Volume 4 No. 1 Issue Date: April, 2019

Southern Equine Consortium banner. Providing research-based information for horse owners and equine operations in the Southeast region. Vol. 4 No. 1 Issue Date: April 2019

Foal Nutrition During the Preweaning Phase

Courteney Holland
Auburn University

The amount of milk broodmares produce peaks when foals are 30 to 60 days old and then gradually declines. Nutrient content of the milk also peaks during the first 30 days of lactation and declines as lactation continues. Mare's milk alone may not provide enough energy to meet the requirements of a 4-month-old or even younger foal.

Foals should be introduced to feed in small amounts (2 to 3 pounds a feeding), and the amount fed should be gradually increased until feed is available free-choice to the foal. Free-choice feeding allows the foal to eat small, frequent meals, which is a natural situation mimicking the foal's nursing schedule. Free-choice feed also gives timid foals a chance to eat when dominant foals are away from the feeder. However, feeding foals free-choice does increase the level of management needed in comparison with the level required for feeding foals distinct meals. When feeding foals free-choice, managers must carefully monitor the feeder for spoilage and must make sure that fresh feed is always available. Ideally, enough feed must be provided so there is only a small amount left in the feeder the next time feed is given. If the feeder has been empty for a long period, a hungry foal that is allowed free-choice access when the feeder is replenished could overeat and colic. If foals are sorting through the feed and leaving a particular ingredient uneaten, use pelleted feed to ensure that the foals receive a balanced creep ration.

Providing a nutritionally balanced feed for the foal by 2 months of age will increase preweaning growth and acquaint the foal with the feed it will eat when weaned. Feed should be formulated especially for foals to provide the correct amounts of nutrients needed for proper growth and development. Most feeds formulated for mature horses (even high-quality brood-mare feeds) do not provide enough overall protein, calcium, or phosphorus for foals. Feeding foals these feeds may result in a deficiency in lysine, the first limiting amino acid that foals need for growth. Broodmare feeds may give the foal enough energy for weight gain without providing the basic nutrients needed for proper growth and skeletal development, resulting in fat foals with improperly developed musculoskeletal systems.

Since feed tags usually do not indicate the energy density of a feed, the energy density has to be estimated by the percentages of crude fiber and crude fat listed on the tag. Crude fiber is inversely related to energy (more crude fiber equals less energy), and crude fat is directly related to energy (more crude fat equals more energy). With a constant fat concentration, the minimum percentage of crude protein, calcium, and phosphorus needed in the feed will decrease as fiber content increases because the foal will consume more of the feed. However, remember that young foals are unable to consume and use large quantities of fiber, so feeds should be carefully balanced.

Protein quality, reflected by the amount and type of essential amino acids contained in the protein, is also a consideration in selecting a feed. High-quality protein sources, such as soybean meal, alfalfa meal, animal protein, or milk protein, should be used in formulating a feed. Table 1 shows minimum amounts of crude protein, calcium, and phosphorus needed in feeds containing various amounts of crude fiber at a constant level of crude fat (3 to 3.5 percent crude fat is the amount occurring naturally in most horse grains). Table 2 is a similar table showing minimum amounts of crude protein, calcium, and phosphorus needed in feeds containing supplemental fat, which increases the total crude fat concentration of the feed to a constant 8 to 8.5 percent. Practically, a commercial feed containing at least 16 percent crude protein, 0.8 percent calcium, and 0.5 percent phosphorus should meet the foal's nutritional needs. When feeds contain smaller amounts of these nutrients, it is difficult for the foal to consume enough of these nutrients in a reasonable amount of daily feed.

Table 1. Minimum percentages of protein, calcium, and phosphorus needed in feeds containing 3-3.5% crude fat & varying amounts of fiber.

Crude FiberCrude ProteinCalciumPhosphorus

Table 2. Minimum percentages of protein, calcium, and phosphorus needed in feeds containing 8-8.5% crude fat and varying amounts of fiber.

