CHANGES IN PLASMA AMINO-ACID PATTERNS AND WOOL GROWTH DURING LATE PREGNANCY AND EARLY LACTATION IN THE EWE

Pregnancy and lactation result in depressed growth, fibre diameter and tensile strength of wool. Competition for nutrients between wool foll icles, maternal tissues and the foetus may cause these changes. Change s in the concentrations of individual free amino acids in plasma, duri ng late pregnancy, were used as indicators of limiting amino acids in this experiment. A group of pregnant ewes was maintained in the animal house during late pregnancy and early lactation and measurements made on amino acids in plasma. Liveweight, wool growth and quality charact eristics and sulfur in wool were also measured. Comparisons were made between the different time periods in pregnancy and lactation and betw een the reproducing ewes and a group of non-reproducing ewes maintaine d under the same conditions. During the last 3 weeks of pregnancy, the re was a 31% decline in the concentration of the total, free, essentia l amino acids in plasma. There was also a significant decline in the c oncentration of arginine (60%), lysine (55%) and threonine (48%). The concentrations of these amino acids increased during the first 3 weeks of lactation. There was no change in concentration of methionine or c ystine. Wool growth rate was lowest in the last 3 weeks of pregnancy a nd the reproducing ewes had significantly lower wool growth, fibre dia meter, staple strength and sulfur in wool than the non-reproducing ewe s. The results indicate that a lack of the sulfur-containing amino aci ds is unlikely to be limiting, but a lack of arginine, lysine or threo nine may be limiting wool growth and protein deposition in late pregna ncy.