WATER PARTITIONING AND INTAKE PREDICTION IN DRY AND LACTATING HOLSTEIN COWS

Data from four energy and N balance trials with lactating Holstein cows (n = 329) and-one trial with dry cows (n = 60) were used to predict free water intake and water-related traits. Lactating cows were between 36 and 159 DIM and, individually, were allowed ad libitum water and forage (com silage without or with wilted haycrop silage) plus concentrates; dry cows accessed ad libitum water and single forages (grass, clover, or alfalfa, as hays or as wilted silages, or com silage) varying in maturity. Intake of DM per day and dietary DM percentage were significant and positively related predictors of free water intake in dry and lactating cows. Daily milk yield (range 16 to 52 kg/d) was related linearly to water consumption (.60 L/kg of milk), and season effect in lactating cows was curvilinear; peak water intake was in late June and nadir in late December. Ration CP percentage (DM basis) affected free water intake only in dry cows; 1 unit of increase resulted in an increase of about 1 kg/d in water intake between 12 and 13% CP. As ration moisture dropped from 70 to 40%, free water intake increased about 7 L/d in dry cows, but this was accompanied by a drop of 15 L/d in total water intake (free plus feed water). Free water intakes were predicted with R2 of .64 and .69 in dry and lactating Holstein cows, respectively. Fecal water and urine outputs also were predicted. We found no significant relationship between DM content of the diet and the resulting ad libitum intake in either dry or lactating cows.