The Effect of Level of Feeding on the Reproductive Capacity of the Ewe

Abstract

A study was made, in 1953 and 1954, of the effect of feed level on the reproductive capacity of yearling ewes. Ewes (short-yearlings) were divided at random into two groups; one group was fed on roughage-plus-grain, and the other was fed on roughage-only beginning in January of both years. The feeding regimen was continued until the time of slaughter in the fall. Half of the ewes on each feed level was slaughtered 3 days post-coitum, and the other half at 40 days post-coitum (except some ewes that showed a second heat after breeding and were rebred and killed 3 days later). The study includes observations on ovulation rate, fertilization rate, normality of the ova as well as measurements and weights of structures and organs of the reproductive tract, and weights of embryos, embryonic membranes and fluids. The results were as follows: Ewes on the high level of feeding had significantly higher ovulation rate, larger follicles, and higher number of follicles 2 mm. or more in diameter. Fertilization rate was higher, though not significantly so, for the ewes on the higher level of feeding. The embryonic survival rate was lower in the ewes on the higher level of feeding. The difference in embryonic survival rate between the two groups of ewes was highly significant in 1954. Also there was a significant interaction between year and level of feeding on embryo survival. Ewes on the higher level of feeding had significantly larger uteri (slaughtered 3 days post-coitum). The weight of the 40-day pregnant horn of ewes (cotyledons trimmed off) was significantly affected by feed level. Also the non-pregnant horns of ewes fed on grain-plus-roughage were significantly larger than for ewes fed on roughage-only. Level of feeding did not have a significant effect on weight of cotyledons in the pregnant uterine horn, but a significant interaction between feed level and size of litter on the weight of cotyledons was shown in 1953. Feed level had no significant effect on crown-rump length of 40-day embryos, weight of embryos, amnion weight, amnionic fluid weight, chorionic fluid weight, and size of amnionic vesicle. There was a significant effect for feed level on weight of chorion. Comparing the pregnant horns only, it was shown that ewes which had twin embryos (each in separate horn) had significantly larger and heavier horns (cotyledons removed) than pregnant horns of ewes having single embryos. Crown-rump length of embryos, weight of embryos, weight of amnions, weight of chorions, weight of amnionic fluid, and size of amnionic vesicle were greater for singles than for twins under both levels of feeding, but differences only in chorion weight and in size of amnionic vesicle were statistically significant. Migration from one uterine horn to the other occurred for at least 12 percent of the embryos. One case of suspected identical twins was observed.