Feeding hay-based diets deficient in protein to dairy cows during early lactation

Abstract

In two experiments, 87 Friesian cows were fed diets of moderate (141%), moderate-low (117%), or low protein content (9.2%) for the first 12 weeks of lactation. These diets contained 5 kg dry matter (DM)/cow.d of either rolled lupins, a 1:1 mixture of rolled lupins and rolled barley, or rolled barley together with cereal hay ad libitum. During weeks 13-24 of lactation, all cows were fed 2 5 kg DM/cow.d of rolled barley as a supplement to cereal hay ad libitum in experiment 1, and pasture ad libitum in experiment 2. All cows were fed cereal hay or hay plus grain during weeks 25-36 of the experiments. Mean estimated intakes of hay DM during the first 12 weeks of lactation were 14.6, 14.8 and 11.9 kg/cow.d in experiment 1, and 15.7, 14.8 and 12.8 kg/cow.d in experiment 2, for cows fed diets of moderate, moderate-low, and low protein content, respectively. Significant differences ( P < 0.05) in liveweight were recorded during the first 12 weeks of lactation. Liveweight differences between groups were evident for a larger part of the lactation in experiment 1 than in experiment 2. The mean daily yields of milk during the first 12 weeks of lactation in both experiments were higher (P<0.00 1) for cows fed diets of moderate (21.9 and 23.5 litres) or moderate-low (20.7 and 22.1 litres) protein content than those of cows fed diets of low protein content (1 6.4 and 15 5 litres). Milk yields for weeks 13-24 and 25-36 did not differ (P> 0.05) between treatment groups in either experiment; milk composition did not differ (P>0.05) between treatment groups in any 12-week period in experiment 1 or 2. Cows fed low protein diets were less efficient in the use of feed or body reserves for milk production than cows fed diets of moderate or moderate-low protein content. Economic data indicate that it is currently profitable to ensure that the protein content of hay-grain diets fed during early lactation is at least 14% of DM irrespective of likely feeding regime over the remainder of the lactation.