Treatment protocol for L4 larvae in the anterior mesenteric artery | The Whole Horse Veterinary Clinic / Central Texas Equine (2023)

Treatment protocol for L4 larvae in the anterior mesenteric artery | The Whole Horse Veterinary Clinic / Central Texas Equine (1)Osteopathic examination of the horse's spine is extremely helpful in finding the presence of L4 Large Strongyle larvae in the area of ​​the mesenteric artery. The horse with a larval problem will have limitations on one side of the back from Th12 to L4. This limitation is found on both sides. horses with EPM, which are often found in the presence of L4 larvae; it may be too flexible on the opposite side of your spine.

We have found that the presence of the L4 larvae in the equine anterior mesenteric artery weakens the immune system and allows other diseases such as EPM to enter and become infected. Texas A and M University tested a large population of horses for antibody titers here in Texas and found that 85% of the horses tested had antibodies to EPM. Many of these horses never showed clinical signs. I believe that a horse with a healthy immune system can attack and kill invading protozoa without the horse showing any clinical signs. A horse with a compromised immune system is more likely to develop clinical signs of the disease. Young horses that are about to start training, road horses that compete in a different venue every weekend, and horses with any other type of stress on their bodies such as fatigue. B. ulcers; they are also more likely to develop a complete case of clinical EPM.

Other signs of L4 parasites in horses include a mane that breaks easily, a dry and unhealthy coat, moodiness, reduced productivity, diarrhea and colic. Common performance issues include string box discomfort, not doing tight barrel turns, coming out of the barrel with less power, not making stops, an unwillingness to jump, and less desire to raise your back in dressage.

An extreme presence of L4 larvae can cause thromboembolic colic. This type of colic occurs when the Strongylus vulgaris parasite (bloodworm) enters the arteries near the horse's intestines. This is where they can cause blood to clot, and clots can block blood flow to some of the arteries that supply the intestines. This inflammation and heart attack (death of intestinal tissue) cause this type of colic. Some horses may not be clearly ill, others may show mild colic with a mild fever. Others may have severe colic.

The life cycle of Strongylus vulgaris can last from six to eleven months. These larval forms do not die in freezing conditions, but some of them can die in very hot and dry weather. They eventually develop into L4 larvae and migrate from the colon to the anterior mesenteric artery, where they cause inflammation. I often find that the presence of these L4 larvae causes the walls of the anterior mesenteric artery and dorsal aorta to thicken. Most of these horses have a negative egg count in their feces when tested. The adult worms have died, so there are no eggs, but the L4 larvae persist in the tissue.

Depending on their state of health, I treat these horses delicately. If the horse is strong and healthy, I do the following:

I suggest using colloidal silver during the deworming process to protect the horse's intestines from injury and inflammation caused by the dewormer and dying parasites. I use homemade colloidal silver or commercial colloidal silver from Silver Biotics brand. I stick to the recommended human dose on the bottle for the commercial product. I dilute about two drops of homemade colloidal silver in a little distilled water and pour it over the horse's feed morning and night. I start the colloidal silver about 2 days before the first deworming. If the horse is prone to or has ulcers, I also like to use a probiotic like Advanced Biological Concepts Pro-Bi or Kam Animal Products KLPP. I will start the probiotic a few days before the deworming and continue it along with the colloidal silver throughout the deworming process.

If the horse is weak, I can have him do an organ cleanse before starting the deworming protocol. This prepares the organs for the toxins released by the dying parasites. I use a product specially formulated for my clinic called Stage 1.

If the horse has not been wormed in more than 4 months or the worming history is unknown, I will start one dose of ivermectin before the rest of the protocol. Ivermectin will slowly and gently kill any adult worms in the intestine so that many worms do not die suddenly, which could cause impacted colic.

Wait at least 3 weeks after ivermectin dosing and then start the larvicidal protocol.

Larvicidal protocol:
First of all, you must manage enough Panacur Powerpak for your horse's weight. You can purchase additional unit doses of Panacur if you are treating a horse over 1,250 pounds. The Panacur Powerpak delivers a double dose of dewormer daily for 5 consecutive days. Be sure to give your horse double the dosage that is sufficient for his weight. You can safely overdose on fenbendazole by a hundred pounds or so. Give a little more than a little less than the weight of the horse. If your horse is allergic to fenbendazole, you can use a double-dose oxibendazole product instead. I found that oxybendazole puts a little more pressure on the horse's gut and I prefer the Panacur Powerpak. I also prefer the brand name over the generic. We get better results with the brand.

Wait ten days for the horse to recover from the dewormer; but not long enough for the L4 larvae to recover... and give the first dose of moxidectin according to the horse's weight (NOT a double dose). The larvae are still attacked by Panacur Powerpak and cannot migrate from the dewormer to the intestines and blood vessels.

After moxidectin, wait another ten days and re-administer Quest Plus (moxidectin plus praziquantel) at a dose equal to your horse's weight.

You want to give your horse enough Quest to kill the parasites, so it should be enough for at least one animal of its weight. If you don't give enough, you will only teach the parasite to be resistant to the dewormer. Giving too much fetch can make your horse sick.

Let's talk about prevention:

First of all, a complete management program.

  1. Minimize the number of horses per acre to avoid overcrowding.
  2. Pick up and dispose of manure at least twice a week.
  3. Composting manure in a heap instead of spreading it on the grass
  4. Mow and rake grasses regularly to expose parasite larvae to heat and dehydration. Remember that freezing will not kill the larvae.
  5. If possible, alternate pastures with other animals to break the cycle of horse parasites.
  6. Use an automatic feeder to prevent hay and grain from falling directly on the ground.
  7. Use a charcoal block or flea comb to remove bot eggs from the horse's legs before they can lick and ingest them.
  8. Set up a deworming schedule that suits your area and the way you keep horses.

