Water intake by dairy cows selected for high or low milk-fat percentage when fed two forage to concentrate ratios with hay or silage

Water intake (n = 24 cows) and fluid balance (n = 8 cows) were studied in S wedish Red and White Dairy cows selected for low (LFI) and high (HFI) milk- fat content but selected for similar 4% fat-corrected milk yield. Four diet s were given in a changeover experiment of four periods. The forage content of the diets was either grass hay (H) or grass silage (S). The diets consi sted on a dry matter (DM) basis of either 50% forage and 50% concentrates ( 50), or 30% forage and 70% concentrates (30). Milk yield (MY) was higher fr om LFI than from HFI cows (27.5 vs. 22.0 kg d(-1)). LFI cows drank 12% more water than the HFI cows (71.3 vs. 63.6 l d(-1)). Hay-based diets H50 and H 30 caused a higher intake of drinking water than did silage-based diets S50 and S30 (74.7 and 71.1 vs 61.1 and 62.9 l d(-1), respectively). Total wate r intake per kg DM was significantly increased with S50, compared with all other diets. Cows fed the S50 diet had a 24% higher urine excretion and 16% higher faecal fluid losses. Predicted water intake, based on linear regres sion analysis, resulted in the formula: Intake of drinking water = 14.3 + 1 .24 x MY + 0.32 x DM content of the diet (R-adj(2) = 67%).