Investigating the Arabian genome

A study involving Arabian horses from 12 countries found that some populations maintained more genetic diversity and that the breed did not contribute genetically to the modern-day Thoroughbred, contrary to popular thought.

An international team of scientists was led by the University of Florida’s Samantha Brooks, of the University of Florida, and Doug Antczak and Andy Clark at Cornell University.

The group collected and examined DNA samples from 378 Arabian horses from Qatar, Iran, UAE, Poland, USA, Egypt, Jordan, Kuwait, United Kingdom, Australia, Denmark and Canada. The research is published in the journal “Scientific Reports.”

Other than the horse’s location and whether it was used for endurance, racing or showing, the samples were anonymised for data analysis purposes.

The researchers also incorporated information gained in previous studies, which included breeds such as Thoroughbreds, Persian Arabian, Turkemen and Straight Egyptians.

“The Arabian horse has a special mystique due to the long-recorded history of the breed,” Brooks said. “Arabian horse breeders, in particular, know their horse’s bloodlines many generations back. What we found was that in the area where this breed originates – likely the near East region, but we don’t know exactly – there’s a healthy level of diversity. This is particularly evident in populations from Bahrain and Syria, which suggests these are some pretty old populations.”

The Arabian is prized for characteristics like heat tolerance and endurance, as well as its unique appearance, with a dish-shaped facial profile, wide-set eyes, an arched neck and a high tail carriage. It has been exported from its ancestral homeland for centuries, with some modern lineages drawn strictly from these smaller genetic pools, giving the breed a reputation for inbred disorders. While this was true for some groups they tested, Brooks noted, they also found remarkable diversity when considering the breed as a whole.

Brooks contrasted the discovery of more diverse populations with the samples they received from racing Arabians. Another longstanding myth says that the Arabian contributed genetically to the modern Thoroughbred, but the racing Arabians’ DNA told a different story. The research team found little influence of the Arabian in the modern Thoroughbred’s DNA

“What we found in these samples was not that much Arabian ancestry was part of the Thoroughbred line, but the opposite: that Thoroughbred DNA exists in most of the modern racing Arabian lines, indicating a more recent interbreeding within this group,” Brooks said. “I can’t speculate on the how or why, but this is clearly the story the DNA is telling us.”

Another implication of this study, Brooks said, is the potential to identify the genetic regions that determine some of the Arabian’s unique traits, like their facial profile. This could be expanded to identify the marker for other horse breeds’ head shapes, for example.

The study has a long list of co-authors, with contributors from the University of Tehran, Iran; Weill Cornell Medical College in Qatar; the University of Kentucky; the University of Agriculture in Kraków, Poland; the Hong Kong Jockey Club; the Equine Veterinary Medical Center in Doha, Qatar; and the University of Veterinary Medicine Vienna, Austria. Elissa Cosgrove from the Clark lab and Raheleh Sadeghi, a visiting scientist from Iran in the Antczak lab, shared first co-authorship of the study.

“An exceptional aspect of this project was the wonderful level of open collaboration and sharing of resources by veterinary geneticists, equine scientists, and horsemen from around the world,” Antczak said. “It was a great pleasure to conduct this global study for the benefit of the horse.”

For more details, see:

Genome Diversity and the Origin of the Arabian Horse

Elissa J. Cosgrove, Raheleh Sadeghi, Florencia Schlamp, Heather M. Holl, Mohammad Moradi-Shahrbabak, Seyed Reza Miraei-Ashtiani, Salma Abdalla, Ben Shykind, Mats Troedsson, Monika Stefaniuk-Szmukier, Anil Prabhu, Stefania Bucca, Monika Bugno-Poniewierska, Barbara Wallner, Joel Malek, Donald C. Miller, Andrew G. Clark, Douglas F. Antczak & Samantha A. Brooks

Scientific Reports (2020) vol 10, Article number: 9702 (2020)

https://doi.org/10.1038/s41598-020-66232-1

Screening for strangles carriers

Serological screening cannot be relied on to prove a horse is not a strangles carrier, a recent report warns.

