GROWTH OF YEARLING HORSES COMPARED TO STEERS ON HIGH-ENDOPHYTE AND LOW-ENDOPHYTE INFECTED TALL FESCUE

A grazing study was conducted to determine whether grazing endophyte-i nfected tall fescue (Festuca arundinacea Schreb.) will adversely affec t the growth and development of horses. Average daily gain (ADG), chan ge in wither height, and rectal temperature were measured for yearling horses grazing paddocks with either high- or low-endophyte infection levels (greater-than-or-less-than 75% or less-than-or-equal-to 25%). Y earling steers were grazed in paddocks of similar infection levels as a control group for comparing ADG and rectal temperature. Average dail y gain for yearling horses on the high-infection level (.24 kg) was lo wer (P <.01) than for those on the low-infection level (.56 kg). Steer ADG was .23 and .69 kg for the high and low infection levels, and hor se ADG was not different (P >. 10) from that of the steers for either the high or low infection levels. Change in wither height for horses, and rectal temperatures for both horses and cattle did not differ betw een the high- and low-infection levels. Results of this study indicate d that weight gain by horses grazing endophyte-infected tall fescue ca n be reduced to a similar extent as that of cattle.