight – visceral tissues after stripping of digesta contents). Empty BW (EBW) was determined by subtracting digesta weight and gravid uterus from the final BW obtained before slaughter. Stomach complex weight was calculated as the sum of the empty rumen, reticulum, omasum, and abomasum weights.

Statistical Analysis

Organ weight data were analyzed as a completely randomized block (breeding group) design within slaughter day (d 85, 140, or 254 of gestation) using a mixed model (SAS Inst. Inc., Cary, NC). In addition, effects of maternal nutrition on BW, percent BW change, BCS, and carcass ultrasonography measurements were examined using repeated measures analysis of the mixed procedure. Factors included in the repeated measures model were block, treatment, day, and the treatment × day effect. Means were separated using the PDIFF option of the LSMEANS statement of SAS and were considered significant when P ≤ 0.05. In the absence of interactions (P > 0.05) for the repeated measures model, significant main effects are reported; otherwise, interactive means are discussed.


RESULTS AND DISCUSSION

Cow BW and BW Change

At d 85 there was no treatment × day interaction (P = 0.12; Fig. 2A) for cow BW. Regardless of nutritional treatment, all cows lost BW after initiation of the experiment until d 85 (day effect, P < 0.001). There was a treatment × day interaction (P = 0.04; Fig. 2B) for maternal BW change (%) for cows slaughtered at d 85. Cow BW change was not different (P ≥ 0.13) from d 30 to 72 of gestation, but BW loss was greater (P ≤ 0.05) in RES than in CON cows on d 79 and 85 of gestation.

Figure 2.
Figure 2.

Cow BW (kg; panel A) and BW change (%; panel B) of cows slaughtered at d 85 of gestation. Cows received either control (CON) diet (100% NRC) or restricted (RES) from d 30 to 85 (60% NRC). There was no treatment (trt) × day interaction (P = 0.12) or treatment main effect (P = 0.49) for cow BW but there was a day effect (P < 0.001). There was a treatment × day interaction (P = 0.04) for cow BW change. *CON cows different (P < 0.05) from RES. The SEM is average of SEM for treatment × day interaction.

 

There was a treatment × day interaction (P = 0.02; Fig. 3A) for cow BW in dams slaughtered at d 140. From d 30 to 100 of gestation, cow BW was similar (P ≥ 0.18) among treatments. From d 107 to 140 RR cows had a decreased (P ≤ 0.04) BW compared to CC, with RC being intermediate (P ≥ 0.13). When cow BW was expressed as percentage change, there was also a treatment × day interaction (P = 0.01; Fig. 3B). Cow BW percentage change did not differ (P ≥ 0.07) among treatments from d 30 to 44 of gestation. From d 51 to 65 of gestation, the RR group had greater (P ≤ 0.03) BW loss compared with CC and RC being intermediate (P ≥ 0.07). From d 72 to d 93, the RR group tended to have greater (P ≤ 0.06) BW loss compared with CC and RC cows. At d 100, RR group had greater (P = 0.01) BW loss compared with CC and RC being intermediate (P ≥ 0.21). From d 107 to 135 of gestation RC and RR had greater (P ≤ 0.04) BW loss compared with CC. On d 140, RR cows had the greatest BW loss (P < 0.05) followed by RC, and CC had the least (P ≤ 0.04) percentage BW change (RR = –18.78%, RC = –13.12%, and CC = –6.68%; SEM = 2.92%).

Figure 3.
Figure 3.

Cow BW (kg; panel A) and BW change (%; panel B) of cows slaughtered at d 140 of gestation. Cows received the control diet (100% NRC) from d 30 until 140 (CC), restricted from d 30 to 85 (60% NRC) and then realimented to 100% of the NRC requirements until d 140 (RC), and restricted from d 30 to 140 (60% NRC; RR). There was a treatment (trt) × day interaction (P ≤ 0.02) for cow BW and BW change. *CC cows significantly different (P < 0.05) from RR and RC being intermediate; **CC cows different (P < 0.05) from RR and RC; ***CC cows different (P < 0.05) from RC and RC different from RR. The SEM is average of SEM for treatment × day interaction.

