Genetic defect associated with painful eye condition identified

An interdisciplinary team of scientists and clinicians, led by Dr. Rebecca Bellone at the University of California Davis Veterinary Genetics Laboratory, has identified a genetic variant associated with distichiasis in Friesian horses. 

Distichiasis, is a condition affecting the eye in which aberrant hairs grow from abnormal positions along the eyelid. These hairs rub on the cornea, causing irritation and pain. Severe cases may progress to corneal ulceration, leading to vision impairment and even loss of the eye. 

 

The condition can be treated, by removing the offending hairs, for example with thermocautery. However, the condition has been reported to recur in up to 50% cases.

 

Friesians are by far the most likely breed to be affected. They are known for being relatively highly inbred and prone to a range of genetic diseases. This knowledge prompted the research team to investigate the genetic basis of the condition. 

 

For a start, researchers traced the family trees of affected horses which provided evidence of an autosomal recessive mode of inheritance. Then they conducted a Genome Wide Association Study comparing samples from 14 affected and 38 normal animals. This narrowed down the search to a section of the ECA13 chromosome.

 

Investigating the ECA13 further with Whole Genome Sequencing, they identified a large chromosome deletion between two genes that was strongly associated with distichiasis. 

 

Eighteen out of 19 affected Friesian horses were homozygous for (had two copies of) the distichiasis associated variant. This pointed to a recessive mode of inheritance.

 

However, seven out of 75 horses with no evidence of distichiasis were also homozygous for the variant. This led the research team to suggest that distichiasis in Friesians appears to be a trait with incomplete penetrance. (That is, the condition may be expressed in only some individuals that have two copies of the variant, while some homozygous individuals may never show signs of the condition.)

 

To see if the variant occurs in other breeds, they tested samples from 955 horses of 54 different breeds and identified the deletion in only 11 non-Friesians, all of which only had one copy of the variant.

 

"Given the strong association and the frequency of the variant in the population of Friesian horses we evaluated, testing for this variant can be used to avoid crosses that can produce animals homozygous for the variant," said Erin Hisey, the UC Davis veterinary student who was the first author on this study. 

 

Additionally, the results of this test can be used clinically. "Those horses that test homozygous for this variant should be evaluated for abnormal lashes to potentially provide clinical intervention prior to the development of irreversible corneal damage," said Dr. Hanneke, co-author of the study and equine surgeon with a focus in ophthalmology.

 

For more details, see:

 

Whole genome sequencing identified a 16 kilobase deletion on ECA13 associated with distichiasis in Friesian horses. 

Hisey, E.A., Hermans, H., Lounsberry, Z.T. et al. 

BMC Genomics 21, 848 (2020). 

https://doi.org/10.1186/s12864-020-07265-8

 

https://vgl.ucdavis.edu/news/vgl-led-team-identifies-genetic-variant-distichiasis-friesians

Evaluating the impact of lameness on movement and muscle activity

New research is looking at how the pattern of muscle activity changes to produce the altered gait seen in lame horses.

Lameness is a common reason for veterinary examination. Current diagnostic methods rely heavily on subjective assessment, including observing how the horse shifts weight between legs at rest and when moving. More subtle changes in gait can be detected using kinematic gait analysis.

 

To date, interest has concentrated on the changes in gait that occur in lameness, but little is known about the changes in patterns of muscle contractions that lead to the gait alterations.

 

Research, led by Dr Lindsay St George, Research Fellow at the University of Central Lancashire (UCLan), aims to look at how a horse’s muscles and limb movements adjust to accommodate lameness. 

 

“We know that horses alter their movement pattern when they’re lame, but we don’t know much about the functional changes in muscles that facilitate these changes in movement,” she said. “We want to define muscle activity in clinically sound, non-lame horses, and then use this knowledge to quantify adaptive changes in muscle activity that occur when a horse is lame.”

 

St. George’s team uses surface electromyography (sEMG) to quantify muscle function and 3D motion capture technology to quantify movement in horses. 

 

sEMG is a non-invasive technology that measures muscle activation by recording the electrical activity produced by skeletal muscles when they contract. This study uses Delsys Trigno sEMG sensors, which are small, wireless sensors attached to the horse’s skin over-lying superficial muscles of interest.

