A comparison between a dploid and a tetraploid ryegrass for milk production

Abstract

SummaryTwo perennial ryegrass swards – one consisting of S. 24, a diploid variety, and the other of Reveille, a tetraploid variety – were compared in a 20-week grazing experiment with 16 Ayrshire cows in 1968 and again with 12 cows in 1969. Each grass sward was grazed at either a high or a low rate of stoeldng and no other feeds were offered to the cows. On average, the amount of herbage dry matter on offer to the cows was slightly greater on the S. 24 than on the Reveille sward but the contents of total soluble sugars and digestible organic matter were significantly higher in the dry matter of the Reveille than in that of the S. 24. The crude protein contents of the herbage dry matter were similar on the two swards. The mean daily milk yields from cows grazing at the high and the low rates of stocking in 1968 were 14·0 and 15·7 kg/cow respectively on the S. 24 sward and 14·7 and 16·1 kg on the Reveille sward. In 1969 the milk yields from these same treatments were 15·4 and 17·2 kg on the S. 24, and 16·5 and 17·7 kg on the Reveille. The fat content of the milk was not significantly affected by the treatments. In both years the solids-not-fat and the crude protein contents of the milk were higher on the Reveille than on the S. 24 sward, but these differences were significant at the low rate of stocking only. The live weight of the cows did not differ significantly between the two swards. The average output of milk per hectare was approximately 4% higher from the Reveille than from the S. 24 sward but the major factor influencing milk production per hectare was the stocking-rate. On average over the 2 years the output of milk per hectare was 36% higher on the high than on the low rate of stocking. It is suggested that in selecting herbage for milk-production purposes attention should be paid to material with a high digestible organic-matter content and a high content of soluble sugars.