Ovarian weight has been shown to increase markedly in the newborn ewe lamb, and factors which might contribute to this growth were examined. Follicle development was studied in the ovaries of 28 lambs aged 0, 2, 4, 6, 8 and 10 weeks. Plasma samples, pituitaries and one ovary were assayed for gonadotrophin or steroid hormone content.No significant differences between age groups were found in pituitary LH concentration or mean plasma LH. Pituitary FSH concentration increased with age, except for a small decrease at 8 weeks, but no significant changes were seen in plasma FSH. Ovarian progesterone and oestradiol concentrations did not appear to be associated with follicular development.Growing follicles were most numerous at 2 weeks whilst total vesicular follicles reached a peak at 4 weeks. Most vesicular follicles were less than 1 ·4 mm in diameter. Advanced atresia in vesicular follicles became apparent by 4 weeks although early signs were present in younger lambs. Fluctuations in gonadotrophin levels do not appear to be responsible for variations in number and size of vesicular and growing follicles in the lamb ovary. Other possible explanations are discussed.

The fine structure of follicles was studied in ovaries from lambs up to 32 days old. Some animals received pregnant mare serum gonadotrophin prior to sampling. Follicles examined were in the primordial to early antral stages. The oocyte is described and changes associated with its development and the formation of the zona pellucida are recorded. Characteristics in which the lamb oocyte differed from those of other mammals included a greater prominence of smooth endoplasmic reticulum, the presence of microtubules, fine filaments in the peripheral parts and a large number of almost empty vacuoles. The latter were more numerous in oocytes which appeared to be degenerating, including some of those in primordial follicles. Granulosa cells had characteristics usually associated with protein secretion while some theca cells had large amounts of endoplasmic reticulum bearing few ribosomes. In early atresia changes were evident successively in the oocyte, granulosa and theca.There was a weak positive reaction for 3p-hydroxy-AS-steroid dehydrogenase in the theca of some vesicular follicles from both control lambs and lambs treated with pregnant mare serum gonadotrophin. Follicles showing signs of atresia were negative for this enzyme.

Procedures used to determine chemical composition and digestible organic matter in dry matter (DOMD) are slow and expensive. The possibility of using near‐infrared reflectance spectroscopy (NIRS) as an alternative procedure was investigated with annual legumes. Material from cultivars of Medicago murex, Trifolium balansae, T. resupinatum and T. subterraneum was harvested soon after plants had matured. Samples were sorted into stem, leaf and burr fractions and analysed chemically and by NIRS. Data were then sorted into two similar sets, one of which was for calibration and the other for validation. Data for each chemical fraction, in samples used for calibration, were regressed sequentially against the corresponding reflectance spectral data, the log of there reciprocal of which was transformed to first or second derivatives. Equations of best fit were then used to predict the composition of samples in the validation set. Standard errors of calibration and validation respectively, expressed as percentages of the mean, were 0·5 and 0·6 for dry matter (DM), 2·0 and 2·6 for organic matter (OM), 4·8 and 4·3 for DOMD, 6·0 and 7·2 for crude protein, 4·1 and 4·4 for acid‐detergent fibre (ADF), 2·5 and 3·1 for neutral‐detergent fibre (NDF) and 8·9 and 10·9 for lignin.

The numbers of primordial follicles in ovaries of ewe lambs, from two groups of Peppin Merinos that had been selected for (T group) and against (0 group) mUltiple births, were estimated at birth, 7 days and 5 months of age. Peripheral plasma and anterior pituitary levels of LH and FSH were determined by radioimmunoassay in the lambs at 5 months of age. These lambs were either entire or unilaterally ovariectomized (hemispayed) at 7 days of age.There was no difference in primordial follicle numbers between lambs at birth and 7 days of age, but when paired ovaries of hemispayed lambs at 7 days and 5 months of age were compared there was a significant increase in follicle numbers with age (34903 v. 48047). O-group lambs had more primordial follicles than T-group lambs at birth and 7 days of age (65501 v. 37797) and there was a similar but not significant difference at 5 months of age (53934 v. 44057).Peripheral plasma LH was higher in T-group than in O-group lambs and plasma LH levels were correlated to pituitary LH content (r = o· 75). Vesicular follicles larger than 2 mm in diameter were present only in ovaries of lambs with plasma LH levels above 3· 0 ng/m!. Pituitary FSH levels were considerably higher in hemispayed lambs than in entire lambs and there was a trend to higher levels in T-group lambs when compared with O-group lambs.It is concluded that genetic selection for the incidence of multiple births has resulted in changes in the number of ovarian primordial follicles of the post-natal lamb and it is suggested that these changes may be related to the levels of pituitary gonadotrophins.

Progesterone (P) is anti-uterotrophic in the oestradiol (E2)-stimulated uterus of the mouse but not the sheep. To further understand this species difference, the time course of some early effects of a single injection of P on the E2-stimulated uterus has been examined. In the mouse, P caused a prompt (2-4 h) decline in uterine wet weight and in vitro rate of RNA synthesis, and a more gradual decrease (4-12 h) in RNA: DNA and protein: DNA ratios and in vitro rate of protein synthesis in whole uterus. In the sheep, P had no effect at any time on either whole uterus or caruncular endometrium. The results support the concepts that (l) anti-uterotrophic effects of Pin E2-stimulated mice are mediated by a direct P effect on nuclear E2 receptor level, and (2) in the sheep P is not anti-uterotrophic because it does not regulate nuclear E2 receptor level.