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Journal of Animal Science - Animal Production

Effect of growth implant regimen on health, performance, and immunity of high-risk, newly received stocker cattle1

 

This article in JAS

  1. Vol. 93 No. 8, p. 4089-4097
     
    Received: Dec 19, 2014
    Accepted: May 14, 2015
    Published: July 2, 2015


    2 Corresponding author(s): pbeck@uaex.edu
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doi:10.2527/jas.2014-8835
  1. J. T. Richeson*,
  2. P. A. Beck 2,
  3. H. D. Hughes*,
  4. D. S. Hubbell,
  5. M. S. Gadberry§,
  6. E. B. Kegley#,
  7. J. G. Powell# and
  8. F. L. Prouty33
  1. * Department of Agricultural Sciences, West Texas A&M University, Canyon 79016
     Southwest Research and Extension Center, University of Arkansas, Division of Agriculture, Hope 71801
     Livestock and Forestry Research Station, University of Arkansas, Division of Agriculture, Batesville 72501
    § Cooperative Extension Service, University of Arkansas, Division of Agriculture, Little Rock 72204
    # Department of Animal Science, University of Arkansas, Division of Agriculture, Fayetteville 72701
     Zoetis, Louisburg, KS 66053

Abstract

Growth implant efficacy may be affected when administered to nutritionally stressed calves, whereas the procedure may alter health or the humoral immune response to respiratory vaccination. The study objective was to determine the effect of different administration times (d 0, 14, or 28) of a growth implant containing 200 mg progesterone and 20 mg estradiol benzoate on health, performance, and metabolic and immunologic variables in high-risk, newly received beef calves used in a 120-d receiving/grazing stocker system. Crossbred bull and steer calves (n = 203) were weighed (initial BW = 203 ± 2.7 kg), stratified by castrate status on arrival, and randomly assigned to experimental treatments consisting of 1) negative control (no growth implant administered), 2) growth implant administered on d 0, 3) growth implant administered on d 14, and 4) growth implant administered on d 28. There were no differences (P ≥ 0.16) in BW or ADG during the 42-d receiving period. However, ADG during the subsequent grazing period and overall was greater (P ≤ 0.01) for implanted calves versus the negative control. Growth implant timing did not affect the rate of clinical bovine respiratory disease morbidity (P = 0.52; 94% morbidity overall) or bovine viral diarrhea virus type 1a antibody titer concentration (P = 0.61). Indicative of an overall negative energy balance on arrival, NEFA decreased sharply subsequent to d 0 (day effect, P < 0.001), but was not affected (P = 0.47) by the timing of growth implantation. Blood urea N concentrations increased transiently (day effect, P < 0.001); however, no treatment effect was observed (P = 0.72). Therefore, under conditions of this study, the timing of growth implant administration did not affect growth implant efficacy, health, or metabolic or immunologic variables in newly received, high-risk beef stocker calves. Overall, our observations suggest that there is not a clear benefit to delaying growth implantation and that a growth implant does not affect health or vaccine response in newly received beef calves.



INTRODUCTION

Cattle experiencing stress-induced physiologic and metabolic alteration are commonly received at a stocker or feedlot facility, because stressful factors such as weaning, commingling, handling, and transportation are imposed during the marketing process (Taylor et al., 2010). Growth implants have been used in the United States for nearly 50 yr to improve gain and feed efficiency of beef cattle; however, the concept that stress may affect growth implant efficacy has been minimally explored. Serum hormone concentration is increased rapidly subsequent to growth implant administration (Bryant et al., 2010). Implanting with exogenous growth-promoting hormones on receiving may impact the immune response, because anabolic effects of the growth implant could modify metabolism to favor tissue accretion rather than immune products during a time when pathogenic infection is most prevalent. Therefore, administration of a growth implant in highly stressed cattle may reduce efficacy of the growth implant, increase clinical morbidity, or decrease the humoral immune response to a respiratory vaccine. Conversely, the catabolic effects of proinflammatory cytokines (i.e., IL-6 and TNF-α) released by stimulated leukocytes during stress and infection may be mitigated by an exogenous growth implant (McMahon et al., 1998), thereby enhancing intake and growth performance of stressed cattle.

