282 Metabolic and Endocrine Changes in Dairy Cows fed Different Diets at dry-off

Concentrate withdrawal and feed restriction reduce milk production to facilitate dry-off. We investigated the impact of feed rations providing different amounts of nutrients in combination with feed restriction on performance, endocrine, and metabolic responses before and after abrupt dry-off. Forty-three cows were studied from d 12 before until d 6 after dry-off (56 d before scheduled calving). Cows were fed experimental concentrates rich in either crude protein (nitrogenic, n=14), glucogenic precursors (glucogenic, n=14), or lipids (lipogenic, n=15). On d 3 before dry-off, total feed allowance was restricted to 50 % in one-half of the animals of each dietary group whereas feed allowance remained unchanged in the other animals. Statistical analysis (SAS, version 9.4) was carried out using a mixed model with dietary group, time, and diet×time interaction as fixed effects (Significance assumed at P< 0.05). Feed restriction immediately resulted in a negative energy balance (NEB) and decreased milk production (P< 0.05). Concomitantly, concentrations of non-esterified fatty acids (NEFA) increased, whereas insulin, insulin-like growth factor-1 (IGF-1), and glucagon decreased (P< 0.05). After dry-off, energy balance turned positive and plasma NEFA decreased again. Plasma glucose, insulin, and IGF-1 concentrations increased in all groups after dry-off. Glucose, insulin, and glucagon concentrations in plasma were greater in non-restricted compared with restricted animals after dry-off (P< 0.05). Milk and plasma urea concentrations were increased in cows fed the nitrogenic concentrate (P< 0.05). Overall, metabolic and endocrine adaptations supporting milk synthesis were continued during the first days after dry-off despite cessation of milking. Thus, the abrupt dry-off resulted in a short-term increase of glucose and triglyceride concentrations, with a delayed endocrine response to re-establish nutrient homeostasis in blood.