Crude FiberCrude ProteinCalciumPhosphorus

A young foal has the potential of gaining 2.5 to 3 pounds daily. Feeding the foal with a balanced ration in order to compensate for the nutritional deficiencies in the mare’s milk allows owners to increase the foal's growth rate while minimizing bone and joint disorders (developmental orthopedic disease, or DOD) sometimes found in large-framed, rapidly growing horses. This disease complex includes problems such as contracted tendons, epiphysitis, osteochondrosis, and enlarged or deformed joints. Genetic predisposition, nutrient imbalance, and excessive exercise of stalled horses have all been identified as possible causes of DOD in horses. Inadequate protein, vitamin, and mineral concentrations relative to the energy concentration of the diet may promote DOD in foals. However, feeding foals with a balanced ration does not contribute to DOD. Remember that the purpose of feeding is to increase foal growth and development by compensating for the nutritional deficiencies in the mare's milk. Maximal growth and overly fat foals are not goals of a feeding program and may contribute to bone and joint disorders in young horses.

In order to protect the initial investment in the foal and to optimize its health and productivity after birth, horse owners should practice good horse management, including gentling, halter breaking, creep feeding, and overall health care. Friendly, confident foals that are gentled before being weaned are usually less stressed during the weaning process and may learn more rapidly than unhandled foals do. Feeding foals with a balanced ration can optimize growth and introduces the foal to the feed it will be eating after weaning.

Chronic Anhidrosis in the Horse (non-sweaters)

Laura Patterson-Rosa1, Heather Holl1, Martha Mallicote2, Robert Mackay2, Samantha Brooks1 University of Florida, 1Department of Animal Sciences and 2 College of Veterinary Medicine

Anhidrosis is a scientific term that refers to a decreased or complete loss of the ability to sweat in response to appropriate stimuli (1). In horses, it is characterized by the reduced or lack of sweat response to increased body temperature. This is a poorly understood condition with a varying prevalence in the United States horse population. In Florida, 6-25% of Thoroughbreds were diagnosed with clinical signs of anhidrosis. In non-racetrack operations, incidence varies between 2-11% of the horse population. Although of particular concern in warm climates, such as the southern US, horses in any environment can experience anhidrotic bouts during travel or a summer heatwave (2). Clinical signs include partial or complete loss of sweat response, heavy breathing, elevated body temperature (hyperthermia), reduced appetite (anorexia), decreased water intake, hair loss (alopecia), dull hair coat, and depression. Severe cases result in collapse due to overheating, leading to convulsions, and can ultimately lead to death. Anhidrotic horses suffer considerably during work and warm seasons of the year, do not perform well athletically, and have a reduced quality of life (3). These horses need intensive medical management, restricted physical activity in warm weather, and sometimes early retirement from breeding or competition.

Signs of Anhidrosis:

  • Partial or complete loss of sweating
  • Hyperthermia (overheating)
  • Fast breathing with flared nostrils
  • Reduced appetite
  • Decreased water intake
  • Hair loss, usually on chest, croup and face
  • Dull hair coat
  • Depression

Horses have an exquisite cooling system, utilizing a large transpiration capacity in sweat glands distributed throughout nearly the entire body. In order to disperse excess body heat, the horse relies mostly on evaporation of abundant sweat from the skin. However, the equine heat regulatory system can be overwhelmed, resulting in critical overheating. Environmental temperatures exceeding just 77°F (25°C), together with 70-90% relative humidity, will begin to compromise heat loss, leading to the increase in body temperature. Without the sweat response, traveling a distance of ~2 miles at the gallop is estimated to increase the core temperature of a horse by 11°F.

Inadequate conditioning for the required level of physical performance often leads to an exhaustion of thermoregulatory mechanisms and acute or temporary decrease in the sweat ability due to over-training and electrolyte imbalance. Yet, sometimes drugs can lead to temporary anhidrosis, although this condition usually resolves in a matter of days or weeks (4). In contrast, chronic idiopathic anhidrosis (CIA) occurs for more than one consecutive summer season and does not resolve despite changes in housing, diet and exercise schedule (5). However, the factors that distinguish acute but reversible anhidrosis from a permanent loss of sweat ability are still unknown, and the underlying cause of chronic idiopathic anhidrosis remains unclear (6). Sweat glands of acutely anhidrotic horses may appear normal, suggesting a short-term or functional issue. In contrast, in chronic cases skin cells have lost their normally cube-like shape, becoming flattened (7). A quantitative intradermal sweat test (with terbutaline) known as QITSTs can be used by veterinarians for identification of the sweating ability of horses (8).