We hypothesized that the efficacy of an exogenous growth implant is reduced when administered to calves on arrival when physiological stress is typically increased. Our objective was to determine the effects of growth implant administration in high-risk calves and whether the timing of administration impacts health, performance, and immunity.


MATERIALS AND METHODS

Animal methods were approved by the University of Arkansas Animal Care and Use Committee.

Animals and Experimental Treatments

Male beef calves (n = 203; 203 ± 2.7 kg) were received at the University of Arkansas Livestock and Forestry Research Station near Batesville in northeast Arkansas (35°50′ N, 91°48′ W) on 2 dates: September 12, 2011 (Block 1; n = 102 calves), and October 31, 2011 (Block 2; n = 101 calves). Cattle were acquired from regional auction markets and health history was unknown. Experimental treatments consisted of 1) negative control (CON; no growth implant administered), 2) growth implant (containing 200 mg progesterone and 20 mg estradiol) administered on d 0 (IMP0; Synovex S; Zoetis, Kalamazoo, MI), 3) growth implant administered on d 14 (IMP14; Synovex S), and 4) growth implant administered on d 28 (IMP28; Synovex S). Treatments were evaluated in a randomized complete block design with inferences made on growth performance, bovine respiratory disease (BRD) morbidity rate, percentage chronically ill (nonresponsive), mortality, and days to first antimicrobial treatment. Furthermore, 5 randomly selected animals from each pen were bled via jugular venipuncture using a plain vacuum tube and serum was collected to evaluate humoral vaccine response (bovine viral diarrhea virus [BVDV] type 1a antibody titer), blood urea N (BUN) concentrations, and NEFA concentrations on d 0, 14, 28, and 42. In addition, a tube containing EDTA was used to sample blood for a complete blood count via automated hemocytometer (CELL-DYN; Abbott Laboratories, Abbott Park, IL) to explore immune alteration (total and differential peripheral blood leukocyte concentrations, hemoglobin, hematocrit, and platelets) on each of the above sampling dates. Serum urea N and NEFA concentrations were determined using commercially available kits (B551 [Teco Diagnostics, Anaheim, CA] and HR Series NEFA-HR(2) [Wako Chemicals USA, Inc., Richmond, VA], respectively). For BVDV titer analyses, the serum samples from the 5 steers/pen were pooled by pen and day and submitted to the Iowa State University Veterinary Diagnostic Laboratory (Ames, IA). Upon completion of the 42-d receiving phase of the trial, calves were commingled and allowed to graze small grain pasture for an additional 78 d.

Upon arrival at the research unit (d –1), calves were individually weighed and individually identified, castrate status was determined, and calves were ear notched and tested for persistently infected BVDV status at a commercial laboratory (CattleStats LLC, Oklahoma City, OK). No experimental calves tested positive for persistently infected BVDV. Calves were then stratified by d –1 BW and castrate status (bull or steer) and randomly assigned to 1 of 8 pens (12 to 13 calves/pen). Treatments were then randomly assigned to pen. Pen was considered the experimental unit, and treatments were replicated 2 times during Blocks 1 and 2, resulting in a total of 4 pen replicates for each experimental treatment. The following day (d 0), calves were weighed, bled, vaccinated with a pentavalent (bovine herpesvirus-1, BVDV type 1a and 2a, bovine respiratory syncytial virus, and parainfluenza-3 virus) modified live virus vaccine (Bovi-Shield GOLD 5; Zoetis), a multivalent clostridial/Mannheimia haemolytica bacterin-toxoid approved for single-dose efficacy (One Shot Ultra 7; Zoetis), and a concentrated tetanus toxoid (Colorado Serum Company, Denver, CO). Calves were dewormed (Dectomax; Zoetis) and castrated by banding method if applicable (InoSol Co. LLC, El Centro, CA). Also on d 0, calves assigned to the d-0 implant treatment received the growth implant administered subcutaneously in the caudal aspect of the right ear. On d 14 or 28, calves assigned to the appropriate implant treatment were administered their growth implant.

