Abstract

The value of legumes for milk production has been attributed to higher intakes by cows and a higher nutritive value compared to ryegrass. However, abrupt changes in diet can adversely affect production, even when the change is to feed with a higher feeding value. A 13-day indoor experiment compared the responses of 12 cows that were changed from ryegrass to lucerne (Medicago sativa L.) (L) on Day 4, with 12 cows remaining on ryegrass (R). Immediately after the change to lucerne there was a 24% decrease in milk yield; this was temporary, as from four days after the change these cows averaged 20% more milk than those fed ryegrass (L = 15.7, R = 13.1 kg milk/cow/d; P <0.001). The temporary decrease in milk yield was not due to decreased intake as lucerne-fed cows had higher intakes (L = 16.5, R = 14.8 kg dry matter/cow/d; P <0.001). Only small differences in the rumen microbial populations were apparent on the day diets changed. The temporary decrease in milk yield was more likely associated with a change in metabolism of the resident bacteria. Improved understanding of the microbial consequences of an abrupt dietary change will enable better management decisions to be made on-farm.

SL, Woodward, GC Waghorn, GC Attwood, and D Li

Proceedings of the New Zealand Society of Animal Production, Volume 70, Palmerston North, 57-61, 2010