Beef production from grass and silage with autumn-born calves. 1. The influence of grazing intensity on efficiency of herbage utilization and live-weight gain of cattle

SUMMARY 1. Two experiments are described in which groups of 12 autumn-born calves were strip-grazed at different intensities. In Experiment 1 (1966), ‘standard’ and ‘high’ grazing intensities were compared. In Experiment 2 (1967), ‘standard’ and ‘low’ intensities were compared. In both experiments the same meadow fescue—ryegrass ley provided 0·24 ha per head for grazing and conservation; herbage surplus to grazing requirements was conserved as silage. 2. The grazing season was divided into three parts according to the type of grazing, and estimates were made of daily herbage allowances, herbage quality, efficiency of herbage utilization and the live-weight gain of the cattle. 3. Grazing intensity was regulated by controlling daily herbage allowances by strip-grazing. Within grazing seasons, differences in grazing intensity had little effect on the digestibility of the herbage dry matter on offer. Dead herbage accumulation was low (10%) in the early and late parts of the season, but rose to 25% in mid-season. 4. The efficiency of herbage utilization was estimated in three ways: from sample cuts of herbage on offer and refused; from measurements of herbage intake; and from feeding standards for maintenance and gain. Efficiency was highest for the ‘high’ group of Experiment 1 and lowest for the ‘low’ group of Experiment 2. The validity of efficiency estimates is discussed in relation to measurements of pasture yield, herbage intake and the assessment of the nutrient requirements of growing cattle. 5. Live-weight gain over the whole season was 0·59 and 0·89 kg/head per day for the ‘high’ and ‘standard’ groups of Experiment 1, respectively. In Experiment 2, the ‘low’ and ‘standard’ groups gained weight at 0·95 and 0·84 kg/head per day, respectively.