Ja. Archer et al., Effect of divergent selection for yearling growth rate on female reproductive performance in Angus cattle, LIVEST PROD, 57(1), 1998, pp. 33-40
Beef cattle are often selected for increased growth performance. There has
been some concern that selection for increased growth rate may reduce repro
ductive performance of females and increase the incidence of dystocia. A se
lection experiment was conducted where Angus cattle were selected for eithe
r high or low growth rate from birth to yearling age and a randomly bred co
ntrol line was also maintained. Reproductive performance of cows following
ten years of selection were evaluated. Cows from the high growth rate line
had similar reproductive rates per cow joined at time of pregnancy testing
(mean of 0.86), calving (mean of 0.86) and weaning (mean of 0.83) compared
to the control line (means of 0.85, 0.84 and 0.78 respectively), while cows
from the low growth rate line had lower reproductive rates (means of 0.77,
0.77 and 0.69 respectively) compared to the controls. Heifers from the hig
h growth rate line were younger at puberty (mean of 324 days) than control
line heifers (mean of 336 days), whereas heifers from the low growth rate l
ine were older at puberty (mean of 355 days) than control line heifers. Amo
ng the cows that calved, there was no difference between the selection line
s in the length of time from exposure to the bull to calving (means were 30
2, 304 and 302 days for high growth rate, control and low growth rate lines
respectively), although gestation length was longer in the high growth rat
e line (mean of 281.5 days) compared to the control line (mean of 279.3 day
s), and shorter in the low growth rate Line (mean of 278.1 days). There was
no significant difference in the incidence of heifer dystocia between the
lines (means were 0.03, 0.05 and 0.04 for high growth rate, control and low
growth rate lines respectively). The results show that selection for high
growth rate did not compromise reproductive performance. (C) 1998 Elsevier
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