Nitrogen and sulfur mobilised from body tissue can be used for wool growth

The hypothesis was tested that when nitrogen (N) and sulfur (S) are mobilis ed from body tissue the rate of wool growth is determined both by the amoun t of N and S apparently digested and by the amount of N and S mobilised fro m body tissue. The experiment consisted of seven 5- day periods (Periods 1- 7) and N and S retention were measured during each period in 12 mature Meri no wethers. During Periods 2 and 3, casein and methionine were infused into the abomasum of all sheep to increase the amount of N and S absorbed in th e small intestine. Three nutritional regimes were used in order to manipula te the amount of N and S mobilised from body tissues after the cessation of the abomasal infusion: one group of sheep (n = 4) was fed ad libitum throu ghout the experiment (Group A), another group (n = 4) was fed at a level ca lculated to maintain liveweight throughout the experiment (Group M), and th e third group (n = 4) was fed ad libitum pre-infusion and during the infusi on but was then fed at a level calculated to maintain liveweight after the infusion ceased (Group AM). The infusion of the supplement increased wool g rowth, and when the infusion ceased, it took 10 days for wool growth to ret urn to a steady rate of growth. Wool growth per unit of apparently digested N or S increased markedly when N or S was mobilised from body tissue, indi cating that mobilised protein was used for wool growth. Based on the relati onship between the apparent retention of N and S in body tissues excluding wool, and changes in plasma amino acid concentrations, it appeared that the supply of S-containing amino acids from body tissue limited the use of mob ilised protein for wool growth.