Changes in herbage mass and time of herbage allocation modify nutritional and metabolic status of dairy cows

In temperate milk production systems, it is important to study the effect of grazing strategies in both the quantity and quality of the diet, resulting in potential impacts on animal metabolism. The aim was to evaluate the effect of timing of herbage allocation and herbage mass on blood indicators. Forty Holstein-Friesian cows were grouped according to milk production (24.7 ± 2.8 kg cow^-1), body weight (580.6 ± 51.7 kg) and days in milk (74 ± 17.1 d). The groups were randomly allocated to one of four treatments: 1) L-AM, access to new herbage allocation after morning milking with herbage mass of 2000 kg DM ha^-1; 2) L-PM; access to new herbage allocation after afternoon milking with herbage mass of 2000 kg DM ha^-1; 3) H-AM; access to new herbage allocation after morning milking with herbage mass of 3000 kg DM ha^-1; 4) H-PM; access to new herbage allocation after afternoon milking with herbage mass of 3000 kg DM ha^-1. Milk production was only different for H-PM in 1.1 kg higher than L-PM. Urea in milk was affected by treatments, being 22% higher for L-AM than other treatments. β-Hydroxybutyrate and blood urea concentrations were 47% and 30% higher, respectively, for AM compared to PM treatments. Plasma albumin concentration was lower for H-PM compared to other treatments at week 3 of blood sampling. PM treatments modify the herbage composition and animal metabolism, while combining it with a high herbage mass impacts positively in production and milk composition.

Keywords
Autumn pasture; dairy cows; grazing system; metabolism; pasture management.