The partitioning of nitrogen between wool, skin and other body tissues in sheep
A partitioning model was proposed and established by regression analysis of data available in the literature. Breed was found to significantly affect nitrogen partitioning (p< 0.001), whereas gender did not. The influence of diet was variable. An equation to predict wool nitrogen deposition from empty body weight was found and was a good predictor of wool nitrogen deposition in growing lambs (p&60 0.001), particularly when the data were split into high (e.g. Merinos) and low (e.g. Southdowns) wool producer groups. There was no influence of diet or gender on the prediction equation. Both the prediction equation and the partitioning model were tested experimentally. The effects of gender (castrate male v. female), diet (high v. low nitrogen) and breed (Wiltshire Horn v. Suffolk crosses) were found to influence partitioning; gender p< 0.05 and breed p< 0.001. The prediction model described wool growth in the Suffolk crosses well, but was 5 times too great for the 'short-haired' Wiltshire Horn. This low wool production also meant that, whilst the partitioning model obtained for the Suffolk crosses was similar to that produced by the regression analysis of equivalent breeds, that of the Wiltshire Horn was significantly different (p&60 0.001) with proportionately less nitrogen being deposited as wool. The β-adrenergic agonist, cimaterol, was then examined for its potential as a repartitioning agent of nitrogen from wool to other body tissues. It was found that cimaterol, supplied in the diet, depressed wool nitrogen deposition whilst increasing nitrogen retention, so the proportion of nitrogen deposited as wool was halved. Protein FSR in ovine skin was measured by the large dose technique using three different amino acid isotopes serially; leucine, phenylalanine and valine. There was no effect of using the different amino acids for FSR measurement.