Submitted to: Western Section of Animal Science Proceedings
Publication Type: Proceedings
Publication Acceptance Date: 6/1/2001
Publication Date: 6/1/2001
Citation: FOSTER, H.A., WHITTIER, J.C., BURNS, P.D., BRUEMMER, J.E., BAKER, D.S., ENGLE, T.E., FIELD, T.G., WAILES, W.R., ANDERSON, D.C., GEARY, T.W. USE OF BOVINE SOMATOTROPIN IN CONJUNCTION WITH THE CO-SYNCH AND SELECT SYNCH PROTOCOLS FOR SYNCHRONIZING ESTRUS AND OVULATION IN BEEF COWS. WESTERN SECTION OF ANIMAL SCIENCE PROCEEDINGS. 2001. v. 52 p. 66-69. Interpretive Summary: We evaluated the ability of bovine somatotropin (bST) administration at different times before AI to increase pregnancy rates of beef cows synchronized with the CO-Synch or Select Synch protocols. Administration of bST at the time of the gonadotropin hormone releasing hormone (GnRH) injection increased the estrous response of cows receiving the Select Synch protocol by approximately 10%. Administration of bST at the time of prostaglandin with the Select Synch protocol resulted in a lower conception rate. When administered at the time of the GnRH injection with the Select Synch protocol, pregnancy rates were numerically higher than cows receiving no bST. No beneficial effects of bST with the CO- Synch protocol were observed. The cost of bST administration ($5.35 per dose) would probably prohibit its adoption among commercial beef producers. Based on these results bovine somatotropin does not appear to improve fertility of beef cows receiving either the CO-Synch or Select Synch estrus synchronization protocols.
Technical Abstract: Objectives were to examine effects of exogenous bovine somatotropin (bST) on pregnancy rates in conjunction with two separate estrus synchronization protocols: CO-Synch and Select Synch. In the CO-Synch trial, lactating beef cows (n=690) from 3 locations were administered 100 mcg of GnRH on d 0 and 9, PGF (25 mg) on d 7 and artificially inseminated (AI) on d 9. Cows were assigned to the following treatments: 500 mg of bST on d 0(Trt 1), d 7 (Trt 2), d 9 (Trt 3), and no bST (Control). Pregnancy rates for treatments 1,2,3 and Control were 30.0, 26.9, 33.1, and 27.1%, respectively, and did not differ (P>0.05). Thus, bST had no effect on pregnancy results in the CO-Synch estrous synchronization protocol. In the second trial, lactating beef cows (n=581) were synchronized using the Select Synch protocol. On d 0, cows received 100 mcg of GnRH, followed 7 d later by 25 mg of PGF, combined with heat detection and AI on d 6-11. Cows were assigned to the following treatments: 500 mg of bST on d 0 (Trt 1), d 7 (Trt 2), and no bST (Control). Estrus response rates were higher for Trt 1 (69.84 +/- 4.9; P<0.05), but there were no differences for estrous response rates between Trt 2 (58.4 +/- 4.9) and 3 (58.9 +/- 4.9; P>0.05). Conception rates were higher (P<0.05) for cows in Trt 1 (64.1%) than for cows in Trt 2 (35.5%). However, conception rates for Trt 1 cows were not higher than Control (60.2%, P>0.05). Based on this trial, bST does not have a beneficial effect on conception rates, but does have a deleterious effect when administered at the time of PGF.