 

There was a treatment × day interaction (P = 0.002; Fig. 4A) for BW on cows slaughtered at d 254 of gestation. However, on further means separation no significant differences existed among groups. There was also a treatment × day interaction (P = 0.01; Fig. 4B) for percentage BW change of cows slaughtered at d 254. From d 30 to 100 of gestation, maternal percentage BW change was not affected (P ≥ 0.14) by treatment. From d 107 to 114 of gestation, RRC cows had decreased (P < 0.05) percentage BW change compared to CCC cows and RCC being intermediate (P ≥ 0.13). From d 121 to 135 RRC cows had greater (P ≤ 0.05) BW loss than CCC and RCC cows. At d 142 there was no difference (P ≥ 0.19) among treatments. From d 149 until 163 RRC cows had increased (P < 0.05) BW loss than RCC, with CCC being intermediate (P ≥ 0.12). At d 170, percentage BW change was similar (P = 0.15) among treatments and by d 177 RCC cows had increased (P = 0.05) percentage BW change compared with CCC and RRC. All treatment groups were similar (P ≥ 0.18) at d 184. By d 191 RCC had greater (P = 0.02) percentage BW change compared with RRC and CCC. From d 198 to 205 there was no difference (P ≥ 0.07) among treatments. At d 212 RCC had greater (P ≤ 0.03) percentage BW change compared with RRC and CCC. From d 219 to 240 treatment groups did not differ (P ≥ 0.11). By d 247 until 254, RCC cows had greater (P < 0.03) percentage BW change compared with CCC cows and RRC being intermediate (P ≥ 0.09).

Figure 4.
Figure 4.

Cow BW (kg; panel A) and BW change (%; panel B) of cows slaughtered at d 254 of gestation. Cows received the control diet (100% NRC) from d 30 until 254 (CCC), restricted from d 30 to 85 (60% NRC) and then realimented to 100% of the NRC requirements until d 254 (RCC), and restricted from d 30 to 140 (60% NRC) and then realimented to 100% of the NRC requirements until d 254 (RRC). There was a treatment (trt) × day interaction (P ≤ 0.01) for cow BW and BW change. *CCC cows different (P < 0.05) from RRC and RCC being intermediate; **CCC and RCC cows different (P < 0.05) from RRC; ***RCC cows different (P < 0.05) from RRC and CCC being intermediate; †RCC cows different (P < 0.05) from CCC and RRC; ‡CCC cows different (P < 0.05) from RCC and RRC being intermediate. The SEM is average of SEM for treatment × day interaction.

 

Nutrient restriction at d 85 of gestation did not affect BW; however, percentage BW loss was greater towards the end of nutrient restriction compared to control cows. At d 140 of gestation cows that were restricted for a longer period of time lost more BW, and percentage BW change was also greater compared with other treatments. At d 254 of gestation, greater loss in percentage BW change occurred in cows experiencing a longer nutrient restriction (restriction from d 30 to 140 of gestation). Cows that were realimented during early gestation (i.e., d 85) had the greatest increase in BW change compared with other treatments. Control diets were calculated to meet or exceed NE requirements; however, control cows lost BW, especially during early gestation, suggesting that cows had greater nutrient requirements than estimated. This could be due to several factors including differences in genetics or fetal growth (NRC, 2000); however, we had similar cattle and they were bred to the same bull. Previous research in beef cows has shown a decrease in BW during nutrient restriction from d 30 to 125; however, these cows had increased BW after realimentation and were similar in BW to controls by d 245 of gestation (Meyer et al., 2010). However, Meyer et al. (2010) restricted animals to a predicted 68.1% of NE recommendations and realimented cows above NRC NE recommendations to accomplish this.

