The Caterpillar Is Innocent

By Jenny Taylor -- As a scientist with over 20 years of veterinary diagnostic experience, I have found it is important to have a basic understanding of the physiology of an animal to identify a causative disease problem. Look to the animals and let them tell you what is happening.

In 2001 and 2002, I blood-tested a large group of mares in Kentucky to determine the patho-physiologic changes that occurred in mares that aborted in association with mare reproductive loss syndrome (MRLS). A summary of my finding was presented in the June 2002 edition of the Journal of Equine Veterinary Science. For the first six months of the study, the Woodford and Hagyard-Davidson-McGee veterinary laboratories ran my blood evaluations. Any major horse farm that checked the blood of horses at that time can verify the trend of elevated values. The conclusions that I arrived at were supported by published scientific research quoted at the end of the Journal article.

The culprit for MRLS was an unseasonable weather-induced pasture change, which caused pregnant mares to have an acute nitrogen overload, and subsequent ammonia-induced abortions. This nitrogen overload/ammonia toxicity explains previously unaccounted for MRLS conditions, such as the pericarditis and ocular symptoms, fetal hypoxia, and the overgrowth of specific bacteria.

The flocculation that occurs in affected fetuses, as observed by ultrasound, can be explained due to the fact that protein in plasma and amniotic fluid precipitates out of solution when exposed to excessive ammonia. Excessive ammonia formation in the body has also been previously well recognized as a cause of abortion and fertility problems in sheep, cattle, and humans. However, no research has been done in the horse.

The presence of the Eastern tent caterpillar (ETC) was merely an indicator of the pasture areas that were most affected. These insects are nitrogen eaters and congregate where their food source is most abundant, so horses grazing in their vicinity are more likely to be at risk from this high nitrogen area. As for the ETC experiments, it must be kept in mind that just because a mare aborts does not mean it is the cause of MRLS. The daily forced-feeding of 50 grams of a noxious caterpillar will cause mares to abort due to the high histamine levels from an allergic reaction on exposure to a foreign protein. If one first autoclaves the caterpillar, there is denaturation of this protein, and thus no reactive abortion. There is no known histamine involvement with MRLS.

Further questions that should be asked are:

--Were the caterpillars involved in the previously recognized spikes in abortions in 1980 and 1981?

--Where is the ETC now that similar spikes in abortions are occurring in the fall of 2002?

The answer to both questions is that they were and are conspicuously absent.

The recognition of the nitrogen/ammonia component of the MRLS abortions represents a most important breakthrough in mare reproductive physiology. Kentucky has the best foal growing pastures in the world, which is why it was so drastically affected, but due to the changing global weather conditions this will be occurring elsewhere with increasing frequency. Kentucky has the opportunity to be the world leader in directing research and eliminating this syndrome.

From my studies in 2001 and 2002, through the monitoring of nitrogen and ammonia levels in the mares' blood, I found that the affected mares could be identified before they aborted. It was possible to identify mares with placentitis associated with the "red bag" syndrome before delivery, and corrective measures could be taken to save affected foals.

It has been shown that putting pregnant mares in dry lots or muzzling mares can prevent MRLS, but this is only a stopgap measure. In my studies I used the blood results of the mares to determine the changes necessary, in the areas of pasture management and feeding practices to pregnant mares, which can eliminate this mare abortion problem overnight. Please let us re-evaluate the direction of the current research projects or the industry will likely face more multi-million-dollar losses worldwide in the following years. With this knowledge we have the ability to reduce the abortion rate from this syndrome to close to zero.

Jenny Taylor is an Australian scientist.