Control of Horn Flies (Haematobia irritans) and Gastrointestinal Nematodes and Its Relation with Growth Performance in Stocker Cattle12

The objective of this study was to assess the effects of horn fly and gastrointestinal (GI) nematode control on the performance of stocker cattle grazing Bermudagrass in Louisiana. A total of 168 (56 per trial) weaned calves were available for 3 trials. Stocker cattle were stratified by sex and BW and randomly assigned to 2 replicate treatment groups. The treatments were 1) no horn fly or GI nematode control; 2) horn fly control administrated with insecticidal ear tags, sprays, and pour-ons; 3) GI nematode control administrated every 28 d with fenbendazole; and 4) both horn fly and GI nematode control. Lengths of the trials were 84, 98, and 112 d for trials 1, 2, and 3, respectively, and trials were initiated in early to mid-May of each year. Horn fly and fecal egg counts were conducted periodically. Stocker cattle treated for horn flies had lower (P < 0.05) fly counts than control cattle for each trial; however, counts for treated stocker cattle ranged from 42 to 62 flies per side. Stocker cattle treated with fenbendazole had lower (P < 0.01) fecal egg counts than controls 14 d posttreatment in all 3 trials. In trials 1 and 2, stocker cattle treated for both horn flies and GI nematodes had 0.14 and 0.23 kg greater ADG (P < 0.06), respectively, compared with untreated stocker cattle. Under the conditions of this study, even with a lack of effective horn fly control, improved growth rates were achieved for stocker cattle when treated for both external and internal parasites.