PSI-2 Effects of extended release eprinomectin on heifer performance while grazed on endophyte-infected tall fescue or housed in drylot

Abstract

Abstract Objectives were to evaluate the effects of LongRange, an extended-release eprinomectin, on beef heifer performance while grazed on endophyte-infected tall fescue or housed in drylot. Fall-born, Angus × Simmental heifers (n = 153) were utilized in a split-plot design. Heifers were stratified by BW and assigned to 6 groups. Groups were randomly assigned to 1 of 2 environmental treatments: grazed endophyte-infected tall fescue (Pasture) or housed in drylot and fed alfalfa hay. Within environmental treatment groups, heifers were randomly assigned to LongRange (LR) or control (Saline). Prior to experiment initiation, heifers were treated with oral fenbendazole (SafeGuard) to minimize parasite load. Data were analyzed using the MIXED procedure of SAS. At d 0, 56, and 112, heifer BW, ADG, BCS, hair coat score (HCS), and fecal egg counts (FEC) were collected. Treatments did not affect (P ≥ 0.17) BW on d 0 and 56. On d 112, drylot heifers tended (P = 0.08) to be heavier than pasture heifers and LR increased (P = 0.01) BW. There was an interaction (P = 0.02) for ADG; LR increased ADG to a greater magnitude in pasture than drylot heifers. On d 0, 56, and 112, there was no interaction or LongRange effect (P ≥ 0.11) on BCS; however, pasture heifers had greater (P = 0.05) d 112 BCS than drylot heifers. On d 56, there was an interaction (P = 0.01) on HCS; LR decreased HCS in pasture heifers, but did not affect HCS in drylot heifers. Although treatment did not effect (P ≤ 0.33) FEC at d 0, there was an interaction (P = 0.01) observed on d 56. LongRange decreased FEC in pasture heifers but not in drylot. In conclusion, LongRange increased heifer growth performance with a greater difference for heifers grazing tall fescue, compared with heifers in drylot.