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Pregnancy rate in peripuberal beef heifers following treatment with syncro-mate-B and gonadotropin releasing-hormone
THERIOGENOLOCY
PREGNANCY RATE IN PERIPUBERAL BEEF HEIFERS FOLLOWING TREATMENT WITH SYNCRO-MATE-B AND GONADOTROPIN RELEASING-HORMONEayb John C. SpitzerC Department of Animal Science, Texas A&M University College Station, Texas 77843
Received for Publication: September 23, 81 Accepted: February 4, 1982 ABSTRACT A study was conduct d to evaluate the effectiveness of treatment 2 with Syncro-Mate-B (SMB) and gonadotropin releasing-hormone (GnRH) on inducing a fertile estrus and/or ovulation in peripuberal beef heifers. Two hundred and twenty-three, 13 to 15 month peripuberal beef heifers , primarily of Angus or Simmental breeding, were alternately allotted by weight and age within breed to a non-treated control group (C) and three groups which received the SMB treatment regime. Treated groups differed in that one group was inseminated approximately 12 hr after detected in estrus (T) while two other groups were inseminated at a fixed time after implant removal (T-G-142, T-148). Heifers in group T-G-142 received 125 pg GnRH at 30 hr, and were inseminated 42 hr after implant removal. The remaining group of SMB-treated heifers received no additional hormone therapy but were inseminated 48 hr after implant removal (~-148). Age had no significant effect on estrous response or pregnancy rate nor were there significant age by weight interactions on these parameters. Weight was a significant source of variation on interval from start of breeding to pregnancy (p<.Ol) and the effect on interval to estrus approached statistical significance (R.09). In control heifers, increased weight had a positive effect on estrous response during the first 21 days of breeding (R.05). Conversely, weight had no effect on estrous response during the 5-day synchronized period in heifers treated with SMB and observed for estrus (group T). Cumulative estrous response in control heifers was 10, 47, 48 and 55% in 5, 21, 27 and 45 days of breeding, respectively.
(a)
Texas Agricultural Extension Service, The Texas A&M University System. Published with the approval of.The Director of The Texas Agricultural Experiment Station as Technical Article 16304
(b)
Supported, in part, by a grant from Searle Veterinary Research and Development, Elburn, IL 60119
(c)
Present address: Animal Science Department, Clemson University Clemson, SC 29631
(d)
G. D. Searle and Company, Chicago, IL
APRIL 1982VOL. 17 NO. 4
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THERWGENOIAX3Y
Cumulative estrous response in SMB-treated heifers observed for estrus (group T) was 88, 91, 91 and 91% in 5, 21, 27 and 45 days of breeding, respectively. Pregnancy rate after 5 days of breeding was 9, 27, 18 and 30% for heifers in groups C, T, T-G-142 and T-148, respectively. Pregnancy rate after 21 days of breeding for heifers in groups C, T, T-G-142 and T-148, respectively, was 33, 38, 21 and 41%; after 27 days of breeding was 36, 43, 40 and 48%; after 45 days of breeding was 48, 61, 51 and 69% and after the total 88-day breeding season was 59, 68, 71 and 72%. While a large percentage of peripuberal beef heifers with adequate age but insufficient weight were induced into estrus with the SMB treatment, pregnancy rates were low. Timed insemination programs with or without GnRH do not appear to be effective in improving pregnancy response in non-cyclic beef heifers. INTRODUCTION Early calving cows continue to calve early, have higher pregnancy rates and wean heavier calves than late-calving cows (1, 2, 3). It therefore seems critical that replacement heifers be bred to calve early with their first calf. However, heifers cannot be bred to calve early unless they reach puberty prior to, or early in, their first breeding season. Onset of puberty is influenced by genetics, age and weight. where heifers to be bred are 13 to 16 months Under practical situations, of age, weight is the primary controlling factor (4). Under some alternatives to the often large feed requirements circumstances, necessary for heifers to reach appropriate weights prior to breeding migh be desirable. Successful induction of puberty in beef heifers following the Syncro-Mate-B (SMB) treatment regime has been reported (5, 6, 7, 8). this treatment has been most successful in heifers of an age and However, weight approaching normal for spontaneous attainment of puberty, or in Heifers without adequate weight or older heifers lacking in weight. less than 12 months of age did not give favorable response to SMB treatSmith and others noted that many lightweight heifers with ment (8). induced estrus following SMB treatment were neither pregnant nor continued to have estrous cycles (7). In postpuberal beef heifers treated with SMB, a single timed insemination following implant removal yielded pregnancy rates equal or better than pregnancy rates following a detected estrus Kaltenbach and others (10) reported ZZ;lsequent to imp&t removal (9). that injections of 250 ug of gonadotropin releasing-hormone (GnRH) at 24 or 36 hr following removal of a norgestomet implant decreased the This would imply that variation in time of LH release and ovulation. GnRH might be used to decrease variation in ovulation time and enhance pregnancy rate with timed insemination following SMB treatment. As little as 125 pg GnRH administered 30 hr after implant removal causes a predictable ovulatory LH release following the SMB treatment regime in cyclic heifers and cows (T. G. Dunn, personal communication).
