1822
Effects of niacin supplementation and forage type on milk, digestibility, blood parameters and body temperature in lactating dairy cows
This experiment evaluated the effect of niacin combined with either corn silage (CS) or grass silage (GS) based diets on apparent total tract nutrient digestibility, milk yield and composition, body temperature, and blood parameters. Four ruminally-cannulated Holstein cows were used in a 4 x 4 Latin square design with a 2 x 2 factorial arrangement of treatments with 28-d periods. Treatments were CS or GS based diets without or with 12 g niacin/d. One primiparous and three multiparous late lactation cows (225 ± 12 d in milk) were used. One cow was removed during the third period due to unrelated causes. Each period, dry matter intake (DMI) and milk production were recorded (d 19-28), and samples of blood (1300h, d 28), milk (0630 and 1730 h for 2 d), feeds (0545 and 1745 h on d 19-28), feces, and body temperature (both at 2-h intervals on d 26-28) were taken. Serum was analyzed for glucose and non-esterified fatty acids. Feed and feces were analyzed for acid insoluble ash, and digestibility was determined for dry matter (DM), organic matter (OM), crude protein (CP), neutral detergent fiber (NDF), acid detergent fiber (ADF), starch, fat, and hemicellulose (NDF-ADF). Data were analyzed using the mixed procedure of SAS. Orthogonal comparisons were used to evaluate main effects and interactions. Repeated measures were used to analyze body temperature and means were separated using Tukey’s test. Intake of DM was greater (P=0.01) for cows fed CS than for cows fed GS (29.01 and 24.09 kg/d, respectively). Digestibility of NDF was greater (P=0.002) for cows fed GS than for cows fed CS (63.7 and 45.8%, respectively). Digestibilities of DM, OM, ADF, CP, and starch were similar among treatments. Hemicellulose digestibility was greater (P=0.002) for cows fed GS versus cows fed CS (82.2 and 53.1%, respectively) because cows fed GS had lower DMI. Fat digestibility was greater (P=0.02) for cows fed CS versus cows fed GS (93.0 and 82.4%, respectively). Milk yield was less for cows fed GS versus CS (20.0 and 29.9 kg/d, respectively). Fat (0.77 and 1.07 kg) and protein yields (0.61 and 0.96 kg) were less for cows fed GS versus CS (P= 0.02 and 0.04, respectively). Body temperature tended (P=0.08) to be lower for cows fed GS and niacin (37.7°C) versus cows fed only CS (38°C). Niacin did not improve any parameter except for lowered body temperature.
Keywords: niacin corn silage grass silage