Abstract:
422 Proc. Aust. Soc. Anim. Prod, Vol. 17 BLOOD METABOLITES IN EWES SELECTIVELY BRED FOR HIGH OR LOW CLEAN FLEECE WEIGHTS: POSSIBLE USE FOR SELECTION OF SUPERIOR ANIMALS + G.M. HOUGH,+* A.J. WILLIAMS,** G.H. MCDOWELL and E.F. ANNISON+ It is widely recognized that there is substantial variation within flocks of sheep for such characteristics as growth rate, fecundity and fleece weight. Indeed, this recognition has led to the creation of flocks of superior animals by selection and planned breeding. Determination of physiological/metabolic characteristics correlated with improved productivity would allow early identification of superior animals and faster progress in establishment of superior flocks. Concentrations of several metabolites and hormones in blood or plasma of Merino ewes selectively bred for high (fl+) or low (fl-) wool production were measured with the view to identifying differences between the genotypes which might prove useful for identifying superior animals. Fifteen non-pregnant, non-lactating mature ewes of each genotype were housed individually in pens and offered a good quality ration (9.6 MJ metabolizable energy and 218 g crude protein per kg of dry matter). Ewes were offered the ration at either 0.8, 1.0 or 1.3 times calculated maintenance requirements once daily between 08.00-08.30 hours. All ewes were accustomed to handling; blood samples were collected from catheterized jugular veins each hour between 13.00-16.00 hours. Samples for each ewe were pooled and subsequently analyzed for metabolites and hormones. Table 1 Liveweight, wool production and metabolite or hormone concentrations of ewes selectively bred for high or low clean fleece weights Marked differences occurred between fl+ and fl- ewes for plasma cl-amino-N Further, differences were measured for and cystine and also plasma thyroxine. blood acetate and lactate as well as wool sulphur content,hence differences in plasma metabolites are likely to reflect differences in utilization of nutrients related to genetic capacity for wool production. Measurements of plasma a-amino-N, cystine and thyroxine may prove useful for identifying sheep with the genetic potential for high wool production. Department of Animal Husbandry, University of Sydney, Camden, N.S.W. 2570 + * Present address: Department of Agriculture, Bunbury, W.A. 6230 ** Department of Agriculture, Orange, N.S.W. 2800