Cow BCS and Carcass Ultrasonography Measurements

No treatment × day interaction (P ≥ 0.48) or main effect of treatment (P ≥ 0.37) was observed for BCS for cows slaughtered at d 85, 140, or 254 of gestation. For cows slaughtered at d 85 of gestation, there was a day effect (P = 0.02) where the average BCS for all cows was 4.4 ± 0.6 at d 30 of gestation, decreased to (P = 0.02) to 4.1 ± 0.6 by d 57, and then remained similar (P = 0.77) until d 85 of gestation. No interactions or main effects of treatment or day (P ≥ 0.18; data not shown) for carcass ultrasound traits (12th rib back fat thickness, 0.65 ± 0.23 cm; REA, 76.7 ± 7.1 cm2) were observed for the group slaughtered on d 85. Cows slaughtered at d 140 of gestation also showed a day effect (P < 0.001) where the average BCS was 5.1 ± 0.1 at d 30 and decreased to 4.5 ± 0.1 by d 140 of gestation. There was no treatment × day interaction or main effect of treatment (P ≥ 0.13; data not shown) on 12th rib back fat thickness (0.45 ± 0.08 cm) and REA (71.4 ± 4.1 cm2) for groups slaughtered at d 140. However, there was a day effect (P = 0.04) for 12th rib back fat thickness and REA for cows slaughtered at d 140 where both measures decreased as gestation advanced (data not shown).

There was no day effect (P = 0.07) for BCS on cows slaughtered at d 254. The average BCS for all the cows at d 30 was 4.8 ± 0.2 and 4.9 ± 0.2 before slaughter at d 254. There was no treatment × day interaction or main effect of treatment (P ≥ 0.13; data not shown) for 12th rib back fat thickness and REA for groups slaughtered at d 254. However, cows slaughtered at d 254 showed a day effect (P < 0.001; average of 0.80 ± 0.16 cm at d 30 and 0.42 ± 0.07 cm at d 254) for 12th rib back fat thickness and day effect for REA (P < 0.0001; average 92.4 ± 4.3 cm2 at d 30 and 60.5 ± 4.3 cm2 at d 254). Both ultrasonography measurements decreased across time during gestation (from d 30 to 254). Even though BCS did not change through gestation for cows slaughtered at d 254 of gestation, carcass 12th rib back fat and REA measured by ultrasonography decreased from early to late gestation regardless of dietary treatment. Perhaps cows were mobilizing muscle and fat stores to keep up with nutrient demands from the growing conceptus.

The observed change in BW and percentage BW change in our current study was not accompanied by a change in BCS by nutrient restriction. Interestingly, all cows slaughtered at d 85 and 140 of gestation started losing BCS around d 57 of gestation until their slaughter day. However, cows slaughtered at d 254 of gestation had similar BCS regardless of treatment, which may have been due to the realimentation. Cows slaughtered at d 254 were realimented for a longer period of time compared with cows that were slaughtered on d 140. Miller et al. (2004) reported a decreased in BCS by d 45 in cows that were nutrient restricted from d 30 to 140 of gestation compared with controls. However, BW in those cows followed a similar pattern as BCS. In addition, Miller et al. (2004) realimented cows to achieve a similar BCS by d 220 of gestation; therefore, it is difficult to compare the effects of nutrient realimentation with our study.

Cow Composition and Organ Mass at Slaughter

Cow BW, carcass weight, and EBW at d 85 slaughter were not affected (P ≥ 0.50; Table 2) by maternal nutrient restriction. Carcass REA did not differ (P = 0.97) between treatments whereas 12th rib back fat thickness was decreased (P = 0.05) in RES cows compared with CON cows. While the majority of organ weights were similar (P ≥ 0.15) between CON and RES cows, weights of the abomasum and large intestine were altered. Abomasum and large intestinal weights were greater (P = 0.05) in RES cows compared with CON at d 85. Similarly, when expressed relative to EBW, RES cows tended (P = 0.07) to have greater abomasum and large intestinal weights compared with CON cows. Lung weight tended (P = 0.10) to be greater in RES cows compared to CON cows.


