FACTORS AFFECTING WATER INTAKES OF LACTATING DAIRY-COWS OFFERED GRASSSILAGES DIFFERING IN FERMENTATION AND INTAKE CHARACTERISTICS

The objective of this study was to investigate the effects of silage c haracteristics on water intake of lactating dairy cows and to examine the prediction of water intake. Sixteen grass silages, differing in fe rmentation and intake characteristics, were offered ad libitum to dair y cows in early lactation supplemented with 7 kg/day of concentrate (1 3.3 MJ metabolizable energy per kg dry matter (DM) and 216 g crude pro tein per kg DM). Four silages were offered in each of four incomplete change-over design experiments, consisting of three 3-week periods. Wa ter intakes were recorded through individual Kent water meters and pre ss water bowls over the final week of each period. Free (drinking) wat er intake ranged from 20.1 to 89.9 (mean = 45.2; s.d. = 12.96) l/day w hilst total water intake (also including food water) ranged from 48.4 to 123.8 (mean = 87.3; s.d. = 14.12) l/day. Water intake increased wit h increasing silage DM concentration, ho however free water replaced s ilage water at a rate less than 1. Milk yield and silage D value (dige stible organic matter; g/kg DM) were strongly positively correlated wi th free water intake (r = 0.751 and 0.595 respectively), though fermen tation indices were not good single predictors of water intake. Furthe r analysis revealed problems owing to collinearity within the predicto rs of water intake: DM intake, silage D value and milk yields being si gnificantly correlated, as were pH and volatile fatty acids as a propo rtion of total fermentation acids. The ridge regression technique was used to reduce collinearity problems and produce stable equations. The best prediction equations for water intake involved a combination of both animal and analytical information: diet DM concentration, milk yi eld and silage pH. The use of fermentation information, whether from t itration or high-performance liquid chromatography did not describe re al variation in water intake beyond that described by silage pH. Free water intake tons higher with higher diet DM concentrations, higher mi lk yields and higher silage pH.