ENVIRONMENTAL AND YIELD EFFECTS ON REPRODUCTION IN PRIMIPAROUS HOLSTEINS

Environment and yield effects on days from parturition to first service, first service conception rate, and number of services were studied in primiparous Holsteins. Recorded breedings and DH1 production records were from six experimental herds. Seasonal subsets included daughters of sires having .gtoreq. 5 progeny calving in April through July (n = 817) and August through March (n = 1162). Subsets based on production were <7250 kg 3.7% FCM (1174 cows), 7250 to 9750 kg (1978 cows), and > 9750 kg FCM (241 cows). Highest and lowest conception rates were for December (56.7%) and May (261%) calvings with opposite results for number of services (December, 1.80; May, 2.74). More than one cow in estrus on day of first service reduced interval to first service in August through March calvings but increased that trait in April through July parturitions. For both seasonal subsets, >1 estrual cow increased first service conception, but .gtoreq.4 cows in estrus decreased conception in April through July. In production subsets with >7250 kg FCM, first service conception declined (11.9%) and number of services increased (.28) per 1000 kg more FCM. However, yield did not affect conception rates or days to first service for lowest producers (<7250 kg FCM).