Th is study evaluated effects of a single stocker implant (Revalor G) on growth and reproductive performance of yearling beef heifers in the Nebraska Sandhills. Crossbred heifers, grazing native Sandhills range, were randomly assigned to either be implanted 82 ± 2 days prior to estrus synchronization, or not implanted, to determine the effects of growth implants on heifer performance. Heifers were bred via artificial insemination followed with clean- up bulls. Implanted heifers gained more and were heavier at the end of the trial, but had a reduced pregnancy rate than non- implanted heifers. Implanted heifers also had a lower pregnancy rate in their second breeding season. Implanting yearling beef heifers increased average daily gain; however, it decreased initial and subsequent pregnancy rate compared with heifers not implanted. When deciding to implant replacement females, the current (or expected) market conditions for pregnant and feeder heifers must be considered

Funston, Richard N.

Nielson, Hazy Rae

Ramsay, K. H., Ramsay

Tibbitts, Benjamin T.

English

DigitalCommons@University of Nebraska

University of Nebraska - Lincoln DigitalCommons@University of Nebraska - Lincoln Nebraska Beef Cattle Reports Animal Science Department 2017 Growth and Reproductive Performance of Yearling Beef Heifers Implanted with Revalor G in the Nebraska Sandhills Benjamin T. Tibbitts University of Nebraska-Lincoln Hazy Rae Nielson University of Nebraska-Lincoln, hnielson21@gmail.com K. H. Ramsay Ramsay Rex Ranch, Ashby, NE Richard N. Funston University of Nebraska - Lincoln, rfunston2@unl.edu Follow this and additional works at: https://digitalcommons.unl.edu/animalscinbcr  Part of the Large or Food Animal and Equine Medicine Commons, Meat Science Commons, and the Veterinary Preventive Medicine, Epidemiology, and Public Health Commons Tibbitts, Benjamin T.; Nielson, Hazy Rae; Ramsay, K. H. Ramsay; and Funston, Richard N., "Growth and Reproductive Performance of Yearling Beef Heifers Implanted with Revalor G in the Nebraska Sandhills" (2017). Nebraska Beef Cattle Reports. 1005. https://digitalcommons.unl.edu/animalscinbcr/1005 This Article is brought to you for free and open access by the Animal Science Department at DigitalCommons@University of Nebraska - Lincoln. It has been accepted for inclusion in Nebraska Beef Cattle Reports by an authorized administrator of DigitalCommons@University of Nebraska - Lincoln. 2017 Nebraska Beef Cattle Report · 13 ©  Th e Board Regents of the University of Nebraska. All rights reserved.greater than 50% of the rub- off  coating had been removed from the Estrotect patch and were AI 12 h later. Following the AI period, mature bulls were then placed with heifers at ratios of 1:49 and 1:35 at L2 and L3, respectively, for 19 d to conclude a 25 d breeding season.Heifers were managed on native Sand-hills range throughout the summer grazing period. Pregnancy diagnosis was conducted via transrectal palpation approximately 45 d following bull removal and ending BW measured. Non- pregnant heifers were mar-keted as stocker cattle. During the second production year, heifers (n = 1,667; 706 and 961, for IMP and CON, respectively) retained as replacements were managed in 3 groups and grazed native upland range throughout the year without further treat-ment. Cows were off ered 1 lb/d of a 32% CP supplement range cube for 30 d (15 d prior to breeding until 15 d following bull turn-out). Pregnancy diagnosis was performed via transrectal palpation approximately 45 d following bull removal.Economic EvaluationWinter grazing cost was estimated to be one- half the grazing costs for a mature cow ($0.46/d) based on heifer BW at wean-ing. Winter range with supplement was valued at $0.75/d. Summer grazing costs were $0.55/d for upland grass. Additional development costs, including feed deliv-ery costs, breeding costs, and health and veterinarian costs, were charged at $0.36/head/d. Average heifer purchase and cull prices were based on USDA Agricultural Marketing Service prices reported in Ne-braska for each date. Th e total value of cull heifers was subtracted from the total cost of all developed heifers. Total costs were then divided by the number of heifers exposed to determine the total cost of 1 pregnant heifer. Th is value was divided by fi nal preg-nancy rate to determine the total net cost of 1 pregnant heifer.to the label, which in general is from 30 to 45 d of age and prior to weaning. Since traditional heifer development programs focus on maximizing reproductive rates, reproductive risk associated with implants not intended for breeding females has been avoided.Th e objective of the present study was to evaluate eff ects of a single stocker implant (Revalor G) on growth and reproductive performance of yearling beef heifers in the Nebraska Sandhills.ProcedureIn 2011, 12 mo old crossbred beef heifers (n = 3,242; 525 ± 4 lb) grazing native Sandhills range at 3 locations were randomly assigned to be implanted with Revalor G (40 mg trenbolone acetate and 8 mg estradiol, IMP) or not implanted (control, CON). Heifers were implanted at the beginning of the grazing period (May 1). At the time of implant, all