Effect of Environmental Temperature on Ruminal Volatile Fatty Acid Levels with Controlled Feed Intake

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Abstract
Six rumen-fistulated nonlactating Holstein cows were subjected to temperatures of 1.6, 18.2, and 37.7[degree] C in the climatic laboratory. Relative humidity was maintained at approximately 50%, and cows were subjected to each temperature for a period of at least 1 wk. Feed intake was kept constant by feeding through the can-nula when necessary. Rumen fluid samples were collected under controlled conditions, analyzed by gas-liquid chromatography, and data subjected to factorial analysis. Significantly different levels (P< .01) of acetic, propionic, and total volatile fatty acids (VFA) were obtained when temperatures of 18.2 and 37.7 C were compared. Differences obtained from 1.6 and 18.2[degree] C were not statistically significant (P> .05). The mean levels for acetic, propionic, and total VFA were 94.4, 37.6, 153.1; 94.7, 33.3, 147.9; and 47.2, 10.6, 66.3 mEq/liter of rumen fluid for 1.6, 18.2, and 37.7 C, respectively. These data indicate that high environmental temperatures influenced rumen VFA content when feed intake was controlled at constant levels. As temperature increased, the molar percentage of acetic acid increased, whereas the propionic acid percentage declined. The volume of water consumed was not significantly different (P> .05) between 18.2 and 37.7[degree] C, but the frequency of drinks was significantly different (P< .05).