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Relation of Ambient Temperature and Time Postfeeding on Ruminal, Arterial and Venous Volatile Fatty Acids, and Lactic Acid in Holstein Steers ^1,2,4,

Department of Daity Husbandry, University of Missouri, Columbia 65201

ABSTRACT

Four fistulated and catheterized (coccygeal artery and jugular vein) Holstein steers consuming a pelleted high concentrate diet were subjected to cool (12.8 C and 30% relative humidity) and hot (35 C and 25% relative humidity) treatments for 3 weeks. Ruminal fluid, arterial and venous blood samples were collected prior to feeding and up to 7 hours thereafter during the final 2 days of each treatment. Samples were analyzed for volatile fatty acids and lactic acid. The hot environment was associated with decreased feed intake and increased rectal temperature and respiration rate. Ruminal and arterial total volatile fatty acids peaked earlier in the hot environment and declined at a slower rate with time postfeeding. Acetate was the major metabolite responsible for the difference. Increased ruminal lactate occurred earlier in the hot treatment. Venous volatile fatty acid peaks in hot were relatively smaller than in the cool treatment, suggesting a greater volatile acid metabolism and utilization from arterial blood in the hot temperatures. Relationships between eating a meal and blood metabolite are shown by these data. The effect of volatile fatty acids and lactic acid may be different in hot than in cool ambient temperatures.

¹ Contribution from the Missouri Agricultural Experiment Station. Journal Series 5856.

² These data are from the Ph.D. thesis presented by M. Mishra while a participant in the USAID Study Program, University of Missouri.

⁴ Supported in part by grant funds from U.S. Public Health Service Biomedical Division.

³ Present address: College of Veterinary Science and Animal Husbandry, Orissa University of Agriculture and Technology, Bhubaneswar-3, Orissa, India.