August 2012 Summer Sore Alert

Recent outbreaks of ‘summer sores’ on horses have prompted us to issue this alert to let horse owners know how to recognize this alarming condition.

Summer sores, also known as Habronemiasis, are seen in the summer during fly season, and are the results of infected flies depositing the larvae of the equine stomach worm Habronema on wounds and moist areas of a horse’s body.Commonly affected areas are the eyelids, the sheath, the corners of the mouth and skin wounds.Infected tissues become inflamed and swell suddenly, with affected skin wounds producing excessive granulation tissue which protrudes above the surrounding skin.Severe itching is often seen.Infected wounds often have characteristic yellow granules which can be seen in the reddish wound surface that are about the size of a grain of rice.These are the dead larvae surrounded by inflammatory debris.

During fly season if your horse has a minor skin wound that suddenly looks much worse, or suddenly develops swelling of the eyelid, lips or sheath it may be Habronemiasis.Have your veterinarian examine your horse.

The treatment of Habronemiasis involves administering an avermectin dewormer (ivermectin or moxidectin), as well as topical treatment of the area.Systemic medications may also be given to control the severe inflammation which can result.

If caught early, summer sores are easily treated.In all cases treatment needs to be aggressive.In severe cases treatment may need to continue until fly season ends in the fall.

Life Cycle

The life cycle of the stomach worm is dependent on house and stable flies.Adult stomach worms live in the lining of the stomach and lay eggs which are shed in the feces.House and stable flies then lay their eggs in the same feces and the developing fly maggots ingest the Habronema larvae which develop within the growing fly maggots.The maggots then pupate into adult flies which then deposit the Habronema larvae on the lips of horses.The horses swallow the Habronema larvae which develop into adults in the stomach, and the life cycle is complete.

Early exercise in the horse

Abstract: Across all equestrian disciplines, the single largest reason for wastage is musculoskeletal injury. It is, therefore, of importance that management and competition structures are in place to optimize the development of the equine musculoskeletal system to minimize wastage.Data from other species and, in particular, humans have demonstrated the benefit of early exercise and the dire consequences of inactivity. The horse has evolved as a cursorial animal capable of covering up to 10 km/d within 9 days of birth. Yet, modern equine management systems restrict, rather than promote, early exercise. Foals were shown to have a positive response to early preweaning paddock exercise (greater cartilage health), and more recent work has demonstrated that exercise over and above that normally occurring with pasture-reared foals, introduced as early as 3 weeks old, had positive effects on the equine musculoskeletal system. The response of juvenile horses to additional exercise is because of the tissue being responsive to priming. Epidemiological data indicate that the window for tissue modification may still be open when the horse is a yearling and even as a 2 year old.However, the method in which the exercise is applied may be of as much importance as the timing of the stimuli. A recent prospective study of both Thoroughbred and Standardbred horses demonstrated that the horses that entered training as 2 year olds had longer and more successful racing careers than those that entered training later in life. It would appear that even the initial stages of training are enough to provide a positive stimulus, as horses first registered with a trainer at 2 years old had the same advantages as those that raced as 2 year olds.The physiological, clinical, and epidemiological data indicate that, rather than restrict exercise and the use of horses at a young age, we should realign expectations with the capability of the horses’ musculoskeletal system and evolutionary template to maximize orthopedic health.

Equine insect bite hypersensitivity: What do we know?

from pubmed: horse by Schaffartzik A, Hamza E, Janda J, Crameri R, Marti E, Rhyner C

Equine insect bite hypersensitivity: What do we know?

Vet Immunol Immunopathol. 2012 Apr 3;

Authors: Schaffartzik A, Hamza E, Janda J, Crameri R, Marti E, Rhyner C

Insect bite hypersensitivity (IBH) is an allergic dermatitis of the horse caused by bites of insects of the genus Culicoides and is currently the best characterized allergic disease of horses. This article reviews knowledge of the immunopathogenesis of IBH, with a particular focus on the causative allergens. Whereas so far hardly any research has been done on the role of antigen presenting cells in the pathogenesis of IBH, recent studies suggest that IBH is characterized by an imbalance between a T helper 2 (Th2) and regulatory T cell (T(reg)) immune response, as shown both locally in the skin and with stimulated peripheral blood mononuclear cells. Various studies have shown IBH to be associated with IgE-mediated reactions against salivary antigens from Culicoides spp. However, until recently, the causative allergens had not been characterized at the molecular level. A major advance has now been made, as 11 Culicoides salivary gland proteins have been identified as relevant allergens for IBH. Currently, there is no satisfactory treatment of IBH. Characterization of the main allergens for IBH and understanding what mechanisms induce a healthy or allergic immune response towards these allergens may help to develop new treatment strategies, such as immunotherapy.

