The effects of body weight and level of nutrition before, during, and after joining on ewe fertility

Abstract

Four experiments were designed to assess the independent effects of body weight and nutritional level on the reproductive performance of Border Leicester x Merino ewes. Ewes in experiments 1, 2, and 3 were joined in summer (December-January) and in experiment 4 in autumn (March-April). The reproductive performance of two groups of ewes in experiment 1, joined at different body weights, was assessed from mating and lambing data. A factorial (3 x 2 x 2) design was used for experiments 2, 3, and 4. The experimental treatments consisted of different levels of nutrition applied before and after mating. The reproductive performance of ewes in experiment 2 was assessed from mating and lambing data. Ewes in experiments 3 and 4 were slaughtered 19-28 days after mating, and their genitalia were observed for presence of corpora lutea and embryos. Body weight at mating and level of nutrition during three weeks before mating independently affected the multiple birth or ovulation rate. High body weight at mating was consistent with a high multiple birth or ovulation rate, and a higher proportion of the ewes receiving a high level of nutrition during the three weeks before mating (i.e. flushed ewes) had multiple births or multiple ovulations. The results also demonstrated that above 90-100 lb, the proportion of ewes mating and becoming pregnant was relatively independent of body weight at joining. The level of nutrition and body weight had only minor effects on early reproductive failure, but there was a higher proportion of egg wastage from multiple ovulation ewes than from single ovulation ewes.

The effects of body weight and its components on lambing performance in some commercial flocks in Britain

“…With such a relationship as that of Figure 3, there is clearly a body condition below which barrenness will increase markedly (as found, for example, by Coop (1966), Killeen (1967), Bramley et al (1976) ), and a higher body condition above which the number of multiple ovulations will increase (as found, for example, by Coop (1966), Killeen (1967), Gunn et al (1969)). Furthermore, it is clear that, if an experiment is performed at two different body conditions which are definitely on either side of an average threshold level, a body condition effect on ovulation will be seen, but not otherwise.…”

“…This effect appears to be largely a reflexion of differences in ovulation rate (Killeen, 1967;Guerra, Thwaites and Edey, 1971), modified by effects of embryonic mortality (Edey, 1969).…”

Reproductive performance of ewes grazing lucerne during different periods around mating

“…Furthermore, the fecundity of ewes in the senescent pasture treatment group (1.49 foetuses per pregnant ewe) is greater than the average reported for Merino ewes (Kleemann et al, 2006), making it unlikely that ovulation rate was suppressed by this treatment. High ovulation rates can result from ewes in fat condition when fed submaintenance diets (Allen and Lamming, 1961), ovulation rate was not reduced in ewes fed sub-maintenance diets in the study by Cumming (1977) and the ovulatory response to increased nutrition appears to be independent of body weight at mating (Killeen, 1967).…”

Embryo survival in mature Romney ewes relative to live weight and face cover

“…The lack of an effect of live weight is clear from the transfers in 1964 where the two groups (HR, LR) of ewes from the same flock and selected for a live-weight difference showed similar fertility (HR ewes: 21 pregnant, 20 non-pregnant, 46% ova survived; LR ewes: 19 pregnant, 18 non-pregnant, 47% ova survived). Furthermore, as live weight has been shown to be associated with ovulation rate (Wallace 1961;Killeen 1967;Allison 1968;Lino and Braden 1968; and in the present mated ewes), it is notable that in Experiment 1 both the conception rates and ovum survival rates were independent of the numbers of corpora lutea recorded in the recipient ewes.…”