Composition of the diet of sheep grazing swards of differing white clover content and spatial distribution

Abstract

Thirty swards containing either alternating strips of pure grass and pure clover or mixed grass and clover were developed by herbicide treatment to give nominal white clover proportions of 10, 30, 50, 70, and 90%. Diet selection was estimated in 3 periods using both oesophageally fistulated sheep and pre- and post-grazing cuts to determine the effect of spatial distribution and white clover content of the sward of diet content. Clover in the sward varied from 1.1 to 90.4%. White clover was intensely selected in Period 1 in both mixed and strip swards because clover leaves overtopped a canopy of mainly dead grass. There was no evidence for preferential selection of clover from mixed swards in Periods 2 and 3, but preference was shown on the strip swards. Preference for weed species was marked, with some being grazed to ground level. There was no correlation for either grass of clover between preference and sward content on mixed plots. This implies that sheep were grazing to optimise energy intake. On strip plots, preference for white clover decreased above 50% sward content suggesting that some form of nutritional constraint may have been important. Sheep showed a strong preference to graze on the clover strips in the strip swards and appeared to discriminate in favour of clover within this strip. High levels of white clover are needed in mixed swards if clover is to make an important contribution to animal nutrition, but the provision of strips of clover is unlikely to be economic.