- Email: [email protected]
estradiol implant on growth and carcass characteristics of beef heifers
ELSEVIER
EFFECTS OF IMMUNIZATION AGAINST GnRH, MELENGESTROL ACETATE, AND A TRENBOLENE ACETATE/ESTRADIOL IMPLANT ON GROWTH AND CARCASS CHARACTERISTICS OF BEEF HEIFERS R. B. Cook, 1 J. D. Popp, 2 T. A. McAllister, 1 J P. Kastelic la and R. Harland 3 ]Agriculture and Agri-Food Canada, Box 3000, Lethbridge. AB, Canada T1J 4B1 2Manitoba Department of Agriculture, Minnedosa, MB, Canada 3Biostar Inc., Saskatoon, SK, C..,ada Received for publication" du]y ] ], 2000 Accepted September 20, 2000 ABSTRACT A 2 x 3 factorial experiment was conducted to determine the effects of an implant (trenbolene acetate/estradiol or no implant) and method of estrus suppression (immunization against CnkRi-I, melengestrol acetate, or no suppression) on growth performance and carcass characteristics of heifers fed for slaughter At the start ofa 21-d feed adaption phase, crossbred beef heifers (n = 144, 390 + 2.8 kg) were given their first dose of an anti-GnRH vaccine or started on melengestrol acetate (MGA). Thereafter, heifers were fed a high-concentrate diet (78% barley grain) for 84 d (Days 0 to 83), received implants on Day 0, a second vaccination on Day 21, and were slaughtered on Days 84 or 85. Implanting increased average daily gain (1 72 vs 1.50 kg/d, P < 0.01), feed efficiency (6.02 vs 6 75 kg dry matter intake/kg gain, P < 0 01), preslaughter weight (532 vs 513 kg, P < 0.01), carcass weight (301 vs 289 kg, P < 0 01), and ribeye area (88.6 vs 85.9 cm2, P < 0.05), but had no affect (P > 0.05) on dry matter intake, grade fat thickness, marbling score, or lean yield. Com~0,aredto heifers fed MGA, those immunized against GnRH had a greater ribeye area (90.0 vs 84.6 cm ) and lean yield (63 vs 61%), and had thinner grade fat (7.5 vs 8.6 mm; P < 0.05 for each) Furthermore, immunized heifers had lower (P < 0.001) plasma progesterone concentrations than control heifers on Days 42, 63 and 83 Heifers fed MGA had less estrus mounting activity (P < 0.05) and lower plasma progesterone concentrations (P < 0.001) than the remaining heifers Method ofestrus suppression did not affect (P > 0.05) preslaughter weight, average dally gain, dry matter intake, feed efficiency, carcass weight, or marbling score. In conclusion, implanting significantly increased growth performance and preslanghter and carcass weights. Compared to heifers fed MGA, immunization against GnRH significantly increased ribeye area and lean yield, and reduced grade fat thickness. © 2001 by Elsevier Science Inc.
Key words: GnRH, trenbolene acetate, estrus suppression, carcass, heifer Acknowledgments Lethbridge Research Centre Contribution No. 3879988. Appreciation is expressed to Biostar Inc. and Agriculture and Agri-Food Canada's Matching Investment Initiative for financial support and to C. Cockwill, D. C-iacchetta, D. Walker, I Walker, and R Wilde for technical assistance. Portions of these data were presented at the American Society of Animal Science national meeting in Denver, Colorado, July, 1998 aCorrespondence and reprint requests: [email protected] Theriogenology 55:973-981, 2001 02001 Elsevier Science Inc.
O093-691X/o1/$-see front matter PII: S0093-691X(01)00458-7
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INTRODUCTION Heifers fed for slaughter are favoured less than steers, because they generally have lower feed efficiency and a slower growth rate, characteristics that are often attributed to estrus-related mounting (2, 11, 23). Although melengestrol acetate (MGA; a synthetic progestin incorporated in the feed) is the predominant method of suppressing estrus in heifers (23), its effect on heifer performance has been variable (1). Moreover, ifMGA intake decreases below the effective threshold (e.g. through reduced feed intake, inadequate mixing of feed, or inadvertent omission of MGA from the feed), a high proportion of heifers may display estrus, resulting in excessive mounting activity and possible injury Immunization against GnRH has been studied as an alternative to MGA to suppress ovarian function and estrous behaviour (1, 19, 22). Immunization of prepubertal heifers against GnRH delayed the onset of puberty (22) or resulted in an 82-d anestrus period in 95% of treated heifers (19). Although the average daily gain was slightly reduced in immunized heifers, this could be overcome with growthpromoting implants (2). To date, development of an efficacious, yet practical, GnRH antigen has faced problems of ineffective immunization and/or extensive purification processes that increase cost (14). One alternative is to use a carrier protein to stimulate a strong immune response (14) When beef cattle are finished for slaughter, deposition of fat increases while muscle deposition slows, resulting in slower and less efficient gain Trenbolene acetate, a potent synthetic analog of testosterone, is thought to increase muscle growth by causing a decline in the catabolic action of cortisol and increased synthesis of muscle proteins (9). A combination implant oftrenbolene acetate and estrogen (120 and 24 rag, respectively) was shown to increase the average daily gain of feedlot steers for the first 116 d e r a 143-d finishing period (10). The objectives were to determine the effects of an implant (trenbolene acetate/estradiol or no implant) and method of estrus suppression (immunization against GnRH, MGA, or no suppression) on growth performance and carcass characteristics of crossbred beef heifers fed for slaughter.
MATERIALS AND METHODS Heifers (n = 144; mean weight 390.2 + 2.8 kg) of composite breeding (1/4 Charolais, 1/4 Simmental, 7/16 British and 1/16 Limousin) were used. These heifers average 417 d of age (range, 388 to 446 d) and had been backgrounded on a high-roughage diet after weaning. Heifers were blocked by weight and randomly assigned to a 2 x 3 factorial combination of treatments Treatments were no implant (n = 72) or an implant containing 140 mg trenbolene acetate and 14 nag estradiol benzoate (Revalor H*, Hoechst Roussel Vet., Regina, SK, Canada; n = 72) in combination with no estrus suppression (CTRL; n = 48), oral melengestrol acetate, 0.4 mg/d (MGA, Pharmacia and Upjohn, Orangeville, ON, Canada; n = 48), or a recombinant fusion protein anti-GnRH vaccine (GnRH; n = 48). All heifers were used and cared for in accordance with the guidelines of the Canadian Council on Animal Care (17) The heifers were housed in 24 small feedlot pens (8 heifers in each pen, thereby replicating each treatment 3 times). The proportion of grain in the diet was increased over a 21-d feed adaptation period, until the heifers were being fed a total mixed ration consisting of(dry matter basis) 78% rolled barley grain, 10% barley silage and 12% supplement. The trial was then conducted for an 84-d period (Day 0 to Day 83).
