A semicontinuous culture technique was used to investigate the influence of niacin supplementation and an N source, either NH4Cl or a soybean meal-like mixture of crystalline amino acids (AA), during a series of 6- or 24-h in vitro fermentations. Establishment of rumen-like fermentations was confirmed by low H2 concentrations and relatively normal proportions of acetate, propionate and butyrate after 3 d of incubation. Niacin supplementation (100 ppm) increased (P<.05) microbial protein synthesis (control, 7.70 vs niacin, 13.69 mg protein/g substrate added) and niacin concentration (control, 9.2 vs niacin, 16.3 μg/g spent culture) regardless of N source and length of incubation. Total pyridine nucleotide pool concentration was increased (P<.05) by niacin supplementation regardless of N source during the 6-h incubations and by using NH4Cl as the N source during the 24-h incubations. Ammonia concentration, total gas or methane production, pH, free tryptophan concentration, tryptophan content of microbial protein or total VFA production were not influenced by either N source or niacin supplementation. Under the conditions of this investigation, the semicontinuous culture technique was useful in establishing rumen-like fermentations, and under those conditions niacin supplementation increased the efficiency of microbial protein synthesis.
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Shields et al. (1983) studied this question.