Geldings behaving badly

Some horses display stallion-like behaviour despite appearing to have been castrated. Before embarking on exploratory abdominal surgery, how do you distinguish between those with a retained testis (cryptorchid or “rig”) and those that just behave badly?

One technique is to assess resting serum testosterone concentrations to identify horses with functioning testicular tissue.

Recently published research suggests that testosterone levels vary through the year and that this should be borne in mind when interpreting the results. Apparently, spring is the best time to use a serum testosterone assay to confirm the presence of a suspected retained testicle.

Researchers at the Gluck Equine Center, University of Kentucky, and the University of California Davis (UCD), examined data from blood samples submitted from suspected cryptorchids to the clinical endocrinology laboratory at UCD.

Serum from 179  suspected cryptorchids with serum testosterone greater than 100pg/ml were included in the study. In the UCD laboratory, testosterone levels lower than 50pg/ml are interpreted as evidence of absence of testicular tissue, while levels >100pg/ml confirm the presence of testicular tissue.

The research team found that serum testosterone concentration varied with season, being higher in spring than at other times of the year and lower in fall compared with summer and winter. Concentrations of testosterone reached a peak in May and were lowest in November.

They also noticed a significant association between age and testosterone concentration – with testosterone levels  being lower in cryptorchids less than two years old. Testosterone levels also declined  in horses older than nine years old.

They advise that borderline low testosterone concentrations found late in the year might still be positive – so a further test should be performed the following spring if the animal continues to display stallion-like behaviour.

Horsecare smartphone app released

US veterinarian Doug Thal has developed a new smartphone app to help horse owners with equine health matters.

The aim of the app is not to replace the owner's veterinarian, but rather to improve the quality of communication between horse owner and vet, for the benefit of the horse, he says.

Dr. Thal believes that horses receive the best care from well-educated owners that have a strong relationship with their veterinarian. “In fact, good communication with your veterinarian at the onset of equine healthcare problems will likely give you more options, cost you less in the long run, and enable you to do the best by your horse“.

Horse owners are increasingly turning to the internet for information about horse health, he says. Sometimes they do so instead of calling the veterinarian. Too often this approach results in inappropriate or delayed treatment, and may eventually cost more.

Dr Thal, an equine veterinarian for 20 years, states that the Horse Side Vet Guide™ (HSVG) provides easy access to essential equine healthcare information, powered by a constantly growing knowledge base. “The idea that a horse owner could make an observation and immediately access credible information about that observation- literally “horse side” – is the driving concept behind this product”.

All the text records in HSVG  are downloaded to the phone, and so are available at any time, even without access to the internet. Videos, providing short demonstrations of skills that might be needed in an emergency, as well as anatomy images and tables of normal values, are also stored in the quick reference section. However, in order to keep the size of the app reasonable, access to many other videos, media, and outside resources do require an internet connection.

Horse Side Vet Guide is currently available for iPhone and costs $4.99.  An Android version is being developed.

Further details are available from: http://horsesidevetguide.com/

Australian search for anthelmintic plants

Scientists in Western Australia have been investigating the anthelmintic effect of various plant extracts. In a laboratory investigation, they screened extracts of 37 plants to see if they inhibited the development of cyathostome eggs. The results have been published in the journal Veterinary Parasitology.

Extracts from seven species completely inhibited larval development. A further ten species  resulted in 90% inhibition compared with controls.

The research team then took the seven most effective plants extracts and tested how their inhibitory effects were affected by diluting them. The most effective plants,  Alectryon oleifolius and Duboisia hopwoodii, had IC50 (concentration that resulted in a 50% inhibition of development) of 47.2μg/ml and 30.9 μg/ml respectively. In comparison, ivermectin had an IC50 of 0.0000817μg/ml - considerably more effective.

Further tests showed that the effective constituents of many of the plant extracts were likely to be tannins. Tannins may limit palatability, so plants whose anthelmintic  properties rely on them may not be ideal candidates.

However, the researchers identified two plants, Acacia melanoxylon and Duboisia hopwoodii, with anthelmintic properties that were not reliant on tannins.

A further consideration was that the plants may contain other constituents with possible adverse effects.  For example,  D hopwoodii, the most effective plant tested in this study, contains alkaloids such as nicotine and nornicotine, which are toxic for animals.

The search for plants with anthelmintic properties for use in horses is still in the early stages. This study looked at the effect on larval stages, while any anthelmintic would have to be effective against adult worms. Further work also needs doing to identify the active    constituents of the plant that are responsible for the anthelmintic effect.

Eventually, it may be possible to isolate and concentrate the active compound. The researchers calculated that a daily intake of 120g of the anthelmintic plants would expose parasitic worms in the horse's colon to concentrations of 1400 μg/ml – the concentration used in the initial screening test. So it would be feasible exert control over the helminth population by grazing pasture containing the plant or including it in the diet as a feed additive.

They conclude: this study “suggests that Australian plants may be useful in forming part of an integrated parasite management program for horses, but more studies are needed before developing appropriate applications.”

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