Milk urea concentration as an index for diagnosis of nutritive balance in dairy cows

Resumen

A study with two feeding regimens of milk production was carried out to examine theeffect of grazing or silage conditions on milk urea (MU) concentration. Milk yield andcomposition were analysed from March to August in three herds of Holstein-Friesian dairycows (n = 92) at different stages of lactation, two under grazing (G): spring-calving (S) andautumn-calving (A), and one indoors (I) and spring-calving (S) under supplementation.Pasture production, quality, and sward utilisation were measured for the grazing treatments.The objective of this experiment was to evaluate the MU concentration as a managementtarget to balance the ration in dairy cows, which allows us to correct the deficiencies ofdairy cattle in pasture conditions, as well as in silage feeding. There were no significant differences in milk production between the GS and IS (24.3 and 25.6 kg day–1, respectively)compared to 18.4 kg day–1 for the GA. Estimates of the MU content in the grazing treatments indicated that there was a balance between protein and carbohydrates with high grassquality and total dry matter intake. The MU concentration was significantly higher in the ISthan in the GS. Protein deficiencies were detected by a decrease in milk urea in the IS