SEASONAL-VARIATION IN VOLUNTARY FOOD-INTAKE AND POST-WEANING GROWTH IN LAMBS - A COMPARISON OF GENOTYPES

Voluntary food intake (VFI) was measured daily and live weight (LW) was measured weekly in a total of 39 growing lambs of six genotypes given a similar complete chopped-straw based diet in experiments in 1983, 1985, 1987 and 1988. The six genotypes and the years of study were: Scottish Blackface (BF), 1983 and 1988; Suffolk X (Border Leicester X BF) (BL X BF), Suffolk X (East Friesland X Cheviot) (EF X NCC), Suffolk X (East Friesland X BF) (EF X BF), 1985; Welsh mountain (WM) and Beulah (BH), 1985. Measurements were made on lambs penned individually within 6 weeks of weaning at 5 to 6 months of age through to slaughter in the following spring. During this period there was an increase in LW and VFI associated with growth. Regression lines were fitted to LW and weekly means of daily VFI against week for each individual. Analysis of deviations about these lines showed a decline in VFI in BF lambs around December and to a lesser extent in BL X BF from December to January. The decline in VFI in BF was observed in two different years. A negative deviation from the normal rate of increase in LW was also apparent although it was much less marked and present in EF X NCC lambs as well as BF and BF X NCC. Any such variability of seasonal cycles between genotypes of growing lamb would influence the extent to which nutrition and growth may be manipulated. This should be considered when choosing a feeding or growth regime for a particular genotype, or vice versa.