Rg. Holroyd et al., EFFECTS ON REPRODUCTION OF ESTROUS-CYCLE VARIATIONS, RECTAL TEMPERATURES AND LIVEWEIGHTS IN MATED BRAHMAN CROSS HEIFERS, Theriogenology, 40(3), 1993, pp. 453-464
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.