Submitted to: Kentucky Beef Report
Publication Type: Other
Publication Acceptance Date: 6/9/2006
Publication Date: N/A
Interpretive Summary: Tall fescue is a cool-season perennial grass that is persistent under heavy grazing and lower inputs of management. Although tall fescue is the predominant grass managed in the upper transition zone, beef calves grazing fescue can exhibit toxicosis at the onset of warm temperatures. Symptoms of this malady are high body temperature, labored breathing, retainment of winter haircoat, low serum prolactin concentrations, and poor weight gain. The malady has been linked to consumption of ergot alkaloids produced by a fungal endophyte that inhabits most tall fescue plants. Poor weight gain on endophyte-infected tall fescue is a major concern of cattlemen, but there also is concern of the carry-over effects of toxicosis into the feedyard and for breeder stock reared on fescue and moved to non-toxic pastures. An experiment was conducted to compare changes over time in rectal temperature and serum prolactin, a hormone marker for fescue toxicosis, between pregnant and open heifers following grazing of either MaxQ (cv. Jesup with the non-toxic AR 542 endophyte strain) or endophyte-infected Kentucky-31 (KY31; toxic) and placed on bermudagrass pasture. Heifers grazed on the toxic KY31 had higher rectal temperatures and lower serum prolactin relative to those grazed on non-toxic MaxQ tall fescue; however, serum prolactin in KY31 heifers increased and stabilized over a 10 day period to concentrations similar to MaxQ heifers and rectal termperature in KY31 heifers declined and stabilized over an 18 day period to those similar to MaxQ heifers. Results indicated that heifers can be removed from toxic fescue pastures in the early summer and placed on non-toxic diets to alleviate heat stress in approximately 18 days. This information can be useful for preconditioning heifers that subsequent breeding or transport to the feedyard.
Technical Abstract: Rectal temperature and serum prolactin were monitored for 24 pregnant and open beef heifers following a grazing experiment that compared weight gain performance between MaxQ (non-toxic endophyte) and Kentucky-31 (toxic endophyte, KY31) tall fescue. The objective was to determine if heifers grazed on toxic tall fescue and exhibiting 2 symptoms of toxicosis (high rectal temperature and low serum prolactin) can be placed on bermudagrass (non-toxic) pastures to alleviate these symptoms over time relative to heifers that grazed MaxQ, a non-toxic control. Rectal temperatures for pregnant and open heifers grazed on KY31 declined over an 18-d period to those conducive to a healthy and non-stressed animal. Rectal temperatures for MaxQ heifers were never above a temperature to indicate heat stress but declined over an 18-d period. Serum prolactins for pregnant and open heifers grazed on KY31 were similar and both increased and stabilized in 10 d. Initial prolactin concentrations were greater for MaxQ than for KY31 heifers. Although prolactins in pregnant and open MaxQ heifers decreased and stabilized in 10 d, the stabilized concentrations were greater in pregnant heifers. Results showed that heat stress can be alleviated in 18 d and further indicated that alkaloids produced by the MaxQ endophyte can cause some shift in the physiology of heifers that may not be of consequence to animal health.