RESUMEN
Halofuginone lactate (HL) is registered in several countries for the prevention of calf cryptosporidiosis, but the compound's utility in the presence of co-infection with other enteropathogens is not well understood. We performed a randomized controlled field trial of the efficacy of HL for the prevention of natural calf cryptosporidiosis, in the presence of co-infection with rotavirus and Salmonella Typhimurium. Newborn calves on one farm were sequentially enrolled and allocated to a full dose (n=15), half dose (n=15), or a placebo control group (n=15), using a randomized block design. The Cryptosporidium oocysts in fecal specimens collected on Days 6, 8, 10, 14 and 20 were counted and the severity of the diarrhea was assessed using fecal consistency scores (solid, semisolid, or liquid). The oocyst numbers and fecal consistency scores were statistically compared between the groups. Ninety one percent of the calves shed Cryptosporidium parvum oocysts during the trial. The full dose group had a longer prepatent period than the control group, but no statistical difference in the number of oocysts was identified between the groups after controlling for the effects of sex and breed. The fecal consistency scores and mortality rates did not differ between the groups. These results indicated that the anti-Cryptosporidium activity and clinical benefit of HL were limited. It is concluded that in order to maximize the clinical efficacy of HL in the field, diagnostic efforts should aim to rule out the presence of other enteropathogens.