After initial processing, calves were fed an identical receiving supplement based on corn gluten feed (89% DM, 24% CP, 12% ADF, 35% NDF, and 72% TDN) at rates increasing up to a maximum of 1.8 kg/d with ad libitum access to bermudagrass hay (10% CP and 57% TDN, DM basis). Feed bunks were evaluated each morning at approximately 0800 h; if feed bunks were empty, the amount of supplement offered the following day was increased by 0.23 kg/animal until the maximum rate of 1.8 kg/d was reached. After the quantity of feed to be provided to each pen was determined, that amount was weighed and hand fed each morning at approximately 0830 h.

For Block 1, calves were weighed on 2 consecutive days at the initiation of the experiment (d –1 and 0); d 14, 28, 42, 63, 64, and 91; and on consecutive days at the end of the grazing period (d 119 and 120). Although the predetermined end of the receiving period was d 42, the pastures at the site were not adequately developed for grazing turnout. Therefore, calves in Block 1 were placed back in their assigned receiving pens and continued to receive corn gluten feed and hay until forage availability was sufficient for grazing turnout on d 64.

For Block 2, calves were weighed on 2 consecutive days at the initiation of the experiment (d –1 and 0); d 14, 28, 42, 43, 64, and 91; and on consecutive days at the end of the grazing period (d 119 and 120). On d 43, 91 of the 101 steers in Block 2 were randomly selected and shipped to the University of Arkansas Southwest Research and Extension Center, near Hope, AR (346 km and 4-h transit time), for grazing cool-season annual pastures.

All calves were observed daily for signs of BRD throughout the receiving and grazing period. Signs of BRD included nasal or ocular discharge, increased respiration, gaunt appearance, or depression. If 2 or more signs existed for an animal, they were moved and restrained in a chute and rectal temperature was recorded. If rectal temperature was ≥40°C, calves were treated according to a predetermined antimicrobial regimen consisting of initial treatment with tulathromycin (Draxxin; Zoetis), secondary treatment with florfenicol (Nuflor; Merck Animal Health, Summit, NJ), and tertiary treatment with ceftiofur hydrochloride (Excenel RTU; Zoetis). The posttreatment interval for tulathromycin and florfenicol was 8 and 2 d, respectively.

Pasture Establishment and Management

Following the receiving period, Block 1 steers grazed 38 ha of wheat pasture. The study site consisted of Peridge silt loam soil, a deep well-drained upland soil with moderate native fertility. Wheat (Triticum aestivum L. cv. DK9108) was established in the first week of September in 21 ha of dedicated crop fields using either conventional tillage or no-till as described by Bowman et al. (2008) and Morgan et al. (2012) and interseeding into 17 ha of bermudagrass (Cynodon dactylon) pastures as described by Beck et al. (2011). Steers were commingled across treatments and allocated to pastures at stocking rates set independently for each pasture, ensuring an average initial forage allowance of 3.6 kg forage DM/kg steer BW and the average stocking rate was 2.6 steers/ha.

Following the receiving period, 91 steers from Block 2 were shipped on December 13, 2011, to the University of Arkansas Southwest Research and Extension Center, near Hope, AR (33°42′ N, 93°31′ W). Soils were primarily Smithdale fine sandy loam but also included areas of Sawyer loam, which are deep, moderately well drained, and low in native fertility, with low soil pH and OM. Pastures consisted of 48-ha bermudagrass pastures that had been interseeded to a blend of small grain and annual ryegrass (Lolium multiflorum Lam. cv. Marshall) in mid September. One 12-ha pasture was planted to wheat (cv. DK9108) and ryegrass, a total of 19 ha (in 4 separate pastures) was planted to oats (Avena sativa L. cv. Bob) and ryegrass, and 17 ha (in 6 pastures) was planted to rye (Secale cereale L. cv. Elbon) and ryegrass. Stocking rate decisions were made independently for each pasture allocating an average initial forage allowance of 4.2 kg of forage DM/kg BW, and the average stocking rate across pastures was 1.9 steers/ha. Research reported by Beck et al. (2005a, 2007) found few differences in performance of steers grazing these species of small grains.

