Effects of dietary fiber on intake, milk yield, and digestion by lactatingdairy cows during cool or hot, humid weather

Lactating cows were offered diets with increasing neutral detergent fiber c oncentrations to determine the effects on intake, milk yield and compositio n, blood hormones, and nutrient digestion during cool or hot weather condit ions. Tifton 85 bermudagrass hay was substituted for corn silage so that th e forage portion of diets were: 1) 40% corn silage (control), 2) 32.4% corn silage, 7.6% bermudagrass, 3) 24.8% corn silage, 15.2% bermudagrass, or 4) 17.2% corn silage, 22.8% bermudagrass (dry basis). Dietary neutral deterge nt fiber concentrations (% dry matter) were 30.2, 33.8, 37.7, and 42.0, res pectively. Intake of dry matter declined with increasing dietary neutral de tergent fiber during cool and hot periods, but intake adjusted for cool wea ther treatment differences did not change further during hot weather. Milk yield declined linearly with increasing neutral detergent fiber during cool weather and changed quadratically during hot weather. Milk temperature dec lined with increasing dietary neutral detergent fiber for the p.m. milking during the cool period and declined with increasing dietary neutral deterge nt fiber for the a.m. and p.m. milkings during the hot period. Digestibilit y of neutral detergent fiber improved and ruminal turnover of particulate d igesta was increased with greater dietary neutral detergent fiber content. No dietary fiber level by hot weather interaction was observed, suggesting that total energy intake may have had a greater effect on milk yield than d ietary fiber content during hot, humid weather.