Grazing preference of Merino sheep for naturalized annual clover species relative to commonly sown clover species

摘要

Selective grazing of white clover (Trifolium repens) over grass species in temperate pastures results in reduced clover abundance and availability over time. Within sheep- and cattle-grazed dryland (800mm annual rainfall) hill and high country areas of New Zealand, naturalized unsown annual clover species show greater persistence and abundance over sown clovers. With a view to understanding legume abundance in these areas, Merino sheep grazing preference was investigated for pure swards of naturalized species Trifolium dubium, T.glomeratum, T.arvense and T.striatum and commonly sown species T.repens and T.subterraneum. The Chesson-Manly preference index was used to explore the hypothesis that grazing preference differs between these species and changes as plants mature. Herbage offtake was quantified at vegetative (mid-late spring; November) and reproductive (early summer; December) stages of plant maturity. Significant preference distinctions between species (P005) occurred in December, with relative preference ranging from 0248 for T.repens to 0065 for T.dubium. Reduced relative preference for naturalized species was related to decreasing nutritive value from spring to summer, reflecting increased stem and flower sward content. Relative preference was negatively related to increasing acid detergent fibre and neutral detergent fibre and positively related to greater crude protein and dry-matter digestibility. Naturalized annual clover species of lower grazing preference at reproductive maturity will benefit pasture sustainability via herbage and seed production and associated nitrogen-fixation inputs.