374
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THERIOGENOLOGY
This study was conducted to provide data on estrous response and pregnancy rate following SMB treatment in heifers with adequate age (i.e. 13 to 15 months) and covering a wide range of weights. Additionally, two groups of heifers were inseminated at predetermined times after implant removal, with or without GnRH as an adjunct treatment, in an attempt to eliminate detection for estrus. MATERIALS AND METHODS Two hundred and twenty-three beef heifers 13 to 15 months of age at time of treatment were utilized for this study. Heifers consisted of 83 Angus or 314 Angus x l/4 Hereford (hereafter referred to as Angus heifers) and 140 Simmental x Hereford, Simmental x Angus, Simmental x (Angus x Hereford) or 3/4 Simmental x l/4 British Breed (hereafter referred to as Simmental heiyers). Following weaning these heifers were grouped in one drylot and fed a diet consisting primarily of corn silage. This feeding-management resulted in Angus heifers weighing 236 to 363 kg and Simmental heifers weighing 229 to 399 kg at time of treatment. Heifers were alternately allotted by weight and age within breed to one of four groups. Non-treated control heifers (C) were inseminated approximately 12 hr following a detected estrus. Heifers in the remaining three groups received the SMB treatment regime as outlined by Miksch -et al. (1978) and Spitzer et al. (1978). An implant containing 6 mg of norgestomet was implanted subcutaneously in the convex surface of the ear and remained in situ for 9 days. An intramuscular injection of 5 mg of estradiol -valerate (EV) and 3 mg of norgestomet was administered on the day the implant was inserted. Heifers in the three treated groups were assigned to be inseminated approximately 12 hr following a detected estrus (group T); inseminated regardless of estrus, 12 hr following a single intramuscular injection of 125 ng of GnRH given 30 hr after implant removal (group T-G-142); or inseminated 48 hr following implant removal, regardless of estrus (group T-148). The breeding season began when implants were removed from treated heifers. The first 45 days of breeding was via artificial insemination (AI), and was followed by a 43-day exposure to natural service for a total breeding season of 88 days. Heifers in groups T-G-I42 and T-148 were maintained in separate groups until inseminated at 42 and 48 hr, respectively, after implant removal. No attempt was made to detect estrus in these two groups of heifers. All heifers in groups C and T were maintained together in one drylot during the 5 days immediately subsequent to implant removal (synchronized period). Heifers were observed for standing estrus three times per day, at 0600, at noon and at 1900; although observations were even more frequent during the synchronized period. When detected in estrus, heifers were moved to a holding pen to await AI. Subsequent to the 5-day synchronized period, all heifers from the four groups were together for the duration of breeding. Equal numbers of heifers from each group were inseminated with semen from each bull used. Equal numbers of heifers in each group were inseminated by one of two experienced technicians for the total AI breeding season. Pregnancy was determined by palpation -per rectum 44 days after ending AI breeding and again 80 days after the end of the total breeding season.
APRIL 1982 VOL. 17 NO. 4
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THERIOGENOLOCY
Since the two breeds utilized represented differing types and were expected to reach puberty at different weights, heifers were grouped according to weight classifications described by Beverly and Spitzer (4). That is, heifers in weight-group 1 (WGl) were Angus heifers weighing less than 250 kg and Simmental heifers weighing less than 283 kg. Heifers in WG2 consisted of Angus heifers weighing 250-272 kg and Simmental heifers weighing 283-306 kg, while WG3 was Angus heifers weighing 273-295 kg and Simmental heifers weighing 307-340 kg. Heifers in WG4 consisted of Angus heifers weighing more than 295 kg and Simmental heifers weighing more than 340 kg (Table 1). Distribution of age of heifers within weight-group is displayed in table 2.
TABLE 1. Group
CLASSIFICATION OF WEIGHT-GROUP BY BREED AND WEIGHT Angus weight (kg)
WGl WG2 WG3 WG4
Simmental weight (kg)
~283 283-306 307-340 >340
< 250 250-272 273-295 >295
Treatment differences were analyzed by chi-square contingency table. Where indicated, additional independent comparisons were made (11). Intervals from start of breeding to estrus and pregnancy, in heifers showing estrus and becoming pregnant, were analyzed by a general linear model procedure (12). The model utilized contained age, weight and breed as main effects and all two-way interactions. TABLE 2.
