Effect of water restriction on feeding and metabolism in dairy cows

We investigated how lactating cows are able to cope with a sustained water restriction. In experiment 1, body weight and meal patterns were recorded w ith ad libitum access to water (baseline) and during 8 days of 25 and 50% r estriction of drinking water relative to ad libitum intake. In experiment 2 , indirect calorimetry was combined with nitrogen and energy balance and pl asma hormone and metabolite measurements to assess the effects of 50% water restriction on digestion and metabolism. In experiment 1, food intake and body weight declined during the first 3 days of water restriction depending on the restriction level and stabilized thereafter at a lower level. The d aily food intake reduction with 50% water restriction was entirely due to a reduction of meal size. The size of the first meal on every day was marked ly (>50%) reduced with 25 and 50% water restriction. In experiment 2, urea concentrations in milk and blood as well as plasma sodium and hematocrit we re increased by 50% water restriction. Energy balance was not affected by 5 0% water restriction, but nitrogen balance became negative, because, relati ve to intake, nitrogen excretion via urine and milk was higher. The lower e nergy intake during 50% water restriction was compensated by a lower milk p roduction, a higher digestibility of organic matter and energy, and, appare ntly, a more efficient energy use. Through these changes and a preserved wa ter balance, the cows reached a new equilibrium at a lower water turnover l evel, which enabled them to cope with a sustained drinking water restrictio n of 50%.