Reproductive Performance of Holstein Cows Receiving Somatotropin

摘要

Some dairy producers resist using bovine somato- tropin (bST) beginning at 9 wk postpartum because of the concern that fertility is compromised. We conducted a trial with a total of 205 Holstein cows, 100 multipa- rous and 105 primiparous, to evaluate reproductive per- formance in two high producing herds in Arizona and southern California. Rolling herd averages for both herds for milk production exceeded 10,700 kg/yr. Data were collected for cows calving December 1996 through Angust 1997. The voluntary waiting period was 60 d postcalving, with cows randomly assigned to receive bST or no treatment (controls). In the 180-d interval after calving, 65.4/100 (68/104) of the control cows were diagnosed pregnant. With bST-treated cows, 48.5/100 (49/ 101) were pregnant in that same interval. A chi-square value from a linear model indicated that pregnancy outcome differed significantly between treatment groups. With a similar method of analysis, first-service conception rate was not significantly different between treatment groups. An extended voluntary wait and breeding interval is recommended for cows receiving bST, similar to suggestions from other published reports.