DISTRIBUTION OF AGE OF HEIFERS WITH WEIGHT-GROUP Heifer age by percent
Group
15 mo
14 mo
13 mo
WGl WG2 WG3 WG4
10 18 35 45
66 65 53 49
24 16 12 6
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RESULTS AND DISCUSSION Age was not a significant source of variation on interval from start of breeding to first estrus, interval from start of breeding to pregnancy, percent in estrus or percent pregnant. These results were expected since heifers were 13 to 15 months of age. Breed was a significant source of variation for these variables, but not when heifers of each breed were categorized into the four weight groups. Weight was a significant source of variation on interval from start of breeding to pregnancy (pC.01) and the effect on interval to estrus approached significance These data concur with Beverly and Spitzer (4) who concluded that (B.09). across most breeds of beef heifers from 13 to 16 months of age, weight was the primary factor contributing to onset of estrus and pregnancy. Due to experimental design, effects of weight and treatment on estrous response can only be accurately evaluated in groups C and T. In group C, weight just prior to breeding had a significant effect on estrous response during the first 21 days of the breeding season (Table 3). Fifteen, 23, 68 and 69% of control heifers in weight groups 1-4, respectively, were observed in estrus. Conversely, weight had no effect on estrous response during the 5-day synchronized period in heifers treated with SPQ3. In group T, 80 to 92% of heifers were observed in estrus during the 5-day synchronized period. Overall, 47% of heifers in group C were detected in estrus during the first 21 days of breeding while 88% of heifers in group T were detected in estrus during the first 5 days of breeding (Pc.05).
TABLE 3.
ESTROUS RESPONSE FOLLOWING PROGESTIN TREATMENT IN PERIPUBERAL BEEF HEIFERS
Weight group
Heifers in estrus (%)a ____-____---_______--------_----_-----_ C T
WGl WG2 WG3 WG4
15b 23b 68c 69'
85 80 92 89
a Heifers in estrus during first 21 days of breeding in group C and during 5-day synchronized period in group T. bc
Figures with the same column with different superscripts differ significantly (p.05).
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THERIOCENOLOCY More heifers in the heavier weight groups (3 and 4) were pregnant during the first 21 days of the breeding season for control heifers (Table 4). Control heifers in weight groups 1-4, respectively, had pregnancy rates of 0, 15, 53 and 54%. The general trend in all groups treated with SMB was for heifers in the heavier weight groups to respond with higher pregnancy rates. With all treated heifers (groups T, T-G-142 and T-148) combined, 9, 17, 26 and 34% of heifers in weight groups 1-4, respectively, were pregnant during the 5-day synchronized period.
TABLE 4.
Weight group
WGl WG2 WG3 WG4
PREGNANCY RATE FOLLOWING PROGESTIN TREATMENT IN PERIPUBERAL BEEF HEIFERS
Heifers pregnant (%>a _______-_-___---------~------------_-_-_---_-_----------C T T-G-142 ALL TREATED T-148
Ob lsb 53c 54=
15b 2obc 2gbC 44c
Ob 14bC gb 33c
11
gb
18 43 27
17bC 26Cd 34d
a Heifers pregnant of total heifers in group during first 21 days of breeding in group C, during S-day synchronized period in group T and from a single, timed insemination in groups T-G-142 and T-148. bed
Figures within the same column with different superscripts differ significantly (R.05).
Cumulative estrous response and pregnancy rate are presented in table 5 for all heifers in each treatment group. During the S-day synchronized period, 10% of control heifers were detected in estrus as compared to 88% of group T heifers (F.05). Ninety-one percent of heifers in group T exhibited estrus by day 21, of the breeding season which was a significantly higher estrous response rate than the 47. 48 and 55% for control heifers by 21, 27 and 45 days of the breeding season, For heifers treated with SMB, 23, 24 and 20% of respectively (R.05). heifers in groups T, T-G-142 and T-148, respectively, did not return to estrus but were open following 88 days of breeding. Pregnancy rate during the S-day synchronized period was 9, 27, 18 and gn%for heifers in groups C, T, T-G-142 and T-148, respectively (R.05) (Table 5). After 21 or 27 days of breeding, pregnancy rate did not differ greatly among treatments except that it was significantly lower for group T-G-142 than for group T-148 after 21 days of breeding. At the end of the 45-day AI season 48, 61, 51 and 69% of heifers in groups Pregnancy C, T, T-G-142 and T-148, respectively, were pregnant (R.05). rates after the total 88-day breeding season of 59, 68, 71 and 72% for heifers in groups C, T, T-G-142 and T-148, respectively were not statistically different.
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TABLE 5.
