Influence of energy and protein supplements on the productivity of dairy cows grazing white clover swards in spring

Two experiments were conducted to determine the production responses from high-producing dairy cows grazing white clover (Trifolium repens cv. Haifa) swards while being supplemented with maize (Zea mays) silage with or without additional protein and/or energy. The white clover swards in experiments 1 and 2 comprised 5 and 25% flowers respectively. In each experiment, 6 groups of 4 Friesian cows were offered about 20 kg dry matter (DM)/cow.day of pure white clover for 5 weeks in spring-early summer. Each group was assigned to one of 6 supplementary feeding treatments: (i) no supplement; (ii) 5 kg DM/cow of maize silage; (iii) 5 kg DM/cow of maize silage with 75 g of urea; (iv) 3 kg DM/cow of maize silage plus 2 kg DM of rolled barley; (v) 3 kg DM/cow of maize silage plus 2 kg DM of cottonseed meal; or (vi) 3 kg DM/cow of maize silage and 1 kg DM of barley and 1 kg DM of cottonseed meal each day. All cows were individually fed supplements but grazed pasture as separate treatment groups. In experiment 1, milk yields averaged 22.0, 24.4, 24.5, 24.0, 25.1 and 25.5 kg/cow.day, respectively, for the treatments listed above. None of the supplemented treatments were significantly different. In experiment 2, corresponding milk yields were 17.9, 20.0, 21.1, 21.5, 22.1 and 21.3 kg/cow.day. Addition of urea, barley or cottonseed meal to maize silage significantly increased milk production above that of the unsupplemented cows. Feeding supplements in experiment 2 also significantly improved body condition. There were no significant biological effects of supplementary feeding treatment on rumen fermentation, although ammonia-nitrogen concentrations were reduced when energy supplements were fed in experiment 1. While the responses from feeding maize silage were consistent with previous research, the results obtained from the replacement of some of the silage with extra energy and/or protein were inconclusive. Certainly trends in milk yield were apparent, particularly from the addition of nitrogen/protein, but the design of the experiments was not conducive to high experimental precision. On the other hand, where barley was included in the ration, it was possibly unrealistic to expect large changes in productivity, unless positive associative effects existed, since the barley probably provided little extra total energy.