Feeding strategies and shade type for growing cattle grazing endophyte-infected tall fescue

摘要

Two experiments were conducted to determine animal performance of alternative feeding strategies to heifers grazing endophyte-infected tall fescue during summer months. In Experiment 1, 40 Limousin heifers (261 (40) kg initial BW) were stratified by weight and assigned to 1 of 4 treatments in a 2 x 2 factorial arrangement of treatments. Diet factors were either a spring harvested tall fescue silage diet fed ad libitum in grass traps (Silage) or grazing endophyte-infected tall fescue pasture with grain supplement (Grain; 2.1 kg DM hd(-1) d(-1)), and shade factors were either natural (NAT; trees) or artificial (ART; 13.38 m(2)/pasture of 80% shade cloth) shade for 80 days. In Experiment 2, 40 Limousin heifers (277(44) kg initial BW) were stratified by weight and assigned to 1 of 4 treatments in a 2 x 2 factorial arrangement of treatments. Diet factors were either a traditional grain supplement (Control) or feather-meal supplement (FM) while grazing endophyte-infected tall fescue pasture, and shade factors were either NAT or ART shade for 98 days. Control and FM supplements provided an estimated 56 and 175 mg metabolizable arginine/kg BW, respectively. Heifers were weighed on two consecutive days at the start and end of each experiment. In Experiment 1, weight gain of heifers was greater (P < 0.05) in Grain than Silage treatments (0.55 vs. 0.13 kg/d) and was greater (P < 0.05) for NAT than ART shade (0.39 vs. 0.29 kg/d). cost of gain was greater (P < 0.05) for heifers fed Silage than Grain (7.26 vs. 1.56 $/kg of gain). in Experiment 2, there was no difference (P > 0.10) in weight gain or cost of gain between Control and FM supplements. Heifers with NAT shade had a greater (P < 0.05) weight gain (0.74 vs. 0.65 kg/d) and lower (P < 0.05) cost of gain (2.01 vs. 2.27 $/kg of gain) than ART shade. In conclusion, feeding early-spring harvested tall fescue silage or a supplement with high metabolizable arginine did not improve performance, and current recommendations for design of artificial shade structures may not be adequate for cattle grazing endophyte-infected tall fescue during summer.