Antimicrobial Resistance: EVJ Virtual Issue

 

Antimicrobial resistance is an emerging clinical problem, recognised internationally as one of the largest threats to human and animal health. All major health and veterinary organisations are working to try and limit the development of resistance so that effective antimicrobials can be retained for use in clinical practice.

The Equine Veterinary Journal (EVJ) has released a free online collection of articles on antimicrobials. It highlights the current understanding of equine antimicrobial resistance and how the veterinary profession can preserve the effectiveness of these essential medicines.

 

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Controlling problem behaviour in mares

Some mares are difficult to manage when in season and perform poorly as a result.

Most methods of controlling this behaviour are based on suppressing the oestrus cycle. The cyclic events of oestrus are associated with the development of follicles in the ovary. In the normal cycle, one of these follicles will develop, releasing oestrogen, which makes the mare receptive to the stallion as ovulation approaches. It is during this phase that some mares become uncooperative.

Once ovulation has occurred, a "corpus luteum" (CL) forms at the site of the recently ovulated ovarian follicle. This secretes progesterone that prepares the uterus for pregnancy.

If the mare does not become pregnant, the uterus releases hormones ("prostaglandins") which break down the CL, allowing the cycle to be repeated.

If the mare is pregnant, the embryo reaches the uterus about 6 or 7 days after ovulation. It then spends over a week migrating around the uterus, releasing molecular signals that prevent the uterus releasing prostaglandin. This ensures that the CL continues to produce progesterone, preventing a return to oestrus, and allowing the pregnancy to proceed.

To prevent behavioural signs associated with the mare coming in season it is necessary to maintain adequate levels of progesterone. This can be done by getting the mare pregnant. But pregnancy itself may interfere with the mare's ability to perform. Other methods include progesterone by injection or the daily administration of synthetic progesterone-like drugs ("progestagens") in the food.

 

Another option for prolonging luteal function and suppressing oestrus is oxytocin treatment. Dr Dirk K. Vanderwall, describes two protocols:

The first involves administering 60 units of oxytocin intramuscularly (IM) once daily on days 7 to 14 after ovulation. This induces prolonged CL function in 60% to 70% of treated mares.

Alternatively, by extending the duration of oxytocin treatment to 29 days, administration of 60 units of oxytocin IM can be initiated randomly at any point in the estrous cycle with no loss in efficacy (i.e., over 70% response).

Vanderwall suggests that, given these options, it may be time to end the practice among veterinarians of using intrauterine glass balls for oestrus suppression in mares.

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Atypical myopathy in New Zealand

Atypical myopathy, or seasonal pasture myopathy (SPM), has been reported with increasing regularity from Europe and the USA, where is it associated with grazing on land contaminated with the seeds (“samaras”) of the sycamore and box elder trees.

However, the condition is not confined to the northern hemisphere, as shown by a recent report from New Zealand.

Dr Rabecca K McKenzie described four horses aged between 5 months and 9 years, that presented with various clinical signs including recumbency, stiffness, lethargy, dehydration, depression, and myoglobinuria suggestive of acute muscle damage. Two horses were subjected to euthanasia, but two recovered.  In all cases seeds of sycamore maple or box elder were present in the area where the horse had been grazing.

Affected horses showed laboratory signs characteristic of atypical myopathy, including raised muscle enzymes and changes in the acylcarnitine profile. Hypoglycin A, the toxin responsible for atypical myopathy, was found in the serum of the affected animals, but not in unaffected ones.

Hypoglycin A was identified in seeds of Acer spp. collected on premises where atypical myopathy cases had occurred. 

The toxin was also found in 10/15 samples of seeds from sycamore maple and box elder from other areas of the country where cases had been recorded previously.

The authors conclude that sycamore and box elder trees in New Zealand are a source of hypoglycin A, the toxin associated with atypical myopathy. They advise that if pastured horses show signs of severe muscle damage then the environment should be checked for the presence of these trees. Horses should be prevented from grazing seeds from Acer spp. in the autumn.

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Painted horses for anatomy teaching

Body painting has become popular as an aid for teaching surface anatomy in both humans and horses.

But does it help students learn?

Photo: Gillian Higgins / www.horsesinsideout.com

 

A recent study, conducted in Brazil, examined the response of 21 veterinary students to the use of body painting in addition to traditional lecture-based teaching.

Rather than endure a traditional anatomy lecture, students took part in a 90-minute session in which they were presented with painted horses and had opportunities to palpate the anatomic locations on the horses.

The response to the teaching approach was positive. A subsequent questionnaire found unanimous approval among the students.

Also, in practical tests immediately before and one hour after the sessions, students showed a significant improvement in their understanding.

The researchers concluded that bodypainting has great potential for supporting traditional lectures on the equine locomotor apparatus.

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