Effects of reduced concentrate feeding on energy metabolism and milk production in early lactation dairy cows

We studied the effects of two different dietary concentrate proportions, 37.5% and 50% of diet dry matter (DM), on milk yield (MY), feed intake and metabolism of dairy cows. The experimental design was a randomized block-design, starting from calving. In total, 30 Finnish Ayrshire cows of second parity or greater were assigned to pairs based on parity, expected calving date, milk production data from the beginning of previous lactation and body weight. The amount of concentrate was adjusted from the milking robot and both groups had ad libitum access to the same partial mixed ration (PMR) consisting of grass silage and cereal concentrate. Cows fed a high-concentrate diet received 8 kg/d of concentrate from the milking robot and cows with low-concentrate diet 2 kg/d. Feed intake and milk yield were recorded daily during the first two months of lactation and milk samples were collected once per week during weeks 1,2,3,4,6 and 8, rumen fluid samples once per week during weeks 1,3 and 6 and blood samples once per week during weeks 1,2 and 3 after calving. Fecal spot samples were collected on three consecutive days on the sixth week of lactation. Feed samples from silage, robot concentrate, and concentrate used in PMR were collected weekly. Data were analyzed with repeated measures ANOVA. The model included the fixed effect of treatment, week, treatment x week and the random effect of pair and week x pair. Digestibility of the grass silage was moderate, average D-value (concentration of digestible organic matter in DM) was 661g/kg DM. There were no differences in total DM intake between dietary treatments, while cows fed a low-concentrate diet had greater PMR intake. Cows fed with less concentrate had 4.1 kg/d lower (p < 0.01) MY and 2.4 kg/d lower (p < 0.10) energy-corrected milk yield. Dietary concentrate proportion had no effect on milk composition, although the fat and protein contents were numerically greater [protein 36.6 vs 35.5 g/kg (SEM 0.66) and fat 45.9 vs 43.7 g/kg (SEM 1.60)] when cows received less concentrate. There were no differences between the two groups in daily rumination time, body weight or plasma concentrations of non-esterified fatty acids, beta-hydroxybutyrate or glucose. Cows fed a highconcentrate diet had lower (p < 0.01) fecal pH and tended (p < 0.10) to have lower reticular pH. Despite moderate digestibility of the silage, cows fed with less concentrate did not have more signs of metabolic problems, such as ketosis, when compared to cows that were fed with high concentrate proportion. Based on these preliminary results, reducing concentrate feeding decreased MY substantially. Additional analyses will be conducted to assess the dietary effects on cow metabolism and welfare, as well as the economic and environmental impacts.