By Glen Aiken, USDA-ARS Forage-Animal Production Research Unit

Ergot alkaloids produced by a fungal endophyte that infects most plants of ‘Kentucky 31’ tall fescue can induce fescue toxicosis. Cattle exhibiting signs of toxicosis: 1) tend to maintain rough hair coats, 2) have elevated body temperatures that causes cattle to be vulnerable to severe heat stress, and 3) have reduced prolactin hormone concentrations that can reduce milk yields by nursing cows. Consequently, the heat stress associated with consumption of ergot alkaloids can combine with the negative impact of ergot alkaloids on dry matter intake and nutrient digestive absorption to cause average daily gain (ADG) of weaned calves to be unacceptably low for profitable stocker production or heifer development. For this reason, the 5 million acres of tall fescue in Kentucky has been primarily utilized for cow-calf production and not for stockers.

Technologies have been developed that show promise as management tools for reducing the challenges of producing stockers on tall fescue. Research has reported that new cultivars that are artificially infected with non-toxic endophytes (novel endophyte tall fescue) can alleviate the incidence of fescue toxicosis. Fescue pastures can also be overseeded with clovers to dilute ergot alkaloids in the diet and another option, chemical seed head suppression, can reduce the toxicity of the fescue and enhance forage quality.

Another management to cost effectively provide weight gains that are suitable for stocker production while reducing the effects of toxicosis on animal health is to supplement with coproducts like soybean hulls (SBH). We conducted a two-year grazing study with cross-bred steers, initially weighing approximately 500 lb., that were either fed 5.0 lb. SBH/steer/day, ear implanted with an estradiol-progesterone implant with no feeding of SBH, ear implanted and fed 5.0 lb. SBH /steer/day, or with no implant or feeding of SBH (control). The ADG for the implant-only treatment (1.78 lb./steer/day) was 12% greater than for the control, and ADG for the SBH-only treatment (2.09 lb./steer/day) was 31% greater than for the control. Combining the two treatments, however, resulted in very high ADG (2.71 lb./steer/day) that was 70% greater than the control. The implant-only treatment increased ADG without reducing the severity of toxicosis, but the SBH treatment, with and without implantation, had two-times greater prolactin concentrations and a higher percentage of sleek hair coats than these on the control treatment. Further, the cost for the increases in ADG with combining SBH and implantation were below the breakeven cost over a wide range of SBH costs and cattle markets.

Combining SBH with implanting a management approach to cost effectively produce stockers on toxic endophyte-infected tall fescue.

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