Genetic and environmental factors affecting some reproductive traits of Holstein cows in Cuba

A total of 296 651 fertility records of dairy cows obtained from 1980 to 1988 was studied in order to determine the environmental and genetic factors affecting the reproductive performance of Holstein cows under Cuban conditions. Only 43.9% of the inseminated females were pregnant at first service; however, for heifers this value was 63.1%. The seasonal variability was higher for heifers and for primiparous than for older lactating cows. The best performance was found from February to April, whereas during the hot and humid summer (July to September) poorer results were obtained. Age at calving or number of calvings was another important environmental source of variation: the earlier the calving the poorer is the next reproductive performance. The genetic analyses were made within calving number with the REML procedure. For heifers (226 sires, 45 575 records) the heritability and the genetic coefficient of variation were: 2.26 and 10.94%, 3.24 and 11.24%, and 3.04 and 6.19% for conception rate (CR), numbers of services per conception (SG) and conception status (CS = 1/SG), respectively. For first calving females (280 sires, 43 647 records) the results were: 1.94 and 15.93%, 3.25 and 12.80%, and 3.47 and 9.47% for CR, SG and CS, respectively. For the second and third calving, the results were poorer. For the calving interval and days open, the heritabilities were between 1.86 and 4.64%. The results of SG were selected as the best and more useful traits showing high genetic correlations (> 0.60) for the same traits in different calving number.