Small grains were planted at 100 kg/ha to a depth of 2.5 cm in 17 cm rows; annual ryegrass was planted at 22 kg/ha at a depth of 1 cm in 17 cm rows. The conventional tillage establishment protocol was to offset disk following removal of calves after grazeout the previous spring, chiseling twice, and light disking before planting, resulting in <4% residue cover at planting. No-till pastures were sprayed with glyphosate (2.3 L/ha; Roundup Original Max; Monsanto Co., St. Louis, MO) 3 times (on removal of calves following grazeout the previous spring, in mid summer, and before planting) as a chemical fallow and wheat was planted directly into the residue of the previous crop, with >85% ground cover from residue. Pastures interseeded into bermudagrass were mob grazed with cow–calf pairs to reduce herbage mass to less than 4 cm in standing height to increase the seed-to-soil contact and reduce shading of the sown crop and were sprayed with glyphosate (1.17 L/ha; Roundup Original Max; Monsanto Co.) as described by Beck et al. (2011).

The forage allowance used in this study was reported by Beck et al. (2013) to provide the greatest likelihood that forage would not limit DMI or performance during the grazing period. Steers in all pastures were allowed free access to drinking water sourced from a well. Steers in each pasture were given free-choice access to nonmedicated mineral (Sunbelt Custom Minerals, Inc., Sulfur Springs, TX), which contained 14% Ca and 7% P from CaCO3 and Ca2PO4, 5% Mg from MgO, and 14% NaCl as well as vitamins (661,500 IU/kg vitamin A, 221 IU/kg vitamin E, and 66,150 IU/kg vitamin D) and trace minerals (1,000 mg/kg Mn from MnSO4, 2,355 mg/kg Fe from FeSO4, 1,250 mg/kg Cu from CuSO4, 3,000 mg/kg Zn from ZnSO4, 20 mg/kg Co from CoCO3, and 25 mg/kg I from ethylenediamine dihydroiodide).

Forage DM yield was estimated during the experiment using a rising-plate meter as described by Michell and Large (1983). Forage heights were measured at 20 locations in each pasture; rising plate readings were calibrated by clipping the forage within two 30.5- by 30.5-cm quadrants in each pasture. Calibration samples were dried to a constant weight (50°C) in a forced-air oven and then forage DM yield was regressed on height. Forage nutritive value samples were collected monthly by hand plucking to mimic the forage selection by grazing cattle. Each shipment of supplemental feed offered during receiving was sampled on delivery. Small grain forage, receiving supplement, and hay samples were dried to a constant weight (50°C) in a forced-air oven and ground to pass a 2-mm screen (Thomas Wiley Laboratory Mill, model 4; Thomas Scientific, Swedesboro, NJ) for analysis of nutritive value. Samples were analyzed for nutritive quality using near-infrared reflectance spectroscopy (Feed and Forage Analyzer model 6500; FOSS North America, Eden Prairie, MN). The CP calibration equation had a SE of calibration (SEC) of 0.92, a SE of cross-validation (SECV) of 0.93, and R2 of 0.96. The NDF calibration equation had a SEC of 2.63, a SECV of 2.73, and R2 of 0.95. The ADF calibration equation had a SEC of 1.66, a SECV of 1.70, and R2 of 0.93.

Statistical Analyses

A randomized complete block design was used. Block (arrival group of cattle) was considered a random effect in the model. Animal performance data during the receiving period were analyzed with pen as the experimental unit. Steers were commingled across treatments and pens during the grazing period; therefore, performance data recorded during this time was analyzed using individual animal as the experimental unit. Computations of performance variables were made using the MIXED procedure of SAS (SAS Inst. Inc., Cary, NC). Morbidity data were analyzed as binomial data using the GLIMMIX procedure of SAS. Hematological parameters and BVDV type 1a antibody titer, urea N, and NEFA concentrations were evaluated using the MIXED procedure with repeated measures. For repeated measures analyses, the repeated statement was day and fixed effects included treatment, day, and the treatment × day interaction. Autoregressive was the covariance structure used. The random statement included group, and the subject was identified as pen within group. Treatment means were compared using least significant difference and a significance level of P ≤ 0.05 was established for all analyses. Before analyses, the UNIVARIATE procedure was used to test for normality. Data were log transformed before statistical analyses; if that improved the normality, geometric means are presented in the tables and figures.