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Heifers were fed once-daily, with the amount of feexidelivered adjusted to minimize orts (they were weighed and discarded weekly). Representative samples of the diet were collected every 7 d throughout the trial. Feed samples were dried and ground through a 1-mm screen (Wiley mill) and analyzed for moisture [Association of Official Analytical Chemists (AOAC, 1990) method 7.007], Kjeldahl nitrogen [AOAC (1990) method 7.021 ], starch (8) and acid and neutral detergent fiber (21) There were no significant differences between control and MGA diets, overall, the diet contained 12.2% crude protein, 12.7% acid detergent fiber, 34.0% neutral detergent fibre, and 61.2% starch The anti-GnRH vaccine was produced by Biostar Inc. (Saskatoon, SK, Canada). A carder protein leukotoxin, produced by Pastenrella haemolytica, was used to generate a strong antibody response A chimeric protein was formed by ligating an oligonuceleotide synthesized to code for the peptide CmRH (8 copies, fused to both the carboxy- and amino-ends of the leukotoxin carrier protein) and produced through a highly regulated bacterial expression system (14). The product, a recombinant fusion protein anti-CmRH vaccine, was combined with a commercially acceptable adjuvant and administered by subcutaneous injection. The initial dose of the vaccine was given at the start of feed adaptation (Day -21) with a second vaccination on Day 21 The MGA was incorporated into a pelleted supplement and fed at a rate of 4 5 mg/100 kg of final diet, from the start of the 21-d adaptation period to the end of the experiment (last fed approximately 24 h before slaughter) To prevent cross-contamination, heifers not receiving MGA were fed first (after feeding cattle on other studies not receiving MGA) and heifers receiving MGA were fed last Estrus activity was monitored for a 94-d period (Day - 10 to Day 83) by a single, highly experienced operator. Visual observations were done for 30 rain periods at both dawn and dusk (6:00 AM and 9:00 PM, respectively) and only heifers that stood to be mounted were considered to be in estrus. Body weight and feed consumption were determined at 2 l-d intervals. Heifers were weighed after overnight (14 h) withdrawal of water. At the time of weighing, blood samples were collected by jugular venipuncture, centrifuged and the plasma frozen. Plasma progesterone concentrations were determined with a commercial RIA (Coat-A-Count, DPC, Los Angeles, CA, USA); the limit of detection was 0.02 ng/mL and the intra- and inter-assay coefficients of variation were 4.9 and 7.1%, respectively. Anti-GngH titres were determined by RIA (15). Heifers were slaughtered on Days 84 or 85. Carcass evaluation, conducted by an experienced grader, included warm carcass weight, grade fat thickness, dbeye area, marbling score, lean yield, and yield grade (3) Reproductive tracts were collected and uterus and ovary weights were determined All statistical analyses were conducted with the Statistical Analysis System (SAS Institute, Cary, NC, USA). The average daily gain (ADG) was calculated from body weights using linear regression. For all end points, a General Linear Models A_NOVA was used to determine the main effects of implant and estrus suppression, and their interaction. If there was a significant main effect or interaction, a Least Significant Difference test was used to locate differences Linear correlations were calculated between all end points, then stepwise regression analyses were performed to determine best-fitting linear regression models for several end points as dependent variables For each regression, independent variables were considered for inclusion if they were correlated 0 a < 0.15) with the dependent variable To avoid intercorrelation, if 2 candidate independent variables were correlated (P < 0.15), then only the independent variable that was more highly correlated with the dependent variable was included in the regression analysis.
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Implanting significantly increased preslaughter weight, ADG and feed efficiency, but had no significant effect on dry matter intake (DMI; Table 1). However, the method ofestrus suppression had no significant effect on any of these end points Carcass characteristics and uterus and ovary weights are shown in Table 2. Implanted heifers had a significantly greater carcass weight, ribeye area and uterus weight than those that were not implanted. Heifers in the GnRH group had significant increases in both ribeye area and lean yield and significantly thinner back fat than heifers in the MGA group. Estrus activity was not significantly affected by implants, but was significantly lower in the MGA group than inboththe CTRL and GnRH groups (Table 3). Plasma progesterone concentrations were significantly lower in implanted than non-implanted heifers (up to Day 42, and tended to be lower thereafter) and were significantly lower in MGA-treated heifers than in the CTRL or CmRH groups. Plasma progesterone concentrations were not significantly different between CTRL and GnRH groups on Days 0 and 21, but were significantly lower in the GnRH group on Days 42, 63 and 83. Anti-GnRH titres were significantly higher in the GnRH group than in the CTRL and MGA groups on all sampling days.