View Full Table | Close Full ViewTable 2.

The effects of nutrient restriction on maternal organ weight in beef cows at d 85 of gestation

 
Nutritional treatments1
Item CON RES SEM P-value
BW, kg 556.5 550.3 36.9 0.88
EBW,2 kg 419.4 426.8 28.7 0.84
REA,3 cm2 64.5 69.7 4.32 0.42
Carcass weight, kg 278.34 294.56 21.4 0.50
Back fat at 12th rib, cm 0.66 0.33 0.23 0.05
Gravid uterus, kg 2.51 2.80 0.20 0.19
Heart, kg 1.87 1.88 0.09 0.96
    g/kg EBW 4.47 4.44 0.32 0.95
Lung, kg 3.12 3.90 0.39 0.10
    g/kg EBW 7.61 9.05 1.02 0.15
Adrenals, kg 0.03 0.03 0.01 0.37
    g/kg EBW 0.07 0.08 0.01 0.52
Kidneys, kg 1.10 1.13 0.05 0.67
    g/kg EBW 2.67 2.67 0.14 0.98
Perirenal fat, kg 1.64 1.12 0.69 0.43
    g/kg EBW 3.71 2.46 1.45 0.40
Stomach complex, kg 15.8 15.8 0.75 0.99
    g/kg EBW 38.0 37.4 1.39 0.77
Abomasum, kg 1.85 2.16 0.09 0.05
    g/kg EBW 4.48 5.13 0.22 0.07
Omasum, kg 5.75 6.02 0.83 0.71
    g/kg EBW 13.8 13.7 1.24 0.96
Reticulum, kg 1.25 1.22 0.06 0.73
    g/kg EBW 2.99 2.89 0.13 0.58
Rumen, kg 6.85 6.78 0.51 0.88
    g/kg EBW 16.5 15.4 1.84 0.46
Small intestine, kg 4.12 4.43 0.17 0.24
    g/kg EBW 10.0 10.5 0.62 0.58
Large intestine, kg 3.43 4.40 0.20 0.01
    g/kg EBW 8.45 10.11 0.83 0.07
Spleen, kg 0.57 0.67 0.07 0.19
    g/kg EBW 1.40 1.55 0.18 0.40
Liver, kg 3.50 4.05 0.53 0.46
    g/kg EBW 8.71 9.55 1.45 0.66
Pancreas, kg 0.39 0.44 0.04 0.39
    g/kg EBW 0.94 1.04 0.07 0.37
Omental and mesenteric fat, kg 11.2 10.6 2.41 0.85
    g/kg EBW 28.22 25.58 7.19 0.74
1Cows received either control (CON; 100% NRC) diet (n = 6) or restricted (RES; 60% NRC) from d 30 to 85 (n = 6).
2EBW = empty BW: final BW – (gravid uterus + digesta).
3REA = ribeye area (LM muscle area).

Body weight, carcass weight, EBW, and REA were not affected by maternal nutrient restriction when cows were slaughtered at d 85. At this time point, gestating cows were restricted for only 55 d compared with CON cows. However, 12th rib back fat was decreased in RES cows compared to CON; therefore, RES cows might be mobilizing fat to compensate for the nutrient restriction. It was surprising that the overall weight of the gravid uterus was also not impacted by maternal nutrient restriction. The only organ masses that were impacted by this 55 d restriction included abomasum and large intestine. Similarly, Meyer et al. (2010) found greater relative abomasum weight (g/kg of EBW) in cows that were restricted from d 30 until d 125 compared to controls. However, they did not observe differences in large intestine weight. In ewe lambs that were nutrient restricted during gestation, a decrease in large intestine mass was observed (Reed et al., 2007). Scheaffer et al. (2001) did not find differences in large intestine weight as pregnancy progressed in growing heifers suggesting that this organ is not affected by stage of pregnancy or by the demands of the growing fetus. The lack of differences in organ masses in the current study is not surprising as BW was similar between treatments when cows were slaughtered at d 85. Perhaps mature cows, as used in the current study, are less sensitive to nutrient restriction during early gestation than young ewes. While percentage BW change started decreasing towards the end of the restriction period, this was not due to observable changes in organ mass. During nutrient restriction an important adaptation that has been observed in sheep is the reduction in visceral organ masses (Burrin et al., 1989; Reed et al., 2007). This might be an adaptation to the reduced nutrient intake in order for the animal to survive (Ferrell and Jenkins, 1985; Reed et al., 2007).

