Ac. Clutter et al., UTERINE CAPACITY AND OVULATION RATE IN MICE SELECTED 21 GENERATIONS ON ALTERNATIVE CRITERIA TO INCREASE LITTER SIZE, Journal of animal science, 72(3), 1994, pp. 577-583
After 21 generations of selection for alternative criteria to change l
itter size in mice, responses in uterine capacity and ovulation rate w
ere evaluated. Females from Generations 22 and 23 were sampled from 12
lines, representing three replicates of four selection criteria: LS =
direct selection on litter size; M = selection on an index of ovulati
on rate and the proportion of ova shed that resulted in fully formed o
ffspring; UT = selection on uterine capacity measured as litter size,f
rom females unilaterally ovariectomized at 4 wk of age; and LC = unsel
ected control. All females in the present evaluation (a total of 1,932
) were unilaterally ovariectomized (either left or right ovary excised
) at 4 wk, mated at 9 wk, and killed at d 17 of gestation. The number
of corpora lutea and number of fetuses were counted to measure ovulati
on rate and uterine capacity, respectively. Selection in IX, LS, and U
T increased (P < .01) ovulation rate from unilaterally ovariectomized
females but by a greater amount (P < .01) in M and LS than in UT. Sele
ction also increased (P < .01) uterine capacity of IX, LS, and UT (ave
rage response relative to LC = 1.76 pups); response was at least as gr
eat in LS and M as in UT. Direct selection in UT was successful at imp
roving uterine capacity but was no more effective than M or LS selecti
on. Cases in which ovulation rate limited expression of uterine capaci
ty in UT may have shifted some selection emphasis to ovulation rate an
d reduced response in uterine capacity.