THE HORSE LISTENER

Sometimes you just don’t know what you don’t know

CANDIDA BAKER recently discovered that wormers ain’t wormers, when it comes to those pesky little cyathostomes.

Eighteen months ago I adopted a beautiful grey thoroughbred mare, Tyra, to come to my place with a few young ones in order to be their matriarch. A job, I must say, she did in a splendid fashion, keeping them in order, but kindly.

I fell in love with her extremely gentle and loving nature, and very quickly decided that she’d found her forever home with me.

When she arrived, the first thing I did was to worm her. I knew that she had been wormed regularly; I was careful about rotating wormers; she was coming onto a ten-acre paddock with plenty of feed that had not been over-stocked, and she had good weight on her, so all in all, she was (and is) a very healthy large mare.

However, I noticed as soon as she arrived that she had some grey-horse melanomas under her chin, and a few tell-tale bumps around her bum, and when Richard Gregory, from Mullumbimby Veterinary Clinic, my dentist and also my vet, came to do her teeth, he confirmed there were a few in her mouth. I also knew, having cared for several grey horses with them, that horses, as Richard says, are more likely to die with them than because of them, so I wasn’t too concerned.

She was also scouring a little when she arrived, and in the weeks after, but again, it was something that didn’t surprise me too much, I’d seen horses come from very dry areas arrive onto the lush green grass of the Northern Rivers, and take some months to adjust to the (usually) plentiful grass. I checked with Richard, and he suggested I should add a product such as Dynavyte or Fibre Protect into her feed as well, to help boost the probiotics in her gut, and I duly did that.

Both products certainly helped, and I’m a fan of both of them for keeping horses really healthy – plus horses seem to truly love the taste of Fibre Protect. For a long time, the scouring was so minimal that it seemed that it was possibly just a case of an older horse, a different diet, and potentially internal melanomas, and since Tyra was obviously fit, happy and active, it didn’t occur to me that it could be another problem.

But back in August, just when I was due to go on holidays for over a month, the scouring suddenly got worse. I brought forward my next worming because of being away, and mentioned to the people feeding her for me that if she was still scouring when I got back I would do something about it, and fit it in with her Hendra vaccination – particularly important in our area because of the amount of bats present flying over pasture.

When I got home, Tyra was still scouring – although not as badly – and I also noticed she had a couple more new lumps and bumps. They seemed a little different to the melanomas, more like raised bumps after a mosquito or tick bite, so I treated them with some antiseptic cream, and called the vet to organize the Hendra appointment, and asked him to give her a general health-check.

And this was when I found what I didn’t know. “She’s showing signs of a cyathstomin infection,” he told me.

I knew enough to say that I wormed her regularly and rotated wormers regularly. “Yes,” he said, “but do you use a wormer that kills all cyathostomes?” he asked.

Now, I know full-well that worming strategically involves worming your horse based on the parasite lifecycle, and the lifecycle of different parasites mean that they may be more active at different times of the year – with autumn and spring being the most important times to worm all horses.

What I didn’t know is that in a lot of older horses who have been on mectin, as in ivermectin-based wormers, for some years, the small strongyles, i.e the cyathostomes, have developed resistance. Research suggests that it is not just a problem of resistance, but also that it’s possible the dormant/hypobiotic larvae within the intestinal wall are able to evade the wormer because it can’t penetrate the intestinal wall at great enough concentration.

Typically, a horse with an overload of cyathostomes will experience scouring, and perhaps the presence of small sores – often referred to as summer sores – as well. Also the encysted larvae can live in the animal’s large intestine for anything from two months up to three years before symptoms appear, depending on the species. If untreated the horse may become lethargic, have extreme diarrhoea and possibly colic.

I was at least able to say to myself that Tyra was still in fine fettle, just scouring a little, with the presence of these tiny mosquitostyle bites, but I felt very guilty that I had not done my ‘worm’ homework more thoroughly. It seemed as if she had been a host for these worms for sometime, and because of all the logical reasons associated with her scouring, I had overlooked the importance of changing my wormer to one that would counteract all worms.

Richard recommended Equest Gel, if I wanted to do only one treatment since it has proven efficacy against the dormant stages, or a product such as Equimax Elevation, with a second treatment two-to-four weeks later. When I researched further, I also read that the combination of the ivermectic, pyrantel and praziquantel is actually supposed to help delay resistance, although that has not been scientifically proven.

I got so interested in the different brands of wormers and what they do, I disappeared down a worm-hole for several days. (One warning, a wormer that only contains mectin plus a tapewormer should be not be used in horses less than two-years-old because of the risk of Ascarid worms in foals resistant to mectin based wormers.)

What I discovered was that when I was worming her, it was helping, and accounted for the lack of severity of her symptoms. However, the resistance to the wormer and the fact that the cyathostomes she was carrying were the type that can have arrested development meant that the symptoms were on-going.

If I’d also thought outside the square I might have got a Faecal Egg Count (FEC)

Candy administers worming medication

At left: Photomicrograph of encysted mucosal cyathostomin larvae in the large colon and worming medicine. Main image: Candy and Tyra. (Photography: Paulina Howfield.)

done which could have given me an instant insight into the worms she was carrying, that were not being killed by my choice of wormers. The good thing about an FEC is that it can mean less reliance on wormers, and more targeted treatments as well.

So I found out that I didn’t know what I didn’t know, and I’m very happy to report that Tyra responded incredibly quickly to the treatment. Richard recommended following up with another worming dose, Equixmax this time, rather than Elevation, a few weeks later, which I duly did. Tyra now has absolutely zero scouring, and is looking as fit as a fiddle, and I’ve learned yet another valuable lesson.

Candida Baker runs a Facebook page, The Horse Listener. She is also the President of Equus Alliance.

Equine Cyathostominae

Etiology: There are two nematode subfamilies: the Strongylinae (large strongyles) and Cyathostominae (known variously as small strongyles, small redworms, trichonemes, cyathostomes, or cyathostomins).

Epidemiology Eggs are shed by horses of all ages, the life cycle is direct, infective larvae develop seasonally on pasture, and hypobiotic cyathostomin larvae can cause severe disease when they resume development in late winter.

Signs

General strongylosis: Ill-thrift, weight loss, poor hair coat, and impaired performance

Verminous arteritis (associated with

Strongylus vulgaris): Variable, including colic and diarrhea

Larval cyathostominosis: Rapid weight loss, often with sudden onset diarrhea Clinical pathology: Strongylid eggs in feces (except disease caused by larvae); reduced hemoglobin, erythrocyte counts, and packed cell volumes; leukocytosis; eosinophilia (with migrating larvae); reduced hemoglobin, erythrocyte counts, and packed cell volumes; leukocytosis; eosinophilia (with migrating larvae); hyperglobulinemia, particularly IgG(T).

Larval cyathostominosis: Ivermectin, moxidectin. Cyathostominae (small strongyles/cyathostomins) – eight general – over 50 species, of which 10 occur commonly.

• Direct, non-migratory life-cycle. • Adult stages – large intestinal. • Prepatent period – 6 to 20 weeks. • Arrested larval development in large intestinal mucosa – period of arrest may be from several months to two to three years duration.