When cows were slaughtered at d 140, BW was decreased (P = 0.05; Table 3) and EBW tended to decrease (P = 0.10) in RR compared with CC cows (P = 0.04), with RC being intermediate (P ≥ 0.15; Table 3). Carcass weight, REA, and back fat at the 12th rib were not affected (P ≥ 0.12; Table 3) by treatment. A greater number of organ masses were influenced by maternal diet at d 140 than was observed at d 85. While abomasal and large intestinal masses were not different by d 140 (Table 3), there were differences in liver and rumen weights, with tendencies (P ≤ 0.10) observed in small intestine, total stomach complex, and reticulum weights. Liver weight (kg) was decreased (P = 0.02) in RR cows compared with CC (P = 0.006) and RC being intermediate (P ≥ 0.20). However, when expressed relative to EBW, liver weight (g/kg) was not affected (P = 0.55) by treatment at d 140. At d 140 of gestation, rumen weight was decreased (P = 0.003) in RR compared with CC and RC cows. When rumen was expressed relative to EBW, RR cows tended (P = 0.10) to have greater relative weights than CC and RC at d 140 of gestation. Reticulum and total stomach complex weights (kg) tended (P = 0.09) to decrease in RR cows compared with CC (P = 0.03), with RC being intermediate (P ≥ 0.12). However, when expressed relative to EBW, reticulum or total stomach complex weights were not affected (P = 0.50) by treatment at d 140 of gestation.


View Full Table | Close Full ViewTable 3.

The effects of realimentation after nutrient restriction on maternal organ weight in beef cows at d 140 of gestation

 
Nutritional treatments1
Item CC RC RR SEM P-value
BW, kg 609.2a 584.2ab 527.4b 28.6 0.05
EBW,2 kg 450.5 439.8 399.6 24.5 0.10
Carcass weight, kg 311.0 299.4 269.9 22.1 0.12
REA,3 cm2 64.3 63.1 64.6 4.45 0.97
Back fat at 12th rib, cm 0.43 0.28 0.15 0.20 0.21
Gravid uterus, kg 11.0 11.3 11.7 0.50 0.86
Heart, kg 2.08 2.06 2.00 0.10 0.84
    g/kg EBW 4.69 4.83 5.01 0.28 0.70
Lung, kg 3.54 3.40 3.67 0.20 0.66
    g/kg EBW 7.95 8.00 9.18 0.62 0.21
Adrenals, kg 0.04 0.05 0.03 0.01 0.51
    g/kg EBW 0.08 0.12 0.08 0.03 0.54
Kidneys, kg 1.20 1.07 1.11 0.06 0.32
    g/kg EBW 2.70 2.52 2.79 0.18 0.60
Perirenal fat, kg 1.81 1.90 1.25 0.53 0.66
    g/kg EBW 4.04 4.72 2.95 1.28 0.48
Stomach complex, kg 17.4 15.4 14.8 0.77 0.09
    g/kg EBW 39.0 36.2 37.0 1.90 0.50
Abomasum, kg 2.01 1.88 2.81 0.59 0.52
    g/kg EBW 4.51 4.49 6.51 1.05 0.34
Omasum, kg 5.58 4.69 4.80 0.58 0.49
    g/kg EBW 12.3 10.5 12.4 1.63 0.55
Reticulum, kg 1.47 1.35 1.18 0.08 0.09
    g/kg EBW 3.32 3.18 2.94 0.19 0.39
Rumen, kg 8.29a 7.47a 6.05b 0.34 0.003
    g/kg EBW 18.7 17.8 15.2 1.07 0.10
Small intestine, kg 4.56 4.30 3.85 0.26 0.10
    g/kg EBW 10.2 10.1 9.66 0.59 0.81
Large intestine, kg 3.52 3.71 3.35 0.29 0.61
    g/kg EBW 7.93 8.75 8.26 0.60 0.65
Spleen, kg 0.71 0.59 0.70 0.06 0.41
    g/kg EBW 1.59 1.41 1.71 0.11 0.22
Liver, kg 4.37a 4.01ab 3.74b 0.15 0.02
    g/kg EBW 9.79 9.40 9.34 0.36 0.55
Pancreas, kg 0.47 0.38 0.40 0.03 0.17
    g/kg EBW 1.06 0.89 0.98 0.06 0.21
Omental and mesenteric fat, kg 11.2 10.6 7.47 3.10 0.16
    g/kg EBW 23.9 23.1 18.4 5.96 0.40
a,bMeans without a common superscript letter differ, P < 0.05.
1Cows received the control diet (100% NRC) from d 30 until 140 (CC; n = 6), restricted from d 30 to 85 (60% NRC) and then realimented to 100% of the NRC requirements until d 140 (RC; n = 5), and restricted from d 30 to 140 (60% NRC; RR; n = 6).
2EBW = empty BW: final BW – (gravid uterus + digesta).
3REA = ribeye area (LM muscle area).

