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From Breeding to Foaling
The essentials to properly managing your broodmare
The first step of deciding to breed your mare or buying a brood mare is to determine whether she is able to conceive and if she is able to maintain a pregnancy. A breeding soundness examination is an important step to ensure you have a fertile mare to breed. Your veterinarian can perform this and it will consist of a detailed general and reproductive history, a thorough general physical examination, body condition scoring, and a comprehensive reproductive examination. Good body condition is necessary for fertility and maintaining a pregnancy. Research indicates that mares with a body condition score (BCS) of 6-7 have higher pregnancy rates. This is based on a scale from 1-9 with 1 being emaciated and 9 being severely obese. Additionally, overall good health is necessary as any illness or injury can result in decreased fertility.
The reproductive examination will include evaluation of the external genitalia, a speculum examination of the vestibule, vagina, and cervix, and a transrectal reproductive ultrasound to examine the uterus for fluid, cysts, or any other abnormalities. A uterine cytology, culture, and biopsy will be performed as well to determine if endometritis (inflammation and infection of the uterus) is present and if the endometrium is capable of maintaining a pregnancy. The endometrial biopsy is probably the single most important indicator of a mare’s ability to conceive and maintain a pregnancy. The biopsy results are placed into 3 categories: 1) 80-100% chance of pregnancy 2a) 50-80% chance 2b) 10-50% chance 3) Less than 10% chance.
Once your mare has “passed” the breeding soundness examination, you may start the breeding process. You first have to choose the stallion and decide whether you would like to breed via live cover or artificial insemination. Your veterinarian will need to check your mare with transrectal ultrasound periodically to determine when she is in estrus (heat) and the best time to breed. Depending on the tendency of the mare to develop post-breeding endometritis, she may need non-steroidal anti-inflammatories (NSAIDs) or corticosteroids at the time of breeding.
The vulvar conformation of the mare is very important in maintaining a pregnancy. If 2/3 of the vulvar lips are above the pelvic brim fecal contamination of the vestibule and vagina is more likely, which can result in inflammation and prostaglandin release that is not compatible with pregnancy as well as provide an avenue for ascending infection. Additionally, mares that are windsuckers will also have inflammation of the vagina and vestibule resulting in prostaglandin release. A caslicks procedure can be performed on these mares at the time of breeding or at pregnancy diagnosis. A caslicks is where the edges of the vulvar lips are incised and sutured together to prevent fecal contamination and/or air irritation. The caslicks will need to be removed just prior to foaling.
The mare should be checked for pregnancy around 14 days after ovulation. The uterus should be thoroughly evaluated for the presence of twins. If two pregnancies are present, one will need to be reduced at that time, as the equine uterus does not tolerate twins well. At the time of reduction, it would be wise to administer a NSAID and supplement with altrenogest (ex. Regu-Mate) in order to provide a healthy uterine environment for the remaining embryo. Normal healthy broodmares do not require altrenogest supplementation; however, if any irregularity is present at the 14-day pregnancy check, such as poor uterine tone, increased uterine fluid, decreased progesterone, odd appearance to the corpus luteum, or any other worrisome finding, altrenogest supplementation until day 120 of gestation may be warranted.
14-day equine pregnancy ultrasound
The fetal heartbeat is present by day 25 of gestation. An ultrasound to evaluate the presence of fetal heartbeat should be performed around that time. Fetal sexing can be determined via ultrasound in two windows: day 58-73 or day 110-120 of pregnancy. Further recheck ultrasounds can be performed periodically throughout pregnancy; the frequency depends on the individual mare and veterinarian preference.
Vaccinating broodmares is imperative for disease prevention, passing immunity to the foal, and prevention of abortion. Equine herpes virus one (EHV-1) is a major cause of abortion in mares. The virus is inhaled and without adequate local immune protection it can cause viremia (systemic illness), which results in uterine ischemia (lack of blood flow) and death to the fetus. Pregnant mares should be vaccinated at 5, 7, and 9 months of gestation. It is possible, although rare, for properly vaccinated mares to abort due to EHV-1. Therefore, it is essential to institute management tactics to prevent infection as well. Such methods include separating all pregnant mares from the rest of the herd as well as isolating mares that have aborted and any horses those mares have come in contact with.