Horses competing in hot, tropical climates are at higher risk of these conditions, yet both chronic and acute anhidrosis are frequently recognized in many non-tropical regions, especially temperate climates with the sudden onset of hot and humid summers. Mapping the location of cases demonstrates that anhidrosis is not necessarily limited to hot/humid regions. Even if removed from the hot and humid climate, many anhidrotic horses never regain the ability to sweat. With a globally warming climate, this condition is likely to become more widespread in the future.

Quite a few “treatments” are often used for this condition; most of which are based on speculation, anecdotal reports and at best, uncontrolled and unreplicated studies conducted in a small set of horses (2). Owners and clinicians frequently rely on dietary supplements, electrolytes, methyldopa, clenbuterol, and thyroid supplementation, to name just a few attempted therapies. Alternative therapies like acupuncture are also popular, though in at least one report, acupuncture and herbal supplements were shown to be ineffective (9). To date, no treatment for anhidrosis has passed even the lowest standard for evidence-based medicine.

Environmental triggers like over-training, failure to acclimate following travel to a hotter climate, electrolyte imbalance and dehydration can start an acute anhidrotic episode (2). However, CIA defies these trigger factors and may be frequently seen in some breeds and bloodlines. A previous study conducted by University of Florida revealed that, at the individual animal level the risk for anhidrosis varies significantly by breed, with Thoroughbreds and Warmbloods at higher risk. It was also observed that the odds of anhidrosis are 21.67 times higher in horses with a family history of anhidrosis, highlighting a strong genetic component to this disease (5).These findings strongly support the theory that there is a hereditary/genetic component contributing to anhidrosis in horses.

Preliminary data from a pilot research study conducted by the University of Florida and supported by the American Quarter Horse Foundation has shown that Chronic Idiopathic Anhidrosis is a highly heritable trait in the horse. Heritability (h²) is predicted to be around 76%. A heritability of this extent is comparable to estimates for height and other conformation characteristics of the horse (10, 11) and is higher than estimates for complex diseases such as Osteochondritis Dissecans (OCD) in the Thoroughbred (TB) (12). While this research is still ongoing, it will be concluded earlier than expected due to lack of funding resources. Although equine anhidrosis is widely recognized as a life-threatening condition, especially in warm-climate regions, oversight of its frequency has restricted scientific research towards this disease.

The remarkably strong heritable component to CIA disease shows that research can facilitate advancements through genetic selection. Novel discoveries will allow future work to develop preventive strategies, treatments and tools for early diagnosis/detection, as well as immediately permitting selective breeding to eliminate hereditary risk factors. This knowledge will also confer veterinarians the background information to develop treatments that target directly the defective sweat response. These treatments can be used in currently affected horses, helping alleviate symptoms and supporting welfare. Only with better under-standing of the cause, an effective treatment can be developed.

Tips if you have a Chronic Anhidrotic Horse:

  • Work horses during the cooler parts of the day such as evening or early morning.
  • Observe your horse closely for signs of overheating, rapid heart rate, and high body temperature.
  • When introducing a new horse to a hot and humid climate, allow the horse to adjust with turnout time and light work.
  • Start your horse’s spring/summer workout regimen earlier, so that they are fitter for the hottest parts of the season.
  • Always make sure shade is available. Misters and fans can be used for added cooling.
  • Hosing off your horse during the hottest parts of the day will help keep his internal body temperature down.


1. Breuhaus BA. Thyroid Function in Anhidrotic Horses. Journal of Veterinary Internal Medicine. 2009;23(1):168-73. doi: 10.1111/j.1939-1676.2008.0217.x. PubMed PMID: WOS:000262283900025.

2. MacKay RJ, Mallicote M, Hernandez JA, Craft WF, Conway JA. A review of anhidrosis in horses. Equine Veterinary Education. 2015;27(4):192-9. doi: 10.1111/eve.12220. PubMed PMID: WOS:000351360100008.

3. Jenkinson DM, Elder HY, Bovell DL. Equine sweating and anhidrosis - Part 1 - equine sweating. Veterinary Dermatology. 2006;17(6):361-92. doi: 10.1111/j.1365-3164.2006.00545.x. PubMed PMID: WOS:000241777400001.

4. Stieler AL, Sanchez LC, Mallicote MF, Martabano BB, Burrow JA, MacKay RJ. Macrolide‐induced hyperthermia in foals: Role of impaired sweat responses. Equine veterinary journal. 2015.