Longer nutrient restriction decreased BW compared with control cows that were slaughtered at d 140 of gestation. We observed decreased 12th rib back fat in RES cows at d 85 slaughter; however, when a similar length of restriction (55 d) was followed by realimentation there was no difference in 12th rib back fat at d 140 slaughter. Surprisingly, carcass REA and 12th rib back fat were not affected in cows that were nutrient restricted for 110 d. There was also a tendency for EBW to follow a similar pattern as BW. Moreover, it was surprising that cows that experienced a 110 d restriction still had a similar gravid uterine weight compared to adequately fed control cows. Differences observed in abomasum and large intestine weight when cows were slaughtered at d 85 were not present when cows were restricted from d 30 until d 85 and then realimented and slaughtered at d 140 of gestation. It is difficult to explain why nutrient restriction for 55 d increased mass of these organs but restriction for 110 d did not. Perhaps after a certain period of nutrient restriction, the dam no longer has large enough nutrient reserves (from body energy and protein mobilization) to draw from to increase visceral organ mass in an attempt to maintain fetal tissue development. The liver and rumen were the only organs for which weight was affected by nutrient restriction at d 140 where both organ masses were decreased in RR cows compared to CC and RC being intermediate. Similar to our data, Meyer et al. (2010) reported decreased liver and rumen weight in nutrient restricted cows from d 30 to 125 of gestation. Scheaffer et al. (2001) reported no differences in liver weight in pregnant heifers suggesting that the liver might not increase due to stage of pregnancy. Previous research in sheep indicated that liver mass increases in pregnant mature ewes compared with nonpregnant ewes (Scheaffer et al., 2004). In vitro oxygen consumption studies have shown that hepatic oxygen consumption decreases as feed intake is reduced (Burrin et al., 1989). However, hepatic oxygen consumption has been shown to increase in mature ewes as gestation progresses (Freetly and Ferrell, 1997). In addition, previous researchers have demonstrated that the decrease in oxygen consumption is partially driven by a decrease in tissue weight (Ferrell and Koong, 1985). It has been shown that pregnant beef heifers have decreased oxygen consumption in the ileum and decreased energy use in ileum and total small intestine due to pregnancy (Scheaffer et al., 2003). This might suggest an adaptation from the dam to conserve energy during gestation.