It is important to booster all routine vaccines 4-6 weeks prior to the expected foaling date so that adequate antibodies are transferred to the foal in the colostrum. Routine vaccination includes tetanus, rabies, eastern equine encephalitis, western equine encephalitis, Venezuelan equine encephalitis (if it affects that area), and west nile virus. Additionally, if the farm has a known problem with Rotavirus, which causes profuse watery diarrhea in foals, then the mare should be vaccinated at 8, 9, and 10 months of gestation. Other vaccinations, such as influenza, strangles, botulism, and Potomac Horse Fever, can be discussed on an as needed basis with your veterinarian.
Excellent nutrition based on the mare’s metabolic needs for her reproductive stage is a necessity. Mares have to be in good body condition for fertility and they must maintain the body condition throughout pregnancy. Mares have similar metabolic needs through the first 8 months of gestation. Late gestation dramatically increases metabolic needs of the mare due to the fact that 60-65% of fetal growth occurs during this period. Consequently, the mare will need a significant increase in feed during late gestation (9-11 months). Lactation is also a very metabolically demanding time. Mares will produce 3% of their body weight in milk on a daily basis during the first 12 weeks of lactation; this means the mare needs 70% more calories than her maintenance diet. Determining a feeding regiment that is right for your mare(s) can be done with the consultation of your veterinarian and/or an equine nutritionist. Ensuring the mare has an oral exam annually and teeth floated as needed is important to assist in the maintenance of body condition.
One crucial aspect of nutrition is to keep the mare off of tall fescue grass during breeding and throughout gestation. There is as symbiotic relationship between fescue grass and an endophyte fungus, Acremonium coenephialum, which results in a variety of negative effects on gestation and the foal. Mares who consume this grass can have decreased fertility rates and/or early embryonic death. Pregnant mares consuming the grass can also suffer from prolonged gestation, abortion, dystocia, premature separation of the chorion, placentitis (thickening of the placenta), retained placenta, and agalactia (suppressed milk production). Negative effects on the foal include abnormal maturation, weakness, reduced immunity, and starvation from agalactia. If it is not possible to prevent the broodmare from grazing fescue, there are drugs available to counteract the effects, such as domperidone and reserpine.
Routine deworming of the mare is important prior to and during gestation to produce a healthy foal. The best deworming protocol for your horse/herd should be determined with your veterinarian. It is recommended to deworm at least twice a year. Most dewormers are safe to use during pregnancy; however, it is critical to check the label before administering any drug to a broodmare. It is a common practice to give the mare ivermectin on the day of foaling to decrease the transmission of Strongyloides westeri, which can be spread via nursing four days post foaling.
Lastly, it is essential to properly prepare your mare for foaling. It is wise to move the mare to a clean and dry location that can be closely monitored 4-6 weeks prior to the expected foaling date. This will allow her to acclimate to her environment as well as build up an immune response to that particular environment that she can then pass on to her foal. The mare’s udder and her underside where the foal may try to nurse should be cleansed. If a caslicks was performed, the vulva should be opened to prevent tearing at parturition. Knowing the signs of impending parturition will help to better predict the time of foaling. Physical changes include relaxation and edema of the vulva, mammary gland development, scant vulvar discharge, relaxation of the tailhead, and changes in the udder secretions.
Mammary gland development, also referred to as bagging up, and secretions are the most useful tools to predict impending parturition. The mammary gland begins developing one month prior to foaling and has a drastic increase in size within two weeks of parturition. The udder is typically engorged within days of foaling. Udder secretions may start as early as one month prior to foaling, and they will change from a clear or yellow color to white and milk-like. The appearance of waxy secretions on the teats usually occurs 1-4 days prior to foaling but can occur as early as 2 weeks. The waxy secretions are from early colostrum formation. Colostrum is the first milk the mare produces, and it contains all of the antibodies she will pass to the foal. Therefore, if the mare is leaking a significant volume several days to weeks prior to parturition, it is strongly encouraged to collect and freeze that colostrum so that it can be fed to the foal at birth to ensure adequate passive transfer. Mammary gland secretions can provide valuable information on impending parturition. There are several milk tests available to determine the electrolyte levels, which change related to fetal maturity and viability, and therefore are informative on the proximity of foaling.
