This time of the year it is common to see cows standing in the shade and wading in ponds in an effort to find relief from the heat. Unfortunately, the summer sun is not the only factor affecting heat stress on cattle grazing Southwest Missouri pastures.
Tall fescue comprises a significant portion of most pastures in Southwest Missouri and is widely known to commonly be infected with an endophyte fungus. The endophyte fungus lives between cells within the fescue plant and provides benefits to the plant itself including drought and pest resistance. Unfortunately, the endophyte is responsible for several health related side effects in cattle grazing infected pastures. These side effects compound the heat stress experienced by cattle during the summer months.
Specifically, the endophyte produces compounds collectively called ergot alkaloids that have been identified as the toxic compounds of the fungus. These compounds act within the body of the animal to produce several undesirable side effects. These effects include poor weight gain, low milk yield, decreased reproductive performance and reduced blood flow to the extremities resulting in a decreased ability to dissipate heat. Cattle may also have decreased feed intake and exhibit a rough hair coat. Together, these side effects are termed ‘fescue toxicosis’. Because of the diminished ability to dissipate body heat, fescue toxicosis is seen most dramatically during the summer months when temperatures exceed 87 degrees Fahrenheit. Understandably, fescue toxicosis has earned the common name ‘summer slump’.
Summer slump can really add up to substantial economic loss to the producer. For this reason, many efforts have been made to discover new ways to avoid fescue toxicosis in cattle. Forage management has been the primary focus for most producers. The most reasonable approaches include pasture dilution with other grass species and legumes and mowing pastures or increasing stocking density to minimize plant maturity. Increased plant maturity correlates with increased toxicity. Pastures may also be re-established with endophyte-free fescue or fescue infected with a novel endophyte that provides the benefits to the plant without the toxicity to the animal. Crossbreeding cattle with more heat resistant breeds such as Brahman may provide some genetic resistance to summer slump. Scheduling the breeding season in the spring or fall can also help to avoid reproductive losses by avoiding the mature and more toxic pastures and extreme heat. Additionally, minimizing parasite burden has been shown to help cattle cope with fescue toxicosis more adequately.
Fescue is an excellent forage and has many advantages to the cow-calf producer in particular. Fescue toxicosis is the most significant disadvantage to this unique forage and unfortunately there is no real cure or simple, economically reasonable solution to the problem at this time. Understanding applicable pasture management and animal management are the best tools for producers to minimize the summer slump and preserve animal performance during the heat this year.
Darren Loula, DVM, is a large animal veterinarian at Fair Grove Vet Service in Fair Grove, Mo.
