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Response to superovulation in yearling beef heifers after synchronization of estrus with an oral progestogen
THERIOGENOLOGY
RESPONSE TO SUPEROVULATION IN YEARLING BEEF HEIFERS AFTER SYNCHRONIZATION OF ESTRUS WITH AN ORAL PROGESTOGEN D. J. Patterson’, L. D. Nelson’, C. F. Nelson*, J. M. Kearnan’, N. W. Bradley’, and K. K. Schillo’ ‘Department of Animal Sciences, University of Kentucky, Lexhgton, KY 40546 USA and ‘Nelson Reproductive Services, Versailles, KY 40383 USA Improved conception rates and higher twirming rates reported recently among cows that are treated with an oral progestogen prior to prostaglandin raise questions concerning the possible role of progestogens on fertility in the bovine female (Patterson et al., 1991, J. Anim. Sci. 69(Suppl,1):395). A study was designed based on this observation to determine differences in response to superovulation in yearling beef heifers after synchronization of estrus with an oral progestogen compared with prostaglandin F,a. Twenty purebred Angus heifers were stratified by age and weight to one of two treatments. Ten heifers, assigned to treatment I, received 0.5 mg/head/day of the oral progestogen melengestrol acetate (MGA) for 14 days in a grain supplement carrier. The ten heifers assigned to treatment II received 2 injections of 500 ug cloprostenol (PGF) 12 days apart and grain carrier without MGA. Pubertal status of heifers prior to assignment to treatments was based on and confirmed by: 1) presence of a corpus luteum determined by ovarian ultrasonography and, 2) increased concentrations of progesterone ( > 1 ng/ml) in plasma obtained from two blood samples collected 10 days apart, prior to the initiation of treatments and at the time ultrasound was performed. Average age and weight of heifers at the initiation of treatments was 367 days and 364 kg, respectively, for heifers assigned to treatments I and II. Superstimulatory treatments began 14 days after the end of treatment with MGA for heifers in treatment I, and 12 days after the second injection of PGF for heifers in treatment II. Superstimulatory treatments (40 mg FSH) were administered twice daily in decreasing dosages (7.5, 5, 5, 2.5 mg) over 4 days. Sixty and 72 hours after initiating superstimulatory treatments, all heifers were treated with 750 ug, and 500 ug i.m. cloprostenol. Heifers were observed continuously for signs of behavioral estrus beginning 84 hours after the initiation of superstimulatory treatments and 12 hours after the last injection of cloprostenol. Heifers that exhibited estrus were inseminated at standing estrus, and 12 and 24 hours from the onset of estrus with 1, 2 and 1 unit of semen, respectively. Semen for all inseminations was obtained from a single ejaculate of a proven sire, and all inseminations were made by a single technician. Eight of 10 heifers in each of the treatments exhibited estrus and were inseminated. Mean interval to estrus was 27.9 and 24.8 hours for heifers in treatments I and II, respectively. Mean number of ova and embryos collected, percent fertilized and transferable by treatment are shown in the table below. There were no significant differences between treatments for any of the variables considered.
IIMean
number
of ova/embryos
collected,
Treatment
Total ova/embryos
I
II
percent fertilized and transferable
6
I
12.3
I
bv treatment.
Fertilized no. %
Transferable no. %
1.8
29.2
1.8
29.2
3
24.4
2.4
19.5
1
II
II
These data suggest that estrus synchronization with MGA prior to superovulation is a viable means of preparing donor females for embryo transfer. However, pretreatment with MGA offered no significant improvement in the number or quality of embryos recovered.
272
JANUARY
1992 VOL. 37 NO. 1
RESPONSE TO SUPEROVULATION IN YEARLING BEEF HEIFERS AFTER SYNCHRONIZATION OF ESTRUS WITH AN ORAL PROGESTOGEN D. J. Patterson’, L. D. Nelson’, C. F. Nelson*, J. M. Kearnan’, N. W. Bradley’, and K. K. Schillo’ ‘Department of Animal Sciences, University of Kentucky, Lexhgton, KY 40546 USA and ‘Nelson Reproductive Services, Versailles, KY 40383 USA Improved conception rates and higher twirming rates reported recently among cows that are treated with an oral progestogen prior to prostaglandin raise questions concerning the possible role of progestogens on fertility in the bovine female (Patterson et al., 1991, J. Anim. Sci. 69(Suppl,1):395). A study was designed based on this observation to determine differences in response to superovulation in yearling beef heifers after synchronization of estrus with an oral progestogen compared with prostaglandin F,a. Twenty purebred Angus heifers were stratified by age and weight to one of two treatments. Ten heifers, assigned to treatment I, received 0.5 mg/head/day of the oral progestogen melengestrol acetate (MGA) for 14 days in a grain supplement carrier. The ten heifers assigned to treatment II received 2 injections of 500 ug cloprostenol (PGF) 12 days apart and grain carrier without MGA. Pubertal status of heifers prior to assignment to treatments was based on and confirmed by: 1) presence of a corpus luteum determined by ovarian ultrasonography and, 2) increased concentrations of progesterone ( > 1 ng/ml) in plasma obtained from two blood samples collected 10 days apart, prior to the initiation of treatments and at the time ultrasound was performed. Average age and weight of heifers at the initiation of treatments was 367 days and 364 kg, respectively, for heifers assigned to treatments I and II. Superstimulatory treatments began 14 days after the end of treatment with MGA for heifers in treatment I, and 12 days after the second injection of PGF for heifers in treatment II. Superstimulatory treatments (40 mg FSH) were administered twice daily in decreasing dosages (7.5, 5, 5, 2.5 mg) over 4 days. Sixty and 72 hours after initiating superstimulatory treatments, all heifers were treated with 750 ug, and 500 ug i.m. cloprostenol. Heifers were observed continuously for signs of behavioral estrus beginning 84 hours after the initiation of superstimulatory treatments and 12 hours after the last injection of cloprostenol. Heifers that exhibited estrus were inseminated at standing estrus, and 12 and 24 hours from the onset of estrus with 1, 2 and 1 unit of semen, respectively. Semen for all inseminations was obtained from a single ejaculate of a proven sire, and all inseminations were made by a single technician. Eight of 10 heifers in each of the treatments exhibited estrus and were inseminated. Mean interval to estrus was 27.9 and 24.8 hours for heifers in treatments I and II, respectively. Mean number of ova and embryos collected, percent fertilized and transferable by treatment are shown in the table below. There were no significant differences between treatments for any of the variables considered.
IIMean
number
of ova/embryos
collected,
Treatment
Total ova/embryos
I
II
percent fertilized and transferable
6
I
12.3
I
bv treatment.
Fertilized no. %
Transferable no. %
1.8
29.2
1.8
29.2
3
24.4
2.4
19.5
1
II
II
These data suggest that estrus synchronization with MGA prior to superovulation is a viable means of preparing donor females for embryo transfer. However, pretreatment with MGA offered no significant improvement in the number or quality of embryos recovered.
272
JANUARY
1992 VOL. 37 NO. 1