RESULTS AND DISCUSSION

Animal Health and Performance

Performance data are presented in Table 1. There were no differences (P ≥ 0.16) in steer BW or ADG during the receiving period. During the first 21 d of the grazing period (d 42 to 63), steer gains were lower than what would be expected based on the forage quality. This phenomenon is common when steers are removed from a dry lot consuming primarily hay-based diets and placed on high-quality cool-season annual pastures. Lower than expected growth performance typically occurs during the transition period from a lower quality forage with a slower rate of passage to a higher quality forage with a faster rate of passage (Phillips et al., 2003; Beck et al., 2005c); a portion of the weight difference is due to reduction of gut fill and a portion is potentially due to ruminal adaptation to the small grain diet (Lippke and Warrington, 1984; Lippke et al., 2000; Beck et al., 2005b). Phillips et al. (2003) reported that Angus calves grazing wheat pasture lost BW during the first 10 d of grazing and BW after 20 d of grazing was similar to initial BW, whereas BW was increased by only 10 kg by d 30 of grazing. Research evaluating performance of calves transitioning onto winter pasture indicates there is potential for ruminal acidosis to occur in calves grazing high-quality cool-season forages when warm-season hay diets are fed during the backgrounding period, limiting intake and animal performance within the first 20 d of grazing (Lippke and Warrington, 1984; Lippke et al., 2000).


View Full Table | Close Full ViewTable 1.

Effect of timing of growth implant administration on performance of newly received beef calves

 
Treatment1
SEM P-value
Item Control IMP0 IMP14 IMP28
BW, kg
    Initial2 200.9 203.6 203.2 204.5 2.7 0.79
    Day 14 218.2 223.6 218.2 222.3 3.1 0.52
    Day 28 232.3 239.1 230.9 236.4 3.2 0.25
    Day 423 246.4 253.2 248.6 249.5 4.9 0.61
    Day 634 255.5 263.6 261.4 263.6 3.9 0.36
    Day 915 285.9a 304.5b 300.0b 301.8b 4.1 0.10
    Final BW6 313.2a 333.2b 329.5b 335b 4.2 <0.01
ADG, kg/d
    D 0 to 14 1.24 1.41 1.09 1.24 0.12 0.16
    D 14 to 28 1.00 1.12 0.92 1.04 0.12 0.27
    D 28 to 42 1.01 0.99 1.26 0.93 0.30 0.34
    Receiving ADG7 1.08 1.17 1.09 1.07 0.10 0.28
    D 42 to 63 0.43a 0.53ab 0.60b 0.64b 0.18 0.01
    D 63 to 91 1.09a 1.43b 1.38b 1.40b 0.33 <0.01
    D 91 to 120 0.96a 1.01a 1.05a 1.18b 0.09 <0.01
    Pasture ADG8 0.85a 1.02b 1.04bc 1.10c 0.05 <0.01
    Overall ADG9 0.93a 1.08b 1.05b 1.09b 0.02 <0.01
a–cLeast squares means within a row with differing superscripts differ (P < 0.05).
1Control = no growth implant administered; IMP0 = growth implant administered on d 0; IMP14 = growth implant administered on d 14; IMP28 = growth implant administered on d 28.
2Average BW of steers on d –1 and 0 of receiving period.
3Body weight of steers at the end of the receiving period.
4Body weight of steers on d 21 after receiving.
5Body weight of steers on d 49 after receiving.
6Average BW of steers on d 119 and 120.
7Average daily gain of steers from d 0 to 42.
8Average daily gain of steers from d 42 to 120.
9Average daily gain of steers from d 0 to 120.

Steers that were implanted later in the receiving period (IMP14 and IMP28) gained BW faster (P ≤ 0.01) from d 42 to 63 than CON, whereas ADG of IMP0 was intermediate. From d 63 to 91, implanted steers gained weight 0.32 kg/d more rapidly (P < 0.01) than CON. Later in the grazing period from d 91 to 120, IMP28 gained weight more rapidly (P ≤ 0.01) than steers that were not implanted or were implanted on d 0 or 14, which did not differ (P ≥ 0.12). This indicates that the growth response from implants administered early in the receiving period had decreased at this time, whereas implants administered later (d 28) in the receiving period remained active during the grazing period.

