Steroid production and LH receptor concentrations of ovarian follicles and corpora lutea and associated rates of ova wastage in ewes given high and low levels of food intake before and after mating

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Abstract
Two groups of eives were fed to provide 1·5 × (high, H; no. = 13) or 0·5 × (low, L; no. = 12) energy requirements for maintenance of live weight from 12 days before a synchronized mating in November until slaughter at 14 days after mating and the effects on embryo survival and associated patterns of gonadotropin secretion, and ovarian follicle and corpus luteum function were investigated. Proportionately, there were more pregnant ewes in the H group than the L group (0·62v.0·08; %2 = 7·67;P< 0·01) at day 14 of pregnancy but there were no differences in mean LH concentrations, LH pulse frequencies or amplitudes, either before mating and ovulation (follicular phase) or at day 10 after mating (luteal phase). The mean size (mm) of the three largest follicles (H: 5·69; L: 5·65; s.e.d. = 0·21), the proportion of these follicles that were oestrogenic (secreting > 500 pg oestradiol per h; H: 0·29; L: 0·28; y) = 0·01;P> 0·05) and secretion (pg/h) in vitro of oestradiol (H, 294; L, 386; s.e.d. = 146) (pg/h) and testosterone (H: 636; L: 508; s.e.d. = 293) by these follicles were similar for both treatments. There were no treatment differences in LH receptor concentrations (pg hormone bound per mg protein) in granulosa (H: 69·02; L: 67·76; s.e.d. = 0·20) and thecal (H: 46-88; L: 50·82; s.e.d. = 0·19) tissues. However, there was a higher concentration of receptors in the thecal tissue of oestrogenic follicles ofL than H ewes (167v.62; s.e.d. = 18;P< 0·05). Mean weights (g) of corpora lutea (H: 0·72; L: 0·59; s.e.d. = 0·003; P = 0·09), progesterone secretion (ng/mg per h) in vitro by luteal tissue (H: 1·75; L: 1·78; s.e.d. = 0·30) and LH receptor concentrations in corpora lutea (H: 58·16; L: 54·27; s.e.d. = 25·14) were similar for both treatments. It is concluded that the reduction in embryo survival associated with a reduced level of food intake was not attributable to a reduction in LH secretion, inadequacies in follicle growth and development or in the capacity of the corpora lutea to synthesize and release progesterone.