Submitted to: Journal of Animal Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/21/2010
Publication Date: 11/1/2010
Citation: Carter, J.M., Aiken, G.E., Dougherty, C., Schrick, N. 2010. Steer responses to feeding soybean hulls and steroid hormone implantation on toxic tall fescue pasture. Journal of Animal Science. 88:3759-3766. Interpretive Summary: Tall fescue is a cool-season perennial grass that is the predominant pasture grass in the region commonly referred to as the ‘fescue belt” that extends from the lower temperate northeast to the upper subtropical southeast and west to the Great Plains. A fungal endophyte that infects most plants of tall fescue imparts tolerances to drought, heat, and grazing, and facilitates its persistence. Unfortunately, ergot alkaloids produced by the endophyte can cause fescue toxicosis. Symptoms of the malady include elevated body temperature and respiration rate, decreased prolactin concentrations, retention of winter hair coats through the summer months, and reduction in DM intake and growth. Weight gain of yearling steers grazing endophyte-infected tall fescue can be improved by implanting with steroid hormones or fed by-product feeds to dilute the ergot alkaloids in the diet. A grazing experiment was conducted to determine if feeding pelleted soybean hulls in combination with implanting with steroid hormones have additive effects on steer weight gain and favorable impacts on physiology. Results indicated that feeding pelleted soybean hulls can provide a 31% increase in average daily gain,, but weight gain can be increased 64% if steers are fed pelleted soybean hulls is combined with steroid hormone implantation. Analysis of breakeven costs showed that the additive effects of combining pelleted soybean hulls with steroid hormones implants were sufficient to achieve a net return from the additional ADG with relatively high PSBH costs (> $220/ton) and low cattle prices. A higher percentage of cattle fed pelleted soybean hulls had sleek hair coats compared to unfed steers. Combining feeding pelleted soybean hulls with steroid hormone implants can cost effectively increase weight gain and dilute ergot alkaloids in the diet to reduce the severe effect that fescue toxicosis has on weight gain and physiology.
Technical Abstract: Yearling steers were grazed on endophyte-infected ‘Kentucky-31’ tall fescue (Lolium arundinaceum) pastures for 77 days in 2007 and for 86 days in 2008 to evaluate effects of feeding pelleted soybean hulls (PSBH) and steroid hormone implants (SHI) on steer performance and physiology. Steers were stratified by body weight for assignment to six, 3.0-ha toxic tall fescue pastures. Herds with or without daily feeding of ground soybean hulls as the main plot treatment were randomly assigned to pastures. Pelleted SBH were group-fed to provide 2.3 kg/steer/d (as fed). Subplot treatments of with or without SHI (200 mg progesterone – 20 mg estradiol) were assigned to subgroups within each pasture. Treatment effects were analyzed for forage mass, average daily gain (ADG), serum prolactin, and hair coat rating. An economic analysis was conducted to determine if costs of additional ADG with PSBH feeding were below breakeven costs over a range of PSBH costs and cattle prices. Forage mass declined linearly over time, but the rate of decline was greater (P = 0.001) in 2007 than in 2008. Forage mass was never below 2300 kg DM/ha in either year. There was a tendency of SHI to affect (P = 0.063) ADG, but feeding PSBH without SHI increased (P < 0.001) ADG 31%. Combining PSBH and SHI resulted in the greatest increase (71%) in ADG (P < 0.001). Breakeven costs for PSBH without SHI over the four cattle prices were = $US 110/ton, whereas with SHI they were = $US 220/ton. Steroid implants did not affect (P = 0.826) serum prolactin concentration; however, PSBH increased (P = 0.003) prolactin concentrations two-fold. Similarly, SHI did not affect (P = 0.182) hair coat ratings, but there was a lower frequency of rough hair coats with feeding PSBH (P = 0.03). Results indicate that combining PSBH and SHI can cost effectively increase steer weight gain and that PSBH can increase prolactin concentrations and induce some shedding of winter hair.