Over the entire fall and winter grazing period, pasture ADG of CON was 0.2 kg/d less (P < 0.01) than calves that received a growth implant, whereas ADG of IMP0 was 0.08 kg/d less (P = 0.05) than IMP28 and gain of IMP14 tended (P = 0.11) to be 0.06 kg/d less than IMP28. Overall ADG (receiving and pasture combined) was 0.11 kg/d greater (P < 0.01) for steers on implant treatments compared with CON, and there were no differences (P ≥ 0.36) among implant treatments. Similar to our findings, Munson et al. (2012) did not detect differences in ADG or feed conversion in feedlot steers implanted with a long-acting growth implant on arrival or delayed 45 d.

There were no differences (P ≥ 0.30) in BRD morbidity (Table 2) or the number of days to first treatment. Morbidity rate was exceptionally high (94% morbidity overall). The average days to first treatment was 1.4, suggesting the calves had developed BRD during the marketing process before arrival. In a previous study, delaying implantation 45 d reduced the percentage of animals salvaged early due to chronic respiratory disease, but no other health parameters were affected (Munson et al., 2012).


View Full Table | Close Full ViewTable 2.

Effect of timing of growth implant administration on health of newly received beef calves

 
Treatment1
SEM P-value
Item Control IMP0 IMP14 IMP28
Bovine respiratory disease treatment, %
    Treated once 89.7 96.0 93.8 98.4 8.7 0.52
    Treated twice 24.1 12.4 25.8 27.8 12.9 0.30
    Treated thrice 1.1 0.5 1.6 2.3 2.8 0.69
Days to first treatment 1.2 1.2 1.6 1.3 0.23 0.66
1Control = no growth implant administered; IMP0 = growth implant administered on d 0; IMP14 = growth implant administered on d 14; IMP28 = growth implant administered on d 28.

Forage Yield and Nutritive Quality

Pastures in Block 1 provided an average forage mass of 2,260 ± 210 kg DM/ha in November, 2,340 ± 647 kg DM/ha in December, and 1,640 ± 233 kg DM/ha in January, so that forage allowance was 3.6, 3.4, and 2.1 kg forage DM/kg steer BW, respectively. Pastures in Block 2 provided an average forage mass of 1,760 ± 297 kg DM/ha in December, 1,850 ± 469 kg DM/ha in January, 1,940 ± 531 kg DM/ha in February, and 2,560 ± 978 kg DM/ha in March, so that forage allowance was 4.2, 4.3, 3.8, and 4.5 kg forage DM/kg steer BW, respectively. These levels of forage mass are above the parameters described by Redmon et al. (1995) that would limit forage DMI and thus limit BW gain. Forage allowance was also maintained at levels that Beck et al. (2013) indicated would provide for maximum steer performance.

Wheat pasture forage was extremely high in CP, averaging in excess of 23 ± 2.8% CP (DM basis) at all points during the experiment. Wheat forage was also low in fiber, averaging from 33 to 44% NDF and 15 to 25% ADF (DM basis) during the experiment. The CP and detergent fiber content in the current study is in agreement with research published by Beck et al. (2013). Crude protein content and estimated energy content of the forages were greater than the quantity required for a 250-kg growing steer to gain in excess of 1.0 kg/d (NRC, 1996).

Serology and Hematology

Response to modified live virus respiratory vaccination, as indicated by BVDV type 1a antibody titer concentration, was affected by day (P < 0.001; Fig. 1) but was not impacted by treatment (P = 0.61) and there was not a treatment × day interaction (P = 0.13). This would suggest that a growth implant administered concurrent with respiratory vaccination did not impact the efficacy of either procedure.

Figure 1.
Figure 1.

Effect of timing of growth implant administration on bovine viral diarrhea virus (BVDV) antibody titers of newly received beef calves. Control = no growth implant administered; IMP0 = growth implant administered on d 0; IMP14 = growth implant administered on d 14; IMP28 = growth implant administered on d 28. Treatment, P = 0.61; day, P < 0.001; treatment × day, P = 0.13.

 

Serum NEFA concentrations decreased sharply from d 0 to 14 (day effect, P < 0.001), which suggests that calves were experiencing a negative energy balance on arrival (Fig. 2). Previous studies show significant relationship between negative energy balance and increased serum NEFA concentration (Bauman and Currie, 1980; Ospina et al., 2010). However, serum NEFA was not affected by treatment (P = 0.82) and no treatment × day interaction was observed (P = 1.00). The nutritional status of calves subsequent to d 0 was likely improved resulting in a decrease in NEFA.