heifers were vaccinated (Pyramid 5, Boehringer Ingel-heim, St. Joseph, MO; and VL5 Staybred, Zoetis, Florham Park, NJ) and treated with a topical endectocide (Ivermax, RXV Products, Westlake, TX). At each location, heifers grazed common upland pastures for 164 ± 4 d.Breeding season began 82 ± 2 d fol-lowing trial initiation. Heifers at location 1 (L1, n = 942) were synchronized with 2 prostaglandin F2α (PG) injections admin-istered 17 d apart (5 ml, Lutalyse, Zoetis, Florham Park, NJ) followed by 5 d of estrus detection and AI. Mature bulls were then placed with heifers at a 1:52 bull to heifer ratio for 20 d to conclude the breeding season. At location 2 (L2; n = 1,184) and 3 (L3; n = 1,116), mature bulls were placed with heifers at a 1:82 bull to heifer ratio 6 d before heifers received a single PG injection followed by 6 d of estrus detection and AI. Estrus detection aids were utilized at all 3 locations (Estrotect, Rockway Inc., Spring Valley, WI) at PG injection. Heifers were considered to have expressed estrus when Benjamin T. TibbittsHazy R. NielsonK. C. RamsayR. N. FunstonSummary with ImplicationsTh is study evaluated eff ects of a single stocker implant (Revalor G) on growth and reproductive performance of yearling beef heifers in the Nebraska Sandhills. Crossbred heifers, grazing native Sandhills range, were randomly assigned to either be implanted 82 ± 2 days prior to estrus synchronization, or not implanted, to determine the eff ects of growth implants on heifer performance. Heifers were bred via artifi cial insemination followed with clean- up bulls. Implanted heifers gained more and were heavier at the end of the trial, but had a reduced pregnancy rate than non- implanted heifers. Implanted heifers also had a lower pregnancy rate in their second breeding season. Implanting yearling beef heifers increased average daily gain; however, it decreased initial and subse-quent pregnancy rate compared with heifers not implanted. When deciding to implant re-placement females, the current (or expected) market conditions for pregnant and feeder heifers must be considered.IntroductionAdministering growth implants in stocker systems results in increased growth, improved effi  ciency, and increased profi t-ability. Initially, growth implants were uti-lized in the fi nishing phase of production, but over the past several decades, growth implants have been incorporated at earlier stages of growth and development. Growth implants have not been widely used in heif-er calves due to reproductive concerns, but suckling calf implants approved in breeding heifers have little or no eff ect on subsequent reproduction when implanted according  Growth and Reproductive Performance of Yearling Beef Heifers Implanted with Revalor G in the Nebraska Sandhills14 · 2017 Nebraska Beef Cattle ReportStatistical AnalysisData were analyzed using the GLIMMIX procedure of SAS. Individual heifer was the experimental unit and synchronization protocol was included as a random variable in the model. Location was experimental unit for economic analysis and in Table 2 where data are presented by location. Least squares means and SE for ADG, BW, and pregnancy rate were obtained using the Tukey function of SAS.ResultsTh e main eff ects of heifer growth and reproductive performance are presented in Table 1 and are presented by location in Table 2. Initial heifer BW was similar (P > 0.10) between treatments (525 ± 4 lb). Im-planted heifers had greater ADG and end-ing BW (P < 0.05; 1.48 vs. 1.39 ± 0.02 lb/d and 765 vs. 750 ± 7 lb for IMP and CON, respectively). Heifers in the current study grazed native upland Sandhills pasture during the trial without supplement. Forage quality of Sandhills rangeland early in the grazing period is high, but decreases with increasing plant maturity (1997 Nebraska Beef Report, pp. 3– 5). Th erefore, heifers on a higher plane of nutrition for the entire grazing period would likely have a greater growth response to implants.In a previous study (1984 Nebraska Beef Report, pp.45– 47), implants were administered to crossbred beef heifers at 1, 6, or 9 mo, or at multiple intervals. Heifers receiving a combination of 2 implants had greater ADG from weaning to breeding than control or heifers implanted 3 times. Conception rates in a 62- d breeding season were comparable for implanted vs. non- implanted control heifers (93 vs. 96%), with the exception of heifers receiving implants at both 1 and 6 mo of age (56%). Calf birth weight, dystocia score, cow re- breeding rate, and calf weaning weight were not aff ected by implant treatment.In the present study, pregnancy rate was greater (P < 0.01) for CON vs. IMP heifers (64 vs. 46 ± 3%). In the 1984 Nebraska Beef Report, pp.45– 47 which observed similar conception rates among non- implanted controls and heifers implanted at 1, 6, or 9 mo of age, implants were administered earlier than in the present study. Strength and type of hormone provided by diff erent Table 1.  