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Relationships between End Products of Rumen Fermentation and Utilization of Metabolizable Energy for Milk Production¹

Dairy Cattle Research Branch, Animal Husbandry Research Division, Beltsville, Maryland

W. E. Stewart

University of Maryland, College Park

ABSTRACT

Three rations in which the proportion of estimated net energy (ENE) derived from hay or a concentrate mixture of corn meal and soybean meal was varied from 50% hay-50% concentrate (Ration A) to 75% hay-25% concentrate (Ration B) or 100% hay (Ration C) were fed to six, mature, lactating Holstein cows. The end products of rumen fermentation (total methane production and molar proportions of volatile fatty acids in the rumen) were studied in relation to lactation efficiency. Indirect calorimetry was used to measure the efficiency of utilization of metabolizable energy (ME).

The molar proportion of acetic acid present in the rumen declined from 71.4 to 65.3% (P < .05) as alfalfa hay ENE was replaced with concentrate ENE. A nonsignificant increase in propionic acid from 16.0 to 18.4% and an increase in butyric acid from 7.9 to 10.4 molar per cent occurred.

The proportions of digestible carbohydrates calculated to be fermented, using a theoretical fermentation balance equation proposed by Wolin, were 86, 84, and 81 % for Rations A, B, and C, respectively.

The simple correlations between volatile fatty acid (VFA) proportions and lactation efficiency were: r = –0.73 for acetic acid, +0.43 for propionic acid, and +0.67 for butyric acid (P < .05).

¹ Data taken from a thesis presented by C. E. Coppock in partial fulfillment of the requirements for the Ph.D. degree, University of Maryland, January, 1964. Scientific Article No. A1131, Contribution No. 3585 of Maryland Agricultural Experiment Station, Department of Dairy Science.

² Ralston-Purina Research Fellow, 1960–61.

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