Table 1. Effects of implants and estrus suppression on ~owth performance of heifers (n=144). Implanted ° Estrus suppression Significan~ ~ Item No Yes CTRL CmRH MGA SEMd I E IxE Initial weight (D 0, kg) 389.7 390.6 388.0 392.8 389.7 2 81 0 86 0 79 0 45 Preslaughter weight (D 83, kg) 513.0 532.2
518.6
Average daily gain (kg/d) D 0 to 42 1.50 1.77 D 0 t o 83 1.50 1.72
523.7
525.5
3.76
0.01
0.74
0.32
1 66 1 53
1.62 1 60
1 62 1 54
0.03 002
0.01 0.01
0 79 0.26
0.08 0.36
9.41 10.02
9.51 995
9.41 10.33
0.10 0.10
0.20 0.89 0.16 0.24
0.15 0.19
DMI e (k~d)
D0to42 D0to83
9.31 9.97
9.57 10.24
Feed efficiency (kg DMI/kg gain) D0to42 6.30 5.45 5.76 5.95 5.91 0.14 0.01 0.78 0.82 D0to83 6.75 6.02 643 6.35 6.37 0.11 0.01 013 0.76 = no implant; Yes = Revalor H¢. CTRL = no estrus suppression; CmRH = anti-CmRH vaccine, MGA = melengestrol acetate eProbability values for effect of implant (I) and estrus suppression method (E) and their interaction
b • N o
~IsXE). EM = standard error of the mean eDMI = dry matter intake
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Table 2. Effects of implants and estrus suppression on carcass and reproductive tract characteristics of heifers (n= 144). Implanted° E~tms supprcssiob Sim~ificance~ No Yes CTRL GnRH MGA SEM d I E IXE Item Carcass wt (kg) 288 7 301.4 294.5 , 296.7 293.7 4.89 0.01 0.82 0.32 Grade fat 0~jLm) 8.11 7.92 7.9g [g 7.5~ f 8.64 g 028 063 0.05 047 Ribeye (cm-) 85.9 88.6 87.0 xg 90.084,6 g 1 02 0 05 0.01 0 41 Marbling (1-9)e 7.92 8 08 8.07, 7.91_ 8.01 0.12 0 36 0.75 0 66 Leanyield (%) 61.82 62.22 62.03 [g 63.03 f 60.99 g 0.32 0.31 0.01 0.30 Yield grade (%) AAA 34.7 26.4 27.1 33.3 31.3 3.94 0 33 0.83 0.36 AA 63.9 70.6 72.9 62.5 66 4 3 90 0.41 0.57 0.29 A 1.4 3.0 0 42 24 1.19 0 5 4 0.43 0.68 Uterus wt (g) 283.53 307.74 302.95 280,46 303 49 8.38 0.03 0.10 0.08 Ovarywt (g) 8.37 7.92 8.45 7,59 8.39 0 61 0.45 0.42 0.45 = no implant, Yes = Revalor I-I*. CTRL = no estrus suppression; GnRH = anti-GnRH vaccine, MGA = melengestrol acetate. CProbability values for effect of implant (I) and estrus suppression method (E) and their interaction
b
•
O
~IsXE). EM = standard error of the mean. d~bling score with 1 = high and 9 = no marbling. gwithin a row and category, means with unlike superscripts differ (P<0.05).
In the GnRH group, there was a positive linear regression (P < 0.05) between warm carcass weight and final anti-GnRH titres, and negative linear regressions (P < 0.05 ) between uterus and ovary weights and final titres. Furthermore, in this group, there were negative linear regressions (P < 0.05) between plasma progesterone concentrations on D63 and D83 and concurrent titres
DISCUSSION Throughout the trial, ADG and feed effciency were 10 to 12% higher in implanted than in nonimplanted heifers (P < 0.01); this improvement was similar to the 5 to 10% implant=mediated improvements in growth performance observed in other studies (2,6,13). In a previous study with similar heifers (18), both feed efficiency and growth rate were up to 30% higher in heifers with a trenbolene acetatelestradiol implant than in heifers without an implant. However, the implant used in that study contained 200 nag trenbolene acetate (compared to 140 mg in the present study) and the finishing phase was only 50 d. In the present study, implanting increased preslaughter weight (P < 0.01), warm carcass weight (1) < 0.01), and ribeye area (P < 0.05), consistent with other studies indicating that trenbolene acetate/estradiol implants increase muscle accretion and reduce fat deposition (4,10,16,18). Implanting increased (P < 0.05) uterus weight at slaughter, but had no significant effect on ovary weight. Although there was no significant effect of implant on the incidence o f standing estrus, implanted heifers had lower plasma progesterone concentrations and higher anti-GnRH titres. Within the GnRH group, there was an effect of implant (P < 0 05) on anti-GnRH titre; implanted heifers had
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Table 3. Effects of implants and estrus suppression on estrus activity, plasma progesterone concentrations and anti-GnRH titres of heifers (~ = 144). Imolanted~ Estrus Supvression Signlfi.cance~ No Yes CTRL GnRH MGA SEM d I E IXE Item Estrus activity (% in standing estrus/d) D 0-21 5.06 5.59 8.73 g 7.26 g 0.00 h 0.38 .8008 .0001 .0001 D 2 2 - 42 3.45 4.97 6.30 g 5.79g 0.55 h 0.28 .3332 .0002 .0007 D43-63 3.11 5.69 5.33 e 7.87 e 0.00~ 0.51 2609 .0048 .0212 D 64- 83 3.54 7.27 6 90 e 8.83 e 0.50 I 0.52 .1525 0114 .0015 Plasma progesterone (ng/ml) D 0 4.04 2.82 D21 4.45 1.98 D42 3.08 1.85 D 63 2.75 1.88 D 83 3.00 2 13
4.89 g 4.45 g 4.41 g 4.28 g 4.77 g
4.96 g 3.94.g 2.47.h 2.36h 2 681~
0.43 h 1.25.h 0 52~. 0.301. 0.261
0.28 0.26 0.23 0.23 0.27
.0293 .0001 .0081 .0591 .1048
0001 .0001 0001 0001 0001
.0001 0001 0001 .0001 .0001
Anti-GnRH titre (1/100 dilution) D 0 1 64 3.03 0.65 g 5.55 h 0.80 g 0 62 .2641 .0010 .0035 D21 5.83 8.05 1.78 g 17.56.h 168 g 1.19 .3533 .0001 .0001 D42 17.15 16.91 2.39 g 45.60.h 3.10 g 2.06 .9530 0001 .0001 D63 15.15 14.96 1.45 g 40.97~, 2.75 g 2.08 .9627 0001 .0001 D 83 13.28 15.66 2.658 3777 n. 3.00 g 1.88 5282 .0001 0001 = no implant; Yes = Revalor H ~. CTRL = no estrus suppression; GnRH = anti-GnRH vaccine; MGA = melengestrol acetate. Cprobability values for effect of implant (I) and estrus suppression method (E) and their interaction
b • l O xE).
