Investigation of dietary niacin supplementation on milk production and composition of Holstein dairy cows in Qom province

This study was performed using 12 multi parturient dairy cows in postpartum stage of early lactation period. Animals were assigned randomly to a 4×4 single Latin square crossover design. Treatments and periods were 4 and the length of each period was 21 days which records were collected at the end of week 3 of each period. Treatments were as as follow: control group (no niacin supplementation), 12 g, 14 g, and 16 g niacin supplementation. Daily milk records were collected and milk samples were analyzed every 15 days regularly. The results showed that niacin supplementation had a significant effect on milk yield (both raw yield and 3.5% and 4% FCM) (p<0.05). Row milk yield, 3.5% and 4% FCM milk yields were higher in 14 and 16 g niacin groups than 12 g niacin and control groups. Also niacin supplementation had a significant effect on milk compositions including milk protein, total solids and solid not fat percentages (p<0.05), but not on milk fat and lactose percentages. In conclusion, higher levels of niacin improved milk production and composition compared to lower levels. As a final result, 16 g niacin per day had the highest effect on the productive parameters in contrast to other treatments.