Question

I get the gist of not feeding broodmares tall fescue given the risk of endophyte infection, but is there any problem feeding tall fescue to young horses like weanlings and yearlings?             

Answer

Currently, the limited research available in young horses suggests little effect of grazing endophyte-infected fescue on growth, but caution is recommended, particularly when the only source of nutrition is tall fescue with high level of endophyte infection.

A research trial conducted at Auburn University reported that growing horses grazing fescue with high endophyte levels as the sole diet exhibited decreases in average daily weight gain compared to those grazing low endophyte-infected pasture, similar to results seen in growing steers. Yet, withers height was not adversely affected.^*

In a study conducted at the University of Georgia, yearlings were fed a 60:40 concentrate-to-forage diet that contained either endophyte-infected or noninfected tall fescue hay. No differences in the average daily gain or withers height between the horses on fescue diet or the control group were reported. Researchers suggested that supplementation with high levels of concentrate may reduce any effects on growth of horses consuming endophyte-infected fescue.^**

A review article that referenced the aforementioned research and many other studies concluded that high-quality fescue could be appropriate for many growing horses.⁺ However, if a horse owner is raising weanlings and maximizing growth rates for sale or competition, endophyte-infected fescue is probably not the ideal choice, although one would expect those growing horses are also being fed concentrate feed to support rapid growth. Without additional research, the ideal ratio of forage:feed when utilizing endophyte-infected tall fescue for young, growing horses is not determined at this time, so caution is warranted.

^*Aiken, G.E., D.I. Bransby, and C.A. McCall. 1993. Growth of yearling horses compared to steers on high- and low-endophyte infected tall fescue. Journal of Equine Veterinary Science 13(1):26-28.

^**McCann, J. S., G. L. Heusner, and H. E. Amos. 1991. Concentrate and endophyte-infected tall fescue hay diets: Digestibility and effects on yearling horse growth rate. In: Proc. 12th Equine Nutrition Physiological Symposium, p. 69.

⁺Russell, M. Managing fescue for horses. Accessed August 6, 2022.