Feed restriction in mid-lactation dairy cows. I: Effects on milk production and energy metabolism-related blood metabolites.

The aim of the study was to describe the metabolic responses on energy metabolism to a period of negative nutrient balance induced by feed restriction (FR). Seven multiparous Holstein cows (93 ± 15 days in milk) were randomly assigned to 7 treatments in a 7 × 4 Youden square design. Daily intake was restricted to provide 60% of energy requirements during 5 d except for one treatment with ad libitum (AL) feeding. While 5 out of 7 experimental treatments involved abomasal supplementation of amino acids or glucose, in this article we evaluated only the effects of a negative nutrient balance by comparing both control treatments (AL and FR). Data of 2 cows within the AL group were removed due to sickness and therefore it had n = 2. Milk and energy corrected milk yield were reduced by FR. Yields of milk protein and lactose were lower during FR than during AL but the yield of milk fat only had a tendency (P > 0.06) to be lower with FR. Milk protein concentration was lower with FR than with AL but concentration of milk lactose and fat were not different between diets. The FR induced a decrease in plasma insulin and glucose concentrations, with quadratic decreasing trends both reaching nadirs on d 3. Simultaneously, non-esterified fatty acids (NEFA) concentration was greater and increased quadratically, peaking at d 3 during FR. There were no differences in daily β-hydroxybutyrate concentration, but it increased linearly until d 4 with FR. Comparison of the variation in concentration after feeding of insulin, NEFA and glucose could indicate a likely increased insulin sensitivity for peripheral NEFA uptake and a resistance for glucose uptake. This mechanism would contribute to decrease NEFA in circulation and sparing of glucose for lactose synthesis, respectively. Metabolic adaptations to a short-term reduction in dry matter intake include lipid mobilization, as well as modulation of peripheral tissue endocrine sensitivity in order to maintain yield of milk components production but prioritizing milk fat and lactose over milk protein.Implications The short-term feed restriction model described in this article can serve as an alternative to study metabolic adaptations during the transition period. The response of energy metabolism observed sets the baseline to measure the effect of nutrients supplementation and identify those candidates that will improve milk production and overall health after calving.Competing Interest StatementThe authors have declared no competing interest.View Full Text