Relationships between clean fleece weight, reproduction and fatness in adult Merino ewes and growth, fleece, carcase attributes and survival in their progeny

Abstract

Concerns that high clean fleece weight (CFW) sheep were likely to be less fit during drought has been expressed by producers and has been supported to some degree by animal house experiments. These experiments predominantly used dry sheep, and found high fleece weight genotypes were leaner and had lower circulating energy levels. Conclusions from the experiments implied that reductions in reproduction will occur as a result of an emphasis on CFW selection. This thesis has examined the hypothesis that breeding ewes, selected for high or low CFW and high or low body weight and held at two levels of stocking rate, will partition nutrition differently with reductions evident in body fat and reproduction for high CFW animals. Also examined were the effects on carcase quality and growth in their offspring. Adult ewes (5-8 y.o.) were selected on the basis of their hogget CFW and hogget offshears body weight (BWT). Over two years, adult ewes were held at two levels of stocking rate throughout pregnancy and from marking to joining and liveweight, body fat score, ultrasound scanned fat and muscle depth and reproduction were recorded. The first drop of wether progeny were retained for slaughter to determine the effects on carcase quality and the first drop of ewe progeny were retained for measures of hogget fleece production. The final experiment examined controlled feed intake and metabolic energy reserves in the dams under animal house conditions, and the implications for rearing twin lambs.