Heterogeneity of lifetime reproductive performance, its components and associations with wool production and liveweight of Merino ewes

Abstract

The heterogeneity in lifetime (2–6 years of age) reproductive performance within three research flocks maintained at the Agricultural Research Centre, Trangie, in central-western New South Wales, was used to establish the potential to improve flock reproductive performance by identifying performance segments for either selection or for differential management. The data comprised a total of 32 716 records from 7322 ewes, collected over the period from 1977 to 2003. Within each of the flocks, there were large differences (P < 0.001) in lifetime net reproduction rate, and each of its components (fertility, fecundity and lamb survival), between each of the net reproduction rate quartiles. The difference in net reproduction between the ewes in the top quartile and those in the bottom quartile was equivalent to an additional lamb per ewe annually. These differences in reproduction rate between the quartiles were not related to pre-joining liveweight or condition score. Higher reproductive rates were associated with a cost to clean fleece weight, although the estimated effects on fibre diameter were small. Opportunities to use this variation to improve reproduction rates are discussed and include retaining high-performing ewes longer in the breeding flock, removing poor performers and targeting management interventions towards ewes that will yield the largest responses.