~$EM = standard error of the mean. IhWithin a row and category, means with unlike superscripts differ (P<0.05) ~'-Within a row and category, means with unlike superscript differ (P < 0.001)
53% higher titres through D42. This difference appeared to be associated with the initial immune response as it was eliminated by D63 and only approached significance (P < 0.07; 24% higher) by the end of the experiment. Therefore, it appears that the implants altered both ovarian function (though final ovarian weight was not significantly different) and immune response. Although trenbolene acetatedestradiol implants alter metabolism (increase protein synthesis), their effect on reproductive function is not clear. It has been suggested that anabolic implants may actually increase mounting behaviour in heifers (12). The method of estrus suppression did not significantly affect body weight, ADG, DMI, or feed efficiency The effect of MGA on growth performance has been reported to be variable (2,23), consistent with the present study In this study, some reductions in heifer performance were noted as MGA was introduced to the diet, perhaps caused by feed refusals and reductions in feed efficiency Furthermore, some heifers fed MGA appeared to 'sort' through feed and displayed estrus. If heifers are effectively immunized against GnRH, responses should be more consistent than a product
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administered in the feed. Immunization of heifers against GnRH at an earlier age than that used in our study did not affect the rate of gain during finishing (7), consistent with the results of the present study. In contrast, other researchers have observed reductions in the rate of gain of cattle (1,2) and ram lambs (20) as a result of immunization against GnRH. The effects of vaccination against GnR/-I on feedlot performance could be determined by many factors, including the vaccine used, the immune response, and diet. The method of estrus suppression did not affect (P > 0.05) warm carcass weight or marbling (Table 2). However, heifers immunized against GnRH had thinner grade fat and a greater ribeye area and lean yield (P < 0.05) compared to those receiving MGA, but CTRL heifers did not differ (P > 0.05) from either MGA or GnRH. Within the GnRI-I group, there was a positive linear regression (P < 0.05) between warm carcass weight and final anti-GnRH titres, indicating that heifers that responded well to vaccination had larger carcasses Previous studies have shown carcass weight, dressing percentage, hackfat and marbling were unaffected by immunization against GnRH (7) This contradicts another study that demonstrated a reduction in protein deposition and an increase in fat deposition in heifers actively immunized against GnRH, when compared to MGA or control heifers (2). Perhaps the nature of the vaccine or the time of administration affect carcass characteristics. Heifers immunized against GnRH tended (P < 0.10) to have a lower uterus weight at slaughter than those in the CTRL or MGA groups. Although there was no significant effects of estrus suppression method on ovary weight, negative linear regressions (P < 0 05) indicated that heifers (in the GnRH group) with the highest anti-GnRH titres had a corresponding decrease in uterus and ovary weights. Plasma progesterone concentrations were consistently significantly lower in heifers receiving MGA than in the remaining heifers and were significantly lower in the CmRH group vs the CTRL group (on Days 42, 63 and 83), in association with increasing anti-GnRH titres, as previously reported (22). In addition, there was a negative linear regression (P < 0.05) between plasma progesterone concentrations on D63 and D83 and the concurrent anti-GnRH titres. While the variability in titres may have resulted from vaccine formulation and/or administration, it provided a range of immune responses that were interpreted with regression analyses In conclusion, the trenbolene ac,~ate/estradiol implant significantly increased growth performance and carcass weight (as a result of increased muscular growth) while marbling was not affected Compared to heifers fed MGA, immunization against GnRH significantly increased both ribeye area and lean yield and reduced grade fat thickness. Although immunization did not significantly reduce estrus mounting activity, there was a significant reduction in uterus weight and plasma progesterone concentrations in heifers with an adequate immune response. With further refinement of vaccine formulation and administration, immunization against OnRH has considerable potential as a nonhormonal method of suppressing estrus in feedlot heifers.
Theriogenology
980 REFERENCES 1.
Adams TE, Adams BM Reproductive function and feedlot performance of heifers actively immunized against CmRH. J Anita Sci 1990, 68.2793-2802.
2.
Adams TE, Dunbar JR, Berry SL, Garrett WN, Famula TR, Lee YB. Feedlot performance of beef heifers implanted with Synovex-H: Effect of melengestrol acetate, ovariectomy or active immunization against GnRH. J Anita Sci 1990; 68:3079-3085
3.
Agriculture Canada. Livestock carcass grading regulations Canada Gazette 1992, Part II. 126" 3821.
4.
Anderson PT. Trenbolene acetate as a growth promotant. Comp Cent Ed Pract Vet 1991, 13: 1179-1190.
5.
Association of Official Analytical Chemists. Official methods of analysis. 1990; 15th ed. AOAC. Washington, DC.
6.
Battle SJ, Preston RL, Brown RE, Grant RJ. Trenbolene acetate/estradiol combinations in feedlot steers: Dose-response and implant carrier effects. J Anita Sci 1992;70" 1326-1332.
7.
Bell M, Daley CA, Berry SL, Adams TE. Pregnancy status and feedlot performance of beef heifers actively immunized against gonadotropin-releasing hormone. J Anita Sci 1997, 75:1185-1189.
8. Herrera-Saldana RE, Huber JT, Poore MH. Dry matter, crude protein, and starch degradability of five cereal grains. J Dairy Sci 1990; 73' 2386-2393 9
Isaacson WK, Jones SJ, Krueger RJ. Testosterone, dihydrotestosterone, trenbolene acetate and zeranol alter the synthesis of cortisol in bovine adrenocortical cells. J Anita Sci 1993, 71 1771-1777.
10
Johnson B J, Anderson PT, Meiske JC, Dayton WR. Effect of combined trenbolene acetate and estradiol implant on feedlot performance, carcass characteristics and composition of feedlot steers. J Anita Sci 1996; 74: 363-371.
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Kreikemeier KK, Unruh JA. Carcass traits and the occurrence of dark cutters in pregnant and nonpregnant feedlot heifers. J Anita Sci 1993; 71"1699-1703.
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Lesmeister JL, EUington EF Effect of steroid implants on sexual behaviour of beef cattle. Herin Behav 1977; 9. 276-280.
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Mader TL, Dahlquist JM, Sindt MH, Stock RA, Klopfenstein TJ Effect of sequential implanting with Synovex on steer and heifer performance. J Anim Sci 1994, 72 1095-1100
14
Manns JG, Barker C, Attah-Poku SK. The design, production, purification, and testing of a chimeric antigen protein to be used as an immunosterilant in domestic animals. Can J Chem 1997; 75: 829-833.
