A Field Trial Comparing the Effects of Supplementation with Aureomycin plus Lasalocid or Monensin on the Health and Production Performance of Dairy Calves1

Holstein female calves (n = 80) from a commercial dairy herd were enrolled in the study within 12 h after birth. At enrollment, calves were allotted randomly to 1 of 2 treatments: monensin (MSN) or aureomycin plus lasalocid (A + L). Feed supplements were mixed into their respective grain starters to provide 60 g/ton of monensin and 350 g/ton of aureomycin and 60 g/ton of lasalocid for the MSN and A + L treatments, respectively. During the first 3 wk of life, calves were fed reconstituted commercial nonmedicated milk replacer, after which they were fed pasteurized waste milk in addition to or as a replacement for milk replacer. From birth to 12 wk of age, calf starter was fed once daily, with feed intake measured and BW recorded weekly. Feed analysis demonstrated that the amounts of monensin, aureomycin, and lasalocid added to the grain starters were lower than formulated, at 44.2, 222.8, and 42.7 g/ton. Treatment did not affect ADG (MSN = 0.66, A + L = 0.64 kg/d; P = 0.42). Similarly, there was no effect of treatment on feed efficiency (MSN = 3.37, A + L = 4.72; P = 0.97). Treatment did not affect the proportion of calves diagnosed with at least 1 event of diarrhea (MSN = 79.5, A + L = 65.0%; P = 0.16) or pneumonia (MSN = 30.8, A + L = 25.0%; P = 0.53). Supplementation with aureomycin and lasalocid did not improve the performance of calves compared with those supplemented with monensin.