YEAR EFFECTS ON THE CARCASS COMPOSITION OF LAMBS SLAUGHTERED OVER A 10-YEAR PERIOD

A trial involving the body and carcass analysis of 7885 lambs sired by 15 different breeds of ram and run at two New Zealand locations (Ruak ura and Manutuke) over a 10 year period was analysed to determine the significance and size of the year effect on lamb composition. Animal s ize (growth rate) differed between sites with the Manutuke lambs being approximately 10% larger. Year had a very significant effect on the m uscle, fat, and bone measurements investigated, with this effect remai ning after adjusting measurements to the same carcass weight. Carcass fatness was strongly influenced by carcass weight which differed betwe en years. At the same carcass weight, lambs differed by around 5% fat as a proportion of carcass weight or around 20% fat as a proportion of total fat, between the most extreme years at each location. Year diff erences were as large as those associated with identifiable management factors (breed, strains, sex, etc). Unfortunately, the underlying fac tors contributing to the year effect are at this stage unknown, but ma y provide a fruitful field for additional research.