Variation in feed intake of grazing crossbred ewes and genetic correlations with production traits

Abstract

Feed for maintenance of the ewe flock is a major cost in lamb production systems and a reduction in these feed requirements could have an effect on carrying capacity and both biological and economic efficiency in sheep flocks. Inclusion of feed intake in breeding programs requires knowledge of its genetic variation and genetic relationships with other production traits. This study reports on the variation in relative digestible dry matter intake (rDDMI) of 2528 mature, non-pregnant, crossbred ewes that are the progeny of 91 rams of various maternal breeds. Feed intake of pasture under grazing conditions was estimated using the faecal marker dilution technique with chromium sesquioxide controlled-release devices. There was significant variation in intake associated with liveweight, liveweight gain, prior reproductive status, fat depth, and muscle depth of the ewes. Sire breed was not significant for rDDMI, although there was a considerable range of >30% across sire progeny groups within most sire breeds, and rDDMI had an estimated heritability of 0.41 ±  0.07 (s.e.). The genetic correlations with a range of production traits (growth, carcass, wool, and reproduction) were all close to zero. The potential for inclusion of genetic improvement of efficiency of feed utilisation in breeding programs for sheep is discussed.