Effect of Subclinical Hypocalcaemia Induced by Na2EDTA on the Feed Intake and Chewing Activity of Dairy Cows

The effects of induced subclinical hypocalcaemia (SCHC) on feed intake and chewing activity during eating and rumination were studied in dairy cows. Two non-lactating and non-pregnant cows were subjected to three different treatments, with one test per day, such that the plasma free (ionized) calcium ((F)Ca) concentration was maintained at the eucalcaemic level or at one of two constant SCHC levels. The cows and test days followed a 2×3 crossover design. SCHC was maintained for 7 h by repeatedly infusing 5% Na2EDTA so that constant (F)Ca concentrations of 0.8 mmol/L or 0.6 mmol/L in plasma were achieved. Control conditions were achieved by infusing isotonic saline. Feed intake and the number of the rumination periods were recorded during test days. The proportion of feed eaten during each test meal (EatPro) was related to the mean plasma (F)Ca. An almost linear decrease in EatPro was observed when the plasma FCa was 0.6–0.9 mmol/L. The cows showed no other clinical signs of hypocalcaemia during Na2EDTA-infusion. The time spent chewing during eating and rumination, and the number of rumination periods during a test day, decreased with a decline in plasma (F)Ca concentration.