Ewes were fed either 150% (High, H) or 50% (Low, L) of their energy requirements for maintenance of liveweight during early gestation. Effects of maternal nutrition on fetal ovarian size, histological structure and steroidogenic capacity were studied at Day 47 and on ovarian size and structure at Day 62 of gestation. At Day 47 of gestation, there were significantly higher concentrations of oogonia in the ovaries of L fetuses than H fetuses (105.9 v. 76.9 germ cells mm(-2); s.e. 4.94; P < 0.001). The capacity of the ovaries to secrete oestradiol (pg/ovary/24 h) at Day 47 was not affected by treatment when they were incubated either with (H, 773; L, 740; s.e. 179; not significant, n.s.) or without (H, 260; L, 290; s.e. 92.7; n.s.) ovine luteinizing hormone (oLH). At Day 62 of gestation, the process of germ cell degeneration was less advanced in L than H fetal ovaries, as indicated by higher oocyte concentrations in the former (68.4 v. 48.6 germ cells mm(-2); s.e. 3.85; P < 0 01). There was a greater percentage of meiotic cells in L ovaries (76.5 v. 18.6; s.e. 5.82; P < 0.001). It is concluded that undernutrition of the ewe from the time of mating significantly retards ovarian development in fetal ovaries.

An experiment was conducted to examine factors affecting the length of the post-partum anoestrous period and associated effects on LH, FSH and prolactin. Forty-six cows (24 Hereford × Friesian and 22 Blue-Grey) ranging in body condition score at calving from 1·50 to 2·75 were used. They were individually fed chopped barley straw and concentrate at either 50 (low) or 91 (high) MJ metabolizable energy per day from calving. At 34 days post partum half the cows were separated from their calves for 48 h. The duration of the post-partum anoestrous period was estimated from progesterone concentrations in thrice weekly blood samples. Blood samples were collected every 20 min for 10 h periods immediately prior to calf separation, during the last 10 h of calf separation and 1 week later. All samples were analysed for LH, and every third sample was analysed for FSH and prolactin.There were no significant effects of genotype, feeding level or calf separation on the length of the post-partum anoestrous period. There was a negative association between body condition score at calving and the length of the anoestrous period, with each unit increase in body condition score reducing the anoestrous period by 43 (s.e. 20) days. There was some evidence that feeding level affected the number of thin cows (body condition score ≤2·25 at calving) which were still acyclic at the end of the experiment, but not the number of fat cows (body condition score ≥2·5 at calving).FSH levels were not affected by any of the factors examined. Prolactin concentrations were higher in fatter cows, in cows on the higher level of feeding and in Blue-Grey cows. Prolactin concentrations decreased during the period of calf separation. Genotype and feeding level had no effect on LH concentration or LH pulse frequency. LH pulse frequency was increased (P < 0·05) during the period of calf separation, but there was no effect 1 week later. There was a significant positive relationship between LH puise frequency and body condition score at calving in two of the three sampling periods.It is suggested that the effect of body condition on the duration of the post-partum anoestrous period i s mediated through effects on LH pulse frequency.

No abstract

Sheep exhibit photoperiod-driven seasonal changes in appetite and body weight so that nutritional status increases in long days (LD) and decreases in short days (SD); additionally, they are reproductively active in SD and inactive in LD. We addressed the hypothesis that appetite-regulatory genes in the hypothalamus respond differently to changes in nutritional feedback induced by photoperiod as opposed to food restriction, and that responses would be influenced by gonadal steroid status. Castrated oestradiol-implanted male sheep were kept in SD (8 h light/day) or LD (16 h light/day) for 11 weeks, with ad libitum or restricted food (experiment 1; n=8/ group). Rams were kept in SD or LD for 12 weeks with ad libitum or restricted food (experiment 2; n=6/group). Gene expression (by in situ hybridisation) in the hypothalamic arcuate nucleus for leptin receptor (OB-Rb), neuropeptide Y (NPY), pro-opiomelanocortin (POMC) and agouti-related peptide (AGRP) was unaffected by photoperiod treatment, but food restriction increased NPY and AGRP mRNAs, in experiment 1. In experiment 2, mRNAs for POMC and cocaine-and amphetamineregulated transcript (CART) were up-regulated and AGRP down-regulated in SD, while food restriction increased OB-Rb mRNA, increased NPY and AGRP mRNAs only in LD and decreased POMC mRNA only in SD. Thus, gene expression responded differently to photoperiod and food restriction, and the melanocortin pathway was up-regulated in SD in reproductively activated rams but not in oestradiol-implanted castrates. These data support the hypothesis that hypothalamic appetiteregulatory pathways respond differently to changes in nutritional feedback induced by photoperiod as opposed to food restriction, with gonadal steroid feedback additionally influencing the responses.

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.