When the mare is close to foaling, she should be closely monitored throughout the day and night. Commonly used monitoring systems include camera stalls and foal alert systems. The foal alert system involves suturing a device into the mare’s vulva that will separate and produce an alarm at foaling.
When the mare is suspected of foaling that evening, it is recommended to clean and dry the perineal region as well as to wrap the tail for a cleaner environment. There are three stages of parturition. Stage one is the preparatory phase, which can last 30 minutes to 4 hours. During this phase the mare can exhibit signs similar to colic, including flank watching, restlessness, raising and swishing the tail, and urinating small volumes frequently. This phase is very important for the repositioning of the fetus into the “diving position” pictured below. Stage two begins at the rupture of the chorioallantois allowing the allantoic fluid to escape the uterus, also known as the water breaking. This phase includes the expulsion of the foal. If there is a red bag present at the mare’s vulva it should be ruptured immediately. Instantly rupturing the membrane is essential to foal survival, as this is indicative of premature placental separation and lack of fetal oxygenation. Calling your veterinarian after the membrane is ruptured is strongly encouraged. If no red bag is present, the white amnion should appear at the vulva within 5 minutes of the water breaking. The foal will normally pass within 30 minutes. If the foal has not passed in that time or if there is no significant progress over 5-10 minutes, it is strongly encouraged to call your veterinarian for assistance. After the foal has passed through the mare’s pelvis, stage 3 begins. This stage consists of the expulsion of fetal membranes and uterine involution. There is a “1-2-3” rule to follow at this point. The foal should stand within the hour, nurse within 2 hours, and pass meconium within 3 hours. The mare should also pass the full placenta within 3 hours of foaling. The placenta can be tied to itself so it hangs just above the hocks to avoid being stepped on. If the placenta has not passed within 3 hours please contact your veterinarian immediately.
“Diving position” of the foal at birth
The umbilicus usually breaks when the foal attempts to stand or when the mare stands. If the umbilicus does not rupture on it’s own, it should never be cut as that can result in a patent urahcus and/or excessive hemorrhage. There is a pre-determined break site that is evident by a pale strictured area. This point should be identified and the forefingers are used to twist above and below taking great care not to pull excessively on the cord. Once the umbilicus has been torn, the stump should be closely evaluated for hemorrhage, urine leakage, or swelling before being dipped in a dilute 0.5% chlorhexadine solution.
Once the mare has passed the placenta it should be thoroughly evaluated to ensure all pieces are intact. It is crucial to the mare’s health that no pieces of placenta are retained within the uterus as this can result in severe systemic illness. Saving the placenta in a large bag within the refrigerator is recommended so that your veterinarian can evaluate it fully to look for any missing pieces and signs of placentitis. It is strongly recommended to have your veterinarian evaluate both the mare and foal within 12 hours of parturition to ensure they are both in good health and that the foal has adequate passive transfer.
If you have any questions or concerns regarding your mare or foal’s health please feel free to contact New England Equine Medical and Surgical Center.
Kristina McGinnis, DVM
New England Equine Medical and Surgical Center
1. >Brinsko, Steven P., Terry L. Blanchard, Dickson D. Varner, James Schumacher, Charles C. Love, Katrin Hinrichs, and David Hartman. Manual of Equine Reproduction. 3rd ed. Mosby Elseveir. Print.>
Nailed it!!! Direct Penetrating Wounds to the Horse's Foot
by Dr Jordan Koivu
Uh oh... Your horse has a nail in its foot - and it’s not one that the farrier has nailed in on purpose! Many owners have found their horses acutely lame due to a direct penetrating wound to the foot. Whether it is a nail, a screw, or any other sharp object, it is imperative that you have your veterinarian come take a look before removing anything so that they can confirm the tract of the penetrating object.
