Factors Affecting Diet Selection in Sheep Fed Endophyte-Infected Toxic Fescue

Tall fescue (Lolium arundinaceum (Schreb.) S.J. Darbyshire) infected with toxin producing fungi can induce fescue toxicosis in grazing ruminants, reducing performance and altering forage intake. Chemical compounds in red clover (Trifolium pratense), such as biochanin A, have been proposed to mitigate these effects by improving palatability and blood vessel relaxation. This study examined whether the inclusion of ground red clover (GRC), either alone or in combination with hydroxypropyl methylcellulose (HPMC) and polyethylene glycol (PEG), affected voluntary diet selection in lambs offered toxic fescue. Thirty three lambs were housed individually and assigned randomly to one of four diets: (1) toxic fescue silage (CONT), (2) silage + 5% GRC (RC5), (3) silage + 10% GRC (RC10), or (4) silage + 5% GRC with HPMC and PEG (RC5+) during two experimental periods. Diet refusal was measured daily from each lamb over 7 days following a 14-day dietary adaptation, and neutral detergent fiber (NDF) content was analyzed for all feeds and refusal. Differences in percent refusal and NDF intake were not different (P > 0.05) among diets. Linear mixed model and stepwise regression analyses confirmed that diet refusal was unrelated to red clover inclusion or NDF change. Therefore, under the tested conditions, GRC supplementation did not significantly alter diet selection. Another interesting finding was that reliable diet selection data could still be obtained when sheep were fed below the typical 10% refusal threshold used to define ad libitum intake in digestion studies.