EFFECTS ON REPRODUCTION OF ESTROUS-CYCLE VARIATIONS, RECTAL TEMPERATURES AND LIVEWEIGHTS IN MATED BRAHMAN CROSS HEIFERS

Estrous cycle variations and the association of rectal temperature wit h reproductive measurements and liveweight were examined in 25-month-o ld 1/2 and 3/4 Brahman heifers (n = 88). The mean cycle length was lon ger in the 1/2Brahman (24.3 days) than in the 3/4 Brahman heifers (21. 3 days) due to the length of estrus-metestrus, but the overall differe nce was not statistically significant. Cycle length was not influenced by cycle number or liveweight. Cycles were classified into 6 types: n ormal, short, long, anovulatory and those involving embryonic mortalit y and prolonged diestrus. Only 33.6% of 1/2Brahman cycles and 36.1% of 3/4Brahman cycles were of normal duration (18 to 24 days), and 13.3% of 1/2Brahman and 11.6% of 3/4Brahman cycles were classified as embryo nic mortality cycles. On an individual animal basis, 25.0% and 31.8% o f 1/2Brahman and 3/4Brahman heifers, respectively, had cycles in which embryonic mortality was suspected. Heifers that became pregnant were significantly (P < 0.01) heavier throughout mating and had significant ly (P < 0.05) lower mean rectal temperatures. Heifers in which embryon ic mortality had occurred were lighter and had significantly (P < 0.01 ) higher rectal temperatures than heifers in which embryonic mortality had not occurred. Correlations between rectal temperature and ambient temperature were nonsignificant after eliminating the effect of genot ype, but rectal temperature was significantly (P < 0.01) negatively co rrelated with liveweight.