|ROSENKRANS, JR, C|
Submitted to: Western Section of Animal Science Proceedings
Publication Type: Proceedings
Publication Acceptance Date: 4/13/2005
Publication Date: 6/22/2005
Citation: Rosenkrans, Jr, C., Nihsen, M., Flores, R., Yazwinski, T., Kreider, D., Coffey, K., Coblentz, W., Looper, M.L., Schrick, N. 2005. Effects of forage cultivar and anthelmintic on steer responses to immune challenge. Western Section of Animal Science Proceedings. 56:213.
Interpretive Summary: It has been estimated that tall fescue toxicosis costs cattle producers in the Southern U.S. over $500,000,000 annually in decreased productivity and increased cost of production. To date there are no pharmacological products that conclusively improve animal performance while consuming endophyte-infected tall fescue forage. Objectives were to determine the effects of anthelmintic treatment (ivermectin or fenbendazole) and forage cultivar [endophyte-infected (K31+) or non-toxic endophyte-infected tall fescue (HiMag 4)] on weight gain and immune responses of steers. Anthelmintic did not improve animal gain or immune function. This information is of interest to beef producers, extension personnel, and agricultural professionals who advise beef producers on forage/animal management practices.
Technical Abstract: A grazing trial was designed to determine the effects of anthelmintic treatment and forage cultivar on immune and metabolite responses of steers. Steers (n = 6/pasture; BW = 314 ± 19 kg) were allotted to pastures (1.62 ha) of either endophyte-infected (n = 3 pastures; K31+) or non-toxic endophyte-infected tall fescue (n = 2 pastures; HiMag 4) for 92 d. Steers were given daily access to a mineral containing fenbendazole (1 mg/kg BW). Within pasture, one-half of the steers received either ivermectin (0.2 mg/kg BW) or fenbendazole (15 mg/kg BW) every 21 d. On d-84, all calves were given an injection (i.p.) of lipopolysaccharide from Salmonella typhimurium (31.8 ug/45 kg BW). Blood samples were collected at 0, 6, 12, and 24 h post-injection. Whole blood was analyzed for blood cell counts, hemoglobin, and hematocrit. Sera were analyzed for concentrations of prolactin, cortisol, NEFA, and insulin. Fecal egg counts were determined and no internal parasite eggs were detected. Steers grazing HiMag 4 had greater (P < 0.05) weight gain than steers grazing K31+; however, ivermectin did not consistently improve steer gains. Serum concentrations of prolactin were decreased (P < 0.05) at each time point for steers grazing K31+ compared with steers grazing HiMag 4. Concentration of cortisol was decreased (P < 0.05) at time 0 for steers consuming K31+. At 6, 12, and 24 h post-injection, NEFA concentrations were lower (P < 0.05) in the sera of steers consuming K31+. Blood cell profiles were not consistently altered by forage cultivar or anthelmintic. Endophyte-infected tall fescue decreased steer gain and may alter blood metabolites associated with immune response.