HUNGATE, R. E. (University of California, Davis), ROBERT A. MAH, AND MOGENS SIMESEN. Rates of production of individual volatile fatty acids in the rumen of lactating cows. Appl. Microbiol. 9:554-561. 1961.-The rumen fermentation rates in individual lactating cows were measured in four different experiments. The results disclosed that the amounts and proportions of volatile acids formed could vary widely. In one case, a marked difference in the proportions of the acids produced arose within the experiment and correlated with a difference in the proportion of methane formed. The average rate of production per day was 10.5 moles butyric acid, 12.8 moles propionic acid, and 40 moles acetic acid. Manometric estimations of rate gave lower results than those obtained by the zero-time method, due to delay after sampling and to failure of the acids to liberate stoichiometric quantities of carbon dioxide. For those experiments in which zero-time rates were estimated, the average specific absorption rates, i.e., the amount absorbed per hour per micromole of acid l This work was supported in part by research grant E-1266 from the National Institute of Allergy and Infectious Disease. in the rumen, were 0.37 for butyric acid, 0.38 for propionic acid, and 0.26 for acetic acid. The carbon dioxide, acids, and microbial cells produced in the rumen fermentation are estimated to account for about 90 % of the carbon found in the milk and respiratory CO2 of the cows. The carbon dioxide from the fermentation was about 27 % of the carbon dioxide exhaled. Butyrate-1-C14 infused continuously into Hay, grain, and water 12:15-12:45 the portal vein 2nd sample 16:35 AP-II 1st sample 7:40

The transfer rate of the glucose pool in sheep was estimated by methods using labeled glucose. Transfer rates ranged from 0.28 to 0.39 g/hr/kg3/4 when estimated 1 or 16 hr after feeding, but were only 0.18 and 0.20 g/hr/kg3/4 when estimated 96 hr after feeding. Comparable values calculated from data in the literature for rats, dogs, and man range from 0.25 to 0.40 g/hr/kg3/4 at 16 hr after feeding, although they are higher for rats only 4 hr after feeding (0.89 g/hr/kg3/4). Comparison of postabsorptive values (4 hr in rats, 16 hr in sheep) or fasting values (16 hr in rats, dogs, and man, 96 hr in sheep) suggests that the over-all rate of glucose metabolism is lower in sheep.

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