|Koontz, Anne -|
|Kim, Dohyung -|
|Foote, Andrew -|
|Bush, Lowell -|
|Mcleod, Kyle -|
|Harmon, David -|
Submitted to: Journal of Animal Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: May 6, 2013
Publication Date: June 4, 2013
Citation: Koontz, A.F., Kim, D., Foote, A.P., Bush, L.P., Klotz, J.L., Mcleod, K.R., Harmon, D.L. 2013. Alteration of fasting heat production during fescue toxicosis in Holstein steers. Journal of Animal Science. 91:3881-3888. Interpretive Summary: The majority of research on fescue toxicosis has relied on animal consumption to introduce alkaloids into the system. This experiment used a ruminally dosed animal model to bypass the possibility of a reduction in intake altering the quantity of alkaloids ingested by the animal over the course of the experiment. In addition, pair-feeding was utilized to separate the effects of reduced energy intake and alkaloid consumption on energy metabolism. The goal of this experiment was to use these methods to evaluate the interaction between consumption of endophyte-infected tall fescue and environmental temperature on basal metabolism in Holstein steers. Ingestion of endophyte-infected tall fescue resulted in decreased fasting heat production 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, and may alter rumen passage rates in animals grazing endophyte-infected pastures. In addition, a reduction in metabolic rate may lead to the compensatory gain often observed in cattle entering the feedlot after grazing endophyte-infected pastures.
Technical Abstract: This study was designed to examine alteration of fasting heat production (FHP) during fescue toxicosis. Six ruminally cannulated Holstein steers (BW=348 ±13 kg) were weight-matched into pairs and utilized in a two period crossover design experiment. Each period consisted of two temperature segments, one each at 22°C and 30°C. During each period, one steer per pair was ruminally dosed twice daily with 0.5 kg of ground endophyte-infected fescue seed (E+), the other with ground endophyte-free fescue seed (E-) for 7 d. Animals were pair-fed with E+ animals offered alfalfa cubes at 1.5 x NEm. On d 8 of each segment, animals were moved to individual metabolism stalls fitted with indirect calorimetry head-boxes. Rumen contents were removed, weighed and subsampled for DM determinations. The reticulorumen was washed and filled with a buffer (NaCl=96; NaHCO3=24; KHCO3=30; K2HPO4=2; CaCl2=1.5; MgCl2=1.5 mmol/kg buffer) that was gassed with a 75% N2 and 25% CO2 mixture before rumen incubation. During buffer incubation, an E+ or E- fescue seed extract was added at 12 h intervals to maintain treatment presentation to the animal. After a 12-h wait, heart rate (HR), O2 consumption, CO2 production, and urinary output were recorded for 16 h. There was no difference (P > 0.9) in DMI or DMI/kg.75 between endophyte treatments by design; however, intake decreased (P < 0.01) at 32°C. Increased temperature had no effect on other measurements and there were no significant interactions of temperature and endophyte treatment. Heart rate was unaffected by fescue treatment or environmental temperature. Percent DM of rumen contents as well as total rumen DM/kg.75 was increased (P < 0.0001) in E+ animals. Respiratory quotient was elevated (P = 0.02) in E+ animals. O2 consumption decreased (P = 0.04) and CO2 production tended to be reduced (P = 0.07) during E+ treatment. Calculated FHP (kcal/kg BW.75) was also lower (P = 0.006) in animals receiving E+ treatment. These data suggest that consumption of endophyte infected tall fescue by cattle results in a reduction in basal metabolic rate.