Effects Of Nicotinic Acid And Its Antagonist On Ruminal Fermentation Parameter And Lactic Acid Metabolism In Vivo

Intake of high concentrate diet often disturbs ruminal metabolism and increaseslactate level in ruman, which results in ruminal acidosis in ruminants. The effects ofniacin and its antagonist on NAD level, ruminal fermentation parameters and lactic acidmetabolism in vivo were investigated in this study, to explore the mechanism of niacin inregulating ruminal fermentation.A self-control-case experiment design was adopted in this study. Thewhole trial period was divided into4stages. Four different diets were fed to3Jingjiangyellow cattles with rumen fistula in the4stages respectively. Cattles fed with balanceddiet(concentrate-to-forage ratio of5:5) in periodⅠ(control group, CK group), balanceddiet including891mg/kg isonicotinic acid hydrazide(with a similar mole concentration tothe niacin of period Ⅳ) in period Ⅱ(isonicotinic acid hydrazide group, IAH group), highconcentrate diet(concentrate-to-forage ratio of8:2) in period Ⅲ(high concentrate group, Hgroup), and high concentrate diet including800mg/kg niacin in period Ⅳ(niacin group,NA group) respectively. The results showed that:(1)compared with CK group, highconcentrate diet significantly caused a high level of NAD and total NAD(H)(P<0.05or0.01)，had few effect on NADH level but resulted in a big drop of NADH/NAD+(P<0.01).The reducing-sugar level had also increased a lot (P<0.05) due to a promotion effect oncarbohydrate degradation. It also had a great shift-up of concentration for volatile fattyacid(VFA) metabolite including acetic acid, propionic acid, butyric acid and total volatilefatty acid(TVFA). Similar to the VFA, the concentration of ammonia nitrogen(NH3-N) andlactic acid(LA) also be improved remarkably, so did pH in rumen (P<0.01).(2)in contrastwith effect of pure high concentrate diet,800mg/kg niacin conspicuously neutralized itsserious acidification in rumen. For example, production of acetic acid, propionic acid,butyric acid, TVFA, NH3-N and lactic acid had been remarkably depressed, which sloweddown pH decline with pH in rumen rising up to6.0in the second and third days. But, westill get the similar results for NAD+or NADH/NAD+through entire sampling period.(3)as an antagonist to niacin, isoniazid significantly increased NAD+and NAD(H) inrumen as expected when compared with results from balanced diet treatment. However,NADH showed little response to isoniazid addition. So NADH/NAD+showed a bigdownfall, similar to treatment by high concentrate diet. Yet, rumenal fermentation andlactic acid metabolism did not show any obvious change for isoniazid addition. At last,LDH activity was found to be consistent and unrelevant with lactic acid level between fourgroups.Our results demonstrated that as concentrate to forage ratio increased,NADH/NAD+declined as a consequence of NAD+level rise, production of various acidmetabolite went up followed by pH plummeting, finally ruminal acidosis happened. But, under condition of high concentrate diet, niacin addition reversed detrimental effects andprevent ruminal acidosis from happening. Isoniazid could antagonized NAD+decreasecaused by niacin but with few effect on fermentation and lactic acid metabolism.