Measurements of energy balance of grazing beef cows on Mediterranean pasture, the effects of stocking rate and season: 1. Digesta kinetics, faecal output and digestible dry matter intake

Abstract

Intake and digesta kinetics of free-ranging beef cows in two stocking rates were estimated during the course of the grazing seasons, February through June 1998 and 1999. Area allocations were 0.9 and 1.8 ha/cow in the high (HSR) and low stocking rates (LSR), respectively. Cows with their calves were introduced to the plots from January to July and the calves were weaned in May each year. Intake measurements were carried out in eight cows in each plot three times in 1998 and twice in 1999. The herbage in the plots was sampled and analysed for chemical composition and in vitro digestibility at each time of measurements, and the standing biomass in the plot was determined at the same times. Intake and digesta kinetics were estimated from faecal concentrations of chromium and cobalt, following a single dose of Cr-mordanted NDF and Co-EDTA to the rumen. Dry matter and digestible matter intakes were calculated from the faecal output (FO) and in vitro DM digestibility. The effects of herbage composition and standing biomass on intake and digesta kinetics are presented and discussed. Dry and digestible matter intakes decreased, and digesta retention time increased as the season progressed from winter lush to summer dry herbage. The effect of stocking rate on intake was small and insignificant, but retention time of particles was numerically shorter in the high than in the low stocking rate in all the measurements, and those of solutes were shorter in the high than in the low stocking rate only in the winter. Intake was larger, and mean retention time of digesta was shorter in lactating then in non-lactating cows.