Aside from bone, there are many important soft tissue structures in the foot, including the navicular bursa, coffin joint, deep digital flexor tendon, and digital flexor tendon sheath to name a few. Therefore, if you notice that your horse has a nail stuck in the foot, it is best to call your veterinarian immediately so that they can come and take radiographs to determine the direction that the object has travelled within the foot. Once the tract of the nail has been confirmed, appropriate treatment can be instituted in order to have the best possible outcome.
While you are waiting for your vet to arrive, or if you have to walk the horse a significant distance to get tot the barn, you can always tape a small block of wood to the non affected side of the sole, or cute a hold out of a block of wood where the nail would go and tape the wood to the foot. These two methods still allow the horse to walk without driving the nail further into the sole of the foot. If the nail is unable to be left in place for any reason, the vet can use a sterile probe or contrast dye to determine the direction of the tract.
Depending where the nail has penetrated the foot, different structures have the potential to be infected. If the nail has penetrated within the sole, typically the main areas of concern include the sensitive laminae of the hoof and the coffin bone. Possible sequelae to damage in that area can include sub solar abscesses, coffin bone fractures, or pedal osteitis. If the nail has penetrated the middle third of the frog, then it could affect the digital cushion, deep digital flexor tendon, coffin joint, navicular bone or bursa, digital flexor tendon sheath, or digital cushion. If there is a concern that a synovial structure has been affected, a sample of that joint fluid can be collected and synovial fluid analysis can be performed. Prognosis is determined by the depth of penetration, size of the penetrating object, location of penetration, tissues involved and the duration of time before treatment is initiated.
Once the extent of the wound has been confirmed, treatment can be instituted.
Thorough cleaning and debridement of the wound is typically the first step, and the farrier can certainly play a role in this. If no soft tissue structures are involved and the wound does not require surgical intervention, then a hoof knife can be used to tidy up the frog and sole, and then a curette to debride the tract to allow for better drainage as well as remove any impacted debris. Concurrent treatment typically involves antibiotics to help prevent or control infection, as well as analgesics to control pain and inflammation. A culture and sensitivity can be performed to ensure that the appropriate antibiotics are used. If no soft tissue structures or bones are affected, then the foot can be bandaged as though it were a foot abscess, using poultice to draw any debris from the wound.
If deeper soft tissue structures or bones are affected and surgery is required, the horse is anesthetized and the puncture wound is debrided and all devitalized tissue is removed. The wound is usually enlarged to improve drainaige, then thoroughly lavaged. Some may choose to pack the solar defect with antibiotics and sterile gauze, before bandaging it. Following surgery, adjunctive therapies such as regional limb perfusions and continuing to pack the solar defect with antibiotic soaked gauze may be instituted. A special shoe, referred to as a hospital plate, can be made by the farrier to protect the solar defect and maintain cleanliness post-operatively.
Below are radiographs of two separate cases involving direct penetration wounds to the foot. Case 1 shows a nail that on the lateral view appears as though it is contacting the navicular bone and bursa, as well as the deep digital flexor tendon. However, when examining the dorsopalmar view, the nail is actually on the medial aspect of the sole, entering along the white line, giving this horse a good prognosis pending no complications. Case 2 shows a more complicated scenario, where the screw has penetrated into the frog and has made contact with the coffin bone. This horse underwent surgical treatment followed by intense post-operative care involving intravenous antibiotics and analgesics, regional limb perfusions, and antibiotic infused gauze packing in the solar defect as well as a hospital plate.
Case 1. Lateral and dorsopalmar views of the right front foot.
Case 2. Lateral and dorsopalmar views of the left front foot.
In conclusion, it is possible for these penetrating wounds to have good outcomes if they are treated immediately and aggressively. Both veterinarian and farrier can play an important role in the management of these cases. Finally, it is always important to remember that tetanus can be a fatal complication of these incidences. Therefore, if the horse has not been vaccinated for tetanus within the last six months, then it should receive a tetanus vaccine.
