Seasonal changes in intake and digestion of chopped timothy hay (Phleum pratense) by three breeds of sheep

Abstract

SUMMARYThe voluntary food intake (VFI) and apparent digestibility of chopped timothy hay by six Scottish Blackface (BF), Shetland (SH) and Dorset Horn (DH) non-breeding ewes were assessed in summer and winter. In two experiments VFI was higher in summer than in winter but did not differ between the breeds. In Expt 1, the seasonal difference in VFI was greater in BF and SH than in DH ewes and the apparent digestibility of dry matter (DM), organic matter (OM) and total nitrogen was consistently higher in all three breeds in summer than in winter. The higher digestibility of DM of the hay in summer than in winter was confirmed in Expt 2, in which the whole tract mean retention time (MRT) of the undigested residues was measured using 103ruthenium-phenanthroline as a marker. The MRT was lower in all three breeds in summer than in winter. In a third experiment, following at least 6 months ad libitum feeding on the hay, for all three breeds the contents of DM and liquid in the reticulorumen were smaller in summer, and the liquid fraction formed a greater proportion in summer than in winter. The results contrast with the expectation that intake and digestibility within a given forage type are negatively correlated. Although an increase in digestibility may facilitate a higher VFI in summer (BF and SH) it does not necessarily do so (DH).