The American Association of Equine Practitioners is aware of the problem of worms developing resistance to the dewormers we currently have access to. To prevent further development of resistance to the deworming agents we currently use, you must ensure that your horse receives a dose that is appropriate for his weight. If you dose your horse for less than its weight, you will sicken all the worms and kill ANY of them. They develop resistance to the antiparasitic. Many states are successfully implementing a system where only horses that shed worm eggs are dewormed. It appears that only a small proportion of horses appear to carry most of the parasites. We call these horses "eliminators". In theory, if we only deworm the "peelers" we reduce the possibility of resistance developing. If your horse has a high egg count after a certain type of dewormer, you can try using a different ingredient (don't just buy a different brand of dewormer, be sure to use a different ingredient).

Here are some ways to combat resistant parasites:

Regular osteopathic examinations can help the horse to have a strong and healthy immune system; which helps him to be a low eliminator. If a horse sees an osteopath twice a year, he can find and treat the L4 larvae before they can do much damage.

Control ERP and egg renewal time. Depending on the dewormer you use, this is the amount of time after deworming before you start to see eggs in your stool. Here are some examples:
Moxidectin: 10 to 12 weeks
Ivermectin: 6 to 8 weeks
Fenbendazole: 4 to 5 semanas

Perform a FECRT fecal egg count reduction test. Test the horse's feces before deworming and again 2 weeks later to see if the product was effective or not. To be effective, the number of oocytes must be reduced by 90%.

As a general rule, 20% of grazing horses excrete 80% of the parasite eggs found. Separate the low eliminators from the high eliminators and deworm them accordingly. We need to make the worm smart to prevent further resistance from the parasites. Be careful and give your horse enough dewormer for his weight. Dewormer tubes are typically designed for a horse that weighs between 1,000 and 1,250 pounds. If your horse is heavier, you will need to purchase an additional tube of dewormer to achieve an adequate dose for your horse. If you deworm with a less than optimal dose, it trains all worms to be resistant to the dewormer and kills ANY of them.

Worm low droppings less often than high droppings.
Example: For low sheds:
Deworm 2 to 3 times a year depending on its location. In Texas, where it never gets hot or dry enough to kill the larvae; I like to deworm myself at least 4 times a year. Use moxidectin in the spring and fall to kill as many larvae as possible. Consider administering a Panacur Powerpak first if you have strongyle larvae in your area.

For moderate seedlings:
Deworm 3 to 4 times a year depending on its location. When I worked in southern Arizona, where it is hot and dry, we only wormed our horses twice a year and saw very few problems with parasites. In Texas, where year-round moisture protects larvae, consider increasing the amount of dewormers.

For tall sheds:
Deworm these horses every two months. 5 to 6 times a year. Use Moxidectin at least 3-4 times in your rotation and consider prioritizing Panacur Powerpak once or twice a year. You can also do a fecal egg count 4 weeks after the slaughter phase for the last dewormer administered. Test 3 grams of fresh stool, keep samples cool and in airtight containers until ready to test. A sugar float test is preferred. More eggs are found in the fresh sample, and when the clinic sends the stool for analysis, the egg counts are less reliable.

I have not had much success using the fecal test to determine which horses should and should not be dewormed here in Texas. Perhaps this method will work if the horses are not exposed to grass. Most of my clients have horses that graze on some type of pasture and those that do not have parasites in their droppings can still develop L4 larvae in their anterior mesenteric artery if left without parasites for a long period of time. We have also discovered that when we examine the stool in the clinic, we find many more parasite eggs than the laboratory finds when we send out the stool. The eggs appear to be very fragile and seem to break before reaching the laboratory, but examination of the feces while it is still very fresh reveals more eggs.

If your horses are out on pasture in this part of central Texas, I recommend deworming them every 2-3 months with rotary dewormers.

Here is a sample deworming plan for my area near Houston, Texas:

Jan/Feb Double dose of pyrantel pamoate
Marzo/abril oxibendazol o fenbendazol
May/June Moxidectin with Praziquantel
July/August Ivermectin
September/October moxidectin with praziquantel
November/December Oxibendazole or Fenbendazole

Consider using double doses of oxibendazole or fenbendazole in people with high levels of hair loss

Exposure to parasites appears to be more related to immunity in horses than anything else. The best way to protect your horse from worms is to keep his immune system very strong. In other articles on this site, you will learn how to develop a healthy immune system for your horse.

The horses we see in the clinic today with EPM (equine protozoal myelitis) are much less neurological than the presentation many years ago. I believe that a strong immune system helps protect your horse from EPM. Research says that 85% of horses in Texas have been exposed to EPM, but only a small percentage show clinical signs. Horses appear to be developing resistance to the protozoa. We often find that EPM occurs after the horse has parasites in the anterior mesenteric artery that weaken the immune system. We first treated the horse to kill the L4 larvae in the anterior mesenteric artery before moving on to the EPM. We often give a product called Karbo Pellets and Epic liquid to boost the horse's immune system with EPM. There is a natural product called Sefacon that works very well as a protozoan killer. Sefacon cannot be administered within 5 days with any type of antiparasitic. We carry these products here at the clinic. Visit our online store or call us for pricing. (979)243-4969.


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