With the decline in pasture quality in southern Australia, the development of
management strategies to improve nutrient supply for grazing animals is
essential and requires a clear understanding of the interaction between
animals and plants. The impact of grazing intensity on the morphology of
subterranean clover was previously examined. This paper reports the effect of
grazing intensity on the nutritive value of subterranean clover, and the
variation in quality of cultivars during the growing season.
Grazing intensity influenced nutritive value and interacted with cultivar
maturity. Heavy grazing depressed dry matter digestibility (DMD) by 5
percentage units in October for early maturity cultivars but increased DMD by
3 percentage units in September for mid maturity cultivars. The influence of
grazing intensity on nitrogen content was small. Heavy grazing did not affect
acid detergent fibre for the early maturity group, but depressed it for the
mid maturity group throughout the season. Acid detergent lignin remained
comparable for all cultivars during the season. Mineral content of
subterranean clover showed variable response to grazing treatments.
Nutritive value varied among cultivars within each maturity group. DMD ranged
over 53–64%, 44–62%, and 45–53% for
early, mid, and late maturity groups, respectively, at the end of the growing
season. The cultivar rank in all nutritional parameters changed with the
progress of the season. The large ranges in the decline rate of DMD within
each maturity group during the last 8 weeks of growth gave an indication of
the potential quality of the cultivars during late spring and early summer.
Despite the variation in mineral content there were no cultivars in which the
concentration of minerals was below the minimum requirements of sheep. These
results indicate that there is a potential for the selection of high quality
cultivars within a breeding program, and that indicative targets of grazing
intensity need to be further developed with a focus on pasture quality.