Exposure of sheep to a long-day photoperiod during late pregnancy results in greatly increased plasma prolactin concentrations in both the ewe and her fetuses compared to values in animals experiencing short days. To investigate whether the endocrine changes resulting from provision of additional lighting might also influence the pre- and postnatal growth of lambs or udder development in winter-housed ewes, two experiments were carried out. In the first, a group of housed Mule ewes, lambing in early January 1989, were given additional lighting to provide a long-day photoperiod [16 h light: 8 h dark] from 6 weeks before delivery until 6 weeks after lambing. In the second experiment, 50 housed Mule ewes were given additional light for 7 weeks before delivery at the end of March 1990. In both experiments, comparable groups of housed Mule ewes experiencing only the natural shortday winter photoperiod served as controls.

In both experiments, provision of the long-day photoperiod resulted, within 3 weeks, in highly significant increases in plasma prolactin concentrations in the ewes. Plasma prolactin concentrations in the lambs from ewes experiencing the long-day photoperiod were also increased at birth (8-fold) and throughout the suckling period (3–5-fold) compared to values in short-day control lambs.

Despite these large differences in plasma prolactin concentrations, there was no significant effect of photoperiod on the birth weight of the lambs in either experiment. There was also no effect of photoperiod on the postnatal growth of lambs in Experiment 1.

Provision of a long-day photoperiod resulted in some increase in the rate of growth of linear measurements of udder size in ewes during both experiments, but only resulted in a significant increase in estimated udder size at delivery in ewes with twins or larger numbers of fetuses in the first experiment. In both experiments the effect of a long-day photoperiod on udder size was similar to or less than the effect of one additional fetus.

The results do not suggest that prenatal photoperiodic experience results in any major alteration in somatic development in lambs at birth or during early postnatal life. They do, however, give some support to other observations that ambient photoperiod may influence pre-partum udder development in the ewe.

Aspergillus oryzae fermentation extract (AO; 2 g/day) was added to the diet of sheep fed grass hay supplemented with 30 or 70% barley. AO decreased the proportion of propionate in rumen volatile fatty acids with both levels of supplementation (146 and 163 mmol/mol with AO v. 157 and 186 mmol/mol with no addition for the low and high barley diets respectively; P < 0·05), and also caused a small reduction in L-lactate concentration in the high barley diet (1·15 mM v. 1·43 mM in the absence of AO). Rumen pH was not changed significantly. Total viable bacteria in the rumen were stimulated with AO (2·12 and 2·46 v. 0·97 and 1·80 × 109/ml respectively). Numbers of cellulolytic bacteria and ciliate protozoa were unchanged. Hay suspended in nylon bags in the rumen tended to be degraded more rapidly with AO, but the effect was not statistically significant. Neither barley nor AO significantly altered the plasma concentrations of glucose, urea, insulin, gastrin or cholecystokinin. It was concluded that the effects of AO were generally similar for both levels of barley supplementation and that changing the composition of the diet had no detectable effect on the measured indicators of nutritional status in blood.

This group, which is concerned with the applications of mathematics to agricultural science, is sponsored by the Agricultural and Food Research Council. It was formed in 1970, and has since met at approximately yearly intervals in London for one-day meetings. The twenty-second meeting of the group, chaired by Professor J. M. Forbes of the Department of Animal Physiology and Nutrition at the University of Leeds, was held in the Wellcome Meeting Room at the Royal Society, 6 Carlton House Terrace, London on Friday, 10 April 1992, when the following papers were read.

Areas of sulla (Hedysarum coronarium) and pasture (Lolium perenne/Trifolium repens/Holcus lanatus) were grazed by young sheep (29·5–34·8 kg initial liveweight) in four experiments, and effects upon body growth, wool growth and rumen metabolism were measured.

Sulla contained 40–50 g condensed tannins (CT)/kg DM, whilst the pasture contained small amounts of CT (2–6 g/kg DM). After chewing during eating, a lower proportion of total CT was readily extractable and greater proportions were protein-bound and fibre-bound. Nutritional effects attributable to CT were assessed by oral administration of polyethylene glycol (PEG), which binds and inactivates CT, to half the animals grazing each forage. Rates of body growth were consistently higher for lambs grazing sulla than those grazing pasture, with the CT concentration in sulla being neither stimulatory or inhibitory to body growth or voluntary feed intake (VFI). The action of CT reduced carcass fatness in sheep fed both diets, in the one experiment where this was measured. CT present in both sulla and pasture decreased rumen ammonia concentration and decreased molar proportions of iso-butyrate and iso and n-valerate. During spring and early summer, when wool growth rates were highest, CT present in both pasture and sulla increased wool growth rate; when wool growth rates were low during winter, CT had no effect upon the wool growth of sheep grazing either forage. Numbers of protozoa and molar proportions of n-butyrate in rumen fluid were increased by CT in sheep grazing sulla but not pasture.

It was concluded that the higher rates of body growth and VFI in lambs grazing sulla was most likely to be due to its very high ratio of readily fermentable: structural carbohydrate.

Several previous studies have shown that the proportion of clover in sheep diets was greater than the proportion of clover in the mixed species swards being grazed. Various hypotheses have been put forward to explain this observation. One widely held hypothesis is that sheep prefer (actively select) clover to grass. This hypothesis was tested by offering 12 sheep, six that had been recently grazing perennial ryegrass and six that had recently been grazing white clover, the choice between foraging on grass or clover provided as turves. It was found that, rather than prefer clover, the sheep preferred the opposite species to the one they had previously grazed. From these observations, alternative hypotheses are proposed to explain the disparity in composition of the diet relative to the swards observed in previous studies, and the evidence for a constant preference for clover and its basis in grazing behaviour is reconsidered.