 

This study builds on previous work by St. George and her colleagues at Utrecht University*. They placed sEMG electrodes over selected muscles and reflective kinematic markers on each horse’s forelimbs, hindlimbs and back. Each horse was then trotted down a hard surface runway. The data collected from these trials were used to establish a baseline for each horse’s movement and muscle activity patterns when they were clinically sound. 

 

Then, veterinarians induced mild, temporary lameness by applying pressure to the sole, using a modified horseshoe technique. This is a common method used in research to standardise lameness. Left or right forelimb lameness was randomly induced, and horses were trotted to collect data. After a minimum of 24 hours and ensuring the horses did not show residual lameness, sEMG and kinematic data were collected again from baseline and hindlimb lameness conditions.

 

Now the team is analysing the data, looking for differences in the activation timings and amplitude of the sEMG and kinematic signals between the conditions. Analysing both sEMG and 3D kinematic data will allow the researchers to accurately measure the relationships between changes in muscle function and movement during lameness. 

 

“Although gait analysis technologies have been embraced by veterinarians in both practice and research to quantify movement asymmetries that occur during lameness, the clinical application of surface electromyography for evaluating equine locomotion is in its infancy,” said St George. 

 

“There have been huge advances in the use of 3D motion capture and IMU technologies for aiding veterinary lameness evaluation, but these technologies do not reveal anything about adaptive muscle activity, and this is a missing link to understanding potential causes and/or clinical signs of equine lameness. The incorporation of both kinematic and muscle activation data is essential to gain a more comprehensive understanding of the factors at play during equine lameness.”

 

The study, is funded by the Morris Animal Foundation, and is run in collaboration with colleagues at Utrecht University, and Delys Inc.

 

“Lameness is one of the most common problems we see in horses, but we still have a lot to learn about diagnosis and treatment,” said Dr. Janet Patterson-Kane, Morris Animal Foundation Chief Scientific Officer. “If this technique will help us objectively measure the true condition of all of an animal’s musculoskeletal tissues, it will assist in optimizing treatment on an individual basis.”

 

If her study is successful, St. George would like to conduct a similar survey, but collect data from a larger group of horses on different muscle groups and clinical lameness cases.

 

 

For more details, see:

 

https://www.morrisanimalfoundation.org/article/better-assess-lameness-in-horses

 

https://delsyseurope.com/electromyography-emg-and-equine-lameness-expanding-clinical-research-into-equine-biomechanics/

 

*https://beva.onlinelibrary.wiley.com/doi/10.1111/evj.48_13152

Study into end of life decision making

Deciding when the time has come to end a horse’s life is one of the most difficult decisions an owner has 

to make. In cases of catastrophic injury, the choice may be clear. But it is often not the case in more subtle or long-term problems. However, delaying euthanasia may result in prolonged suffering and has been identified as a key welfare concern.

The attitude of British horse owners towards end-of-life decisions for their horses has been investigated by Catherine Bell and Suzanne Rogers of the Equine Behaviour and Training Association. 

 

They used a survey incorporating 30 welfare scenario statements, which was circulated via social media groups. One hundred and sixty owners responded to the survey. The work has been published in the journal Animals, in a special issue devoted to Horse-Human Interactions and their implications for equine welfare.

 

The authors report that, “In almost all cases, the reasons given for euthanasia were predominantly for physical issues … Most gave very specific answers, with colic (19%) and various types of arthritis and lameness (19%) being the most common primary reasons for euthanasia.”

 

Less specific reasons, such as “pain”, “old age” and/or “quality of life” accounted for 15% of responses.

 

The authors suggest that “it would seem that participants were wanting to select euthanasia for a single physical catastrophic and possibly unresolvable event, rather than a more nuanced decline in welfare towards end-of-life.”

 

They conclude that “physical issues, including even mild lameness, are more likely to factor in an end-of-life decision than issues relating to mental health, and horse owners are less likely to account for subtle welfare issues, potentially leading to the delay of euthanasia and prolonged suffering.”

 

 

For more details, see:

 

Attitudes of the Equestrian Public towards Equine End-of-Life Decisions 

Catherine Bell and Suzanne Rogers

Animals. 2021; 11(6):1776. 

https://doi.org/10.3390/ani11061776

Detomidine for reducing fireworks anxiety

Detomidine gel could be a useful tool to alleviate horse’s anxiety during fireworks according to a recent study.

Fireworks seem to be an increasing problem for horse owners to deal with, no longer limited to just one or two nights a year but becoming a more regular nuisance.

