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 with reproductive measurements and liveweight were examined in 25-month-old 1 2 and 3 4 Brahman heifers (n = 88). The mean cycle length was longer in the 1 2 Brahmari (24.3 days) than in the 3 4 Brahman heifers (21.3 days) due to the length of estrus-metestrus, but the overall difference was not statistically significant. Cycle length was not influenced by cycle number or liveweight. Cycles were classified into 6 types: normal, short, long, anovulatory and those involving embryonic nortality and prolonged diestrus. Only 33.6% of 1 2 Brahman cycles and 36.1% of 3 4 Brahman cycles were of normal duration (18 to 24 days), and 13.3% of 1 2 Brahman and 11.6% of 3 4 Brahman cycles were classified as embryonic mortality cycles. On an individual animal basis, 25.0% and 31.8% of 3 4 Brahman heifers, respectively, had cycles in which embryonic mortality was suspected. Heifers that became pregnant were significantly (P < 0.01) heavier throughout mating and had significantly (P < 0.05) lower mean rectal temperatures. Heifers in which embryonic 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 genotype, but rectal temperature was significantly (P < 0.01) negatively correlated with liveweight.