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15. Meloen RH, Turkstra JA, Lankhof H, Puijk WC, Schaaper WMM, Dijkstra G, Wensing CJG, Oonk RB. Efficient immunocastration of male piglets by immunoneutralization of GnRH using a new GnRH-like peptide. Vaccine 1994; 12' 741-746. 16
Muir LA. Mode of action of exogenous substances on animal growth--an overview. J Anita Sci 1985; 61(Suppl. 2). 154-180.
17. Olfert ED, Cross BM and McWilliam AA. Canadian Council of Animal Care Guide to the Care and Use of Experimental Animals. 1993; Vol. 1, 2'~ Ed., Ottawa, ON, Brada Printing 18. Popp JD, McAllister TA, Burgevitz WJ, Kemp RA, Kastelic JP, Cheng KJ. Effect of trenbolene acetate/estradiol implants and estrus suppression on growth performance and carcass characteristics of beef heifers Can J Anim Sci 1997, 77 325-328 19
Prendiville DJ, Enright WJ, Crowe MA, Finnerty M, Hynes F, Roche JF Immunization of heifers against gonadotropin-releasing hormone' Antibody titres, ovarian function, body growth, and carcass characteristics. J Anita Sci 1995; 73' 2382-2389.
20
Schanbacher BD. Responses of ram lambs to active immunization against testosterone and luteinizing hormone-releasing hormone. Am J Physiol 1982; 242:201-205
21.
VanSoest PJ, Robertson JB, Lewis BA. Methods for determining dietary fibre, neutral detergent fibre, and nonstarch polysaccharides in relation to animal nutrition. J Dairy Sci 1991; 74: 3583-3597.
22
WetternanRP, Castree JW. Immunization of heifers against gonadotropin-releasing hormone delays puberty and causes the cessation ofestrous cycles Anita Reprod Sci 1994; 36' 49-59
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Zimbelman RG, Lauderdale JW, Sokolowski JH, Schalk TG Safety and pharmacologic evaluations ofmelengestrol acetate in cattle and other animals: A review J Am Vet Med Assoc 1970; 157: 1528-1536.
EFFECTS OF IMMUNIZATION AGAINST GnRH, MELENGESTROL ACETATE, AND A TRENBOLENE ACETATE/ESTRADIOL IMPLANT ON GROWTH AND CARCASS CHARACTERISTICS OF BEEF HEIFERS R. B. Cook, 1 J. D. Popp, 2 T. A. McAllister, 1 J P. Kastelic la and R. Harland 3 ]Agriculture and Agri-Food Canada, Box 3000, Lethbridge. AB, Canada T1J 4B1 2Manitoba Department of Agriculture, Minnedosa, MB, Canada 3Biostar Inc., Saskatoon, SK, C..,ada Received for publication" du]y ] ], 2000 Accepted September 20, 2000 ABSTRACT A 2 x 3 factorial experiment was conducted to determine the effects of an implant (trenbolene acetate/estradiol or no implant) and method of estrus suppression (immunization against CnkRi-I, melengestrol acetate, or no suppression) on growth performance and carcass characteristics of heifers fed for slaughter At the start ofa 21-d feed adaption phase, crossbred beef heifers (n = 144, 390 + 2.8 kg) were given their first dose of an anti-GnRH vaccine or started on melengestrol acetate (MGA). Thereafter, heifers were fed a high-concentrate diet (78% barley grain) for 84 d (Days 0 to 83), received implants on Day 0, a second vaccination on Day 21, and were slaughtered on Days 84 or 85. Implanting increased average daily gain (1 72 vs 1.50 kg/d, P < 0.01), feed efficiency (6.02 vs 6 75 kg dry matter intake/kg gain, P < 0 01), preslaughter weight (532 vs 513 kg, P < 0.01), carcass weight (301 vs 289 kg, P < 0 01), and ribeye area (88.6 vs 85.9 cm2, P < 0.05), but had no affect (P > 0.05) on dry matter intake, grade fat thickness, marbling score, or lean yield. Com~0,aredto heifers fed MGA, those immunized against GnRH had a greater ribeye area (90.0 vs 84.6 cm ) and lean yield (63 vs 61%), and had thinner grade fat (7.5 vs 8.6 mm; P < 0.05 for each) Furthermore, immunized heifers had lower (P < 0.001) plasma progesterone concentrations than control heifers on Days 42, 63 and 83 Heifers fed MGA had less estrus mounting activity (P < 0.05) and lower plasma progesterone concentrations (P < 0.001) than the remaining heifers Method ofestrus suppression did not affect (P > 0.05) preslaughter weight, average dally gain, dry matter intake, feed efficiency, carcass weight, or marbling score. In conclusion, implanting significantly increased growth performance and preslanghter and carcass weights. Compared to heifers fed MGA, immunization against GnRH significantly increased ribeye area and lean yield, and reduced grade fat thickness. © 2001 by Elsevier Science Inc.
Key words: GnRH, trenbolene acetate, estrus suppression, carcass, heifer Acknowledgments Lethbridge Research Centre Contribution No. 3879988. Appreciation is expressed to Biostar Inc. and Agriculture and Agri-Food Canada's Matching Investment Initiative for financial support and to C. Cockwill, D. C-iacchetta, D. Walker, I Walker, and R Wilde for technical assistance. Portions of these data were presented at the American Society of Animal Science national meeting in Denver, Colorado, July, 1998 aCorrespondence and reprint requests: [email protected] Theriogenology 55:973-981, 2001 02001 Elsevier Science Inc.
O093-691X/o1/$-see front matter PII: S0093-691X(01)00458-7
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INTRODUCTION Heifers fed for slaughter are favoured less than steers, because they generally have lower feed efficiency and a slower growth rate, characteristics that are often attributed to estrus-related mounting (2, 11, 23). Although melengestrol acetate (MGA; a synthetic progestin incorporated in the feed) is the predominant method of suppressing estrus in heifers (23), its effect on heifer performance has been variable (1). Moreover, ifMGA intake decreases below the effective threshold (e.g. through reduced feed intake, inadequate mixing of feed, or inadvertent omission of MGA from the feed), a high proportion of heifers may display estrus, resulting in excessive mounting activity and possible injury Immunization against GnRH has been studied as an alternative to MGA to suppress ovarian function and estrous behaviour (1, 19, 22). Immunization of prepubertal heifers against GnRH delayed the onset of puberty (22) or resulted in an 82-d anestrus period in 95% of treated heifers (19). Although the average daily gain was slightly reduced in immunized heifers, this could be overcome with growthpromoting implants (2). To date, development of an efficacious, yet practical, GnRH antigen has faced problems of ineffective immunization and/or extensive purification processes that increase cost (14). One alternative is to use a carrier protein to stimulate a strong immune response (14) When beef cattle are finished for slaughter, deposition of fat increases while muscle deposition slows, resulting in slower and less efficient gain Trenbolene acetate, a potent synthetic analog of testosterone, is thought to increase muscle growth by causing a decline in the catabolic action of cortisol and increased synthesis of muscle proteins (9). A combination implant oftrenbolene acetate and estrogen (120 and 24 rag, respectively) was shown to increase the average daily gain of feedlot steers for the first 116 d e r a 143-d finishing period (10). The objectives were to determine the effects of an implant (trenbolene acetate/estradiol or no implant) and method of estrus suppression (immunization against GnRH, MGA, or no suppression) on growth performance and carcass characteristics of crossbred beef heifers fed for slaughter.