CUMULATIVE ESTROUS RESPONSE AND CUMULATIVE PREGNANCY RATE FOR AN 88-DAY BREEDING PERIOD FOLLOWING PROGESTIN TREATMENT IN PERIPUBEPAL BEEF HEIFERS
ESTROUS RESPONSE Treatment No. group heifers
C T T-G142 T-148
58 56 55 54
PREGNANCY RATE Treatment group
No. heifers
Cumulative % inseminated (days after implant removal) --------------------------------------------5 21 27 45
10; 1::c 100C
C
ab
c d
58 56 55 54
4aa 91b 100 100
55a 91b 100 100
Cumulative % pregnantd (days after implant removal) --_-_----------________---------------------5
T T-G-142 T-148
47a 91b 100 100
21
ab 9;: 27 18a 3ob
33ab 38 21a 41b
27
45
88
36 43 40 48
4Ba 61ab 51a 6gb
59 68 71 72
Figures within the same column with different superscripts differ significantly (PC.05). All heifers were inseminated with no attempt to observe estrus. Percent pregnant based on all heifers in each group.
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THERIOGENOLOGY
It would appear that after heifers reach the age of 13 to 16 months, weight is the determining factor influencing onset of puberty. While estrus was induced with SMB in some of the light-weight heifers in this study, pregnancy rates were far from acceptable and a high proportion of the heifers did not appear to continue estrous cyclicity following induced estrus. These conclusions are similar to those of Smith and others (7) and Burfening (8). GnRH treatment following the SMB treatment did not appear to be beneficial and, in fact, was associated with a reduced pregnancy rate in these peripuberal heifers. Poor pregnancy rate in this group may be due to a miss-timing of LH release relative to estrus but this timing sequence of GnRH injection and insemination following SMB treatment has given good results in heifers and cows exhibiting estrous cyclicity prior to treatment (T. G. Dunn, personal communication). Managment systems utilizing the SM8 treatment without estrous detection appear to work quite well in postpuberal beef heifers (9). However, in this study, application in peripuberal heifers did not yield satisfactory results. The SMB treatment induced estrus in peripuberal beef heifers with adequate age but light in weight, although pregnancy rates were low. This might reflect an anovulatory induced estrus but this information was not collected as part of the present study. Future experiments with SMB in prepuberal or peripuberal heifers should examine incidence of ovulation and establishment of estrous cyclicity following induced estrus. While the overall response to the SMB treatment regime in these peripuberal beef heifers on pregnancy rate early in the breeding season and after a total of 88 days of breeding was generally greater than for control heifers, it would not appear to be economically practical in most heifer-breeding programs. Heifers should be of sufficient age and weight to reach puberty prior to SMB treatment if acceptable pregnancy rates are desired.
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Literature Cited
1.
Lesmeister, J. L., P. J. Burfening and R. L. Blackwell. Date of first calving in beef cows and subsequent calf production. J. Anim. Sci. 36:1-6. 1973.
2.
Burris, M. J. and B. M. Priode. Effect on calving date on subsequent calving performance. J. Anim. Sci. 17~527-533. 1958.
3.
Spitzer, J. C., D. G. LeFever and J. N. Wiltbank. Increase beef cow productivity by increasing reproductive performance. Colorado State University Experiment Station Bulletin. Gen. Series 949. 1975.
4.
Beverly, J. R. and J. C. Spitzer. Management of replacement heifers for a high reproductive and calving rate. Texas A&M UniversityTexas Agricultural Extension Service Bulletin, B-1213. 1980.
5.
Gonzalez-Padilla, E., R. Ruiz, D. G. LeFever, A. Denham and J. N. Wiltbank. Puberty in beef heifers. III. Induction of fertile estrus. J. Anim. Sci. 40:1110-1117. 1975.
6.
Short, R. E., R. A. Bellows, J. B. Carr, R. B. Staigmiller and R. D. Randel. Induced or synchronized puberty in heifers. J. Anim. Sci. 43:1254-1258. 1976.
7.
Smith, M. F., W. C. Burrell, J. Broadway and J. N. Wiltbank. Estrus and pregnancy in beef heifers following use of the Syncro-Mate-B treatment (SMB). Theriogenology. 12:183-187. 1979.
8.
Burfening, P. J. Induction of puberty and subsequent reproductive performance. Theriogenology. 12:215-221. 1979.
9.
Spitzer, J. C., S. E. Mares and L. A. Peterson. Pregnancy rate among beef heifers from timed insemination following synchroniza tion with a progestin treatment. J. Anim. Sci. 53:1-6. 1981.
10.
Kaltenbach, C. C., T. G. Dunn, T. E. Kiser, L. R. Corah, A. M. Akbar and G. D. Niswender. Release of FSH and LH in beef heifers by synthetic gonadotropin releasing hormone. J. Anim. Sci. 38:357-362. 1974.
11.
Steel, R. G. D. and J. H. Torrie. Principles and Procedures of Statistics. McGraw-Hill Book Co., New York. 1960.
12.
Barr, A. J., J. H. Goodnight, J. P. Sal1 and J. T. Helwig. A user's guide to SAS-76. SAS Institute, Inc. Raleigh, N. C. 1976.