All cows were fed to meet 100% of NE requirements from d 140 to 254. By d 254, maternal BW, carcass weight, and EBW were not affected (P ≥ 0.78; Table 4) by treatment. Also, carcass REA and back fat at 12th rib were similar (P ≥ 0.72) among treatments. There were no impacts of maternal diet on organ weights including the gravid uterus (P = 0.37); however, there was a tendency (P = 0.08) for kidney and pancreas (P = 0.10) weight to be altered. Kidney weight (kg) tended to be greater (P = 0.08) in RCC cows compared with CCC, with RRC being intermediate. However, when expressed relative to EBW, kidney weight did not differ (P = 0.55) among treatments. Pancreas weight tended to be smaller (P = 0.08) in RRC cows compared with RCC, with CCC being intermediate. However, when expressed relative to EBW, pancreas weight did not differ (P = 0.21) among treatments.


View Full Table | Close Full ViewTable 4.

The effects of realimentation after nutrient restriction on maternal organ weight in beef cows at d 254 of gestation

 
Nutritional treatments1
Item CCC RCC RRC SEM P-value
BW, kg 624.2 622.0 605.8 31.2 0.85
EBW,2 kg 420.9 419.3 402.3 22.0 0.78
REA,3 cm2 56.2 53.4 55.5 6.06 0.92
Carcass weight, kg 275.4 277.1 262.7 20.4 0.82
Back fat at 12th rib, cm 0.11 0.08 0.18 0.07 0.62
Gravid uterus, kg 59.1 59.5 65.4 3.40 0.37
Heart, kg 2.06 1.93 1.82 0.12 0.30
    g/kg EBW 4.85 4.68 4.50 0.23 0.57
Lung, kg 3.66 2.99 3.17 0.31 0.13
    g/kg EBW 8.43 7.28 7.82 0.63 0.48
Adrenals, kg 0.03 0.32 0.04 0.19 0.51
    g/kg EBW 0.08 1.10 0.11 0.66 0.51
Kidneys, kg 1.27 1.13 1.23 0.06 0.08
    g/kg EBW 3.00 2.78 3.03 0.17 0.55
Perirenal fat, kg 1.27 1.80 0.99 0.35 0.24
    g/kg EBW 3.02 4.08 2.50 0.77 0.31
Stomach complex, kg 18.1 17.3 17.0 0.65 0.49
    g/kg EBW 43.7 42.0 42.3 1.93 0.80
Abomasum, kg 2.14 2.23 2.19 0.13 0.86
    g/kg EBW 5.09 5.49 5.42 0.39 0.76
Omasum, kg 5.56 5.04 5.03 0.28 0.35
    g/kg EBW 13.5 12.2 12.6 0.76 0.54
Reticulum, kg 1.72 1.38 1.34 0.17 0.25
    g/kg EBW 4.21 3.36 3.35 0.45 0.35
Rumen, kg 8.68 8.63 8.42 0.32 0.83
    g/kg EBW 21.0 20.9 21.0 0.73 0.99
Small intestine, kg 4.68 5.01 4.59 0.15 0.19
    g/kg EBW 11.1 12.4 11.5 0.85 0.56
Large intestine, kg 4.35 4.43 3.81 0.21 0.11
    g/kg EBW 10.5 10.9 9.48 0.80 0.44
Spleen, kg 0.60 0.58 0.58 0.05 0.94
    g/kg EBW 1.41 1.39 1.43 0.08 0.94
Liver, kg 4.31 4.33 4.54 0.19 0.67
    g/kg EBW 10.3 10.4 11.3 0.46 0.20
Pancreas, kg 0.48 0.52 0.39 0.04 0.10
    g/kg EBW 1.13 1.24 0.98 0.09 0.21
Omental and mesenteric fat, kg 10.68 9.49 7.92 1.61 0.49
    g/kg EBW 25.2 21.9 19.7 3.18 0.49
1Cows received the control diet (100% NRC) from d 30 until 254 (CCC; n = 6), restricted from d 30 to 85 (60% NRC) and then realimented to 100% of the NRC requirements until d 254 (RCC; n = 5), and restricted from d 30 to 140 (60% NRC) and then realimented to 100% of the NRC requirements until d 254 (RRC; n = 6).
2EBW = empty BW: final BW – (gravid uterus + digesta).
3REA = ribeye area (LM muscle area).

