It is possible that the deworming medication you are giving your horse may not be effective in killing parasites. At least that is the belief of Dr. Ray Kaplan at the University of Georgia. Dr. Kaplan indicates that the deworming programs many horse owners and farms use was developed back in the 60s. Studies back then revealed that deworming your horse every 8 weeks was the best method and this method worked really well during the 70s and 80s because new deworming drugs were invented that were very effective.
However, now the parasites have changed and become much more resistant to the dewormers we have today. In fact, Dr. Kaplan indicates many horse owners are following recommendations from 30 to 40 years ago, many of the equine dewormers we are using today are totally ineffective and the ones that are effective are not keeping the number of parasites low for as long as they did in the past. In the 70s, the major parasite was the large strongyle that commonly caused colic. However, this parasite is well controlled at this point and the problem is the small strongyle. The problem with small strongyles is that very few dewormers are effective in killing the larval stages and the larvae cause the most problems. The larvae burrow into the wall of the intestine and then cause damage as they break out of the intestinal wall. Most dewormers kill only the adults and these larvae become adults after most of the damage has already been done. So the only method of decreasing intestine damage is to prevent pasture contamination by eggs so fewer larvae will develop. Join us next program when we will talk about methods to decrease pasture contamination.