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PREGNANCY RATE IN PERIPUBERAL BEEF HEIFERS FOLLOWING TREATMENT WITH SYNCRO-MATE-B AND GONADOTROPIN RELEASING-HORMONEayb John C. SpitzerC Department of Animal Science, Texas A&M University College Station, Texas 77843
Received for Publication: September 23, 81 Accepted: February 4, 1982 ABSTRACT A study was conduct d to evaluate the effectiveness of treatment 2 with Syncro-Mate-B (SMB) and gonadotropin releasing-hormone (GnRH) on inducing a fertile estrus and/or ovulation in peripuberal beef heifers. Two hundred and twenty-three, 13 to 15 month peripuberal beef heifers , primarily of Angus or Simmental breeding, were alternately allotted by weight and age within breed to a non-treated control group (C) and three groups which received the SMB treatment regime. Treated groups differed in that one group was inseminated approximately 12 hr after detected in estrus (T) while two other groups were inseminated at a fixed time after implant removal (T-G-142, T-148). Heifers in group T-G-142 received 125 pg GnRH at 30 hr, and were inseminated 42 hr after implant removal. The remaining group of SMB-treated heifers received no additional hormone therapy but were inseminated 48 hr after implant removal (~-148). Age had no significant effect on estrous response or pregnancy rate nor were there significant age by weight interactions on these parameters. Weight was a significant source of variation on interval from start of breeding to pregnancy (p<.Ol) and the effect on interval to estrus approached statistical significance (R.09). In control heifers, increased weight had a positive effect on estrous response during the first 21 days of breeding (R.05). Conversely, weight had no effect on estrous response during the 5-day synchronized period in heifers treated with SMB and observed for estrus (group T). Cumulative estrous response in control heifers was 10, 47, 48 and 55% in 5, 21, 27 and 45 days of breeding, respectively.
(a)
Texas Agricultural Extension Service, The Texas A&M University System. Published with the approval of.The Director of The Texas Agricultural Experiment Station as Technical Article 16304
(b)
Supported, in part, by a grant from Searle Veterinary Research and Development, Elburn, IL 60119
(c)
Present address: Animal Science Department, Clemson University Clemson, SC 29631
(d)
G. D. Searle and Company, Chicago, IL
APRIL 1982VOL. 17 NO. 4
60680
373
THERWGENOIAX3Y
Cumulative estrous response in SMB-treated heifers observed for estrus (group T) was 88, 91, 91 and 91% in 5, 21, 27 and 45 days of breeding, respectively. Pregnancy rate after 5 days of breeding was 9, 27, 18 and 30% for heifers in groups C, T, T-G-142 and T-148, respectively. Pregnancy rate after 21 days of breeding for heifers in groups C, T, T-G-142 and T-148, respectively, was 33, 38, 21 and 41%; after 27 days of breeding was 36, 43, 40 and 48%; after 45 days of breeding was 48, 61, 51 and 69% and after the total 88-day breeding season was 59, 68, 71 and 72%. While a large percentage of peripuberal beef heifers with adequate age but insufficient weight were induced into estrus with the SMB treatment, pregnancy rates were low. Timed insemination programs with or without GnRH do not appear to be effective in improving pregnancy response in non-cyclic beef heifers. INTRODUCTION Early calving cows continue to calve early, have higher pregnancy rates and wean heavier calves than late-calving cows (1, 2, 3). It therefore seems critical that replacement heifers be bred to calve early with their first calf. However, heifers cannot be bred to calve early unless they reach puberty prior to, or early in, their first breeding season. Onset of puberty is influenced by genetics, age and weight. where heifers to be bred are 13 to 16 months Under practical situations, of age, weight is the primary controlling factor (4). Under some alternatives to the often large feed requirements circumstances, necessary for heifers to reach appropriate weights prior to breeding migh be desirable. Successful induction of puberty in beef heifers following the Syncro-Mate-B (SMB) treatment regime has been reported (5, 6, 7, 8). this treatment has been most successful in heifers of an age and However, weight approaching normal for spontaneous attainment of puberty, or in Heifers without adequate weight or older heifers lacking in weight. less than 12 months of age did not give favorable response to SMB treatSmith and others noted that many lightweight heifers with ment (8). induced estrus following SMB treatment were neither pregnant nor continued to have estrous cycles (7). In postpuberal beef heifers treated with SMB, a single timed insemination following implant removal yielded pregnancy rates equal or better than pregnancy rates following a detected estrus Kaltenbach and others (10) reported ZZ;lsequent to imp&t removal (9). that injections of 250 ug of gonadotropin releasing-hormone (GnRH) at 24 or 36 hr following removal of a norgestomet implant decreased the This would imply that variation in time of LH release and ovulation. GnRH might be used to decrease variation in ovulation time and enhance pregnancy rate with timed insemination following SMB treatment. As little as 125 pg GnRH administered 30 hr after implant removal causes a predictable ovulatory LH release following the SMB treatment regime in cyclic heifers and cows (T. G. Dunn, personal communication).
