SummaryTwo lactation trials were undertaken to evaluate the effect of a niacin supplement on milk production and 'the physiological symptoms of ketosis. Blood ketone and non-esterified fatty acid levels were lower and blood glucose concentrations higher in niacin-supplemented cows. These trends were exhibited regardless of whether supplementation began 2 wk prepartum or immediately after calving. A 6 g daily dose was found to be of equal or higher benefit than a 12 g supplement. Cows gi ven niacin consistently produced more milk than controls, though the difference was small.

No abstract

Amino acid composition and nucleic acid content of pure cultures of rumen bacteria (17 species) were analyzed. Amino acid composition between gram-positive and -negative organisms was not different. The total nitrogen content of gram-negative bacteria (10.8%) was significantly higher than gram-positive organisms (9.9%). Deoxyribonucleic acid-nitrogen: total nitrogen (mg/g) differed between gram-positive (8.8) and gram-negative (18.9) bacteria, but there was no significant difference in ratio of ribonucleic acid-nitrogen to total nitrogen. In a second experiment six rumen-fistulated cattle were fed either a high roughage (85% alfalfa hay plus 15% concentrate) or high concentrate diet (15% alfalfa hay and 85% concentrate). Cattle were adapted 14 days and rumen contents sampled on 3 consecutive days. Nitrogen content was higher in protozoa from cattle fed low concentrate (8.4%) than in protozoa from cattle fed high concentrate (7.9%) but was similar in bacteria for both diets. Deoxyribonucleic acid nitrogen: total nitrogen (mg/g in bacteria decreased from 27.2 in cattle fed the low concentrate diet to 20.9 in those fed the high concentrate diet. Differences between sampling days were significant for both bacteria and protozoa for ratio of deoxyribonucleic acid-nitrogen to total nitrogen but were significant only in protozoa for ratio of ribonucleic acid nitrogen to total nitrogen. Ribonucleic acid may serve as a marker for estimating microbial production in the rumen if sources of variation are recognized and corrected adequately.

No abstract

SummaryTwo lactation trials were undertaken to evaluate the effect of a niacin supplement on milk production and 'the physiological symptoms of ketosis. Blood ketone and non-esterified fatty acid levels were lower and blood glucose concentrations higher in niacin-supplemented cows. These trends were exhibited regardless of whether supplementation began 2 wk prepartum or immediately after calving. A 6 g daily dose was found to be of equal or higher benefit than a 12 g supplement. Cows gi ven niacin consistently produced more milk than controls, though the difference was small.