Behavioral and systemic differences in Holstein cows with known severity of rumen acidosis during low and high-grain feeding

This study investigated behavioral and systemic differences in second-lactation Holstein cows with known susceptibility to subacute ruminal acidosis (SARA) when transitioned from a low to high-grain diet. Eighteen cows (9 SARA-susceptible, 9 SARA-resistant; 646 ± 59 kg body weight) were used in a longitudinal experimental design, with two experimental runs. In each run, the cows were first fed a 40 % concentrate diet for 2 weeks followed by a 65 % concentrate diet for 4 weeks. Behavioral parameters (chewing, lying, eating, ruminating, feed sorting), salivary characteristics, milk production, and blood metabolites were evaluated. SARA-resistant cows exhibited greater rumination activity (rumination time, chews per bolus, chews per minute; P < 0.05), higher body weight ( P = 0.04), and elevated serum total protein ( P = 0.01), despite no differences in ruminal pH indices. The dietary shift to high-grain significantly affected most behavioral, production, and physiological parameters ( P < 0.01), including increased sorting for physically effective fiber (peNDF), eating rate, meal frequency, milk yield, milk protein, blood glucose, and salivary osmolality, alongside reductions in rumination time, eating duration, milk fat, and blood lipid metabolites. Significant SARA type × diet interactions were observed in rumination indices, eating behavior (visit size, number of meals), blood glucose, and non-esterified fatty acids concentrations, with SARA-resistant cows showing improved metabolic adaptation during the high-grain phase. In conclusion, cows previously identified as SARA-resistant demonstrated enhanced behavioral and metabolic resilience to high-grain diets, suggesting that prior SARA status may influence adaptation strategies during dietary transitions. Additional research is suggested to evaluate prolonged impact of high-grain diets on behavioral and production parameters across different SARA phenotypes. • Cows resistant to rumen acidosis in the previous lactation had higher rumination activity in this lactation. • Cows resistant to rumen acidosis in the previous lactation maintained higher body weight during high grain feeding. • Cows resistant to rumen acidosis showed better adaptation capacities to high-grain feeding.