Short Communication: the Effects of Histidine-supplemented Drinking Water on the Performance of Lactating Dairy Cows

An experiment was conducted to test the hypothesis that a sufficient proportion of histidine (His) included in the drinking water of lactating cows bypasses the rumen to have an effect on milk synthesis. Eight dairy cows (45 +/- 15 d in milk) were given either 0 or 2.5 g/L of His in the drinking water in a crossover design of two 7-d periods. Cows were offered a corn and alfalfa silage-based total mixed ration for ad libitum intake. Water was provided ad libitum to each cow in an individual automatic drinking vessel with a flow meter attached. Water intake tended to increase from 85.1 to 92.1 L/d when His was added. Concentrations of His in plasma samples collected on the last day of each period tended to increase from 14.6 to 21.6 muM, corresponding to an estimated 0.4% bypass of the imbibed histidine. Other amino acid concentrations in plasma were not affected by His supplementation. Milk yield increased by 1.7 L/d with His treatment, lactose yield increased by 90 g/d, and there were tendencies for protein yield to increase, fat percentage to decrease, and protein to fat ratio to increase. An improvement in postruminal histidine flow can influence milk production and composition but the proportion of imbibed water that bypasses the rumen will have to be increased to take advantage of drinking water as a vehicle to transfer His postruminally.