EFFECTS OF CLIMATIC AND MANAGEMENT FACTORS ON CONCEPTION RATE OF DAIRY-CATTLE IN SUB-TROPICAL ENVIRONMENT

Breeding records, representing 12,038 inseminations at Bassett''s Dairy Farm (Monticello, Florida [USA]), were analyzed to document effects of environmental and management factors on fertility of dairy cattle from Jan. 1, 1975 to Dec. 31, 1977. Conception rates of lactating cows decreased sharply when maximum air temperature on day after insemination exceeded 30.degree. C. In contrast, conception rates for heifers did not decline until 35.degree. C. Virgin heifers had higher conception rates for all services (50%) than lactating cows (34%) and suffered only slight depression of fertility during summer months. Heifers required 1.5 sevices per conception compared with 2.3 for lactating cows. Relationship between conception rate and rainfall on day after insemination was negative and curvilinear. Jerseys had higher conception rates (45%) than Holstein (39%) and Brown Swiss (41%). Services per conception were 1.7, 2.0 and 1.9. Substantial decrease of fertiliy were associated with advancing service number. Estrous status (standing; positive heat detection patch; mounting activity), inseminator and year of service were related to variation of conception rate. Seasonal effects on fertility of lactating cows were marked. Environmental management of the postpartum cow during hot summer months is warranted to maximize fertility.