MATERIALS AND METHODS Heifers (n = 144; mean weight 390.2 + 2.8 kg) of composite breeding (1/4 Charolais, 1/4 Simmental, 7/16 British and 1/16 Limousin) were used. These heifers average 417 d of age (range, 388 to 446 d) and had been backgrounded on a high-roughage diet after weaning. Heifers were blocked by weight and randomly assigned to a 2 x 3 factorial combination of treatments Treatments were no implant (n = 72) or an implant containing 140 mg trenbolene acetate and 14 nag estradiol benzoate (Revalor H*, Hoechst Roussel Vet., Regina, SK, Canada; n = 72) in combination with no estrus suppression (CTRL; n = 48), oral melengestrol acetate, 0.4 mg/d (MGA, Pharmacia and Upjohn, Orangeville, ON, Canada; n = 48), or a recombinant fusion protein anti-GnRH vaccine (GnRH; n = 48). All heifers were used and cared for in accordance with the guidelines of the Canadian Council on Animal Care (17) The heifers were housed in 24 small feedlot pens (8 heifers in each pen, thereby replicating each treatment 3 times). The proportion of grain in the diet was increased over a 21-d feed adaptation period, until the heifers were being fed a total mixed ration consisting of(dry matter basis) 78% rolled barley grain, 10% barley silage and 12% supplement. The trial was then conducted for an 84-d period (Day 0 to Day 83).
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Heifers were fed once-daily, with the amount of feexidelivered adjusted to minimize orts (they were weighed and discarded weekly). Representative samples of the diet were collected every 7 d throughout the trial. Feed samples were dried and ground through a 1-mm screen (Wiley mill) and analyzed for moisture [Association of Official Analytical Chemists (AOAC, 1990) method 7.007], Kjeldahl nitrogen [AOAC (1990) method 7.021 ], starch (8) and acid and neutral detergent fiber (21) There were no significant differences between control and MGA diets, overall, the diet contained 12.2% crude protein, 12.7% acid detergent fiber, 34.0% neutral detergent fibre, and 61.2% starch The anti-GnRH vaccine was produced by Biostar Inc. (Saskatoon, SK, Canada). A carder protein leukotoxin, produced by Pastenrella haemolytica, was used to generate a strong antibody response A chimeric protein was formed by ligating an oligonuceleotide synthesized to code for the peptide CmRH (8 copies, fused to both the carboxy- and amino-ends of the leukotoxin carrier protein) and produced through a highly regulated bacterial expression system (14). The product, a recombinant fusion protein anti-CmRH vaccine, was combined with a commercially acceptable adjuvant and administered by subcutaneous injection. The initial dose of the vaccine was given at the start of feed adaptation (Day -21) with a second vaccination on Day 21 The MGA was incorporated into a pelleted supplement and fed at a rate of 4 5 mg/100 kg of final diet, from the start of the 21-d adaptation period to the end of the experiment (last fed approximately 24 h before slaughter) To prevent cross-contamination, heifers not receiving MGA were fed first (after feeding cattle on other studies not receiving MGA) and heifers receiving MGA were fed last Estrus activity was monitored for a 94-d period (Day - 10 to Day 83) by a single, highly experienced operator. Visual observations were done for 30 rain periods at both dawn and dusk (6:00 AM and 9:00 PM, respectively) and only heifers that stood to be mounted were considered to be in estrus. Body weight and feed consumption were determined at 2 l-d intervals. Heifers were weighed after overnight (14 h) withdrawal of water. At the time of weighing, blood samples were collected by jugular venipuncture, centrifuged and the plasma frozen. Plasma progesterone concentrations were determined with a commercial RIA (Coat-A-Count, DPC, Los Angeles, CA, USA); the limit of detection was 0.02 ng/mL and the intra- and inter-assay coefficients of variation were 4.9 and 7.1%, respectively. Anti-GngH titres were determined by RIA (15). Heifers were slaughtered on Days 84 or 85. Carcass evaluation, conducted by an experienced grader, included warm carcass weight, grade fat thickness, dbeye area, marbling score, lean yield, and yield grade (3) Reproductive tracts were collected and uterus and ovary weights were determined All statistical analyses were conducted with the Statistical Analysis System (SAS Institute, Cary, NC, USA). The average daily gain (ADG) was calculated from body weights using linear regression. For all end points, a General Linear Models A_NOVA was used to determine the main effects of implant and estrus suppression, and their interaction. If there was a significant main effect or interaction, a Least Significant Difference test was used to locate differences Linear correlations were calculated between all end points, then stepwise regression analyses were performed to determine best-fitting linear regression models for several end points as dependent variables For each regression, independent variables were considered for inclusion if they were correlated 0 a < 0.15) with the dependent variable To avoid intercorrelation, if 2 candidate independent variables were correlated (P < 0.15), then only the independent variable that was more highly correlated with the dependent variable was included in the regression analysis.
