The effect of calf removal on estrous response and pregnancy rate of beef cows after SYNCRO-MATE-B treatment

The effect of calf removal on estrous response and pregnancy rate of cows given SYNCRO-MATE-B (SMB) was determined. Two hundred forty three lactating beef cows treated with SMB were allotted to three treatments: treatment 1, no calf removal; treatment 2, 24 hr calf removal and treatment 3, 48 hr calf removal. Calf removal time began with removal of the SMB implant. All cows were artificially inseminated 48 to 54 hr after implant removal. Body condition of cows in each heard was visually appraised as adequate or marginal. At each location, technicians and sires were stratified across all treatments.Estrous response of cows (n=143) was different (P<.01) between treatments which averaged 23, 40 and 77 percent for treatments 1, 2 and 3, respectively. Pregnancy rates of cows (n=243) after the first artificial insemination (AI) were 32, 28 and 46 percent for treatments 1, 2 and 3, respectively. The pregnancy rate was greater (P<.05) for treatment 3 than other treatments. After 25 days of breeding, the pregnancy rates were 59, 58 and 72 percent, respectively, for the three treatments. There was a linear relationship between days postpartum at the time of treatment and estrous response (P<.01) and first service pregnancy rate (P<.05). The partial regression coefficients for estrous response and first service pregnancy rate were 1.2 and .6 percent, respectively.In summary, estrous response and pregnancy rate of lactating beef cows treated with SMB were increased by 48 hr calf removal, compared to no calf removal or 24 hr calf removal, when calf removal time began with removal of the SMB implant.