 

Detomidine has proved a useful sedative for allowing minor surgical procedures to be carried out in the standing horse and is widely used for enabling management tasks such as clipping, farriery, dentistry and wound dressing. A recent study by Francesca Dai and colleagues looked at whether it would help reduce anxiety and fear in horses exposed to fireworks.

 

Sixteen horses that had experienced acute anxiety and fear associated with fireworks noise in the past took part in the study, which was carried out on New Year’s Eve.

 

Eight horses were treated with 30 μg/kg detomidine gel (a little less than the licenced dose for sedation – 40 μg/kg ) and eight with a placebo. Treatment was repeated, if necessary, after a minimum of 2hrs.

 

Response to treatment was assessed by the owners. The horses’ behaviour was also recorded on video and assessed by an expert who was unaware of which treatment each horse had received.

 

The work is published in Frontiers of Veterinary Science. The authors report that, when fireworks were present, 75% of the horses given detomidine were scored by their owners as having a good or excellent treatment effect on anxiety and fear. Interestingly, 50% of horses given the placebo were scored as having a good response.

 

Overall, horses of the placebo group showed more restlessness, vocalization, and signs of colic. Horses given detomidine showed a significant decrease in walking behaviour.

Researchers suggest that the effect was not simply due to sedation – as (for at least some of the time) horses were eating.

 

The only adverse effect reported was sweating in one horse after the first dose of detomidine.

 

The authors conclude that detomidine can be used for alleviating horses' fear during fireworks. They suggest that further research with larger treatment groups is needed to confirm the results.

 

 

For more details, see:

 

Use of Detomidine Oromucosal Gel for Alleviation of Acute Anxiety and Fear in Horses: A Pilot Study

Francesca Dai, Julia Rausk,  John Aspegren,  Mirja Huhtinen,  Simona Cannas and Michela Minero

Front. Vet. Sci., (2020) 7:573309.

https://doi.org/10.3389/fvets.2020.573309

Swift Hendra test developed

A rapid point of care diagnostic kit that can detect Hendra Virus has been developed by scientists at the University of Queensland.

Hendra virus is a serious zoonotic infectious disease affecting horses and occasionally humans. It is transmitted by flying foxes shedding the virus in their saliva, urine, aborted foetuses and/or reproductive fluids. Horses are thought to contract the virus by ingesting feed or water contaminated with one of these sources of infection.

 

University of Queensland (UQ) vets can now diagnose the deadly Hendra virus in horses in under an hour, rather than taking days with existing diagnostic techniques.

 

Veterinarian Professor Ben Ahern said a rapid point-of-care diagnostic test to detect Hendra infections in horses has been sorely needed for decades.

 

“Hendra virus kills humans and horses alike – the virus spreads to horses from flying foxes, with an infected horse occasionally passing the infection on to humans,” Professor Ahern said.

 

“Without vaccination, the virus has a case fatality rate of 57% among humans and 79% among horses – it’s incredibly deadly.

 

“Rather than sending samples off to a lab, which risks an outbreak in the meantime, our testing protocol takes routine samples from a possibly infected horse and inactivates any virus that may be present in those samples.

 

“Following a heat treatment step of samples to inactivate the virus, these non-infectious samples are then tested using a handy molecular diagnostics machine – known as a LAMP Genie III – which is about the size of a box of tissues and is battery powered and completely portable.

 

“This process gives us results in under one hour, which is incredibly fast when compared to the many days it may take from collection of samples, getting them tested at an external lab and obtaining results.

 

“Horses aren’t suffering in the interim and humans giving care to them can avoid becoming exposed.”

 

Development of the point-of-care Hendra virus LAMP test has now advanced to the manufacturing stage and commercial kits are currently being produced.

 

Once approved by the Queensland Chief Veterinary Officer, the Genie machine and associated Hendra virus LAMP kits will be available for veterinarians to purchase and use.

 

“Due to the cost and technical training required, these tests will likely be performed by veterinarians or large equestrian bodies with veterinarian assistance,” Professor Ahern said.

 

“However, with the mobile capacity of this testing system, they can go directly to a farm to diagnose a suspected case, expanding treatment options for horses.”

 

For more details, see:

 

https://www.uq.edu.au/news/article/2021/07/no-horsing-around-super-fast-hendra-test-developed