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The effect on the reproductive performance of Greyface (Border Leicester x Scottish Blackface) ewes of a low level food intake and associated loss of live weight from either 14 days before mating, or from the time of mating, until 11 to 26 days after mating, was investigated. Ewes (252) were allocated to one of three treatments with ewes within each treatment divided into two flocks (flock A: 16 ewes per treatment; flock B: 68 ewes per treatment). Ewes of treatment LL were given a ration providing proportionately 0-5 estimated metabolizable energy (ME) requirements for maintenance from 2 weeks before mating. Those of treatment HL were given a daily ration providing 1-5 estimated ME requirements for maintenance until mating and the restricted ration thereafter. Ewes of treatment HH were given the higher ration throughout the experimental period. Flock A ewes were slaughtered at 11 days post mating and flock B ewes at between 18 and 26 days post mating. Treatment differences in the ovulation rates of flock A ewes were not statistically significant but in flock B, ewes of treatment LL had a lower mean ovulation rate (1-81) than those of treatments HL (2-23) and HH (2-09) (P < 0-001). The lower ovulation rate of LL ewes relative to HL ewes in flock B was reflected in a lower mean potential lambing rate per ewe pregnant than in the HL treatment (1-58 v. 1-79; P < 0-01) and per ewe put to the ram (1-37 v. 1-65; P < 0-01). HL ewes had a slightly lower mean potential lambing rate per ewe pregnant (1-79 v. 1-97; P < 01) and per ewe put to the ram (1-65 v. 1-82; P < 0-05) than HH ewes. Ova wastage rates of LL + HL and HH ewes were 0-26 and 014 (P < 001) respectively at 24 days post mating. Values for LL and HL ewes (0-27 and 0-25 respectively) were not significantly different.Estimated mean conceptus lengths were 370, 500 and 1400 u,m for LL, HL and HH ewes respectively (P < 0-05).It is concluded that low food intake before mating reduced the mean ovulation rate and low intakes after mating compromised embryo growth rate and induced a higher rate of ova wastage; this increase in the incidence of ova wastage was not significantly exacerbated by the low levels of intake prior to mating.

The effects of body fat content (body condition) of ewes on hypothalamic activity and gonadotrophin-releasing hormone (GnRH) secretion and on pituitary sensitivity to GnRH were investigated using Scottish Blackface ewes. Two groups of 12 ewes were fed so that they achieved either a high body condition score (2.98, S.E.M. = 0.046; approximately 27% of empty body weight as fat) or a low body condition score (1.94, S.E.M. = 0.031; approximately 19% of empty body weight as fat) by 4 weeks before the period of study. Thereafter, they were differentially fed so that the difference in mean condition score was maintained. Oestrus was synchronized, and on day 11 of the subsequent cycle half of the ewes of each group were ovariectomized. On day 12, the remaining ewes were injected (i.m.) with 100 micrograms prostaglandin F2 alpha analogue and ovariectomized 30 h later. Numbers of large ovarian follicles and corpora lutea present at ovariectomy were recorded. Blood samples were collected at 15-min intervals for 12 h on day 10 of the cycle (luteal phase) and at 10-min intervals from 24 to 30 h after prostaglandin injection (follicular phase). At days 2 and 7 after ovariectomy, samples were collected at 15-min intervals for 8 h and ewes were then injected with 10 micrograms GnRH and samples were collected for a further 3 h.(ABSTRACT TRUNCATED AT 250 WORDS)

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