Niacin, Metabolic Stress and Insulin Resistance in Dairy Cows

Abstract

The periparturient period in cows is associated with metabolic stress and a state of negative energy balance, which are characterized by increased lipolysis, ketogenesis, hepatic steatosis, oxidative stress and insulin resistance. Such metabolic changes may exert adverse effects on the health and milk yield of lactating cows. The pharmacoki netics of niacin in ruminants is specific as rumen microorganisms facilitate both the synthesis of tryptophan and the degradation of niacin. Niacin administration to cows leads to an increase in the coenzyme activity, encompassing the activity of nicotinamide adenine dinucleotide (NAD) and nicotinamide adenine dinucleotide phosphate (NADP). These coenzymes are actively involved in the metabolism of lipids and carbohydrates, whereas NAD protects the organism from oxidative stress. In periparturient cows, the supplementation of niacin has been found to induce depressed lipolysis and a limited impact of nonesterified fatty acids on all metabolic processes. It also results in decreased lipid peroxidation regardless of the magnitude of lipolysis in the periparturient period. Furthermore, niacin reduces the concentration of ketone bodies, thus preventing the development of fatty lever disease and ketosis in cows. The anti-inflammatory effect of niacin is manifested in stimulating the secretion of adiponectin and inhibiting immune cells. Our results suggest [ 28] that blood NAD and NADP concentrations are a sensitive indicator of the niacin status of cows. The NAD concentrations obtained ranged from 860 to 895 pmol/mL in the control group in the weeks before and after calving. In niacin-supplemented cows, the following NAD concentrations were obtained: 1724.6 pmol/L in the week of calving (week 0), 1968.6 pmol/mL in the first week after calving and 1771.8 pmol/L in the second week after calv ing. The NADP concentrations obtained in the control group ranged from 385.09 to 425.62 pmol/ mL during the entire period under consideration. In niacin-supplemented cows, the following NADP concentrations were obtained: 704.45 pmol/L in the week of calving (week 0), 778.36 pmol/L in the first week after calving and 796.18 pmol/L in the second week after calving.