US owners sought for horse ageing survey

 Owners are invited to help in a study into the ageing process in horses.

University of Kentucky researchers are looking for owners of horses that live in the USA to take part in an online survey. The survey focuses on horses and ponies aged 15yrs and over, although owners of younger horses can also take part.

Your responses and opinions will greatly help the research team understand more about the health status and management of horses aged 15+ years, and how the aging process in horses is perceived.

Click below to go to the survey:

https://uky.az1.qualtrics.com/jfe/form/SV_bxAeIRSVM6gAOvb

Importing anthelmintic resistance

 A salutary reminder of the danger of importing anthelmintic resistance is given in a recent report.

Martin K Nielsen, Schlaikjer Professor of Equine Infectious Disease at the M.H. Gluck Equine Research Center, Department of Veterinary Science, University of Kentucky, Lexington, and others, describe a case of macrocyclic lactone (ML) resistance in a group of Thoroughbred yearlings imported from Ireland to the US.

The findings emphasise that the global movement of horses has the potential to quickly spread ML-resistant parasites around the world.

Anthelmintic resistance to benzimidazole and pyrantel is widespread among the cyathostomins (small redworms). The macrocyclic lactones (such as ivermectin and moxidectin) are generally effective, but there have been occasional reports of resistance.

Thoroughbred yearlings imported from Ireland to the US were found to have evidence of ML resistance when faecal egg count reduction (FECR) tests were carried out. The three batches of imported yearlings had FECR test results ranging from 93.5% to 70.5%. (FECR test is the standard method of assessing resistance in cyathostomins. If the FEC is not reduced by 95% or more after treatment with a macrocyclic lactone such as ivermectin, that is interpreted as evidence of resistance.) When the test was repeated after a further ivermectin treatment in two of the groups the FECR results were even lower.

In contrast, three groups of US bred yearlings had FECR test results of 99-100% after treatment with ivermectin.

Full details of the study are published in the International Journal of Drugs and Drug Resistance. The authors point out that “this case clearly illustrates the importance of quality routine FECR testing, which immediately informed the farm manager of the situation and allowed him to react in time by keeping the populations completely separate, thereby avoiding an introduction of the resistant parasites to the entire facility.”

They strongly recommend that equine operations heed this threat to equine health, and routinely monitor anthelmintic efficacy on a yearly basis. 

For more details, see:

Importation of macrocyclic lactone resistant cyathostomins on a US thoroughbred farm
M K Nielsen, M Banahan, R M Kaplan
Int J Parasitol Drugs Drug Resist (2020)14:99-104.
doi: 10.1016/j.ijpddr.2020.09.004

 Moody mares may benefit from ovariectomy to alter their behaviour and rideability, according to a recent report.

Some mares are difficult to manage and perform poorly as a result. They may be uncooperative or aggressive when handled on the ground. They may kick, buck or rear when ridden or may be aggressive towards other horses.

Unwanted behaviour may result from pain from orthopaedic or other sources. Sometimes it is related to the mare coming in season, in which case it may be improved by suppressing the oestrus cycle.

Some ovarian tumours, although less common, may produce similar effects. Treatment of these cases is likely to involve removing the affected ovary (ovariectomy).

But sometimes there is no obvious explanation for the unwanted behaviour. Would removing both ovaries (bilateral ovariectomy) help?

A study by Daniel Taasti Melgaard, of the Horsholm Equine Clinic, Fredensborg, Denmarkand colleagues looked at whether removing the ovaries from mares with unexplained unwanted behaviour improved the mare’s behaviour or rideability.

Twenty-eight mares underwent surgical removal of both ovaries once the clinicians had ruled out painful causes and after the mares had not responded to a trial period of hormone therapy to suppress oestrus behaviour.

Owners reported that, after bilateral ovariectomy, 80% (8/10) of mares with normal ovaries and 57% (8/14) of mares with ovarian neoplasia were easier to ride. Behaviour was reported to be better in 40% (4/10) of mares with normal ovaries, and in 43% (6/14) of mares with ovarian neoplasia.

A full, open access, report is published in the journal Animals.

The authors emphasise the importance of a thorough diagnostic work up to rule out other conditions, such as orthopaedic, alimentary, vaginal or uterine pathology, before considering ovariectomy for unwanted behaviour.

They suggest that, despite the significant improvement observed in the present study, further research is necessary to confirm whether mares with unwanted behaviour not obviously related to the oestrus cycle and to painful conditions may benefit from ovariectomy to alter their behaviour and rideability.

