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Effects of internal parasite infection at feedlot arrival on performance and carcass characteristics in beef steers
Forty-three cross-bred steers from the Southeastern U.S. (239.74 ± 35.15 kg initial BW; 3.95 ± 0.50 initial BCS; 387.86 ± 131.69 days initial age) were used to examine the impact of internal parasite infections of beef steers at feedlot arrival on subsequent feedlot performance and carcass characteristics. Upon arrival at a SW Iowa feedlot, fecal samples were obtained and cattle were dewormed with a label dose of eprinomectin. Fecal samples were obtained 24 d later for repeat analysis. Cattle were fed as a singular pen and were harvested on 2 different dates based on estimated carcass composition. Serial weights and carcass data were collected by Tri-County Steer Carcass Futurity. Total fecal egg count (FEC) on d 0 was 92.07 ± 109.50 eggs per gram (EPG) with a range from 0 to 466 EPG. Parasite population was 92.35% strongyles and coproculture revealed strongyle population was 58% Cooperia, 14% Haemonchus, and 28% Ostertagia. Fecal exams performed on d 24 detected 0 parasites. For post hoc statistical analysis, steers were categorized into 2 groups based on FEC at processing (≤99 EPG, LO; ≥ 100 EPG, HI). Data were analyzed using the MIXED procedure of SAS, with REPEATED measures used where appropriate. The HI cattle were younger than LO cattle (P = 0.02; 317.69 d vs. 418.27 d); therefore, age at arrival was used as a covariate when significant (P ≤ 0.10). Over the duration of the feeding period, HI cattle had lesser BW than LO cattle (P = 0.03). When compared to LO, HI had reduced ADG during the first 24 d on feed (P = 0.05; 1.60 kg vs. 1.86 kg); however, overall ADG for the feeding period did not differ between groups (P = 0.62; 1.61 kg vs. 1.64 kg). When compared to LO, HI tended to have lesser marbling scores (P = 0.08; 1063.85 vs. 1112.33), dressing percentages (P = 0.09; 60.45% vs. 61.32%), KPH (P = 0.07; 2.15% vs. 2.42%), and back fat (P = 0.07; 1.08 cm vs. 1.21 cm) at harvest. Rib eye area, yield grade, and hot carcass weight did not differ between classification groups (P ≥ 0.15). In summary, although steers with fecal egg counts above 100 eggs per gram at feedlot arrival effectively responded to anthelmintic intervention, they had lesser BW throughout the feedlot phase and tended to have altered carcass composition and reduced marbling scores at slaughter.
Keywords: Beef, Feedlot, Parasite