GENETIC AND ENVIRONMENTAL-FACTORS AFFECTING SOME REPRODUCTIVE TRAITS OF HOLSTEIN COWS IN CUBA

A total of 226 651 fertility records of dairy cows obtained from 1980 to 1988 was studied in order to determine the environmental and geneti c factors affecting the reproductive performance of Holstein cows unde r Cuban conditions. Only 43.9% of the inseminated females were pregnan t at first service however, for heifers this value was 63.1%. The seas onal variability was higher for heifers and for primiparous than for o lder lactating cows. The best performance was found from February to A pril, whereas during the hot and humid summer (July to September) poor er results were obtained. Age at calving or number of calvings was ano ther important environmental source of variation: the earlier the calv ing the poorer is the next reproductive performance. The genetic analy ses were made within calving number with the REML procedure. For heife rs (226 sires, 45 575 records) the heritability and the genetic coeffi cient of variation were: 2.26 and 10.94%, 3.24 and 11.24%, and 3.04 an d 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 ca lving 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 tr aits showing high genetic correlations (> 0.60) for the same traits in different calving number.