Studies in grazing management V. Further determination of the nutrient intake of dairy cows under close-folding and rotational methods of grazing

Abstract

1. The experiments started in 1949 to determine the weight and chemical composition of the herbage dry matter eaten by two groups of dairy cows grazing under a rotational and a close-folding system of management have been continued in 1950.2. Good-quality herbage was fed in adequate quantity to both groups for 20 weeks, in four fiveweekly periods allowing a double change-over system for the groups. The weights of protein, fibre, other extractives, lignin and minerals eaten daily by the close-folded group were determined. Difficulty in obtaining truly representative herbage samples from the rotational paddock made such detailed analyses for the rotationally grazed cattle not worth while.3. The weight of dry matter eaten by the closefolded cows was remarkably constant, the mean was 26 lb./cow/day and the standard deviation ±2·7 lb. The weight eaten by the rotationally grazed cows was more difficult to measure and appeared to vary considerably, the average being 31 lb. dry matter/ cow/day, and the standard deviation ±3·1 lb. Reasons are suggested why this figure of 31 lb. may be at least 5% too high.4. The relationship between the chemical composition of herbage as cut for sampling and the probable composition of the herbage as eaten by the grazing animal is discussed. Correction curves are given to convert the protein and fibre contents of herbage as cut in these experiments to values corresponding to those in the herbage as eaten.5. An attempt has been made to provide a balance sheet, in terms of D.C.P. and S.E., of animal production against nutrient intake. A deficiency of both protein and energy existed during the first spring period in both 1949 and 1950 (according to presentday standards), and although the protein balance became positive later in the season, the energy provided by the grass eaten was still barely adequate.6. Mineral balances calculated for the closefolded cows showed deficiencies of both calcium and phosphorus during the period of high milk yield, with the balances becoming positive later in the grazing season.