One of the coccidiostats can and should be used once the calves are weaned and grouped together. The product chosen should be continued for the time directed on the label for the anti-coccidial effect. The calves are highly susceptible at that age and will certainly be exposed to coccidia, so it is reasonable to protect them. Those in research, including here at USU, have looked at a whole host of medications and products and have found only a couple that are somewhat effective. These are used for human treatment, but are much too expensive for calves.
Colostrum is important for prevention of most diseases of newborn calves.
It is especially important in the prevention of Crypto. Feed at least two quarts of colostrum within one to four hours of birth and repeat that within 12 hours. Some dairies are feeding a gallon of colostrum at the first feeding and find it works well. If problems continue, it may be necessary to sample some calves at 3-5 days of age to determine their absorption of colostrum. Sanitation is important for Crypto as this organism is very resistant.