Sensor-captured modifications in cow behaviour under subacute ruminal acidosis

High-energy diets increase the risk of subacute ruminal acidosis (SARA) in ruminants. Ruminants with SARA show behavioural modifications. However, behavioural changes due to high-energy diet are often confounded with the behavioural changes due to SARA per se. Here, we aimed to disentangle diet-induced effects from SARA-induced effects on cow behaviour. We fed Holstein cows with either a low-starch diet (10.5% starch) or a high-starch diet (31.5% starch) while monitoring their SARA status. Control cows (n = 14) received the low-starch diet for 60 days. Challenge cows (n = 14) received the same low-starch diet except for 10 days when they were gradually switched from the low- to the high-starch diet and the next 14 days when they were fed the high-starch diet only. The eCow rumen bolus and the CowView activity-collar sensors were used to track the rumen pH and cows’ activities. DM intake (DMI) and milk yield of each cow were assessed on a daily basis. SARA status was defined based on a relative decrease in ruminal pH and pH variability. The high-starch diet induced SARA more often than the low-starch diet (SARA on 81% of days when receiving high-starch diet vs 8% of days when receiving low-starch diet). Cows on the high-starch diet also showed decreased milk yield and spent less time eating but ate more quickly (Challenge vs Control cows during the challenge period: milk yield 20.0 vs 18.2 L/d; % time spent eating, 22.5 vs 27.6; eating rate, 77.1 vs 69.6 g DMI/min; P (diet × period) <0.001 in all cases). Cows experiencing SARA during transition or challenge periods also tended to show lower milk yield, less time spent eating, and an increase in eating rate regardless of diet (Challenge vs Control cows: milk yield, −0.5 and −0.3 L/d, P (SARA) = 0.03; % time spent eating, −1.4 and −0.84, P(SARA) = 0.02; eating rate, +4.9 and +3.2 g DMI/min, P(SARA) = 0.06; P (diet × SARA) > 0.50). Based on these findings, an increase in eating rate, especially when combined with a decrease in milk yield, should alert farmers to the risk of ruminal acidosis.