Physiological Consequences of Selecting Merino Sheep for Divergent Wool Production

Abstract

Over the last 40 years, studies of Merino genotypes developed using single-trait selections for superior wool production or liveweight have provided excellent information on the physiological bases for genetic differences in wool or meat production. Increasingly, however, genetic improvement in the sheep industry is being made using selection indices that combine a number of traits such as clean fleece weight, fibre diameter, liveweight, disease resistance and reproductive performance. Although the economic importance of genetic selection for superior wool and meat production traits is clear, how physiological processes are changed by breeding for dual-purpose sheep is still unclear. Two studies, involving a series of experiments, were designed to improve our understanding of the physiological consequences of genetic selection of Merino sheep for wool and body growth. The first study used three selection groups (n = 4) of Merino ewes (3 years of age) from the Trangie QPLU$ flock chosen for high (H) fleece production, high (H) fibre diameter, and low (L) liveweight (i.e. HHL) and LLH and LLL. These animals were used to determine whether these groups exhibited differences in aspects of whole-body protein turnover or partitioned different ratios of absorbed protein to wool and muscle. A second aim was to determine whether a plant protein source (duckweed) with its amino acids uniformly labelled with ¹⁵N offered any advantages over ¹⁵N-glycine as a tracer for determining whole-body protein turnover in sheep.