If you have any other questions concerning penetrating wounds to the foot, feel free to call New England Equine Medical & Surgical Center. >
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What is a Popped Splint?
by Lori M. Smolkovich, DVM
One day as you are getting ready to ride your horse, you notice a bump around the cannon bone. Your horse seems sensitive to palpation, but overall is sound. You ask for advice from other people in the barn. They say it is a "popped splint", and before you know it, you are being flooded with advice and opinions leaving you confused and unsure of what to do. This is a common scenario we as veterinarians hear all the time. There seems to be some confusion among horses owners regarding metacarpal exostosis, better known as "a popped splint" or "splint". In this article, the different types of "splints" will be discussed, along with cause, diagnosis, treatment, and prevention.
Before discussing "splints" and how they occur, some anatomy needs to be reviewed. In the front leg, the horse has metacarpals II, III, and IV. The third metacarpal bone is the cannon bone. The second and fourth metacarpal bones are called splint bones because they are on either side of the cannon bone, "splinting" the leg. The second metacarpal bone is on the medial (or inside) of the cannon bone and the fourth metacarpal bone is on the lateral (or outside) of the cannon bone. The splint bones are held tightly against the cannon bone by the interosseous ligament (inter=between, and osseo=bone). In the hind leg, the anatomy is the same except instead of naming the bones metacarpals, the term is metatarsals.
What is a "splint"?
There are four types of "splints" but only two are common and noticed by horse owners. Those will be the only two types discussed in this article.
True splint: A true splint is tearing of the interosseous ligament. These tears most frequently occur on the medial (or inside) of the leg between the medial splint bone and the cannon bone. Usually the tear is in the proximal third (top third) of the leg. The body's way of repairing itself, is to deposit calcium into the tear to make the area stronger. The "bump" that the owner feels on the leg is a result of inflammation and the deposited calcium.
Traumatic splint: A traumatic splint is the result of trauma to the periosteum. Periosteum is a dense fibrous membrane that covers the surface of bones. As a result of trauma, the periosteum becomes inflamed. If there is sufficient inflammation, the bone will heal itself by depositing calcium. The degree of inflammation is dependent on the level of trauma and the way in which the horse's body responds to that trauma. This is why some bumps are temporary and resolve when the inflammation subsides, and some are permanent, due to calcification deposition. A traumatic splint can occur on the cannon bone or either splint bone.
Why do "splints" occur?
True splints, as already stated, are a result of the interosseous ligament tearing, and that these tears most frequently occur between the cannon bone and medial (or inside) splint bone. A better understanding of anatomy and biomechanics are needed to explain why this happens. When a horse bears weight on a front leg, the lower row of carpal (knee) bones and the medial (inside) splint bone articulate (join) in a way that causes the medial (inside) splint bone to be pushed down and back. If a horse is overworked, or if the area is overloaded, the interosseous ligament cannot handle the stress of being pushed in two different directions, and it tears. Offset carpi, also known as benched knees, is a conformational abnormality that can also cause true splints even if a horse is not overworked. As horses age, the interosseous ligament naturally disappears as the splint bones fuse to the cannon bone. This is why true splints are usually a condition of younger horses, because in older horses, the ossified interosseous ligament can handle a much more demanding workload.
A traumatic splint can occur in many ways; getting kicked by another horse, interference (hitting one leg with the foot from the opposite limb), or hitting objects, are common occurrences. If the "splint" is on the outside of the leg, it is probably the result of external trauma, such as hitting a rail while jumping or being kicked by a pasture mate. If the trauma is on the inside of the leg, interference is the most common cause. Several conformational abnormalities predispose a horse to interfering which can result in "splints". Base narrow horses or toe out conformations are naturally occurring conformational abnormalities, but improperly trimmed and/or shod horses can cause abnormal foot flight and as a result, interference occurs.
