Monday, July 14, 2014

Hair analysis to monitor excess selenium intake

Analysis of tail and mane hair could be used to identify horses that have been exposed to high levels of selenium in their diet, according to recent research.

Selenium is an essential mineral,  required in small amounts to allow the body to function properly. It works as an antioxidant, especially when combined with vitamin E. It plays a role in thyroid function and in the immune system.

But you can have too much of a good thing. And excessive amounts of selenium in the diet can lead to chronic selenium toxicosis (selenosis).

Typically this is the result of grazing selenium rich pasture. Another possible source of excessive selenium is over zealous feeding of selenium-containing dietary supplements.

Typical signs of horses with chronic selenium poisoning include weight loss, hair loss (especially affecting the mane and tail), and lameness in all four limbs. The hoof may separate at the coronary band  and in severe cases the hoof wall may slough off.

Serum samples can be used to detect current high blood selenium levels.

Now scientists, led by Dr T. Zane Davis, at  the U.S. Department of Agriculture 's Poisonous Plant Research Laboratory, in Logan, Utah, have demonstrated that mane and tail hair analysis can be used to identify previous periods of excessive selenium intake.

They analysed the mane and tail hairs of horses exposed to high levels of selenium in their diet. The pasture on which these horses had been grazed, over the previous three summer grazing periods, had a high content of seleniferous plants. The water also contained high levels of selenium.

Selenium is incorporated into the tail hair as it grows and remains more or less unchanged thereafter. So by measuring the selenium content of sequential segments of the hair, the scientists were able to demonstrate the fluctuations in selenium content over time. They identified an increase in selenium content that coincided with the turnout onto pasture and a decline in selenium concentration as the horses came off the pasture later in the year.

In one case they were able to demonstrate the pattern of fluctuating selenium concentration in the tail hair extending back for three years.

They conclude that in some cases hair samples can be used to determine Selenium exposure in horses for up to 3 years post-exposure.

For more details see:
Analysis in Horse Hair as a Means of Evaluating Selenium Toxicoses and Long-Term Exposures.
Davis TZ, Stegelmeier BL, Hall JO.
J Agric Food Chem. 2014 Jun 2.
DOI: 10.1021/jf500861p

Saturday, July 12, 2014

Warning of multiple anthelmintic resistance

Research published recently in the International Journal of Parasitology warns of  impending multi-drug resistance in strongyles on British Thoroughbred stud farms.

The study, involving scientists in Edinburgh, Bristol and Liverpool, looked at the efficacy of  anthelmintics against worms  in horses on 16 stud farms.

To assess the efficacy against strongyles, faecal worm egg count reduction (FECR) tests were carried out on samples from 429 horses. Faecal  egg counts were performed before and 14 -17 days after treatment with one of the four available broad-spectrum anthelmintics: ivermectin; moxidectin; pyrantel or fenbendazole.

Moxidectin was efficacious in all tests, resulting in mean faecal egg count reduction in the range of 99.8-100%. Ivermectin showed reduced efficacy (FECR 85.7% -100%) in one group of yearlings. Five groups of yearlings showed reduced efficacy of pyrantel (FECR ranging from 0-13%). However, pyrantel was still efficacious when administered to mares. Fenbendazole always had low efficacy (FECR  0.4 – 42%).

A different pattern of efficacy was found against the large roundworm Parascaris equorum. Tests  carried out on four farms showed reduced efficacy of ivermectin (FECR  25.5% – 91.2%). However fenbendazole had acceptable efficacy (FECR 97.5% – 99.9%).

The research team also performed faecal egg counts at about 2 week intervals after anthelmintic treatment for up to 12 weeks to determine the strongyle egg reappearance period for moxidectin, ivermectin and pyrantel. They found that the egg reappearance period for all three anthelmintics was shorter than had been observed previously. This is considered to be an early indicator of developing resistance.

“Overall,” they conclude, “our results indicate that ivermectin and moxidectin administration provided acceptable efficacy at 14 days; however, egg reappearance period results suggest that these products are working less effectively than measured previously. As shortened egg reappearance period is believed to be an early indicator of resistance, this highlights the issue of impending multi-drug resistance in strongyles on stud farms.”

