EFFECT OF ENVIRONMENTAL-FACTORS AND BREED GROUP, AND THEIR INTERACTIONS ON PERFORMANCE OF VENEZUELAN DUAL-PURPOSE COWS

Records of milk yield, days open, and 120-day calf weight were obtaine d from 1843 cows on four lowland tropical farms with different levels of management and mean milk yields of 678, 822, 1010, and 2461 kg per lactation. Three main breed groups were represented on each farm: zebu type (Z), medium (M), and high (H) grade European-zebu crosses. The Z cows had the fewest days open and highest calf weight. Overall, the Z and M cows performed similarly, except on the farm with the highest m ean milk yield, where the milk production of the M group was 16% highe r. Although the Z group was probably somewhat selected, they were the best types for environments where milk yields were avout 1000 ky per l actation or less, but M cross-breds were more productive at the higher level. The H cows showed no advantage on any farm for any of the trai ts and their milk yield was adversely affected by calving in the rainy season.