Figure 2.
Figure 2.

Effect of timing of growth implant administration on serum NEFA of newly received beef calves. Control = no growth implant administered; IMP0 = growth implant administered on d 0; IMP14 = growth implant administered on d 14; IMP28 = growth implant administered on d 28. Treatment, P = 0.82; day, P < 0.0001; treatment × day, P = 1.00.

 

A day effect (P < 0.001) was also observed for BUN concentrations (Fig. 3); BUN increased transiently and was greatest (P ≤ 0.005) on d 14. It is likely that the low concentrations found on d 0 were due to feed intake restriction in the marketing channels. There was a treatment × day interaction (P = 0.03) for serum BUN concentrations; on d 28, IMP14 had decreased serum BUN as compared with IMP28, with IMP0 and CON intermediate. However, on d 42, IMP28 had decreased serum BUN compared with IMP14, and IMP0 and CON were again intermediate. It is interesting that these decreased serum BUN concentrations were observed 14 d after the implant was administered; however, this change was not observed for IMP0. Other researchers have also observed decreases in BUN concentrations following administration of estradiol implants (McMahon et al., 1998; Cecava and Hancock, 1994), indicating that protein is spared.

Figure 3.
Figure 3.

Effect of timing of growth implant administration on blood urea N of newly received beef calves. Control = no growth implant administered; IMP0 = growth implant administered on d 0; IMP14 = growth implant administered on d 14; IMP28 = growth implant administered on d 28. Treatment, P = 0.72; day, P < 0.0001; treatment × day, P = 0.03. a,bWithin a day, least squares means differ, P < 0.05.

 

There was no effect (P ≥ 0.34) of implantation timing on any of the hematology variables (Table 3). The only variable for which there was a treatment × day interaction was the concentration of platelets (P = 0.02; Fig. 4); however, differences observed were on d 0 before any treatments were applied. There were effects of day on certain hematology variables collected during the receiving period (Table 4). These day effects were expected and have been observed previously in studies with high-risk cattle (Richeson et al., 2012). Specifically, eosinophils were least on d 0 and increased with time (quadratic, P = 0.001). Previous research suggests that decreased eosinophils on arrival are associated with an increased risk of BRD (Richeson et al., 2013) and eosinophil concentrations in blood decreased sharply after a dexamethasone stress challenge model was imposed in beef calves (May et al., 2015). Neutrophil percentage (quadratic, P = 0.03) and neutrophil:lymphocyte ratio (linear, P = 0.02) decreased with time; neutrophilia is common in highly stressed, newly received beef calves because cortisol may enhance neutrophil influx from bone marrow yet diminish neutrophil L-selectin expression, an important mechanism for neutrophil migration from peripheral blood to tissue (Roth, 1985; Ballou et al., 2015). Platelets were increased transiently on d 14 (cubic, P < 0.001), which may have been impacted by castration, modified live virus vaccination, or other processing procedures on d 0 that occurred for all treatments. Platelets are classically known for their role in hemostasis and tissue restoration; however, they are also a source of CD154, a signaling molecule for B- and T-cell activation (Sowa et al., 2009).


View Full Table | Close Full ViewTable 3.

Overall effects of timing of growth implant administration on hematology of newly received beef calves sampled on d 0, 14, 28, and 42

