Reproduction in the Yearling Ewe as Affected by Breed and Sequence of Feeding Levels. II. Effects on Fetal Development

Publisher Website
Google Scholar
Abstract
Fetal development was studied at 40 days of gestation in 128 yearling ewes of mixed breeding in 1955, and at 25 and 140 days of gestation in 330 grade Hampshire and Columbia ewes in 1956 and 1957 combined. Straight-bred and reciprocal cross-bred fetuses were produced by mating purebred Hampshire and Columbia rams to the grade Hampshire and Columbia ewes. The ewes in each year were subjected to various sequences of grass-alfalfa hay only or the same hay plus grain (full and limited levels of feeding, respectively) from the beginning of the experiment in mid-winter until they were slaughtered the next fall or winter. Breeding was begun in October. Full fed ewes showed greater somatic maturity as indicated by carcass weight, finish grade, carcass length and shin bone circumference than limited fed ewes. These levels of feed had no consistent significant effect on fetal development at any of the stages studied. Fetal development at 140 days was measured in terms of fetus weight, fetus length, head length and width, shin bone length and circumference, hip width, area of eye muscle, kidney weight and liver weight. There was no evidence of a differential effect due to feed on these different tissues or organs. Variations in the individual carcass measurements of the ewes were associated with variations in fetal development at 140 days. The ewes with longer carcasses (indicating greater development) produced heavier fetuses while those with higher finish grades (indicating greater fatness) produced smaller fetuses. This relationship did not exist at either 25 or 40 days of gestation. Significant increases in maternal cotyledon weight due to changes from full to limited feeding were found at 40 days. Similar changes in fetal cotyledon weight at 140 days were noted due to limited feeding in the late part of gestation. The increased amounts of these tissues may have acted to obtain a greater nutrient supply from the mother, thus protecting the fetus against a nutrient shortage imposed by limited feeding of the mother. The Columbia dams provided a better maternal environment than the Hampshire. The additive genetic contribution of the Hampshire parents, however, produced larger fetuses than that of the Columbia. The maternal environment had a cancelling effect on the additive genetic contribution with the net effect for breed of dam for various characteristics tending toward zero. Fetal membrane weight and fetal fluid weight at 25 days of gestation were significantly associated with fetus weight. The weight of the developing maternal cotyledons was significantly associated with fetus weight, independent of fetal membrane and fetal fluid weight at 40 days. At 140 days of gestation, fetal cotyledon weight had a significant direct effect on fetus weight which was greater than its indirect effect through fetal membrane weight. This was true for variation between single fetuses as well as between twin pairs of fetuses. Copyright © . .