678. The effect of variations in nutrient intake upon the yield and composition of milk II. Factors affecting rate of eating roughage and responses to an increase in the amount of concentrates fed

Abstract

1. Rates of eating hay, kale and concentrates and responses to a 3 lb. increase in the daily concentrate allowances when roughage was rationed on a ‘group’ basis, were measured in fourteen Ayrshire cows and fifteen heifers.2. There were significant differences between animals, between days, and significant cow × period interactions, in rates of eating in both groups. The cows were a more variable group and generally ate faster than the heifers. Although the rate of eating fresh kale tended to decrease with increasing dry-matter percentage, the rate of eating kale dry matter was positively and significantly related to the dry-matter percentage.3. There were positive associations between the rates of eating of the three different foods, and of these with live weight, but no effects of milk yield or stage of lactation, and no marked effects of climatic conditions could be detected.4. The errors in the determination of mean rates of eating were such that observations made on 4–5 days gave satisfactory comparisons of individual rates of eating.5. Reponses in milk yield to additional concentrates were positively correlated with milk yield, and no independent effects of stage of lactation could be detected. Responses by the heifers were less then those of cows giving similar yields.6. Responses in solids-not-fat percentage were greatest in those cows with inherently low percentages.7. There was no relationship between rates of eating roughage and responses of milk yield to additional concentrates, but live-weight responses and, to a lesser extent, solids-not-fat responses were negatively correlated with rates of eating in the cows. It was concluded that the level of feeding, system of management and the roughage:concentrate ratio used were such as to eliminate the effects of rates of eating roughage upon milk yields, if indeed such effects exist.