Submitted to: Journal of Animal Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: January 20, 2001
Publication Date: May 1, 2001
Interpretive Summary: A large portion of the beef cows in the southern United States graze on fescue or bermudagrass pastures. Much of the fescue pasture in the US is infested with an internal fungus called an endophyte. This fungus actually helps the plant to be more tolerant of insect pests and drought but can have adverse effects on cattle that consume the forage. It can cause decreased immunity and heat tolerance, as well as alter fat and mineral metabolism. It seems that some breeds of cattle (Brahman for example) are more tolerant of the endophyte than other (mostly British) breeds. Therefore, we conducted this study to evaluate the effects of the endophyte on blood variables of cows and their calves and to evaluate the effects of cow genetics on these variables. The variables we studied are possible indicators of immune function, mineral metabolism, protein metabolism, fat metabolism, and general nutritional state. The results indicated that calves from crossbred cows were more tolerant of the endophyte than calves from straight-bred Angus or Brahman cows. Thus, cow-calf producers can decrease the adverse effects of the endophyte by using a sound cross-breeding program.
Technical Abstract: Over a two year period the effects of genotype and forage on blood metabolites, enzymes, and minerals were determined in Angus (AA), Brahman (BB), Angus x Brahman (AB: sire x dam), and Brahman x Angus (BA) cows, and 129 calves from these cows sired by Hereford bulls. Cows and calves grazed either common bermudagrass or endophyte infested Kentucky-31 tall fescue pastures throughout the year. Blood samples were collected via jugular venipuncture in April, August, October (weaning), and November (after 30 d in a feedlot) of each year. Plasma urea N concentrations of cows and calves were affected by forage (P < 0.01) and breed (P < 0.05). Plasma cholesterol and FFA concentrations of cows were affected by forage (P < 0.01) and breed (P < 0.05). In calves, antibody titers to infectious bovine rhinotracheitis virus were not affected by forage but were affected by breed. Serum inorganic P concentrations of calves and cows were affected by forage (P < 0.05). Serum P concentrations and alkaline phosphatase activity of calves were affected by breed (P < 0.05). Calves grazing bermudagrass had higher (P < 0.05) serum concentrations of Fe and total iron binding capacity (TIBC). There was evidence of maternal heterosis for concentrations of free fatty acids, cholesterol, aspartate aminotransferase, Ca, Mg, alkaline phosphatase, ceruloplasmin, Fe, and TIBC and evidence of grand maternal effects for plasma concentrations of urea N, cholesterol, Ca, P, Mg, and alkaline phosphatase. These results suggest that calves and cows grazing tall fescue are generally on a lower plane of nutrition than those grazing bermudagrass and that BA and AB cows and their calves seem to be more tolerant of the negative effects of the fescue endophyte than the average of their purebred contemporaries.