Selection was conducted on an index of components of litter size (I - 1.21 x ovulation rate + 9.05 x ova success), on uterine capacity (measured as number of pups born to unilaterally ovariectomized dams), and on litter size concurrent with an unselected control. Selection criteria (IX - index, UT - uterine capacity, LS - litter size and LC - control) were applied in each of 3 replicates. After 13 generations, mean ovulation rate, ova success and litter size (measured as number of fetuses at 17 d gestation in intact females) were IX: 14.25, .84, 11.95; LS: 14.15, .82, 11.64; UT: 12.61, .86, 10.77; and LC: 12.27, .82, 9.98. The regression of number born (litter size in IX, LS and LC; uterine capacity with only a functional left uterine horn in UT) on cumulative selection differential was .12 + .01, .09 + .02 and .08 + .02 for IX, LS and UT, respectively. The regression of breeding value for litter size on each selection criterion, estimated as response in the generation-13 evaluation divided by cumulative selection differential, was .11 + .02, .08 + .01 and .05 + .03 for IX, LS and UT, respectively. Regression of response in number born on generation number was .17 + .01, .15 + .04 and .10 + .02 for IX, LS and UT, respectively
Proceedings of the World Congress on Genetics Applied to Livestock Production, Volume XIII. Plenary lectures, molecular genetics and mapping, selection, prediction and estimation., , 240–245, 1990
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