Submitted to: Journal of Animal Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/10/2008
Publication Date: 2/3/2009
Citation: Brown, K.R., Anderson, G.A., Son, K., Rentfrow, G., Bush, L.P., Klotz, J.L., Strickland, J.R., Boling, J.A., Matthews, J.C. 2009. Growing steers grazing high versus low endophyte (Neotyphodium coenophialum)-infected tall fescue have reduced serum enzymes, increasedhepatic glucogenic enzymes, and reduced liver and carcass tissue mass. J. Anim. Sci. 87:748-760.
Interpretive Summary: It is well established that grazing Neotyphodium coenophialum-infected forages results in reduced weight gain and serum prolactin levels of cattle. The objective of this study was to determine the potential effects of toxic endophyte-infected tall fescue consumption on carcass characteristics, blood metabolites, and content of proteins critical for AA metabolism in the liver, kidney, and LM tissue of growing steers. The results of this study indicate that steers grazing tall fescue infected with high levels of endophyte-for at least 89 d displayed classic signs of fescue toxicity. Novel findings were made regarding the relationship between classic serum indices of fescue toxicosis and altered expression by the liver, kidney, and skeletal muscle of several enzymes and transporters critical to interorgan N and carbon metabolism. As a consequence, this research has revealed that the potential for increased liver metabolism of L-aspartate and oxaloacetate, and the shuttle of these carbons into a critical glucogenic precursor (phosphoenolpyruvate) is increased in liver, but not kidney or skeletal muscle, of steers grazing endophyte-infected tall fescue pastures.
Technical Abstract: It is well established that grazing Neotyphodium coenophialum-infected forages results in reduced weight gain and serum prolactin levels of cattle. The objective of this study was to determine the potential effects of toxic endophyte-infected tall fescue consumption on carcass characteristics, blood metabolites, and content of proteins critical for AA metabolism in the liver, kidney, and LM tissue of growing steers. Experimental treatments consisted of steers grazing either a low toxic endophyte (LE; 0.023 µg/g ergot alkaloids) mixed grass-tall fescue pasture (n = 9; BW = 266 ± 10.9 kg; 5.7 ha) or a high toxic endophyte (HE; 0.746 µg/g ergot alkaloids) tall fescue pasture (n = 10; BW = 267 ± 14.5 kg; 5.7 ha) from June 14 through at least September 11 (= 89 d). No treatment difference was observed for BW (P < 0.10) for the overall 85 d growth period. Also, no differences was observed for ribeye area/100 kg HCW (P < 0.91), backfat (P < 0.95), or backfat/100 kg HCW (P < 0.67). However, ADG (P < 0.01), slaughter BW (P < 0.05), hot carcass BW (P < 0.01), dressing percentage (P < 0.01), ribeye area (P < 0.01), whole liver wet weight (P < 0.01), and whole liver wet weight/100 kg of end live weight (P < 0.01) were greater for LE steers than HE steers. After 85 d of grazing, serum levels of alkaline phosphatase (P < 0.05), alanine aminotransferase (P < 0.01), aspartate aminotransferase (P < 0.03), cholesterol (P < 0.01), lactate dehydrogenase (P < 0.01), and prolactin (P < 0.01) were lower for HE than LE steers. At slaughter, hepatic content of cytosolic phosphoenolpyruvate carboxykinase (P < 0.01) was higher in HE steers than LE steers. Hepatic content of aspartate aminotransferase (P < 0.01) also was higher, whereas renal and LM content were not (P = 0.42). No treatment differences (P = 0.15) were observed for hepatic, renal, and LM content of alanine aminotransferase, glutamate dehydrogenase, glutamine synthetase and three glutamate transport proteins. These data indicate that the HE steers displayed classic endophyte toxicity symptoms for growth and blood parameters, classic symptoms that were concomitant with novelly-identified altered glucogenic capacity of the liver and decreases in carcass characteristics.