5. Johnson EB, MacKay RJ, Hernandez JA. An epidemiologic study of anhidrosis in horses in Florida. Javma-Journal of the American Veterinary Medical Association. 2010;236(10):1091-7. PubMed PMID: WOS:000277661700024.

6. Hubert JD, Beadle RE. Equine anhidrosis. Veterinary Clinics of North America-Equine Practice. 2002;18(2):355-+. doi: 10.1016/s0749-0739(02)00016-0. PubMed PMID: WOS:000178315500009.

7. Bovell DL, Lindsay SL, Corbett AD, Steel C. Immunolocalization of aquaporin-5 expression in sweat gland cells from normal and anhidrotic horses. Veterinary Dermatology. 2006;17(1):17-23. doi: 10.1111/j.1365-3164.2005.00498.x. PubMed PMID: WOS:000234673300003.

8. MacKay RJ. Quantitative intradermal terbutaline sweat test in horses. Equine Veterinary Journal. 2008;40(5):518-20. doi: 10.2746/042516408x322409. PubMed PMID: WOS:000257713500015.

9. Mallicote MF, Medina CI, Xie H, Zilberschtein J, Atria S, Manzie M, Hernandez J, MacKay RJ, editors. Acupuncture and herbal medicine used for treatment of anhidrosis2013: WILEY-BLACKWELL 111 RIVER ST, HO-BOKEN 07030-5774, NJ USA.

10. Makvandi-Nejad S, Hoffman GE, Allen JJ, Chu E, Gu E, Chandler AM, Loredo AI, Bellone RR, Mezey JG, Brooks SA, Sutter NB. Four Loci Explain 83% of Size Variation in the Horse. PLOS ONE. 2012;7(7):e39929. doi: 10.1371/journal.pone.0039929.

11. Signer-Hasler H, Flury C, Haase B, Burger D, Simianer H, Leeb T, Rieder S. A Genome-Wide Association Study Reveals Loci Influencing Height and Other Conformation Traits in Horses. PLOS ONE. 2012;7(5):e37282. doi: 10.1371/journal.pone.0037282.

12. Corbin LJ, Blott SC, Swinburne JE, Sibbons C, Fox-Clipsham LY, Helwegen M, Parkin TDH, Newton JR, Bramlage LR, McIlwraith CW. A genome-wide association study of osteochondritis dissecans in the Thorough-bred. Mammalian Genome. 2012;23(3-4):294-303.

Current Horse Transportation Requirements

Dr. Saundra TenBroeck
University of Florida

The Florida Department of Agriculture and Consumer Services (FDACS) regulates entry of horses into Florida and at equestrian gatherings. Rules may vary from state to state, so you should check what documents are necessary when hauling out of state (Interstate Animal Movement Requirements). Traveling with your horse within and outside the state of Florida will require proof of negative Coggins (EIA) test within 12 months. Your veterinarian may use paper forms where identifying marks are drawn and described or they may subscribe to Global Vet Link and submit paperwork electronically with digital photographs. For a more convenient form of verification, you can purchase a laminated Negative EIA Verification Card from FDACS. It is important to note that the EIA verification card is only valid within the state of Florida.

For interstate travel, you also need an Official Certificate of Veterinary Inspection (CVI), more commonly referred to as a “health certificate”. The CVI expires 30 days after the date the horse is inspected. Currently, horse owners can pursue one of two options that will extend the expiration of the CVI to 6 months. One option, the Equine Event Extension is a paper document honored in AL, AR, GA, LA, SC, VA, and WV when accompanied by the CVI and proof of negative EIA test. A second option is called the Equine Interstate Passport Card. It is currently accepted in AL, AR, GA, KY, LA, MS, NY, NC, OK, SC, TN, TX, VA and WV as proof of CVI and negative EIA test.

Changes are coming!

After June 30, 2019, Equine Event Extensions and Passports will no longer be issued. Why? State Animal Health Officials are expected to trace movements of animals so that intervention can be swift if there is a disease outbreak. With passport cards, movements are not readily traceable. Beginning January 1 of 2020, most states will not accept passport cards. The new Electronic Equine CVI, or EECVI, will require the vet to do the initial exam and then the owner must go online and request a permit for each movement or event. The change is being made to provide better documentation of movement of horses, so appropriate measures can be taken if there is a disease outbreak. At the present time Global Vet Link is the only provider of the electronic equine CVI, but a second provider may come online before the deadline of January 2020. A likely candidate is Ag View, a health monitoring company with services across the livestock industry.