When cows were slaughtered at d 254 of gestation, BW, EBW, and carcass ultrasonography measurements were not different among treatments. This could be because the mature cows used in this experiment were less sensitive to nutrient restriction and/or compensatory BW gain after nutrient realimentation compared to control cows. It was surprising that gravid uterus weight was not affected by maternal nutrition at any time point of gestation. However, components of the gravid uterus, namely the fetal, placental, and fetal fluid masses, will be reported in a future manuscript. In addition, the few differences previously observed due to restriction at d 85 and 140 slaughters disappeared. This is probably due to realimentation occurring either at d 85 or 140 of gestation for both treatments that previously were nutrient restricted. Perhaps cows were able to recover from the different periods of nutrient restriction after nutrient realimentation. When nutrient restricted cows were allowed approximately 125 d of realimentation, Meyer et al. (2010) reported no differences in organ weights of cows. Even though the realimentation protocol in our experiment was designed to meet NRC NE requirements whereas the realimentation protocol of Meyer et al. (2010) allowed for cows to be realimented above NRC recommendations to achieve a similar BCS to control animals, we observed similar results by d 254. In a sheep model of nutrient restriction during midgestation followed by a realimentation period (control; 100% NRC recommendations) in late gestation, restricted ewe lambs had greater relative liver, pancreas, reticulum, stomach, small intestine, and large intestine weight than the control ewes during late pregnancy (Carlson et al., 2009). The differences between this study and ours could be due to species differences, time of restriction, and/or age. Carlson et al. (2009) used gestating ewe lambs that were still growing and at the same time providing nutrients to the growing fetus.

Energy expenditure from liver and gastrointestinal tract accounts for close to 50% of the total energy utilized by ruminants (Ferrell, 1988). In addition, during pregnancy maternal oxygen consumption changes reflecting the energy requirements needed for tissue accretion and fetal and maternal metabolism (Stock and Metcalfe, 1994). After nutrient restriction, maintenance requirements for the whole animal have been shown to decrease and a time interval is required to reach a steady state again (Koong and Nienaber, 1985). In addition, nutritional plane has been shown to have an effect on maintenance energy requirements and is highly correlated with changes of visceral organs weights (Ferrell et al., 1986).

A very important adaptation during pregnancy is the increase in blood volume (Thornburg et al., 2006), cardiac output (Stock and Metcalfe, 1994), and decreased total peripheral resistance in the pregnant female (Thornburg et al., 2006). Pregnancy also requires an increase in organ workload, particularly in the gastrointestinal tract, to keep up with the increase in nutrient demands by the conceptus (Ferrell, 1988; Thornburg et al., 2006). Some adaptations by the gastrointestinal tract are increases in organ mass or functional capacity (Stock and Metcalfe, 1994). This increase in the workload of the maternal organs results in increased maternal energy requirements (Ferrell, 1988). Perhaps a restricted diet during early gestation programs the dam to be more efficient with the resources that it may or may not have as gestation continues. In our particular experiment, realimentation appeared to supply the dam with sufficient nutrients for the developing conceptus as gravid uterine weight was similar across treatments near term. So in other words, even though the demands of the early conceptus for nutrients from the dam may be minimal, perhaps we are programming the way the maternal system will utilize its available nutrients throughout the remainder of gestation. This may be a reason why we observed few changes in organ weights (especially after realimentation) in the current study.

In summary, nutrient restriction from early to midgestation followed by realimentation in pregnant beef cows impacts maternal BW and organ masses. Our observations differ from those previously reported using pregnant sheep as a model. Therefore, cows might adapt differently to nutrient restriction than ewes, perhaps being less sensitive to reduced nutrient supply. Further investigations on maternal metabolic changes and effects of nutrient restriction followed by realimentation during early to midgestation on conceptus development are necessary.

 

References

Footnotes


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