Effects of water restriction following feeding on nutrient digestibilities, milk yield and composition and blood hormones in lactating Holstein cows under heat stress conditions

The effects of water restriction following feeding under heat stress conditions on nutrient digestibilities, milk yield and composition and some blood hormones in lactating Holstein cows were evaluated. The design was completely randomized with 30 high producing lactating Holstein cows (80.8 +/- 40.5 DIM) which were assigned to two treatment groups (15 cows per treatment). Treatments were free access to water (FAW) and 2 h water restriction (2hWR) following feeding. Average temperature-humidity index (THI) in the farm was over 80 throughout the experiment which defines heat stress conditions. Neutral detergent fibre, organic matter and ether extract digestibilities increased by water restriction (P<0.05); however, crude protein, acid detergent fibre, nitrogen free extract and dry matter digestibilities were not affected (P>0.05). Water intake was recorded daily during the digestibility period and was not different between FAW and 2hWR group (P>0.05). Fat corrected milk was higher in 2hWR group than FAW group (P<0.05). Milk fat was higher (P<0.05) in 2hWR group than the FAW group whereas milk protein, urea nitrogen, and solids not fat were not different among the treatment groups (P>0.05). Somatic cell counts were greater in 2hWR than FAW group (P<0.05). Free fatty acid concentration in blood was not affected by treatments (P>0.05). Blood prolactin and growth hormone were higher in 2hWR group than the FAW group (P<0.05). It is concluded that water restriction for 2 hours following feeding improved nutrient digestibility of some dietary components and increased milk fat percentage in lactating Holstein cows under heat stress conditions.