Fescue toxicosis is a syndrome of cattle consuming endophyte-infected tall fescue. The endophyte provides a hardiness to the plant allowing the plant to grow in stressful conditions such as drought and cold temperatures. However, the endophyte produces ergot alkaloids that are detrimental to cattle performance. Cattle experience hormonal changes in the production of and response to natural serotonin that result in lower heat tolerance and reduced feed intake.
Serotonin is synthesized in the body from the amino acid tryptophan. One therapy being explored is administration of 5-hydroxytryptophan, which is a step in the synthesis of serotonin from tryptophan. In a recent study, researchers at USDA-ARS tested the effect of 5-hydroxytryptophan on the response of steers fed endophyte-infected fescue seed. By providing 5-hydroxytryptophan, the researchers were able to reverse the negative effects of ergot alkaloids on blood serotonin levels and cattle feed intake (Figure 1). The control steers that were not fed endophyte-infected seed or 5-hydroxytryptophan consumed 1.9% of body weight whereas the steers fed endophyte-infected seed without 5-hydroxytryptophan consumed only 1.8% of body weight. However, when steers fed endophyte-infected seed were also given 5-hydroxytryptophan, feed intake was not different from the control steers indicating that 5-hydrxytyptophan reversed the negative effects of endophyte-infected seed on feed intake.
Giving cattle grazing endophyte-infected tall fescue a dose of 5-hydroxytryptophan would likely greatly improve the performance of these cattle. However, 5-hydroxytryptophan is not ready for commercial application yet. In this study, steers were dosed with 5-hydroxytryptophan through a rumen cannula into the abomasum, thus bypassing the rumen microbes and any possible degradation of 5-hydroxytryptophan. Before 5-hydroxytryptophan could be added to feed, a method to protect it from the rumen microbes will need to be developed. However, this molecule shows great potential to improve performance of cattle grazing endophyte-infected tall fescue.
