247 - Metabolic Adaptation to Short-term of Dietary Nutrient Imbalances in Mid Lactation Dairy Cows

This study investigated the short-term metabolic and endocrine responses to different levels of concentrate formulated to particularly provide one major macronutrient source. Based on parity number, lactational stage, milk yield and BW, 9 mid lactating cows (211 ± 19 d in milk) were grouped into 3 blocks of 3 animals each. Concentrate supplements (aminogenic: rich in crude protein and nitrogen sources; glucogenic: high content of carbohydrates and glucogenic precursors; lipogenic: high lipid content) were fed in a factorial arrangement at 3 increasing levels for 3 d each. Milk yield, BW and feed intake were recorded daily. Blood and milk were sampled every 3 d at the end of each concentrate level. Statistical analysis was carried out using a mixed model with concentrate supplement and level as fixed, and block and animal as random factors. Milk fat, protein, lactose and urea contents were determined. In blood, concentrations of various metabolites, endocrine factors and enzyme activities (e.g. glucose, non-esterified fatty acids (NEFA), β-hydroxybutyrate, urea, cholesterol, triglycerides, insulin, glucagon, ASAT, GGT, GLDH) were measured. Milk yield, milk composition and BW were not affected by diets and concentrate levels. Feed intake increased in cows receiving the aminogenic and lipogenic diet. Milk und plasma urea concentrations were clearly elevated in the aminogenic and to a lesser extent in the lipogenic treatment compared to the glycogenic diet (P < 0.05). Glucose concentrations in plasma were not affected by treatments, whereas insulin and glucagon increased only in the aminogenic treatment with concomitantly reduced NEFA concentrations (P < 0.05). Activities of ASAT, GGT and GLDH as well as the total antioxidant capacity were not affected by diets (P >0.05). To conclude, immediate metabolic and endocrine responses occurred due to the short-term dietary changes. Particularly a surplus of nitrogen supply affected metabolic responses and stimulated insulin and glucagon secretion.