“In conclusion”, they write, “a significant improvement was observed in rideability and behaviour post- ovariectomy, but no statistical difference in improvement after ovariectomy between mares with ovarian neoplasia and mares with histopathologic normal ovaries was observed. The results suggest that mares with and without neoplasia can equally benefit from ovariectomy to improve behaviour and rideability.”

For more details, see:

Moody Mares - Is Ovariectomy a Solution?
Daniel Taasti Melgaard, Trine Stokbro Korsgaard, Martin Soendergaard Thoefner, Morten Roenn Petersen, Hanne Gervi Pedersen.
Animals (Basel) (2020)
doi: 10.3390/ani10071210

Blankets and food intake

Horses wearing a blanket or rug in the winter ate less hay than did their non-blanketed neighbours, a recent study found.

Healthy horses maintain their body temperature within a narrow range (98.5°F to 101°F / 36.9°C to 38.3°C) despite a wide variation in environmental conditions.

In cold weather they use various physiological and behavioural methods to conserve body heat, such as piloerection, shivering, facing away from the wind. Eating roughage generates heat and so helps maintain body temperature.

Research by Michelle De Boer and others at the University of Wisconsin–River Falls, assessed the effect of wearing a blanket on horses’ feed intake, body weight (BW), and body condition scores (BCSs). A report of the work is published in the Journal of Equine Veterinary Science,

The project was carried out over the winter of 2019-2020, when environmental temperatures typically average about -10°C.

Sixteen adult horses were recruited to the study: eight wore a medium weight blanket; the others did not. All horses lived in a dry lot and were fed grass-legume hay ad lib. The researchers recorded hay intake and monitored horses’ body weight and condition score before during and at the end of the study.

Horses without blankets maintained their body weight and condition score despite the cold weather.

The researchers found that the average estimated dry matter intake (DMI) was lower for blanketed horses (2.31% BW) than for non-blanketed ones (2.51% BW) – equivalent to an average of 1kg daily.

The results suggest horses wearing blankets conserve energy leading to decreased feed intake. Horse owners may save (a small amount of) money from reduced hay and labour costs when using a blanket.

The researchers emphasised that, when blanketing a horse, it is important to monitor them regularly to evaluate health, welfare, and BW and condition.

For more details, see:

Dry Matter Intake, Body Weight, and Body Condition Scores of Blanketed and Nonblanketed Horses in the Upper Midwest
Michelle De Boer, Alexandra Konop, Bailey Fisher, Krishona Martinson
Journal of Equine Veterinary Science (2020) vol 94, 103239 

https://doi.org/10.1016/j.jevs.2020.103239

Challenge of identifying asymptomatic strangles carriers

A recent study found that blood tests (serology) alone did not effectively distinguish asymptomatic strangles carriers from non-carriers.

Symptomless carriers present the biggest risk of introducing strangles to a previously unaffected population.

Most horses throw off the infection, caused by Streptococcus equi, within a few months of an outbreak. But some remain infectious. These carriers usually retain the infection in the guttural pouches at the back of the throat. They carry and excrete the bacteria without showing any sign of disease.

The best way to identify carriers is by culturing a series of swabs from the nasopharynx, or by examining a guttural pouch wash for Streptococcus equi DNA (a qPCR test). Such methods can be time consuming and costly.

Serological testing for S. equi antibodies has become popular in clinical practice to screen for strangles carriers. However, a growing body of research suggests that this method cannot be relied on.

A study by John Pringle and colleagues at the Swedish University of Agricultural Sciences, Uppsala, and the Equine Veterinary Clinic, Destedt, Germany, followed three groups of horses for between six months and two years after strangles outbreaks.  A full report of the work is published in the Journal of Veterinary Internal Medicine.

Carriers were defined as horses from which S. equi could be cultured, or S. equi DNA could be found on qPCR test, in samples from the nasopharynx or guttural pouches.

The researchers compared the clinical appearance, guttural pouch endoscopy, and inflammatory markers between carriers and non-carriers and found no real difference between the two groups. Neither did serology distinguish carriers from non-carriers.

“Of particular concern however was that two of the culture positive carriers 14 months after outbreak A, and the culture positive mare associated with outbreak A tested seronegative,” they report, “suggesting lack of persistence of seropositivity despite carriage of viable S. equi.”

They conclude: “Silent carriers of S. equi do not differ clinically or on markers of inflammation to their noncarrier herd‐mates. Moreover, serology alone will not distinguish carriers in comingled horses.”

For more details, see the Open Access article:

Markers of long term silent carriers of Streptococcus equi ssp. equi in horses
John Pringle, Monica Venner, Lisa Tscheschlok , Andrew S. Waller, Miia Riihimäki
Journal of Veterinary Internal Medicine
https://doi.org/10.1111/jvim.15939