374
APRIL
1982 VOL. 17 NO. 4
THERIOGENOLOGY
This study was conducted to provide data on estrous response and pregnancy rate following SMB treatment in heifers with adequate age (i.e. 13 to 15 months) and covering a wide range of weights. Additionally, two groups of heifers were inseminated at predetermined times after implant removal, with or without GnRH as an adjunct treatment, in an attempt to eliminate detection for estrus. MATERIALS AND METHODS Two hundred and twenty-three beef heifers 13 to 15 months of age at time of treatment were utilized for this study. Heifers consisted of 83 Angus or 314 Angus x l/4 Hereford (hereafter referred to as Angus heifers) and 140 Simmental x Hereford, Simmental x Angus, Simmental x (Angus x Hereford) or 3/4 Simmental x l/4 British Breed (hereafter referred to as Simmental heiyers). Following weaning these heifers were grouped in one drylot and fed a diet consisting primarily of corn silage. This feeding-management resulted in Angus heifers weighing 236 to 363 kg and Simmental heifers weighing 229 to 399 kg at time of treatment. Heifers were alternately allotted by weight and age within breed to one of four groups. Non-treated control heifers (C) were inseminated approximately 12 hr following a detected estrus. Heifers in the remaining three groups received the SMB treatment regime as outlined by Miksch -et al. (1978) and Spitzer et al. (1978). An implant containing 6 mg of norgestomet was implanted subcutaneously in the convex surface of the ear and remained in situ for 9 days. An intramuscular injection of 5 mg of estradiol -valerate (EV) and 3 mg of norgestomet was administered on the day the implant was inserted. Heifers in the three treated groups were assigned to be inseminated approximately 12 hr following a detected estrus (group T); inseminated regardless of estrus, 12 hr following a single intramuscular injection of 125 ng of GnRH given 30 hr after implant removal (group T-G-142); or inseminated 48 hr following implant removal, regardless of estrus (group T-148). The breeding season began when implants were removed from treated heifers. The first 45 days of breeding was via artificial insemination (AI), and was followed by a 43-day exposure to natural service for a total breeding season of 88 days. Heifers in groups T-G-I42 and T-148 were maintained in separate groups until inseminated at 42 and 48 hr, respectively, after implant removal. No attempt was made to detect estrus in these two groups of heifers. All heifers in groups C and T were maintained together in one drylot during the 5 days immediately subsequent to implant removal (synchronized period). Heifers were observed for standing estrus three times per day, at 0600, at noon and at 1900; although observations were even more frequent during the synchronized period. When detected in estrus, heifers were moved to a holding pen to await AI. Subsequent to the 5-day synchronized period, all heifers from the four groups were together for the duration of breeding. Equal numbers of heifers from each group were inseminated with semen from each bull used. Equal numbers of heifers in each group were inseminated by one of two experienced technicians for the total AI breeding season. Pregnancy was determined by palpation -per rectum 44 days after ending AI breeding and again 80 days after the end of the total breeding season.
APRIL 1982 VOL. 17 NO. 4
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THERIOGENOLOCY
Since the two breeds utilized represented differing types and were expected to reach puberty at different weights, heifers were grouped according to weight classifications described by Beverly and Spitzer (4). That is, heifers in weight-group 1 (WGl) were Angus heifers weighing less than 250 kg and Simmental heifers weighing less than 283 kg. Heifers in WG2 consisted of Angus heifers weighing 250-272 kg and Simmental heifers weighing 283-306 kg, while WG3 was Angus heifers weighing 273-295 kg and Simmental heifers weighing 307-340 kg. Heifers in WG4 consisted of Angus heifers weighing more than 295 kg and Simmental heifers weighing more than 340 kg (Table 1). Distribution of age of heifers within weight-group is displayed in table 2.
TABLE 1. Group
CLASSIFICATION OF WEIGHT-GROUP BY BREED AND WEIGHT Angus weight (kg)
WGl WG2 WG3 WG4
Simmental weight (kg)
~283 283-306 307-340 >340
< 250 250-272 273-295 >295
Treatment differences were analyzed by chi-square contingency table. Where indicated, additional independent comparisons were made (11). Intervals from start of breeding to estrus and pregnancy, in heifers showing estrus and becoming pregnant, were analyzed by a general linear model procedure (12). The model utilized contained age, weight and breed as main effects and all two-way interactions. TABLE 2.