Another important piece of the biosecurity/traceability puzzle is Premise Registration. Though not mandatory in Florida (unless getting a passport or 840 microchip), premise identification is a program established to plan for, control, and pre-vent the spread of agricultural diseases. It is also used as an early warning system to notify animal owners of a natural disaster such as a flood or fire that could affect their animals or operations. By completing an application for premise registration, and keeping your information up-to-date, you will take an important step in protecting your animals and those of other Floridians. After hurricane Catrina the Louisiana horse industry supported legislation mandating Premise Identification. The Premise number is an alpha numeric representation of a physical location. If you sell your property, FDACS should be contacted and the premise registration information updated.

Horse Identification

Finally, traceability is not possible without proper animal identification. Though recording gender, color, and markings is standard, digital photographs will be required for electronic CVI. Microchips are becoming more widely accepted in the horse industry. USDA 840-ID chips are considered universal by USDA. Several show horse associations are requiring micro-chips. Other indications for microchip use are sale, ownership, theft prevention, rescue, disaster preparedness, health certificate ID, and Coggins official ID and registry.

Insect Bite Hypersensitivity in Horses

Rosanna Marsella1, Nicky Craig1, Carissa Wickens2, & Samantha Brooks2
University of Florida 1College of Veterinary Medicine and 2
Department of Animal Sciences

What Is Allergic Skin Disease?

Allergic skin disease is a very common cause of itching in horses. This arises from a combination of inherited traits and exposure to allergic triggers which are known as allergens. Allergen is a term used to describe anything which can trigger allergic reactions in horses (and people, dogs and cats etc.) with allergies. Which allergens each horse is allergic to depends on the individual, but can include various pollens, molds and grasses in the environment, food allergens and/or insect bites. Allergies can be very challenging to control as the majority of horses are allergic to more than one allergen. Allergies in horses often cause itching, but in some cases allergies in horses may produce lumps known as hives (or urticaria) without also causing itching.

In itchy allergic horses, exposure to allergen causes the skin to itch and become inflamed. Different allergens add up to make these effects worse. The horse responds by rubbing, scratching and biting to try to relieve the itching, which causes the skin to become more damaged and inflamed, often with diffuse or patchy hair loss. The inflamed skin is vulnerable to secondary bacterial infections, which causes even more itching. Inflammation and secondary bacterial infections of the skin can be identified as areas where the coat appears roughened or the hair has been lost, and there may be small lumps in the skin, crusts, scabs, reddened areas or grey scales (skin flakes or dandruff) on the skin. These lesions may become open sores as the horse rubs or chews at them. Allergies often affect the ears, face, mane, girth, groin and tailhead areas in particular. In the ears, inflammation of the skin tends to lead to yeast overgrowth, which can also cause itching, and is visible as greyish color and f lakes or scaling on the skin. The itching can severely affect the horse’s quality of life, leading to the horse wounding itself by biting or scratching, and can affect the utility of the horse.

horse-has-patches-of-hair-loss-scabs-little-lumps-on-skinjpgFigure 1: This itchy allergic horse has patches of hair loss, scabs and little lumps on his skin which indicate he is allergic to something. The areas affected suggest that he’s allergic to insect bites (e.g. Culicoides: biting midges or “no-see-ums”) and may also be infected with Onchocerca. Areas of the horse’s body particularly affected include the face, ears (where you can see tiny grey flakes of skin in the hair and the skin itself in the ear is grey), chest, main and tail (where you can see hair broken from rubbing) and groin areas, which are where these flies prefer to bite.

Managing Allergic Skin Disease

The first and most important stage in addressing your horse’s allergic skin disease is to con-sult your veterinarian to confirm that the horse has allergies and not another condition which looks similar.

Once it is confirmed that your horse has allergic skin disease, management will require working with your veterinarian to identify what allergens the horse is allergic to, avoiding exposure to those allergens wherever possible and treating secondary infections, as well as managing the itching allergen exposure is unavoidable.

For environmental allergies to pollens, molds and grasses etc. allergen immunotherapy shots can be formulated, in which the horse is regularly injected with small amounts of the allergens they are allergic to. This works in the same way as hay-fever or allergy shots in humans and aims to convince the horse’s immune system to tolerate the allergens instead of reacting to them. This is helpful in many horses, even though it can take up to a year to work, but it is not effective against insect bite hypersensitivity.

