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Reactive oxygen metabolites (ROM) and advanced oxidation protein products (AOPP) as influenced by energy intake and niacin supplementation in the periparturient dairy cow
Increasing metabolic requirements related to late pregnancy, calving, and initiation of lactation may result in augmented production of ROM and, if not compensated by endogenous antioxidants, in oxidative stress. Niacin, as a precursor for NAD+ synthesis, upregulates the expression of glucose-6-phosphate dehydrogenase, the rate-limiting enzyme in the pentose phosphate pathway and the principal source of cellular NADPH. Increased levels of NADPH decrease cellular ROM through regulating ROM-generating oxidases or by maintaining anti-oxidant enzymes in active form. We hypothesized that niacin by increasing NAD(P)H levels ameliorates oxidative stress in dairy cows and that this effect will differ depending on the portion of concentrate in the diet fed during late pregnancy and the first 100 d of lactation. Fifty-six Holstein cows were studied from d 42 ante partum (a.p.) through d 100 post partum (p.p.), and were assigned to 1 of 4 treatment groups (n=14 each) in a 2 × 2 factorial arrangement of the level of concentrate feeding (high or low concentrate portion in the diet), with or without 24 g/d of niacin from d -42 to d 24. Blood was collected in weekly intervals (3 d intervals around calving). Derivatives of ROM (dROM; indirect photometric assessment of free radicals) were measured in all serum samples, and AOPP (marker of oxidative protein damage) in sera from d -42, -21, 14, 21, 28 and 35. Data were analyzed by the MIXED procedure of SAS using repeated measure analysis (P< 0.05). The model included the effects of diet, niacin, time, and 2- and 3-way interactions of main effects with time. Serum concentrations of dROM were not affected by concentrate level or niacin supplementation, and no interactions between concentrate and niacin, as well as no 3-way interactions between treatments and time on dROM concentrations were observed. Serum concentrations of dROM were affected by time reaching a nadir around calving, and increasing immediately thereafter to relatively constant concentrations slightly higher than a.p. Serum AOPP was not different between treatment groups, but changed over time. Decreasing dROM values around calving might result from increased antioxidant protection. The two serum markers of oxidative stress selected herein yielded no effects of diet or niacin, however, markers of antioxidant status should additionally be considered.
Keywords: niacin, energy intake, oxidative status, dairy cow