Assessment of Grazing Procedures in the Evaluation of Plant Breeding Material

Four stocking densities (2, 3, 5 and 9 sheep/18 m for one hour) and two times of grazing (morning or evening) were imposed on a spaced plant nursery of nine red clover (Trifolium pratense L.) populations of varying growth habit, in order to optimize measurement of sheep grazing preference. Plant height, spread and leafiness were measured before and after each of three grazings. Sheep preference was viewed multivariately, using combined measurements of these plant characteristics. MANOVA revealed that the effect of stocking density was significant (P-0.05), but that of time of grazing was not. The plant, population and overall heritabilities were non-significant (P>0.05) for before-and-after grazing differences for all characteristics, and also for leafiness after grazing. Overall heritabilities for after-grazing spread and height were significant at 0.37 and 0.30, respectively. Sampling reliability at the 5 sheep/18 m stocking density was 94%, which was superior to the lower grazing intensities; this stocking density was considered to be the best for subsequent evaluation work. Either morning or evening grazings could be used.