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976 RESULTS
Implanting significantly increased preslaughter weight, ADG and feed efficiency, but had no significant effect on dry matter intake (DMI; Table 1). However, the method ofestrus suppression had no significant effect on any of these end points Carcass characteristics and uterus and ovary weights are shown in Table 2. Implanted heifers had a significantly greater carcass weight, ribeye area and uterus weight than those that were not implanted. Heifers in the GnRH group had significant increases in both ribeye area and lean yield and significantly thinner back fat than heifers in the MGA group. Estrus activity was not significantly affected by implants, but was significantly lower in the MGA group than inboththe CTRL and GnRH groups (Table 3). Plasma progesterone concentrations were significantly lower in implanted than non-implanted heifers (up to Day 42, and tended to be lower thereafter) and were significantly lower in MGA-treated heifers than in the CTRL or CmRH groups. Plasma progesterone concentrations were not significantly different between CTRL and GnRH groups on Days 0 and 21, but were significantly lower in the GnRH group on Days 42, 63 and 83. Anti-GnRH titres were significantly higher in the GnRH group than in the CTRL and MGA groups on all sampling days.
Table 1. Effects of implants and estrus suppression on ~owth performance of heifers (n=144). Implanted ° Estrus suppression Significan~ ~ Item No Yes CTRL CmRH MGA SEMd I E IxE Initial weight (D 0, kg) 389.7 390.6 388.0 392.8 389.7 2 81 0 86 0 79 0 45 Preslaughter weight (D 83, kg) 513.0 532.2
518.6
Average daily gain (kg/d) D 0 to 42 1.50 1.77 D 0 t o 83 1.50 1.72
523.7
525.5
3.76
0.01
0.74
0.32
1 66 1 53
1.62 1 60
1 62 1 54
0.03 002
0.01 0.01
0 79 0.26
0.08 0.36
9.41 10.02
9.51 995
9.41 10.33
0.10 0.10
0.20 0.89 0.16 0.24
0.15 0.19
DMI e (k~d)
D0to42 D0to83
9.31 9.97
9.57 10.24
Feed efficiency (kg DMI/kg gain) D0to42 6.30 5.45 5.76 5.95 5.91 0.14 0.01 0.78 0.82 D0to83 6.75 6.02 643 6.35 6.37 0.11 0.01 013 0.76 = no implant; Yes = Revalor H¢. CTRL = no estrus suppression; CmRH = anti-CmRH vaccine, MGA = melengestrol acetate eProbability values for effect of implant (I) and estrus suppression method (E) and their interaction
b • N o
~IsXE). EM = standard error of the mean eDMI = dry matter intake
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Table 2. Effects of implants and estrus suppression on carcass and reproductive tract characteristics of heifers (n= 144). Implanted° E~tms supprcssiob Sim~ificance~ No Yes CTRL GnRH MGA SEM d I E IXE Item Carcass wt (kg) 288 7 301.4 294.5 , 296.7 293.7 4.89 0.01 0.82 0.32 Grade fat 0~jLm) 8.11 7.92 7.9g [g 7.5~ f 8.64 g 028 063 0.05 047 Ribeye (cm-) 85.9 88.6 87.0 xg 90.084,6 g 1 02 0 05 0.01 0 41 Marbling (1-9)e 7.92 8 08 8.07, 7.91_ 8.01 0.12 0 36 0.75 0 66 Leanyield (%) 61.82 62.22 62.03 [g 63.03 f 60.99 g 0.32 0.31 0.01 0.30 Yield grade (%) AAA 34.7 26.4 27.1 33.3 31.3 3.94 0 33 0.83 0.36 AA 63.9 70.6 72.9 62.5 66 4 3 90 0.41 0.57 0.29 A 1.4 3.0 0 42 24 1.19 0 5 4 0.43 0.68 Uterus wt (g) 283.53 307.74 302.95 280,46 303 49 8.38 0.03 0.10 0.08 Ovarywt (g) 8.37 7.92 8.45 7,59 8.39 0 61 0.45 0.42 0.45 = no implant, Yes = Revalor I-I*. CTRL = no estrus suppression; GnRH = anti-GnRH vaccine, MGA = melengestrol acetate. CProbability values for effect of implant (I) and estrus suppression method (E) and their interaction
b
•
O
~IsXE). EM = standard error of the mean. d~bling score with 1 = high and 9 = no marbling. gwithin a row and category, means with unlike superscripts differ (P<0.05).
In the GnRH group, there was a positive linear regression (P < 0.05) between warm carcass weight and final anti-GnRH titres, and negative linear regressions (P < 0.05 ) between uterus and ovary weights and final titres. Furthermore, in this group, there were negative linear regressions (P < 0.05) between plasma progesterone concentrations on D63 and D83 and concurrent titres
DISCUSSION Throughout the trial, ADG and feed effciency were 10 to 12% higher in implanted than in nonimplanted heifers (P < 0.01); this improvement was similar to the 5 to 10% implant=mediated improvements in growth performance observed in other studies (2,6,13). In a previous study with similar heifers (18), both feed efficiency and growth rate were up to 30% higher in heifers with a trenbolene acetatelestradiol implant than in heifers without an implant. However, the implant used in that study contained 200 nag trenbolene acetate (compared to 140 mg in the present study) and the finishing phase was only 50 d. In the present study, implanting increased preslaughter weight (P < 0.01), warm carcass weight (1) < 0.01), and ribeye area (P < 0.05), consistent with other studies indicating that trenbolene acetate/estradiol implants increase muscle accretion and reduce fat deposition (4,10,16,18). Implanting increased (P < 0.05) uterus weight at slaughter, but had no significant effect on ovary weight. Although there was no significant effect of implant on the incidence o f standing estrus, implanted heifers had lower plasma progesterone concentrations and higher anti-GnRH titres. Within the GnRH group, there was an effect of implant (P < 0 05) on anti-GnRH titre; implanted heifers had
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Table 3. Effects of implants and estrus suppression on estrus activity, plasma progesterone concentrations and anti-GnRH titres of heifers (~ = 144). Imolanted~ Estrus Supvression Signlfi.cance~ No Yes CTRL GnRH MGA SEM d I E IXE Item Estrus activity (% in standing estrus/d) D 0-21 5.06 5.59 8.73 g 7.26 g 0.00 h 0.38 .8008 .0001 .0001 D 2 2 - 42 3.45 4.97 6.30 g 5.79g 0.55 h 0.28 .3332 .0002 .0007 D43-63 3.11 5.69 5.33 e 7.87 e 0.00~ 0.51 2609 .0048 .0212 D 64- 83 3.54 7.27 6 90 e 8.83 e 0.50 I 0.52 .1525 0114 .0015 Plasma progesterone (ng/ml) D 0 4.04 2.82 D21 4.45 1.98 D42 3.08 1.85 D 63 2.75 1.88 D 83 3.00 2 13
4.89 g 4.45 g 4.41 g 4.28 g 4.77 g
4.96 g 3.94.g 2.47.h 2.36h 2 681~
0.43 h 1.25.h 0 52~. 0.301. 0.261
0.28 0.26 0.23 0.23 0.27
.0293 .0001 .0081 .0591 .1048
0001 .0001 0001 0001 0001
.0001 0001 0001 .0001 .0001
Anti-GnRH titre (1/100 dilution) D 0 1 64 3.03 0.65 g 5.55 h 0.80 g 0 62 .2641 .0010 .0035 D21 5.83 8.05 1.78 g 17.56.h 168 g 1.19 .3533 .0001 .0001 D42 17.15 16.91 2.39 g 45.60.h 3.10 g 2.06 .9530 0001 .0001 D63 15.15 14.96 1.45 g 40.97~, 2.75 g 2.08 .9627 0001 .0001 D 83 13.28 15.66 2.658 3777 n. 3.00 g 1.88 5282 .0001 0001 = no implant; Yes = Revalor H ~. CTRL = no estrus suppression; GnRH = anti-GnRH vaccine; MGA = melengestrol acetate. Cprobability values for effect of implant (I) and estrus suppression method (E) and their interaction
b • l O xE).