Insect bite hypersensitivity, or allergies to insect bites including mosquitoes, biting flies and Culicoides (biting midges or “no-see-ums”) is one of the most common allergies in horses, with Culicoides in particular being a major problem. The area of the horse which is affected, for example mane and tail, face or midline of the belly, will depend on which species the horse is allergic to and where this species tends to bite.

Controlling the Itch

Itching can be controlled using topically applied sprays, shampoos or lotions containing anti-inflammatory medications such as Hydrocortisone, Triamcinolone or Fluocinolone acetonide. Lotions are particularly useful for the face and ears which are not amenable to shampoo therapy. In severe cases, your veterinarian may prescribe stronger anti-inflammatory drugs such as Prednisolone or Dexamethasone.

Sensitivity or adverse reactions may occur after using any product on animals. If your horse shows increased itching and distress after applying a product, bathe the horse with a mild, non-medicated shampoo, and rinse thoroughly with water. Consult your veterinarian immediately if signs continue.

Treating Secondary Infections

Bacterial Infections

Benzoyl peroxide 2.5% or 4% Chlorhexidine shampoo baths can be used to treat mild secondary bacterial skin infections (some 4% Chlorhexidine shampoos also contain 1% Hydrocortisone to reduce inflammation). Benzoyl peroxide is effective in removing crusts, but it may dry and bleach the coat in some animals. Shampoos containing Ethyl lactate are also effective and appear to be gentler and less drying than other antimicrobial products. For small areas, topical antimicrobial sprays are available for use in horses such as oxychlorine- or ETDA-based products or 0.4% stannous fluoride.

Where necessary, your veterinarian may also prescribe an oral antibiotic such as Trimethoprim sulphate. However, bacterial resistance is increasingly common and other bacterial infections may be present, so if treatment does not result in complete resolution of the infection then samples should be sent for bacterial identification and antibiotic sensitivity testing before deciding on further treatment. Always complete the full course of treatment as directed by your veterinarian: your horse may look better before the infection is completely resolved. (If you see any unexpected or adverse effects from a medication contact your veterinarian for advice.)

Onchocerca Larvae

In addition to causing allergic itching, Culicoides also transmit larvae of the parasite Onchocerca which migrate through the skin causing further itching and crusting.

Treat the horse with Ivermectin as directed according to its body weight, every 2 weeks for 6 weeks (i.e. 3 treatments, 2 weeks apart) to clear the larvae. Alternatively, a single treatment with Moxidectin can be used as directed according to body weight. Some horses react strongly to the death of the larvae and develop areas of swelling 1-3 days following treatment, which should resolve on its own in 7-10 days.

Treating Yeast Overgrowth in The Ears

Scale in the horse’s ears suggests yeast overgrowth following allergic inflammation. This can be treated using Clotrimazole (e.g. Lotrimin) or Miconazole cream applied to the scaling areas in the ears daily for 1-2 weeks. Do not use other antifungal creams unless recommended by your veterinarian, as some are not safe to use in ears.

Preventing Culicoides Bites

  • Use Repellent - Permethrin 1% spray should be used once per day and after bathing or heavy rain. Permethrin can be bought as a 10% solution and diluted 1:10 in water (1L of 10% Permethrin added to 9L of water) to produce a 1% solution. DO NOT USE 10% SOLUTION UNDILUTED! Read and follow the product’s instructions and warnings. Groom horses before treatment to remove dirt and dust, then apply the spray to the whole horse paying special attention to legs, belly, shoulders, neck and face. A cloth or wipe should be used to apply the spray carefully on the face to avoid getting the spray near the horse’s eyes or mucous membranes (inside the nostrils and lips). Follow label instructions to protect yourself from exposure to the product when treating.

If your veterinarian feels it is appropriate, Dexamethasone can be added to the spray at for up to a week to control itching. Wear gloves when handling Dexamethasone spray and protect yourself from exposure.

Where the face and ears are affected Equi-Spot® spot-on Permethrin treatment can be used on the poll area every 2 weeks to protect this area.

As an alternative to Permethrin, Neem oil (e.g. Equiderma fly spray) repellent sprays are also effective in repelling Culi-coides. These should also be used daily and after bathing or heavy rain.

Other insecticides such as pyrethrins do not repel Culicoides and will be ineffective in preventing allergies due to Culicoides bites.

