-This paper discusses the phenomenon of nutritional flushing in ewes whereby increased nutrition stimulates folliculogenesis and ovulation rate. In addition the paper reviews recent findings on the effects of increased levels of nutrition on the blood concentrations of reproductive and metabolic hormones in the ewe and some of the intraovarian changes that take place in response to nutritional stimulation. Finally, in the paper, we propose a model of the physiological mechanism for the nutritional stimulation of folliculogenesis and we review how closely the model fits recent published and unpublished evidence examining the mechanism of flushing. Nutritional stimulation alters the blood concentrations of some metabolic hormones. By using short-term models of nutritional flushing, we have shown that as the blood concentrations of insulin and leptin increase that of growth hormone decreases while that of IGF-I appears unaffected by the nutritional flushing. Nutritional flushing also alters the blood concentrations of some reproductive hormones. Again, using the same model, we have shown that there is a transient increase in FSH and a decrease in oestradiol concentrations in the blood. The changes in oestradiol are particularly evident in the follicular phase of the oestrous cycle. In the ovary, the effect of nutrition is to stimulate folliculogenesis. These changes are associated with intra-follicular alterations in the insulin-glucose, IGF and leptin metabolic systems. The stimulation of these intra-follicular systems leads to a suppression in follicular oestradiol production. The consequence of these direct actions on the follicle is a reduced negative feedback to the hypothalamic-pituitary system and increased FSH secretion that leads to a stimulation of folliculogenesis.insulin / leptin / IGF-I / glucose / FSH / oestradiol

A model for folliculogenesis is proposed that is based as far as possible on a knowledge of physiological, rather than anatomical, changes taking place during follicle development. The model is therefore functional, rather than descriptive, and consists of five classes of follicles that have been defined by their dependency and sensitivity to gonadotrophins. These classes are: primordial, committed, gonadotrophin-responsive, gonadotrophin-dependent and ovulatory. The model is an attempt to encourage discussion and to promote the integration of morphological models of folliculogenesis with recent advances in the molecular endocrinology of the ovarian follicle. Two hypotheses for the mechanisms that determine ovulation rate are developed in light of the model. In the first, multiple ovulation results when the viability of gonadotropin-dependent follicles is enhanced. In the second, multiple ovulation is caused by increasing the number of gonadotrophin-responsive follicles available for further development; this results from the increasing rate of folliculogenesis and the throughput of follicles. The final section of this paper examines how these two hypothetical mechanisms, which are not mutually exclusive, appear to account for most of the known genetical and environmental effects on ovulation rate of sheep. In particular, the effects of nutrition, genotype, exogenous gonadotrophins, immunity to both oestrogens and androgens, and immunity to inhibin are discussed.

An experiment in which a lupin grain supplement was fed to ewes (n = 11) over days 2-13 of the oestrous cycle was carried out. A group of 12 ewes was used as a control and not fed the supplement. Plasma concentrations of LH and GH (20 min intervals) and FSH, insulin and prolactin (hourly intervals) were determined in plasma samples collected every 20 min over 24 h on day 11 of the oestrous cycle. The changes were related to increases in ovulation rate. Ovulation rate was increased (2.5 +/- 0.2 versus 1.9 +/- 0.2 for lupin-supplemented and control groups, respectively; P = 0.073) in the group that received the lupin supplement, but this increase was not associated with significant changes in either LH or FSH concentrations on day 11 of the oestrous cycle. Lupin supplementation had significant effects on the plasma concentrations of prolactin, GH and insulin. There was a transient increase (P < 0.05) in the concentration of prolactin 4-8 h after feeding, whereas insulin concentrations were increased immediately after feeding (P < 0.02) and were still high 24 h later (P < 0.02). Growth hormone concentrations were reduced in ewes fed with lupin grain (P < 0.001). These metabolic responses initiated by feeding a high energy and protein supplement such as lupin grain may be related to changes in ovulation rate. In particular, the sustained increases in insulin concentrations suggest that an increased supply of glucose to the follicle mediates nutritionally stimulated increases in ovulation rate.

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Free-range laying hen systems are increasing within Australia. The pullets for these systems are typically reared indoors before being provided first range access around 21 to 26 weeks of age. Thus, the rearing and laying environments are disparate and hens may not adapt well to free-range housing. In this study, we reared 290 Hy-Line® Brown day-old chicks divided into two rooms each with feed, water and litter. In the enriched room, multiple structural, manipulable, visual and auditory stimuli were also provided from 4 to 21 days, the non-enriched room had no additional objects or stimuli. Pullets were transferred to the laying facility at 12 weeks of age and divided into six pens (three enriched-reared, three non-enriched-reared) with identical indoor resources and outdoor range area. All birds were first provided range access at 21 weeks of age. Video observations of natural disturbance behaviours on the range at 22 to 23 and 33 to 34 weeks of age showed no differences in frequency of disturbance occurrences between treatment groups (P=0.09) but a decrease in disturbance occurrences over time (P<0.0001). Radio-frequency identification tracking of individually tagged birds from 21 to 37 weeks of age showed enriched birds on average, spent less time on the range each day (P<0.04) but with a higher number of range visits than non-enriched birds from 21 to 24 weeks of age (P=0.01). Enriched birds accessed the range on more days (P=0.03) but over time, most birds in both treatment groups accessed the range daily. Basic external health scoring showed minimal differences between treatment groups with most birds in visibly good condition. At 38 weeks of age all birds were locked inside for 2 days and from 40 to 42 weeks of age the outdoor range was reduced to 20% of its original size to simulate stressful events. The eggs from non-enriched birds had higher corticosterone concentrations following lock-in and 2 weeks following range reduction compared with the concentrations within eggs from enriched birds (P<0.0001). Correspondingly, the enriched hens showing a greater increase in the number of visits following range area reduction compared to non-enriched hens (P=0.02). Only one rearing room per treatment was used but these preliminary data indicate 3 weeks of early enrichment had some long-term effects on hen ranging behaviour and enhanced hen's adaptability to environmental stressors.