Back from the Vet: Gastrointestinal Parasites in Goats
There can be a multitude of reasons for any animal to be a poor doer. One common cause for animals not to thrive is gastrointestinal parasitosis.
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Springtime has come, with all of its green and growing. Your goat herd should have recovered from the stresses of winter and kidding and be ready for a productive summer. In any herd, there may be some goats that aren’t gaining as well as expected. There can be a multitude of reasons for any animal to be a poor doer. One common cause for animals not to thrive is gastrointestinal parasitosis.
The primary gastrointestinal parasites of goats are nematodes, or round worms. The most common of which are Haemonchus contortus, Teladorsagio (Osteragia) circumcinta, Ostertagia trifurcata, and Trichostrongylus axei. Haemonchus is more common in tropical and subtropical climates, or those receiving summer rain, while Ostertagia and Trichostrongylus are found in the more temperate climates. One of the nematodes, Haemonchus, causes the most severe disease, as the adult worm consumes large amounts of the host animal’s blood. Although the other nematodes do not result in as severe clinical signs as Haemonchus, infestation of animals with these parasites still results in ill thrift and decreased weight gain.
Most goat gastrointestinal parasite prevention protocols focus on treating infestations of Haemonchus contortus. In order to prevent and treat infestations of this parasite, it is important to understand its life cycle. Haemonchus goes through five stages prior to becoming an adult worm. This cycle takes 21 days. Eggs are passed in feces of infected animals. These eggs develop into L2 larva in the feces in roughly six days. L2 larva mature into L3 larva and leave the fecal material. These larvae survive in the environment for an extended period of time and can move up grass blades two to three inches. The L3 larva is then digested by a grazing animal. Within the abomasum, or true stomach, of the animal L3 will molt into L4. L4 will then either enter a stage called hypobiosis, or mature into an adult. Hypobiosis is a stage of dormancy or arrested development where the L4 encysts in the glands of the abomasum. There are a multitude of signals that can signal the L4 stage to mature into adult worms. These signals include changes in the external environment, like increasing temperatures and rain, as well as internal environment, such as the rise of estrogen within the host. Haemonchus can become dormant during times when external conditions are unfavorable to maturation of larvae, such as cold winters or hot summers.
As mentioned previously, a heavy burden of Haemonchus can cause severe anemia. Anemia can be assessed by examining an animal’s mucous membranes, namely in the eyes and mouth. Haemonchus can also cause a condition called bottle jaw, which is edema, or fluid accumulation, in the tissues under the jaw. Weight loss and decreased production may also be noted. While Haemonhcus does not generally cause diarrhea, the other nematodes, Ostertagia and Trichostrongylus, are noted to do so. Definitive diagnosis of Haemonchus and other gastrointestinal parasites is done by fecal assessment. Feces of a group of animals or individual animals is assessed by veterinary professionals. In herds with Haemonchus infestations, FAMACHA scoring may be used to assess severity of anemia. FAMACHA provides a color graduation chart with indications for when to treat animals for those infections. When concerned about a GI parasite problem within your herd, it is important to work closely with your veterinarian to determine the cause.
Treatment for gastrointestinal parasites is focused on two things; pasture rotation and anthelminthics, or dewormers. Pasture rotation is just as important as deworming as it disrupts the life cycle of the parasite. Animals grazed continuously on the same pasture are more prone to gastrointestinal parasitism. In goats, which are more apt to browse, they should be fed off the ground whenever possible. This decreases the risk of fecal contamination of feed. Pastures that have been grazed down should be allowed to rest, and goats should be moved into another pasture. It is also helpful to alternate the species of animal grazing pastures. Horses and cattle are not the appropriate hosts for the parasites of small ruminants, so it safe for them to graze a pasture after goats without continuing the parasite life cycle. Pastures that have been recently burned or tilled are also good pastures to rotate into, as those processes destroy the parasite larva. Timing of movement from pasture should also be coordinated with the deworming protocol of the farm. If possible, animals should be kept on the same pasture, or dry-lotted for a day or so after deworming. This prevents the transmission of the parasites to the new pasture.
Anthelminthics, or dewormers, are the medications used to treat animals found to have parasite infestations. There are three classes of anthelminthics used in goats; avermectins, benzimidazoles, and imidothiazoles. Avermectins include ivermectin and moxidectin. While these medications are effective against nematodes, they are not FDA approved for use in sheep and goats. Using these medications “extra-label” means that their use requires a prescription from your veterinarian which includes dosage and withdrawal times. Benzimidazoles are labeled for use in sheep and goats. These products include fenbendazole and albendazole, which are white drenches. These products tend to be less effective against Haemonchus than other dewormers. If parasites are resistant to one of these medications, they are likely to be resistant to the entire class of medications (resistance will be discussed shortly). Finally, the only imidothiazole is levamisole. It is also approved for use in goats with fewer issues with resistance and effectivity than the benzimidazoles. When choosing the appropriate medication for your herd, it is important to consider what parasites you are treating as well as route of administration and cost of these medications. Haemonchus is often not the only parasite that needs to be treated. Especially when using drugs not labeled for goats, it is important to seek the advice of a veterinarian to ensure appropriate dosing and administration.
While anthelminthics are the only way to kill these parasites in the case of an infestation, there are now concerns about over-use of these products. Parasites can develop resistance to these medications, especially with repeated use. To reduce the risk of resistance within your herd, several steps must be taken. First, anthelminthics must be used wisely. When dosing, it should be ensured that every animal is receiving sufficient dosage. The easiest way to do this is to set the dosage for the largest animal in every group treated. It is also not necessary to deworm every animal within your herd. Targeting only animals with clinical signs or increased risk reduces resistance as well as cost. FAMACHA scoring and careful consultation with your veterinarian can provide an appropriate protocol. The use of anti-parasitics should also be coupled with appropriate pasture rotation and feeding methods. Animals should not be moved to a new pasture immediately after deworming, as that exposes that pasture only to resistant parasites. Care should also be taken when bringing new animals into your herd. Those with indications of parasite infestation should be avoided, or quarantined. Animals with infestations may easily be identified by sending feces for testing.
Gastrointestinal parasites, and Haemonchus particularly, can result in serious losses within your goat herd. It is very important when beginning a parasite control program to work closely with your veterinarian. Yearly or biannual deworming with alternating anti-parasitics is no longer the recommended protocol, as this can lead to increased resistance within your herd. Creating a parasite control protocol that is effective for your herd is imperative to control parasites and prevention of resistance. This control program should be based not only on deworming, but also on strategic grazing and feeding.
Katie Estill, DVM, is a veterinarian consultant for Goat Journal, Countryside & Small Stock Journal, and Countryside online. She works with goats and other large livestock at Desert Trails Veterinary Services in Winnemucca, Nevada.