Effect of rumen protected niacin and vitamin C additives on productive performance of lactating Friesian cows under heat stress condition

Twenty four lactating Friesian cows with average live body weight of 500 kg and 2-4 of lactation seasons after the peak of lactation were divided into four similar groups (6 cows each) according to their live body weight, milk yield and number of lactation season. All cows were fed a basal ration consisted on DM basis50% concentrate feed mixture + 30% corn silage + 20% rice straw. Cows were unsupplemented in G1and served as control, or supplemented with rumen protected niacin or vitamin C at 10 g/head/ day in G2 and G3, respectively, or rumen protected niacin and vitamin C at 5 g/head/day of each in G4. The animals were under THI range from 78.49 to 83.57. Group 4 showed significantly (P<0.05) the highest digestibility coefficient of all nutrients and subsequently TDN and DCP values, while the lowest values were seen in the control (G1). Ruminal pH value for G4 was lower significantly (P<0.05) compared to other groups and the values were within the suitable range for rumen fermentation. The concentration of NH₃-N was higher significantly (P<0.05) in rumen liquor of G1 compared to other groups. Group 4 had the highest TVFA’s concentration, whereas G1 had the lowest concentration (P<0.05). Concentrations of total protein, globulin and glucose were increased significantly (P<0.05), however, albumin to globulin ratio, concentrations of urea-N and creatinine as well as the activity of AST and ALT were decreased significantly (P<0.05) with supplementation rumen protected niacin and vitamin C or its mixture. Group 4 showed significantly (P<0.05) the highest yield of actual and 4% fat corrected milk, the percentages of fat, protein, solids not fat and total solids as well as all milk constituents yield compared with other groups and the highest output of 4% FCM and net output as well as the improvements of output and net output followed by G2 and G3, while G1 had lowest values.