|KOONTZ, ANNE - University Of Kentucky|
|FOOTE, ANDREW - University Of Kentucky|
|KIM, DO HYUNG - University Of Kentucky|
|BUSH, LOWELL - University Of Kentucky|
|MCLEOD, KYLE - University Of Kentucky|
|HARMON, DAVID - University Of Kentucky|
Submitted to: Kentucky Beef Report
Publication Type: Experiment Station
Publication Acceptance Date: 9/1/2012
Publication Date: 1/1/2014
Citation: Koontz, A.F., Foote, A.P., Kim, D., Bush, L.P., Klotz, J.L., Mcleod, K.R., Harmon, D.L. 2014. Alteration of basal metabolic rate in Holstein steers during fescue toxicosis. Kentucky Beef Report. pgs. 7-9.
Interpretive Summary: This study evaluated the energy status of steers exposed to tall fescue seed with or without an associated fungus (endophyte). Ingestion of endophyte-infected tall fescue results in decreased fasting heat production (a measure of metabolic rate) in cattle. This is indicative of a reduction in maintenance energy requirements and may be related to a decrease in liver size or other metabolic activity in animals grazing endophyte-infected pastures. In addition, a reduction in metabolic rate may lead to the increased (compensatory) gain often observed in cattle entering the feedlot after grazing endophyte-infected pastures. This study aids researchers in understanding how toxins produced by the fungal endophyte found in tall fescue cause decreased performance in animals with fescue toxicosis and also will aid producers who use tall fescue pastures in managing their cattle.
Technical Abstract: The results of this study indicate that consumption of E+ tall fescue by cattle results in a reduction in basal metabolic rate. Six ruminally cannulated steers were weight-matched and pair-fed during a two period crossover experiment. Each period consisted of two temperatures (22°C and 30°C). During each segment, one steer per pair was ruminally dosed twice daily with ground endophyte-infected fescue seed (E+), the other with ground endophyte-free fescue seed (E-). On d8 of each segment, animals were moved to individual metabolism stalls fitted with indirect calorimetry head-boxes. Rumen contents were removed, weighed and subsampled. The reticulorumen was washed and filled with a buffer and an E+ or E-fescue seed extract was added at 12h intervals. After a 12h wait heart rate (HR), urine production, O2 consumption, and CO2 production were recorded for 16h. There was no difference in intake between endophyte treatments by design; however, intake decreased at 30°C. Increased temperature had no effect on other measurements. HR was unaffected by fescue treatment or temperature. DM of rumen contents as well as total rumen DM/ kg BW.75 increased in E+ animals. O2 consumption decreased and CO2 production tended to be reduced in E+ animals. Fasting heat production was reduced in E+ animals, suggesting that animals consuming E+ fescue use less energy for maintenance.