Eff ects of Revalor- G on reproduction and summer BW gain of beef heifers grazing native Sandhills rangelandItem CON1 IMP2 SEM P- valuen 1,621 1,621Spring BW, lb 522 525 4 > 0.10Fall BW, lb 750 765 7 < 0.01ADG3, lb 1.39 1.48 0.02 < 0.01Pregnancy rate, % 64 46 3 < 0.012nd preg. rate, 4 % 96 93 2 0.021CON = Heifers did not receive a growth implant prior to breeding season.2 IMP = Heifers received a Revalor G implant 82 ± 2 d prior to breeding season (Merck Animal Health, Summit, NJ).3 Grazing season ADG (Location 1– 162 d, Location 2– 160 d, Location 3– 168 d).4Second season pregnancy rates (n = 1,667).Table 2.  Eff ects of Revalor G on reproduction and summer BW gain of beef heifers grazing native Sandhills rangeland by locationItem CON1 IMP2  SEM  P- valueLocation L1 L2 L3 L1 L2 L3Spring BW, lb 511 518 540 511 520 545 9 0.20Fall BW, lb 719 774 791 732 794 805 33 0.02ADG, lb3 1.28 1.59 1.48 1.34 1.70 1.54 0.13 0.03Pregnancy rate, % 59 64 67 44 44 51 3 < 0.011CON = Heifers did not receive a growth implant prior to breeding season.2IMP = Heifers received a Revalor G (Merck Animal Health, Summit, NJ) implant 82 ± 2 d prior to breeding season.3Grazing season ADG (Location 1, 162 d; Location 2,160 d; Location 3, 168 d).Table 3. Economics of implanting beef heifers with Revalor G at 12 mo of age1Item CON2 IMP3 SEM P- valueWinter feed costs /$heifer4 102 102 .02 1.0Summer feed cost /$heifer 91 91 .1 1.0Total feed costs, $/heifer 193 193 .02 1.0Total development cost5 $/heifer1,019 1,019 3 1.0Avg. cull heifer value $ 1,102 1,123 46 0.66Cull heifer value $/heifer exposed402 601 18 < 0.01Net cost of 1 pregnant heifer6, $969 901 36 0.131Heifers developed at Rex Ranch on native Sandhills rangeland.2CON = Heifers did not receive a growth implant prior to breeding season.3IMP = Heifers received a Revalor G (Merck Animal Health, Summit, NJ) implant 82 ± 2 d prior to breeding season.4Heifers grazed winter range for 135 d with the equivalent of 1 lb/d 32% CP supplement 3 times per wk.5Includes all fi xed and variable cost associated with initial heifer price, feed, feed delivery, breeding, transportation, and supple-ment.6Total value of cull heifers was subtracted from the total cost of all developed heifers. Total costs were then divided by the num-ber of heifers exposed to determine the total cost of 1 pregnant heifer.2017 Nebraska Beef Cattle Report · 15 demand for replacement females. Some beef stocker enterprises have utilized their resources to market pregnant replacement females and many cow- calf producers have marketed excess pregnant females in response to market demand. It is important to note the implant used in this study is not approved for breeding females, so when pregnant heifer value exceeds feeder heifer value, it is unlikely the additional BW gain in cull females will compensate for the decreased pregnancy rate. However, when pregnant heifer value is comparable to feeder heifer value, the additional BW gain from the implant increases the value and effi  ciency of stocker heifers.Benjamin T. Tibbitts, graduate studentHazy R. Nielson, former graduate studentK. C. Ramsay, Rex Ranch, Ashby, NERick N. Funston, professor, University of Nebraska— Lincoln West Central Research and Extension Center, North Platte, NEthe net cost of 1 pregnant heifer tended (P = 0.13) to be greater in CON heifers due to increased gains in IMP heifers. Cull value did not diff er (P = 0.66) despite a $21 numerical advantage for IMP heifers.Stocker enterprises commonly market cattle in late summer when pasture avail-ability or forage quality may be declining. A disadvantage in the design of the present study is quantifying treatment diff erences in the expense and resource allocation associated with retaining heifers for an extended period beyond normal stocker marketing windows to accommodate preg-nancy diagnosis. It is likely that heifers con-tinued to gain during the extended period prior to pregnancy detection; however, the increased gain due to implant had presum-ably diminished due to implant potency and declining forage quality.ConclusionIn recent years, the beef industry has seen a decline in cattle numbers and high implants may also contribute to variation in pregnancy rates observed between studies. Ralgro was utilized in the 1984 study, whereas Revalor G was used in the present study. Both Ralgro and Revalor G are synthetic hormones; however Ralgro con-tains zeranol, an estrogenic hormone that mimics estradiol, and Revalor G contains trenbolone acetate, an androgenic hormone that mimics testosteroneSubsequent pregnancy rate aft er the fi rst calving season was also lower (P = 0.02) in IMP (93%) vs. CON (96%) heifers, which suggests implanting heifers may have a residual or development eff ect on grow-ing heifers beyond the production yr the implant was administered.Economic AnalysisTh e economic analysis is presented in Table 3. Heifers were developed together by location; therefore, winter and summer feed costs and total development costs were sim-ilar between treatments (P = 1.0). However, 

Growth and Reproductive Performance of Yearling Beef Heifers Implanted with Revalor G in the Nebraska Sandhills

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Growth and Reproductive Performance of Yearling Beef Heifers Implanted with Revalor G in the Nebraska Sandhills

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