~$EM = standard error of the mean. IhWithin a row and category, means with unlike superscripts differ (P<0.05) ~'-Within a row and category, means with unlike superscript differ (P < 0.001)
53% higher titres through D42. This difference appeared to be associated with the initial immune response as it was eliminated by D63 and only approached significance (P < 0.07; 24% higher) by the end of the experiment. Therefore, it appears that the implants altered both ovarian function (though final ovarian weight was not significantly different) and immune response. Although trenbolene acetatedestradiol implants alter metabolism (increase protein synthesis), their effect on reproductive function is not clear. It has been suggested that anabolic implants may actually increase mounting behaviour in heifers (12). The method of estrus suppression did not significantly affect body weight, ADG, DMI, or feed efficiency The effect of MGA on growth performance has been reported to be variable (2,23), consistent with the present study In this study, some reductions in heifer performance were noted as MGA was introduced to the diet, perhaps caused by feed refusals and reductions in feed efficiency Furthermore, some heifers fed MGA appeared to 'sort' through feed and displayed estrus. If heifers are effectively immunized against GnRH, responses should be more consistent than a product
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administered in the feed. Immunization of heifers against GnRH at an earlier age than that used in our study did not affect the rate of gain during finishing (7), consistent with the results of the present study. In contrast, other researchers have observed reductions in the rate of gain of cattle (1,2) and ram lambs (20) as a result of immunization against GnRH. The effects of vaccination against GnR/-I on feedlot performance could be determined by many factors, including the vaccine used, the immune response, and diet. The method of estrus suppression did not affect (P > 0.05) warm carcass weight or marbling (Table 2). However, heifers immunized against GnRH had thinner grade fat and a greater ribeye area and lean yield (P < 0.05) compared to those receiving MGA, but CTRL heifers did not differ (P > 0.05) from either MGA or GnRH. Within the GnRI-I group, there was a positive linear regression (P < 0.05) between warm carcass weight and final anti-GnRH titres, indicating that heifers that responded well to vaccination had larger carcasses Previous studies have shown carcass weight, dressing percentage, hackfat and marbling were unaffected by immunization against GnRH (7) This contradicts another study that demonstrated a reduction in protein deposition and an increase in fat deposition in heifers actively immunized against GnRH, when compared to MGA or control heifers (2). Perhaps the nature of the vaccine or the time of administration affect carcass characteristics. Heifers immunized against GnRH tended (P < 0.10) to have a lower uterus weight at slaughter than those in the CTRL or MGA groups. Although there was no significant effects of estrus suppression method on ovary weight, negative linear regressions (P < 0 05) indicated that heifers (in the GnRH group) with the highest anti-GnRH titres had a corresponding decrease in uterus and ovary weights. Plasma progesterone concentrations were consistently significantly lower in heifers receiving MGA than in the remaining heifers and were significantly lower in the CmRH group vs the CTRL group (on Days 42, 63 and 83), in association with increasing anti-GnRH titres, as previously reported (22). In addition, there was a negative linear regression (P < 0.05) between plasma progesterone concentrations on D63 and D83 and the concurrent anti-GnRH titres. While the variability in titres may have resulted from vaccine formulation and/or administration, it provided a range of immune responses that were interpreted with regression analyses In conclusion, the trenbolene ac,~ate/estradiol implant significantly increased growth performance and carcass weight (as a result of increased muscular growth) while marbling was not affected Compared to heifers fed MGA, immunization against GnRH significantly increased both ribeye area and lean yield and reduced grade fat thickness. Although immunization did not significantly reduce estrus mounting activity, there was a significant reduction in uterus weight and plasma progesterone concentrations in heifers with an adequate immune response. With further refinement of vaccine formulation and administration, immunization against OnRH has considerable potential as a nonhormonal method of suppressing estrus in feedlot heifers.
Theriogenology
980 REFERENCES 1.
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2.
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Prendiville DJ, Enright WJ, Crowe MA, Finnerty M, Hynes F, Roche JF Immunization of heifers against gonadotropin-releasing hormone' Antibody titres, ovarian function, body growth, and carcass characteristics. J Anita Sci 1995; 73' 2382-2389.
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Schanbacher BD. Responses of ram lambs to active immunization against testosterone and luteinizing hormone-releasing hormone. Am J Physiol 1982; 242:201-205
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VanSoest PJ, Robertson JB, Lewis BA. Methods for determining dietary fibre, neutral detergent fibre, and nonstarch polysaccharides in relation to animal nutrition. J Dairy Sci 1991; 74: 3583-3597.
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WetternanRP, Castree JW. Immunization of heifers against gonadotropin-releasing hormone delays puberty and causes the cessation ofestrous cycles Anita Reprod Sci 1994; 36' 49-59
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Zimbelman RG, Lauderdale JW, Sokolowski JH, Schalk TG Safety and pharmacologic evaluations ofmelengestrol acetate in cattle and other animals: A review J Am Vet Med Assoc 1970; 157: 1528-1536.