 
Treatment1
SEM P-value
Item Control IMP0 IMP14 IMP28 Treatment Day Treatment × day
Total white blood cells,2 ×103/μL 9.98 10.02 8.88 10.20 0.081 0.61 <0.001 0.09
Neutrophils,2 ×103/μL 1.60 1.82 1.60 1.57 0.098 0.69 0.64 0.95
Neutrophils,2 % 17.1 18.4 20.1 16.5 0.09 0.41 0.03 1.00
Lymphocytes, ×103/μL 6.84 7.28 6.25 7.71 0.72 0.52 <0.001 0.57
Lymphocytes, % 66.2 66.2 64.8 69.0 3.57 0.87 <0.001 0.98
Neutrophil:lymphocyte2 0.35 0.34 0.40 0.30 0.14 0.55 0.01 0.96
Monocytes, ×103/μL 1.07 1.17 1.07 1.09 0.06 0.57 0.01 0.06
Monocytes, % 11.6 12.4 12.7 11.8 1.35 0.93 <0.001 0.20
Eosinophils,2 ×103/μL 0.08 0.09 0.10 0.08 0.26 0.92 <0.001 0.98
Eosinophils,2 % 0.9 0.9 1.3 0.8 0.20 0.34 <0.001 0.86
Red blood cells, ×106/μL 10.2 10.2 10.2 10.0 0.28 0.98 <0.001 0.93
Hemoglobin, g/100 mL 12.6 12.5 12.7 12.4 0.27 0.89 <0.001 0.99
Hematocrit, % 36.3 35.9 36.5 35.7 0.71 0.87 <0.001 0.98
Platelets,2 ×103/μL 689 635 655 679 0.10 0.93 <0.001 0.02
1Control = no growth implant administered; IMP0 = growth implant administered on d 0; IMP14 = growth implant administered on d 14; IMP28 = growth implant administered on d 28.
2Data were log transformed before statistical analysis. Reported least squares means are the geometric means; the SEM is for the log transformed data.
Figure 4.
Figure 4.

Effect of timing of growth implant administration on blood platelet concentrations. Control = no growth implant administered; IMP0 = growth implant administered on d 0; IMP14 = growth implant administered on d 14; IMP28 = growth implant administered on d 28. Data were log transformed before statistical analysis and least squares means are the geometric means; the SEM is 0.13 for the log transformed data. Treatment, P = 0.93; day, P < 0.0001; treatment × day, P = 0.02. a,bWithin a day, least squares means differ, P < 0.05.

 

View Full Table | Close Full ViewTable 4.

Main effect of sampling day on hematology of newly received beef calves

 
Day
SEM Contrasts, P-value
Item 0 14 28 42 Linear Quadratic Cubic
Total white blood cells,1 ×103/μL 8.58a 9.19a 11.63b 9.93b 0.06 <0.001 0.005 0.08
Neutrophils,1 ×103/μL 1.85 1.50 1.51 1.74 0.14 0.74 0.22 0.92
Neutrophils,1 % 23.2b 17.5ab 13.7a 18.7ab 0.14 0.10 0.03 0.59
Lymphocytes, ×103/μL 5.26a 6.52a 9.26b 7.03ab 0.71 0.001 <0.001 0.17
Lymphocytes, % 57.9a 65.5ab 78.2b 64.6ab 4.05 0.02 <0.001 0.26
Neutrophil:lymphocyte1 0.51b 0.40ab 0.21a 0.33ab 0.23 0.02 0.10 0.32
Monocytes, ×103/μL 1.09b 0.98a 1.20b 1.13b 0.05 0.12 0.71 0.004
Monocytes, % 13.6b 12.2ab 9.6a 13.3b 1.08 0.26 <0.001 0.24
Eosinophils,1 ×103/μL 0.04a 0.09b 0.14b 0.11b 0.21 <0.001 0.001 0.96
Eosinophils,1 % 0.5a 1.1b 1.3b 1.2b 0.19 <0.001 0.007 0.73
Red blood cells, ×106/μL 10.6b 10.0a 10.0a 10.0a 0.15 <0.001 <0.001 0.16
Hemoglobin, g/100 mL 12.8b 12.2a 12.5b 12.6b 0.16 0.44 0.001 0.007
Hematocrit, % 37.9c 35.0a 35.5ab 36.1b 0.43 0.005 <0.001 0.004
Platelets,1 ×103/μL 529a 969c 675b 563a 0.06 0.46 <0.001 <0.001
a–cLeast squares means within a row with differing superscripts differ (P ≤ 0.05).
1Data were log transformed before statistical analysis. Reported least squares means are the geometric means; the SEM is for the log transformed data.

Although weight gains were not different during the receiving period, performance over the entire 120-d ownership period was increased similarly for implanted calves regardless of implant timing. Delaying implantation until later in the receiving period may result in improved performance during the later stages of an ownership period consisting of approximately 120 d. Health or vaccine response were not impacted by administration of a growth implant during initial processing or when the procedure was delayed until d 14 or 28. Under the conditions of the present study, there was no clear benefit to delaying administration of a growth implant in high-risk, newly received beef calves.

 

References

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