AbstractThe objective of this study was to investigate the effects of silage characteristics on water intake of lactating dairy cows and to examine the prediction of water intake. Sixteen grass silages, differing in fermentation and intake characteristics, were offered ad libitum to dairy cows in early lactation supplemented with 7 kg/day of concentrate (13·3 MJ metabolizable energy per kg dry matter (DM) and 216 g crude protein per kg DM). Four silages were offered in each of four incomplete change-over design experiments, consisting of three 3-week periods. Water intakes were recorded through individual Kent water meters and press water bowls over the final week of each period. Tree (drinking) water intake ranged from 20·1 to 89·9 (mean = 45·2; s.d. = 12·96) I/day whilst total water intake (also including food water) ranged from 48·4 to 123·8 (mean = 87·3; s.d. = 14·12) I/day. Water intake increased with increasing silage DM concentration, however free water replaced silage water at a rate less than 1. Milk yield and silage D value (digestible organic matter, g/kg DM) were strongly positively correlated with free water intake (r = 0·751 and 0·595 respectively), though fermentation indices were not good single predictors of water intake. Further analysis revealed problems owing to collinearity within the predictors of water intake: DM intake, silage D value and milk yields being significantly correlated, as were pH and volatile fatty acids as a proportion 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 yield and silage pH. The use of fermentation information, whether from titration or high-performance liquid chromatography did not describe real variation in water intake beyond that described by silage pH. Free water intake was higher with higher diet DM concentrations, higher milk yields and higher silage pH.
Factors affecting feed intake and feed efficiency of lactating dairy cows