Environmental and managemental factors affecting conception rate in a subtropical climate

Data representing 5,062 services during 1960 to 1971 in the Florida Agricultural Experiment Station dairy herd were analyzed by least squares to delineate factors affecting conception rates. Overall conception rate was 37.9%. From a set of 21 climatological measurements, the five selected as most important ranked (1) maximum temperature day after insemination, (2) rainfall day of insemination, (3) minimum temperature day of insemination, (4) solar radiation day of insemination, and (5) minimum temperature day after insemination. Warm months were more closely associated with lower conception rates than were cool months (33.7 compared to 40.1%); month effects appeared to be accounted for by the climatological measurements. Conception rates declined with age: heifers, 47.6%; young cows, 42.7%; older cows, 31.9%. No decline with advancing service number (1 to 5) occurred. Service sire and inseminator effects were detected as expected. Although breeds differed (Aryshires, 33.8; Brown Swiss, 34.6; and Guernseys, 37.0; Holsteins, 35.5; and Jerseys, 48.4%), there was no evidence of breed (Jerseys and Holsteins) by month or breed by season interactions nor was it possible to detect age by season interactions.