Metabolic and productive adaptive response of beef cows to successive short-nutritional challenges.

This study aimed to analyze the response of lactating beef cows to repeated short nutritional challenges with their performance parameters and plasma metabolites. Multiparous lactating beef cows were subjected to three repeated nutritional challenges in the fourth month of lactation. Each challenge consisted of a 4-d feed restriction (55% of their average energy and protein requirements), followed by a 3-d refeeding period (100% requirements). Cows were classified into two groups differing in their performance (milk yield) and metabolic adaptation [non esterified fatty acids (NEFA) and β-hydroxybutyrate (BHB)] to diet changes (metabolic response, MR): High and Low MR cows, where the High MR cows showed a faster and larger response to diet changes than the Low MR cows (P < 0.001). The loss in milk yield during restriction was the smallest in challenge 1 (P < 0.001). Milk urea increased during restriction in challenges 1 and 2 (P < 0.001). The High MR cows had greater NEFA concentrations than their Low MR counterparts during restrictions, and greater BHB concentrations during the restriction of challenge 2 (P < 0.001). Restriction increased NEFA, BHB (only in the High MR cows) and urea (P < 0.01). During refeeding, both milk yield and plasma metabolites recovered basal values (P > 0.05). These results highlight the ability of beef cows to respond to and recover from successive short-term nutrient restrictions, and that despite a certain degree of sensitization of milk yield may have occurred, there were only minimal changes in the metabolic strategies triggered to cope with repeated underfeeding.