Effects of internal parasite infection at feedlot arrival on performance and carcass characteristics of beef steers

Data from 36 southeastern steers (237 ± 33 kg of BW; 3.96 ± 0.46 BCS; 374 ± 117 d of age) were categorized into 2 groups (n = 23, LO; n = 13, HI) based on fecal egg count at feedlot arrival (< 100 eggs/g, LO; ≥ 100 eggs/g, HI). Cattle were managed as a single group and slaughtered when the average 12th-rib fat thickness was 1.15 cm. Although HI BW was not different at feedlot entry (P ≥ 0.69), HI tended to have lesser BW than LO cattle throughout the feedlot phase (P = 0.08). When compared with LO, HI tended to have reduced ADG during the first 24 d on feed (P = 0.15); however, overall ADG did not differ (P = 0.61). A greater proportion of HI tended to be treated during the feedlot phase and tended to be treated more frequently (P = 0.12), resulting in a 4-fold increase in treatment cost (P = 0.08) compared with LO. When compared with LO, HI tended to have lesser back fat (P = 0.11), LM area (P = 0.06), and marbling scores (P = 0.11) at slaughter. Hot carcass weight, DP, KPH, and YG did not differ between classification groups (P ≥ 0.16). Although HI cattle effectively responded to anthelmintic intervention, they did not exhibit compensatory gain, tended to be a greater health risk, and tended to have altered carcass composition at slaughter, highlighting the importance of parasite management before feedlot arrival.