Abstract:
Perennial ryegrass (Lolium perenne L.) cultivars that express higher levels of water-soluble carbohydrate (WSC) in above-ground growth have been released commercially in recent years, notably in the United Kingdom. There is some evidence to suggest that increased WSC concentrations in grasses may alter the dietary preferences and dry matter intake of ruminants. However, there is little information available from field conditions in Australia on the magnitude and consistency of differences between ryegrass lines bred for higher WSC, and normal lines. Non-structural carbohydrate (NSC) concentrations in above-ground dry matter of the perennial ryegrass cultivars AberDawn (notionally high WSC) and AberElan (typical WSC), and white clover (Trifolium repens L.), were monitored for 24 hours on May 11th, June 28th and December 6th 2000. Four replicated plots of each pasture type growing at Kyabram in northern Victoria were randomly selected and eight pasture cuts were taken to ground level at points along a diagonal transect and immediately frozen in liquid nitrogen. Samples were analysed for soluble carbohydrates and starch to determine NSC concentration. Weather conditions on the days of the May and December sampling were favourable for NSC accumulation, whereas in June solar radiation was low due to heavy cloud cover. In May, white clover was lower (P<0.05) in NSC than AberDawn at all times and AberElan at 0800, 1100 and 1700. In June, NSC concentration of white clover was approximately 65% lower (P<0.05) than the grasses, but in December, it was higher (P<0.05) than in both grasses. Differences between AberDawn and AberElan in the concentration of NSC of herbage were small and generally not significant. Expression of the WSC phenotype was apparently affected by the hotter conditions of northern Victoria compared to the more temperate climate of the U.K. where the cultivars were bred.
