Relationships among body composition, circulating concentrations of leptin and follistatin, and the onset of puberty and fertility in young female sheep

The onset of puberty depends on the attainment of critical body mass, so should also be affected by increases in the rate of accumulation of muscle and adipose tissue. Adipose tissue and reproduction are linked by leptin. For muscle, a link has not yet been identified, although one possibility is follistatin. We assessed the relationships among circulating concentrations of follistatin and leptin and the rates of growth and accumulation of muscle and fat during pubertal development in female sheep. We used 326 animals with known phenotypic values for live weight (LW), depths of eye muscle (EMD) and fat (FAT), and known breeding values at post-weaning age for body mass (PWT) and depths of eye muscle (PEMD) and fat (PFAT). Leptin concentration was positively correlated with values for EMD, PEMD, FAT, PFAT, LW and PWT (P < 0.001), whereas follistatin concentration was negatively correlated with values for EMD and PWT (P < 0.001), and PEMD (P < 0.01) and FAT (P < 0.05). Leptin concentration was negatively related to age and positively related to live weight at first oestrus and the proportion of females that attained puberty (P ≤ 0.05), and to fertility and reproductive rate (P < 0.01). Follistatin concentration was negatively related to live weight at first oestrus and to fertility (P < 0.01) and reproductive rate (P < 0.05). There were positive correlations (P < 0.001) between muscle accumulation and leptin concentration, and between muscle accumulation and reproductive performance. We conclude that leptin and follistatin are probably both involved in effects of accelerated accumulation of muscle and adipose tissues on the onset of puberty

Liveweight loss in adult ewes is affected by their sires breeding values for fat and muscle

Ewes that lose more weight at times of nutritional pressure may decrease farm profitability through reduced production but also through reduced stocking rates, increased supplementary feeding costs and labour. Liveweight profiles were derived from the splined liveweight data of adult ewes from the Sheep CRC Information Nucleus Flock and liveweight loss was analysed. This paper reports on the response of liveweight loss to sire breeding values for fat and muscle in two contrasting environments. Overall liveweight loss was affected by significant differences between site, sire breed, ewe age, and previous and current reproductive performance. Sire breeding values for fat were significant, and interacted with site. There was a reduction in liveweight loss as sire breeding values for fat increased at Katanning in WA but an increase in liveweight loss at Kirby in NSW. Sire breeding values for muscle were also significant and different for each site, with the effects being opposite to fat at each site. These results suggest that selection against fat or selection for increased muscling may compromise the ability of ewes to maintain weight during summer and autumn in dry Mediterranean climates, however this may not be applicable for all environments

Pre‐pubertal growth, muscle and fat accumulation in male and female sheep—Relationships with metabolic hormone concentrations, timing of puberty and reproductive outcomes

Metabolic homeostasis is aligned with changes in growth and body composition, through processes mediated by circulating metabolites and metabolic hormones, and is eventually linked to reproductive success. In the present study with sheep, we determined the relationships among phenotypic and genotypic rates of growth, muscle and fat accumulation, and the circulating concentrations of metabolic and tested for relationships with the timing of puberty and subsequent reproductive outcomes. We used 64 females and 62 males with known phenotypic values for depth of eye muscle (EMD) and fat (FAT) and known Australian Sheep Breeding Values at post‐weaning age for live weight (PWT), depth of eye muscle (PEMD) and depth of fat (PFAT). Blood plasma sampled every 20 min for 8 hr via was assayed for growth hormone (GH), insulin‐like growth factor I (IGF‐I), insulin, leptin, ghrelin, follistatin, glucose and non‐esterified fatty acids (NEFA). In males, PWT was positively related to the concentrations of GH, follistatin and glucose, whereas FAT and PFAT were positively related to IGF‐I concentrations (p < .01). Testosterone concentration was negatively related to muscle variables (p < .001) and to PFAT (p < .05). In females, the only significant relationship detected was the positive link between EMD and insulin concentrations (p < .05). Reproductive variables were only measured in females. Live weight at first oestrus was related positively to insulin concentration and negatively to GH concentration (p < .05). No other relationships with reproductive variables were significant. The relationships that were detected suggest subtle differences between the sexes in the way their metabolic homeostasis responds to changes in the rates of growth, and muscle and fat accumulation, perhaps due to interference by testosterone in the males

Follistatin, muscle development, puberty and fertility in ewe lambs

It has been thought that females must accumulate a certain mass of body fat before they can go through puberty and maintain fertility but this theory is being challenged because muscle development also seems to be linked to fecundity. Body fat and reproduction are linked physiologically by leptin, but a link among increased muscling and reproduction has not been explored. One possible link is follistatin (FS), a key player in the regulation of both muscle development and follicle-stimulating hormone secretion. We assessed the relationships between breeding values for muscling, the onset of puberty and fertility, and circulating PS concentrations in Merino ewe lambs (n=136) To detect onset of puberty, testosterone-treated wethers were run with the lambs from 6 to 8 months of age and then replaced by entire rams. Blood FS concentrations determined by RIA decreased as puberty approached and increased as conception approached. The proportion of ewe lambs that attained puberty decreased as FS values increased (P<0.05), but FS concentration had no effect on fertility. We conclude that FS secretion is related to the onset of puberty but not fertility of Merino ewe lambs. The data presented do not imply a cause-effect relationship; however, further research is necessary to clarify the effect of circulating FS on reproductive traits in Merino ewe lambs