PMID: 22575371 [PubMed – as supplied by publisher]


Comment:  Progress on an old age problem.  Always known by deduction,  Culicoides spp. cause dramatic skin reactions in the horse.  The feeding process of Culicoides leaves some horses with profound swelling and intense itching.  To date, teh most effective tool has been exogenous steroid therapy.  As with many mysteries, the first step in the unlocking process is more understanding.  Perhaps hyposensitization therapy is in the future.

Effect of livestock manures on the fitness of house fly, Musca domestica L. (Diptera: Muscidae).

from pubmed: horse by Khan HA, Shad SA, Akram W

Effect of livestock manures on the fitness of house fly, Musca domestica L. (Diptera: Muscidae).

Parasitol Res. 2012 May 11;

Authors: Khan HA, Shad SA, Akram W

The house fly, Musca domestica L. (Diptera: Muscidae) is one of the major pests of confined and pastured livestock worldwide. Livestock manures play an important role in the development and spread of M. domestica. In the present study, we investigated the impact of different livestock manures on the fitness and relative growth rate of M. domestica and intrinsic rate of natural increase. We tested the hypotheses by studying life history parameters including developmental time from egg to adult’s eclosion, fecundity, longevity, and survival on manures of buffalo, cow, nursing calf, dog, horse, poultry, sheep, and goat, which revealed significant differences that might be associated with fitness costs. The maggots reared on poultry manure developed faster compared to any other host manure. The total developmental time was the shortest on poultry manure and the longest on horse manure. The fecundity by females reared on poultry, nursing calf, and dog manures was greater than on any other host manures. Similarly, percent survival of immature stages, pupal weight, eggs viability, adults’ eclosion, survival and longevity, intrinsic rate of natural increase, and biotic potential were significantly higher on poultry, nursing calf, and dog manures compared to any other livestock manures tested. However, the sex ratio of adult flies remained the same on all types of manures. The low survival on horse, buffalo, cow, sheep, and goat manures suggest unsuitability of these manures, while the higher pupal weight on poultry, nursing calf, and dog manures suggest that these may provide better food quality to M. domestica compared with any other host manures. Our results point to the role of livestock manures in increasing local M. domestica populations. Such results could help to design cultural management strategies which may include sanitation, moisture management, and manure removal.

PMID: 22576856 [PubMed – as supplied by publisher]



Comment:  Finally, the horse is exonerated as the major cause of fly production!  This abstract gives good thought to manure management and whether chickens are worth having around, given the differential of fly generation.

Dewormer comparisons – generic vs conventional.

Comparative performance of macrocyclic lactones against large strongyles in horses.

from pubmed: horse by Toscan G, Cezar AS, Pereira RC, Silva GB, Sangioni LA, Oliveira LS, Vogel FS

Comparative performance of macrocyclic lactones against large strongyles in horses.

Parasitol Int. 2012 May 8;

Authors: Toscan G, Cezar AS, Pereira RC, Silva GB, Sangioni LA, Oliveira LS, Vogel FS

Several formulations of macrocyclic lactones (abamectin, ivermectin, moxidectin), including ivermectin combined with pyrantel (tetrahydropyrimidine) and ivermectin combined with praziquantel (pyrazinoisoquinolin derivative), were tested regarding their efficacy to control gastrointestinal nematodes of horses on a stud farm in southern Brazil. In addition, we tested a pharmaceutically produced generic paste containing ivermectin 4%. Similar formulations of avermectins had different efficacies measured by reduction of EPG. Levels of efficacy of the tested drugs varied against Strongylus edentatus, S. equinus and S. vulgaris. The generic paste (ivermectin 4%) was less effective than the conventional drugs.

PMID: 22580448 [PubMed – as supplied by publisher



Comment:  Brand name dewormers are recommended over generic, inexpensive versions.  This study illustrates the potential outcome and difference between these two formulations.

Electrolyte Supplementation in the Horse – is it effective?? Find comments after the abstract.

Gastric emptying and intestinal absorption of electrolytes,and exercise performance in electrolyte supplemented horses.

via pubmed: horse by Lindinger MI, Ecker GL on 5/17/12

Gastric emptying and intestinal absorption of electrolytes,and exercise performance in electrolyte supplemented horses.