For  more details see:

Anthelmintic efficacy on UK Thoroughbred stud farms.
Relf VE, Lester HE, Morgan ER, Hodgkinson JE, Matthews JB.
Int J Parasitol. 2014 Apr 15. pii: S0020-7519(14)00078-2.
doi: 10.1016/j.ijpara.2014.03.006

Thursday, July 10, 2014

Foals from genotyped frozen embryos

In a European first, scientists at the French Institute of the Horse and Equitation (IFCE) and the French National Institute for Agricultural Research (INRA) have announced the births of four foals from the transfer of genotyped and cryopreserved embryos.

They explain that the goal of this work is to better understand embryonic development, control livestock reproduction, and maintain breed genetic diversity. Furthermore, the researchers claim advantages for the horse industry in being able to determine the traits of a future foal.

The technology to maintain embryo viability following genotyping and cryopreservation was developed at the INRA Loire Valley centre at Nouzilly. Seven days after fertilization, embryos were collected from Welsh ponies from INRA’s resident herd. The embryos were genotyped: scientists sampled some of the embryos’ cells to analyse their genomes. In this experiment, embryos were selected based on sex, the idea being to use sex-based selection to test the technique’s feasibility. The embryos were then cryopreserved in liquid nitrogen (at -196°).

Then last summer, several embryos were transferred into saddlebred mares at the IFCE Haras du Pin centre. The foals were born in May 2014. They were of the expected sex: two females and two males.

This is the first time that such an event has taken place in Europe, and it is the product of more than 10 years of various types of embryonic research carried out by INRA and IFCE scientists.

Although embryo preservation techniques are already well developed for cattle, small ruminant species, and even humans, preserving horse embryos is a very complex process. For instance, horse embryos vary greatly in size: 7-day-old embryos range in diameter from 200 to 700 micrometers. It is very difficult to cryopreserve the largest embryos because the liquid inside them forms ice crystals when the embryos are frozen at very cold temperatures. What’s more, horse embryos are surrounded by a capsule that interferes with successful cryopreservation.

The scientists say that being able to cryopreserve embryos will allow us to maintain breed genetic diversity, particularly that of breeds with small population sizes. Furthermore, the factor that currently limits the use of embryo transfer is its cost: the transfer centre has to maintain a team of recipient mares that are reproductively synchronized with the donor mares. Cryopreservation means that the transfer doesn’t have to take place immediately; it can wait until a recipient mare becomes available to receive the embryo. Finally, it may now be possible to directly repopulate horse herds that have experienced losses as a result of various issues, such as disease-related problems, instead of having to use the indirect technique of crossbreeding. 

Why genotype the embryos? The scientists explain that genotyping allows them to choose the embryos they want to use based on different criteria: sex, as in this experiment, the absence of known genetic disorders, or, perhaps in the future, other traits that are tied to behaviour, such as emotivity or sociability. “It is advantageous for the horse industry to be able to determine the traits of a future foal. We will next aim to simplify the process—to make this technology more accessible and user friendly for those in the horse industry.”

For more information (in French):
http://www.inra.fr/portail/Grand-public/Genetique/Tous-les-magazines/Des-poulains-issus-d-embryons-genotypes-et-cryoconserves

Wednesday, July 09, 2014

Equine Oncology Resource

Neoplasia is relatively uncommon in horses compared with other species. Melanoma, squamous cell carcinoma and lymphoma are the usual culprits. Many veterinarians will spend their whole career without identifying any other type. But others do occur. And the new Oncology Virtual Issue from Equine Veterinary Education (EVE), the sister publication to the Equine Veterinary Journal, provides a useful resource of information about many different neoplastic conditions.

The first part consists of case reports and clinical commentaries. These are available free online. The second part provides an equine oncology resource, with review articles on selected neoplastic conditions, which are again free, together with numerous other articles covering topics ranging from skeletal and spinal neoplasia, to neoplasia of the thorax, head and reproductive glands.

More details:

Oncology Virtual Issue Part I: Case Reports and Clinical Commentaries

Oncology Virtual Issue Part II: Equine Oncology Resource