DISTRIBUTION OF AGE OF HEIFERS WITH WEIGHT-GROUP Heifer age by percent
Group
15 mo
14 mo
13 mo
WGl WG2 WG3 WG4
10 18 35 45
66 65 53 49
24 16 12 6
376
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RESULTS AND DISCUSSION Age was not a significant source of variation on interval from start of breeding to first estrus, interval from start of breeding to pregnancy, percent in estrus or percent pregnant. These results were expected since heifers were 13 to 15 months of age. Breed was a significant source of variation for these variables, but not when heifers of each breed were categorized into the four weight groups. Weight was a significant source of variation on interval from start of breeding to pregnancy (pC.01) and the effect on interval to estrus approached significance These data concur with Beverly and Spitzer (4) who concluded that (B.09). across most breeds of beef heifers from 13 to 16 months of age, weight was the primary factor contributing to onset of estrus and pregnancy. Due to experimental design, effects of weight and treatment on estrous response can only be accurately evaluated in groups C and T. In group C, weight just prior to breeding had a significant effect on estrous response during the first 21 days of the breeding season (Table 3). Fifteen, 23, 68 and 69% of control heifers in weight groups 1-4, respectively, were observed in estrus. Conversely, weight had no effect on estrous response during the 5-day synchronized period in heifers treated with SPQ3. In group T, 80 to 92% of heifers were observed in estrus during the 5-day synchronized period. Overall, 47% of heifers in group C were detected in estrus during the first 21 days of breeding while 88% of heifers in group T were detected in estrus during the first 5 days of breeding (Pc.05).
TABLE 3.
ESTROUS RESPONSE FOLLOWING PROGESTIN TREATMENT IN PERIPUBERAL BEEF HEIFERS
Weight group
Heifers in estrus (%)a ____-____---_______--------_----_-----_ C T
WGl WG2 WG3 WG4
15b 23b 68c 69'
85 80 92 89
a Heifers in estrus during first 21 days of breeding in group C and during 5-day synchronized period in group T. bc
Figures with the same column with different superscripts differ significantly (p.05).
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THERIOCENOLOCY More heifers in the heavier weight groups (3 and 4) were pregnant during the first 21 days of the breeding season for control heifers (Table 4). Control heifers in weight groups 1-4, respectively, had pregnancy rates of 0, 15, 53 and 54%. The general trend in all groups treated with SMB was for heifers in the heavier weight groups to respond with higher pregnancy rates. With all treated heifers (groups T, T-G-142 and T-148) combined, 9, 17, 26 and 34% of heifers in weight groups 1-4, respectively, were pregnant during the 5-day synchronized period.
TABLE 4.
Weight group
WGl WG2 WG3 WG4
PREGNANCY RATE FOLLOWING PROGESTIN TREATMENT IN PERIPUBERAL BEEF HEIFERS
Heifers pregnant (%>a _______-_-___---------~------------_-_-_---_-_----------C T T-G-142 ALL TREATED T-148
Ob lsb 53c 54=
15b 2obc 2gbC 44c
Ob 14bC gb 33c
11
gb
18 43 27
17bC 26Cd 34d
a Heifers pregnant of total heifers in group during first 21 days of breeding in group C, during S-day synchronized period in group T and from a single, timed insemination in groups T-G-142 and T-148. bed
Figures within the same column with different superscripts differ significantly (R.05).
Cumulative estrous response and pregnancy rate are presented in table 5 for all heifers in each treatment group. During the S-day synchronized period, 10% of control heifers were detected in estrus as compared to 88% of group T heifers (F.05). Ninety-one percent of heifers in group T exhibited estrus by day 21, of the breeding season which was a significantly higher estrous response rate than the 47. 48 and 55% for control heifers by 21, 27 and 45 days of the breeding season, For heifers treated with SMB, 23, 24 and 20% of respectively (R.05). heifers in groups T, T-G-142 and T-148, respectively, did not return to estrus but were open following 88 days of breeding. Pregnancy rate during the S-day synchronized period was 9, 27, 18 and gn%for heifers in groups C, T, T-G-142 and T-148, respectively (R.05) (Table 5). After 21 or 27 days of breeding, pregnancy rate did not differ greatly among treatments except that it was significantly lower for group T-G-142 than for group T-148 after 21 days of breeding. At the end of the 45-day AI season 48, 61, 51 and 69% of heifers in groups Pregnancy C, T, T-G-142 and T-148, respectively, were pregnant (R.05). rates after the total 88-day breeding season of 59, 68, 71 and 72% for heifers in groups C, T, T-G-142 and T-148, respectively were not statistically different.
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TABLE 5.
