Factors affecting diet selection by sheep. V. Observed and predicted preference ranking for six cultivars of subterranean clover

Abstract

Samples from six cultivars of subterranean clover (Trifolium subterraneum) were harvested at two stages of maturity (vegetative and senescent) and one cultivar (Dinninup) at two additional stages. The samples were freeze dried to 90% dry matter, cut to 25 mm length and offered in pairs to trained sheep to determine their preference rankings. Within each stage of maturity, each cultivar was compared with every other cultivar. The vegetative clovers showed only a small (non significant) range in mean per cent preference (57-41), but the senescent material showed a much larger range (87-20). Preference for a forage was determined as the intake of that forage expressed as a per cent of the total intake of both forages on offer. Preference ranking changed with maturity and did not appear to be related to either oestrogenicity or length of growing season of the clovers in the vegetative stage. However, with the senescent material, clovers with a long growing season tended to have higher preference rankings (except for Dinninup). The 'palatability' of each cultivar of senescent herbage was quantified by comparing it in separate tests with a standard hay cut to several lengths. The preference ranking of the six cultivars predicted from this comparison with the standard hay was in close agreement with the observed rankings from the two-way preference tests. The agreement between the predicted and the observed rankings indicated that the method of establishing preference for forages relative to a standard hay (cut to several lengths) could be used to predict preference ranking between forages without performing a direct comparison. Seventeen of eighteen individual comparisons showed good agreement between predicted and observed preference. Preference ranking within the cultivar Dinninup decreased with maturity, and its ranking relative to the other clovers decreased markedly in the senescent stage comparisons. 'Palatability' and preference ranking may have major implications in the establishment and persistence of pastures, as well as influencing diet selection and subsequent nutrient intake by grazing animals.