Effects of supplementation with protein, or amino acids on performance of grazing dairy cows in late lactation

Abstract

Sixty seven Friesian dairy cows were monitored for eleven weeks in late lactation (weeks 23-33 of lactation) to measure their milk production, intake and live weight response to protein or amino acid supplementation. The cows were grazed on ryegrass pastures, and divided into three groups. Each group was offered a supplement of either barley meal 1 kg; (control), protein meal (soyabean and fish meal) 1 kg; or barley meal (1 kg) with an additional 17 grams amino acids (methionine and lysine), protected from degradation in the rumen. Individual intake of pasture for eight cows per group was determined using the alkane technique during week 28 of lactation. Mean dry matter intake (pasture + supplement) was 15.1 kg DMld, which did not differ between groups. Supplementation with either protein or amino acids did not significantly affect (P>0.05) milk production compared to cows given the control barley diet. Mean production was milk yield 17.5 (l/d) , milk solids 1.49 (kg/d), milk protein 0.64 (kg/d), milk fat 0.84 (kg/d), milk protein 3.70% and fat 4.89%. There was no difference in the live-weight gain between groups, with a mean of 0.17 kg/d. The results from this trial suggest that specific amino acids (methionine and lysine), or the supply of total metabolisable protein, do not limit milk production of dairy cows grazing ryegrass pasture in late lactation.