Asymptomatic carriers are probably the main way that strangles gains access to a previously unaffected yard. Most horses throw off the infection within a few months of an outbreak. But some remain infectious. They carry and excrete the bacteria without showing signs of disease.

These carriers usually retain the infection in the guttural pouches. With time, pus may solidify to form masses known as “chondroids”. These can harbour the bacteria and excrete them intermittently in the nasal secretions - acting as a source of infection for other horses.

The best way of identifying strangles carriers is by culturing a series of swabs from the nasopharynx, or by examining a guttural pouch wash for Streptococcus equi DNA (a PCR test). This can be time consuming and costly.

Blood samples are easier to obtain, and serological testing for Strep equi antibodies has become popular in clinical practice to screen for strangles carriers.

However, recent research suggests that such results should be interpreted with caution and cannot be relied on to be certain a horse is not a strangles carrier.

In a retrospective clinical study, Andy Durham and Jeremy Kemp-Symonds, compared results obtained by serological testing for antibodies against S equi antigens A and C, with the findings of microbiological sampling of the guttural pouches.

The study included 287 horses, that were examined as part of routine surveillance and quarantine procedures on arrival at a welfare charity quarantine unit. Guttural pouch washes were submitted for culture and PCR testing and blood samples were tested for the Strangles A/C ELISA.

(The Strangles A/C ELISA test gives results in terms of optical density (OD). An OD ≥0.5 to either antigen A or C is considered “positive”; OD≤0.2 “negative”; and OD 0.3-0.4 “borderline”.)

The investigators found no significant association between serological status and the presence of S equi in the guttural pouches. 

S equi was found in the guttural pouches of nine horses (3.1%). Of those, only one (11%) was seropositive using a cut-off of OD ≥0.5. A further two horses fell in the borderline category, leaving six horses with negative results.

So, in this study, over half of the horses with S equi in the guttural pouches, were negative on the Strangles A/C ELISA test.

Durham and Kemp-Symonds conclude: “It would appear that the only currently reliable means of determining S. equi carrier status is microbiological sampling rather than serological screening.

For more details, see:

Failure of serological testing for antigens A and C of Streptococcus equi subspecies equi to identify guttural pouch carriers.

Durham AE, Kemp Symonds J.

Equine Vet J. (2020)

 doi: 10.1111/evj.13276

Barley straw as an aid to weight loss

Feeding a mixture of barley straw and hay is a safe and cost-effective way of promoting weight loss in grazing ponies over winter, according to recent research. 

Obesity is a widespread problem in pleasure horses and ponies. In the past, it was accepted that horses and ponies would lose weight over the winter and then gain weight in the spring when grazing quality improved. Nowadays, however, horses are fed to maintain condition over the winter, and, at the same time, they may be doing less work. 

Obese horses and ponies are at higher risk of laminitis; but shedding that weight is often quite a challenge.

A study conducted by Dr Miranda Dosi and colleagues at the University of Edinburgh Royal School of Veterinary Studies and the Redwings horse sanctuary in Norfolk UK, looked at whether feeding a mixture of straw and hay could be used for reducing weight in grazing ponies over the winter. 

A report of the work is published in the Veterinary Record.

The study involved native type ponies maintained in groups at grass over winter. They were fed supplementary roughage – either hay alone, or an equal mixture of hay and barley straw.

The research team weighed the horses regularly during the four-month long study.

They found that, over the study period, all animals in the hay/straw-fed group lost weight. In the hay only group, three horses lost weight, but overall, horses in that group gained weight. 

One concern of feeding straw is that it might lead to digestive problems such as impaction. However, in this study, there were no reports of colic in either group. Neither were there any reports of laminitis. 

An advantage of the higher fibre barley straw is that it may prolong the time spent eating and may reduce behavioural problems such as aggression.

The researchers conclude “straw is a cost-effective and low-energy roughage, which may be a useful alternative to hay alone when trying to induce weight loss in grazing equids over winter.”

For more details, see:

Inducing weight loss in native ponies: is straw a viable alternative to hay?

Dosi MCM, Kirton R, Hallsworth S, Keen JA, Morgan RA.

Vet Rec. (2020)

doi: 10.1136/vr.105793