Diagnosing a "splint"
A "splint" diagnosis is usually fairly straightforward. There is heat, pain, and swelling over the bump. It is very sensitive to palpation and horses are usually mildly lame at the trot on hard footing. A radiograph should be taken to confirm it is a "splint" and not a fractured splint bone, which is a more serious condition. Although the "splint" by itself is usually a temporary lesion with no real long term consequences, it can affect other structures and cause big problems. The suspensory ligament runs in between the two splint bones. Inflammation or calcification deposition that is caused by "splints" can impinge on, or interfere with the suspensory ligament which can have serious effects on the horses long term use. This is why ultrasonic examination is often recommended. Through ultrasound, the suspensory ligament can be assessed. This gives your veterinarian a complete picture of what is going on and the best way to treat your horse.
The goal of treating a "splint" is to reduce inflammation. This is done by the use of non-steroidal medications, like bute, ice therapy, and wrapping the affected limb. Some veterinarians recommend DMSO or a DMSO/furazone sweat wrap underneath the bandage to further treat inflammation. Rest is given until the inflammation has subsided and the horse is sound. This usually takes approximately a month. If suspensory ligament involvement is suspected, treatment is usually more aggressive using intralesional corticosteroid injections, or shockwave therapy in addition to the inflammation reducing techniques already listed.
The likelihood of splints occurring in your horse can be minimized but not completely eliminated. You can not change the way your horse moves or conformation. But by making sure your horse is properly trimmed, not overworking, and having protective wraps or boots on your horse while being turned out and ridden, can help minimize any trauma that might occur.
Should you consider buying a horse with a "splint"?
Overall, "splints" usually cause a temporary lameness with no long lasting problems. Once the inflammation has resolved, the bump that is left is nothing more than a cosmetic blemish. Before considering purchasing a horse with a splint, the splint should be thoroughly evaluated by your veterinarian to ensure the suspensory ligament is not effected and that the splint is not still inflamed or causing problems. The cause of the splint should also be investigated. If the horse has poor conformation, or a tendency for interference when ridden, then there is the likely chance that "splints" will be an ongoing problem.
Stashak, Ted. "The Metacarpus and Metatarsus." Adams' Lameness in Horses. Fifth ed. Philadelphia: Lippincott Williams and Wilkins, 2002. 818-821. Print.
Rooney, James R. "The Abnormal Foreleg Shoulder to Fetlock." The Lame Horse. First ed. Neeah: Russell Meerdink, 1998. 57-60. Print.
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Common Equine Parasites and Deworming Strategies
Deworming protocols are a common discussion amongst barn managers, horse owners, and veterinarians. In order to understand various deworming strategies and apply the one that works best for your horse, you have to know the common parasites that affect the horse.
In years past, Strongylus vulgaris (large strongyles) was the equine parasite of most concern. Large strongyles take approximately two months from the time they are ingested by the horse until they are shed in the manure to further contaminate the pasture. Thus the traditional rotational deworming strategy was developed and adequately controlled large strongyle infections. However, large strongyles are rarely an issue in managed horse populations today, and therefore rotational deworming is no longer needed or recommended.
Cyathostomins, or small strongyles, are considered the major adult equine parasite. Small strongyles are pervasive and infect grazing horses everywhere. Luckily, small strongyles typically only produce disease when the parasitic burden is severely elevated, although they can result in disease at lower levels if the horse’s immune system is compromised in some other way. Since low levels of small strongyles do not result in disease and large strongyles are well controlled in today’s horse populations, frequent deworming is no longer necessary, rather properly timed deworming during the seasons of heavy parasitic burden and transmission is ideal.
Anthelmintic (dewormers) resistance is becoming a problem that can be delayed and hopefully controlled with the use of fecal egg counts (FEC), proper pasture management, and appropriately timed deworming for that particular environment. Parasite refugia is a common term used by parasitologists and veterinarians that refers to the population of parasites that survive the administered anthelmintic; this includes the stages of parasites that are not affected by that drug, the parasites within the horses that were not treated, and all of the living parasite stages on pasture. The larger the proportion of parasites in refugia, the slower resistance can develop. Therefore, it is advised to perform fecal egg counts on your horses biannually and deworm according to parasitic burden so that only a proportion of the horses in the herd will be dewormed at that time rather than deworming all of the horses at once. Another management tactic to slow anthelmintic resistance is to avoid rotating pastures right after deworming as this eliminates the dilution effect. Lastly, avoiding deworming during periods of low parasite transmission/low pasture refugia is advised. Low pasture refugia occurs during periods of extreme temperatures because larvae (parasite eggs) cannot survive in harsh weather, such as the winters in the north or the summers in subtropical and tropical environments.