Exp Physiol. 2012 May 11;

Authors: Lindinger MI, Ecker GL

Horses lose considerably more electrolytes through sweating during prolonged exercise than can be readily replaced through feeds. The present study tested an oral electrolyte supplement (ES) designed to replace sweat electrolyte losses. We measured gastric emptying of 3L of ES (using gamma imaging of 99Tc- sulfide colloid), the absorption of Na+ and K+ from the g.i. tract using 24Na+ and 42K+, and the distribution of these ions in the body by measuring radioactivity within plasma and sweat during exercise. Three L of ES emptied from the stomach as fast as water, with a half time of 47 minutes, and appeared in plasma by 10 minutes after administration (n = 4 horses). Peak values of plasma 24Na+ and 42K+ radioactivity occurred at 20-40 minutes and a more rapid disappearance of K+ radioactivity from plasma was indicative of movement of K+ into cells (n = 3 horses). In a randomized crossover experiment (n = 4 horses), 1h after administration of placebo (water), 1 L or 3 L of ES containing 24Na+, horses exercised on a treadmill at 30% of peak VO2 until voluntary fatigue. 24Na+ appeared in sweat at 10 minutes of exercise, and when horses received 3L of ES the duration to voluntary fatigue was increased in all horses by 33+10 %. It is concluded that an oral ES designed to replace sweat ion losses was rapidly emptied from the g.i. tract, was rapidly absorbed in the upper intestinal tract and rapidly distributed within the body. The ES clearly served as a reservoir to replace sweat ion losses during exercise, and administration of ES prior to exercise resulted in increased duration of submaximal exercise.

PMID: 22581743 [PubMed – as supplied by publisher]



Electrolyte supplementation has been effectively used for many years in the equine sport of endurance riding and racing.  Though feeds provide the primary source, maximal exercise and sweating can create a substantial deficit in electrolytes, leading to possible gastrointestinal and muscle issues.  Any sport or circumstance that causes significant sweating deserves attention for possible supplementation.

Bad behavior or a physical problem? Rearing in a Dutch Warmblood mare

Abstract: Behavior problems in horses are often thought to be due to the horse’s bad attitude, which commonly results in them being punished. However, when these cases are carefully worked up, there may be an underlying physical problem, and pain may play an important role. A 5-year-old Dutch Warmblood mare was presented for rearing and flipping over backward. The mare had been repeatedly examined by an equine veterinarian and a nonveterinarian equine dentist who found no abnormalities. Several different bits were tried, and side reins were used to keep her head down. The mare was whipped every time she reared. None of these measures helped. On presentation to our equine teaching hospital, no abnormalities were detected on routine physical examination. The behavior was observed when the mare was lunged; as soon as a small amount of tension was put on the lunge rein, the mare shook her head horizontally for approximately 1-2 seconds, reared, and flipped over onto her back. Neurological examination revealed that the mare was slow to resume a normal stance when her hind legs were placed in an abnormal position. Dental examination and endoscopy of the upper airways proved unremarkable. Radiography of the atlanto-occipital joint area revealed fractures of the first and second cervical vertebrae and fracture fragments, which are both suggestive for the presence of cervical instability and the possible presence of spinal cord compression. These suggestions were further supported by identification of delayed postural reflexes during neurological examination. The mare was deemed unfit for dressage and was successfully kept for breeding. Horses are frequently punished for “bad behavior.” These behaviors are frequently due to underlying physical problems and not a “nasty” horse. This case highlights the importance of careful history taking and a thorough veterinary examination with the use of further diagnostics (if necessary) when dealing with equine behavior problems.

Ain’t Misbehavin’: Researchers Find Link Between Pony Behavior Problems and Obesity

An equine study, Misbehavior in Pony Club Horses: Incidence and risk factors, was published last month by The Equine Veterinary Journal (EVJ) and is the first of its kind to quantify the incidence of misbehavior in a population of horses. The research, conducted by Petra Buckley, Senior Lecturer in Equine Science at Charles Sturt University, New South Wales, involved 84 Pony Club horses from seven different Clubs in rural Australia. Over the period of a year, owners kept daily records of horse management including nutrition, healthcare and exercise; they also recorded any misbehavior.

Prior Newsletters

On this page download prior newsletters in PDF form:

 May 2011: Feeding Beet Pulp


Nov 2009: Piroplasmosis


Aug 2009: Equine herpes virus myeloencephalopathy (EHM)


Nov 2008: Cushings Syndrome


Aug 2008: Equine Metabolic Syndrome Newsletter


Mar 2008: Breeding Season Newsletter


Dec 2007: Durable Equine Athletes Newsletter


Oct 2007: Chiropractic Care Newsletter


Mar 2007: Equine Viral Arteritis (EVA) Newsletter


Jan 2007: IRAP Newsletter