Gross energy levels in regrowths of six pasture species, and relations with digestibility and chemical composition

Abstract

Gross energy levels and energy digestibilities were determined on 80 single species pasture samples of known dry matter digestibility. Crude protein, ash and ether extract levels were also determined. The pastures consisted of regrowths of six species, Trifolium repens (White clover cv. Grasslands Huia), Lolium perenne x multiflorum (manawa ryegrass cv. Grasslands Manawa), Lolium (multiflorum x perenne) x L. perenne (ariki ryegrass cv. Grasslands Ari ki), Lolium perenne (perennial ryegrass cv. Tasmanian No. 1), Dactylis glomerata (currie cocksfoot cv. Currie) and Dactylis glomerata (apanui cocksfoot cv. Grasslands Apanui), harvested eight times between May 1969 and August 1970. The gross energy levels in pasture dry matter and pasture digestible organic matter were highest with white clover (means 4.64 and 4.98 K cal g-1) and lowest with the ryegrasses (4.50 and 4.80 K cal g-1). They were also higher in the winter (4.60 and 4.91), autumn (4.53 and 4.90) and spring (4.56 and 4.86), and lower in the summer (4.49 and 4.77). Relations between gross energy levels and chemical composition were weak. The strongest relation was with crude protein content (r = +0.41, P < 0.01). Relations of energy digestibility and digestible energy level in pasture dry matter, with dry matter digestibility had high correlations (r = +0.97, P < 0.01, and r = +0.92, P < 0.01) and were similar to previously published relations. However, seasonal differences occurred in both relations and, at low dry matter digestibilities, winter pasture had higher energy digestibilities and higher levels of digestible energy than spring-summer pasture. Species differences occurred in the latter relation and, at high dry matter digestibilities, white clover had higher levels of digestible energy than the grasses.