It is also important to understand that some horses are more sensitive to small strongyle infections, and therefore will always shed more eggs than others. In fact, 20-30% of adult horses in a herd shed approximately 80% of the total eggs. Therefore, horses are divided into three categories based upon their FEC numbers: low (0-200epg), moderate (200-500epg), and heavy shedders (>500epg). On average, if a horse’s FEC is over 200 eggs per gram (epg) then he/she should be dewormed, although individual veterinarians may have different cutoff values. Moderate and heavy egg shedders may require more frequent deworming than twice a year.
Other gastrointestinal parasites that affect the adult horse are Anoplocephala perfoliata (tapeworms), Oxyuris equi (pinworms), and Gasterophilus spp. (bots).
· >Tapeworms are spread through the ingestion of an oribatid mite commonly found on grass pastures. These mites live in moist areas, and therefore tapeworms are usually not an issue in arid environments. Tapeworms have the potential to result in various types of colic. They cause small mucosal erosions at the site of attachment, which can be painful. Also, an infection with tapeworms can result in an ileocecal impaction or a spasmodic colic if the burden is high enough. Tapeworm eggs are intermittently shed in the manure and can be easily missed on fecal floats. Therefore, it is important to deworm with an anthelmintic once a year that is efficacious against tapeworms, such as praziquantel (sold in combination with ivermectin or moxidectin) or a cestocidal dose of pyrantel pamoate. It is recommended to treat for tapeworms in the late fall or early winter.>
· >Pinworms have historically been an issue with young horses; however, they have become increasingly more common in adult horses recently. Pinworm eggs are deposited on the perineum and perianal regions and result in pruritus (an itching sensation), which can lead to intense tail rubbing and skin excoriations. The tail rubbing in addition to sharing grooming materials and tail wraps can spread the pinworms to other horses. The best way to control pinworms is to deworm when clinical disease is present. Ivermectin, moxidectin, pyrantel pamoate, or fenbendazole will eliminate a pinworm infection. Additionally, it is recommended to wash the perineum and perianal regions to provide relief of pruritus and to decrease transmission to other horses.>
· >Bots rarely result in disease but are aesthetically displeasing. Therefore, deworming annually in late fall or early winter will help to decrease transmission the following season. Ivermectin or moxidectin are the only anthelmintics available at this time that are efficacious against bots.>
Parascaris equorum (roundworms) is the primary parasite of foals and weanlings. Infections can result in poor growth, airway inflammation (cough, nasal discharge), and small intestine impactions. Small intestine impactions and subsequent fatal intestinal ruptures can occur when foals/weanlings with a heavy roundworm infestation are dewormed with an efficacious anthelmintic. Small intestine impactions are not seen when foals/weanlings are dewormed with fenbendazole, and therefore that is the drug of choice when deworming foals for the first time. During the first year of life, foals/weanlings should be dewormed a minimum of 4 times beginning at 2-3 months of age with fenbendazole. The second deworming should occur just prior to weaning, and the drug of choice will depend on whether primarily small strongyles or roundworms are seen on the fecal float. The third and fourth dewormings should be performed at 9 and 12 months respectively and they should target small strongyles (ivermectin or moxidectin).
In summary, small strongyles are the parasite of most concern for adult horses today. Having a fecal egg count done on your horse at least twice a year to determine his/her parasitic burden is essential. Deworming at least twice a year is recommended, with additional dewormings as needed based on the parasitic burden of the individual horse. Deworming in late fall or early winter with praziquantel (found in combination with ivermectin or moxidectin) is essential to treat for any tapeworm burden or bot infestation. Discussing your horse(s) with your veterinarian to develop an appropriate deworming strategy is the most important way to keep your horse(s) healthy.
Kristina McGinnis, DVM
New England Equine Medical and Surgical Center
AAEP Parasite Control Guidelines