CUMULATIVE ESTROUS RESPONSE AND CUMULATIVE PREGNANCY RATE FOR AN 88-DAY BREEDING PERIOD FOLLOWING PROGESTIN TREATMENT IN PERIPUBEPAL BEEF HEIFERS
ESTROUS RESPONSE Treatment No. group heifers
C T T-G142 T-148
58 56 55 54
PREGNANCY RATE Treatment group
No. heifers
Cumulative % inseminated (days after implant removal) --------------------------------------------5 21 27 45
10; 1::c 100C
C
ab
c d
58 56 55 54
4aa 91b 100 100
55a 91b 100 100
Cumulative % pregnantd (days after implant removal) --_-_----------________---------------------5
T T-G-142 T-148
47a 91b 100 100
21
ab 9;: 27 18a 3ob
33ab 38 21a 41b
27
45
88
36 43 40 48
4Ba 61ab 51a 6gb
59 68 71 72
Figures within the same column with different superscripts differ significantly (PC.05). All heifers were inseminated with no attempt to observe estrus. Percent pregnant based on all heifers in each group.
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THERIOGENOLOGY
It would appear that after heifers reach the age of 13 to 16 months, weight is the determining factor influencing onset of puberty. While estrus was induced with SMB in some of the light-weight heifers in this study, pregnancy rates were far from acceptable and a high proportion of the heifers did not appear to continue estrous cyclicity following induced estrus. These conclusions are similar to those of Smith and others (7) and Burfening (8). GnRH treatment following the SMB treatment did not appear to be beneficial and, in fact, was associated with a reduced pregnancy rate in these peripuberal heifers. Poor pregnancy rate in this group may be due to a miss-timing of LH release relative to estrus but this timing sequence of GnRH injection and insemination following SMB treatment has given good results in heifers and cows exhibiting estrous cyclicity prior to treatment (T. G. Dunn, personal communication). Managment systems utilizing the SM8 treatment without estrous detection appear to work quite well in postpuberal beef heifers (9). However, in this study, application in peripuberal heifers did not yield satisfactory results. The SMB treatment induced estrus in peripuberal beef heifers with adequate age but light in weight, although pregnancy rates were low. This might reflect an anovulatory induced estrus but this information was not collected as part of the present study. Future experiments with SMB in prepuberal or peripuberal heifers should examine incidence of ovulation and establishment of estrous cyclicity following induced estrus. While the overall response to the SMB treatment regime in these peripuberal beef heifers on pregnancy rate early in the breeding season and after a total of 88 days of breeding was generally greater than for control heifers, it would not appear to be economically practical in most heifer-breeding programs. Heifers should be of sufficient age and weight to reach puberty prior to SMB treatment if acceptable pregnancy rates are desired.
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Literature Cited
1.
Lesmeister, J. L., P. J. Burfening and R. L. Blackwell. Date of first calving in beef cows and subsequent calf production. J. Anim. Sci. 36:1-6. 1973.
2.
Burris, M. J. and B. M. Priode. Effect on calving date on subsequent calving performance. J. Anim. Sci. 17~527-533. 1958.
3.
Spitzer, J. C., D. G. LeFever and J. N. Wiltbank. Increase beef cow productivity by increasing reproductive performance. Colorado State University Experiment Station Bulletin. Gen. Series 949. 1975.
4.
Beverly, J. R. and J. C. Spitzer. Management of replacement heifers for a high reproductive and calving rate. Texas A&M UniversityTexas Agricultural Extension Service Bulletin, B-1213. 1980.
5.
Gonzalez-Padilla, E., R. Ruiz, D. G. LeFever, A. Denham and J. N. Wiltbank. Puberty in beef heifers. III. Induction of fertile estrus. J. Anim. Sci. 40:1110-1117. 1975.
6.
Short, R. E., R. A. Bellows, J. B. Carr, R. B. Staigmiller and R. D. Randel. Induced or synchronized puberty in heifers. J. Anim. Sci. 43:1254-1258. 1976.
7.
Smith, M. F., W. C. Burrell, J. Broadway and J. N. Wiltbank. Estrus and pregnancy in beef heifers following use of the Syncro-Mate-B treatment (SMB). Theriogenology. 12:183-187. 1979.
8.
Burfening, P. J. Induction of puberty and subsequent reproductive performance. Theriogenology. 12:215-221. 1979.
9.
Spitzer, J. C., S. E. Mares and L. A. Peterson. Pregnancy rate among beef heifers from timed insemination following synchroniza tion with a progestin treatment. J. Anim. Sci. 53:1-6. 1981.
10.
Kaltenbach, C. C., T. G. Dunn, T. E. Kiser, L. R. Corah, A. M. Akbar and G. D. Niswender. Release of FSH and LH in beef heifers by synthetic gonadotropin releasing hormone. J. Anim. Sci. 38:357-362. 1974.
11.
Steel, R. G. D. and J. H. Torrie. Principles and Procedures of Statistics. McGraw-Hill Book Co., New York. 1960.
12.
Barr, A. J., J. H. Goodnight, J. P. Sal1 and J. T. Helwig. A user's guide to SAS-76. SAS Institute, Inc. Raleigh, N. C. 1976.
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