  • Avoid Exposure - Culicoides breed in standing water, so keep the horse in dryer areas away from lakes, pools or puddles if possible.

Culicoides are active from dusk until dawn, so keeping the horse in a stable at these times may reduce exposure to bites. If possible, use fans to prevent Culicoides flying into the stable.

Mosquito Magnet® traps can also be used to reduce Culicoides in the environment, and can be effective over an area of up to one acre.

Take Home Message

Itching in horses can be caused by many different problems, which can be difficult to identify, diagnose and manage. Always work with your veterinarian to get the correct diagnosis and the latest management advice. For insect bite hypersensitivity the only fully effective treatment is currently to prevent insect bites by using repellent.

Selected References

Mueller, R.S., Jensen-Jarolim, E., Roth-Walter, F., Marti, E., Janda, J., Seida, A.A. DeBoer, D. (2018) Allergen immunotherapy in people, dogs, cats and horses - differences, similarities and research needs. Allergy, Volume 73, Pages 1989 -1999.

Marsella, R. (2013) Equine allergy therapy: update on the treatment of environmental, insect bite hypersensitivity, and food allergies. Veterinary Clinics of North America: Equine Practice, Volume 29, Issue 3, Pages 551-557.

Schaffartzik, A., Hamza, E., Janda, J., Crameri, R., Marti, E. and Rhyner, C. (2012) Equine insect bite hypersensitivity: What do we know? Veterinary Immunol-ogy and Immunopathology, Volume 147, Issues 3–4, 30 June 2012, Pages 113-126. Scott, D. and Miller, W. (2011) Equine Dermatology. 2nd Edition. Philadelphia: Saunders.

Blister Beetle Toxicity in Horses

Neely Walker
Louisiana State University Agricultural Center

Purchasing hay is routine to many horse owners. While selecting a quality hay is important, it is equally important for horse owners to be aware of a tiny, toxic and potentially fatal passengers in some alfalfa hay bales: the blister beetle.


Blister beetles are members of a family of plant-feeding insects that contain cantharidin, a toxic defensive chemical that protects the beetles from predators. Blister beetles have long (3/4 to 1-1/4 inch) narrow bodies, broad heads and antennae that are about a third of their entire bodies. There are four species of blister beetles that are common throughout the eastern and central states; ashgray, black, margined, and striped. While the amount of cantharidin content contained in each beetle varies; the amount within the striped blister beetle is consistently higher than the other three species. In addition to its high toxin content, striped beetles tend to congregate in large clusters along field margins, which can result in a higher amount of beetles in one section of hay. During the hay crimping process, the beetles are killed and remain in the hay once it is baled. These factors in addition to the fact that blister beetles remain toxic even after they are killed increase the importance of choosing a quality hay.

The lethal dose of cantharidin is between 0.5 – 1.0 mg per kilogram (2.2 lbs) of body weight, but as few as 25 ingested beetles may be toxic to an average sized horse. The severity of the reaction, which ranges from temporary poisoning, reduced digestive ability, to death depends upon the mount of cantharidin ingested and the overall health of the animal. Symptoms typically appear within hours of ingestion and can include inflammation of the digestive and urinary tract, colic, and straining during increased urination. Secondary infection may occur causing kidney failure, increased heart rate and respiration, dehydration, sweating and diarrhea and decreased calcium levels may cause damage to the heart. Animals who recover from the potential intestinal damage may develop complications including laminitis or other systemic infections. Since animals can die within 72 hours it is extremely important to contact your veterinarian as soon as blister beetle poisoning is suspected.

Tips to reduce the chance of blister beetle poisoning:

  • Buy hay from local producers if possible. Develop a relationship with your hay producer and be aware of their production practices.
  • Buy hay harvested in the early part of growing season, when blister beetles are not active.
  • Look for hay that is harvested at the late bud stage or when the first flowers open.
  • Learn to recognize blister beetles and understand their behavior.
  • Check all hay prior to feeding for the presence of blister beetles.

While an effective preventative program will reduce the chances of blister beetle poisoning, there is no efficient way to inspect baled hay carefully enough to be sure that it is completely free of blister beetles. Horse owners must be responsible for identifying and understanding the biology of blister beetles and to follow the suggested tips to protect their horses. If you suspect your horse has come into contact with blister beetles contact your veterinarian immediately.












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