SEASONAL-VARIATION OF VOLUNTARY FOOD-INTAKE AND METABOLIC-RATE IN 3 CONTRASTING BREEDS OF SHEEP

Voluntary food intake (VFI) of chopped timothy hay and metabolic rate were each measured in each month of the year in six non-breeding ewes of each of three breeds. Metabolic rate was measured using indirect ca lorimetry over a range of food intakes and adjusted for intake to an e stimated maintenance metabolic rate (MMR). The breeds compared were th e Dorset Horn (DT), Scottish Blackface (BF) and Shetland (SH), the fir st being less seasonal in reproductive and other characteristics than the other two which are hill or northern latitude breeds. There was si gnificant overall variation between months in VFI which was higher in the summer (July to September) than in the winter (December to Februar y) months (P < 0.001). There was a significant breed X month interacti on (P < 0.01), the seasonal effect being most strongly observed in the BF and SH ewes, whose VFI in summer was proportionately 0.1 greater t han the year-round mean but was 0.1 lower in the winter. The DT ewes s howed much less seasonal variation in VFI. There was no overall differ ence in VFI between breeeds (DT: 43.7; BF: 49.5; SH: 48.1 g dry matter per M0.75 live weight per day, P > 0.1). Although MMR varied signific antly between months (P < 0.001), there was no systematic variation be tween summer and winter. There was no significant breed X month intera ction, but the MMR differed significantly (P < 0.001) between breeds g iving a high overall MMR in BF (DT: 322.7; BF: 356.6; SH: 324.5 kJ/kg M0.75 per day). No significant correlation existed (P > 0.05) between the monthly mean MMR and VFI in any of the breeds. The causal relation ship between seasonal cycles of basal metabolic rate and VFI is questi oned.