Efficacy of halofuginone lactate against Cryptosporidium parvum in calves.

The efficacy of halofuginone lactate against natural Cryptosporidium parvum infection in 150 neonatal market calves of a mixed Belgian breed was tested. The drug was administered orally in the milk replacer over a period of 3 to 14 days at doses ranging from 30 to 500 micrograms/kg of body weight. Over a period of 4 weeks, the animals were examined twice a week for shedding of C. parvum oocysts and were scored semiquantitatively for diarrhea. Weight gain was assessed after 2 and 4 weeks. Subclinical infections by rota-, corona-, and bovine picobirnaviruses were equally distributed in the different groups. In total, 93% of the unmedicated calves eliminated C. parvum within 10 days after arrival at the rearing unit and 62% of them showed diarrhea. Immediately after treatment with halofuginone was started, no more signs of Cryptosporidium-associated diarrhea were established. From the level of 60 micrograms/kg on, oocysts were no longer detected in 98% of animals 5 to 6 days after the start of treatment. Animals remained negative for at least 7 days after withdrawal of the drug. From 7 to 10 days after withdrawal, some animals excreted oocysts again. The number of shedders was closely linked with increasing doses of the drug, which indicates that lower doses do not interrupt infection completely and allow development of immunity. In this respect, a dose of 60 to 125 micrograms/kg over a period of 7 days seems most appropriate in practice. Toxic side effects were noticed only at 500 micrograms/kg.