Current deworming advice (Shepherd’s Notebook)
(Editor’s note: Susan Schoenian is a sheep and goat specialist with the University of Maryland.)
Sheep/goat producers almost always cite worms as the primary health problem affecting their livestock.
While small ruminants can be affected by many different kinds of parasites, the primary one affecting them during the summer grazing season is the barber pole worm (Haemonchus contortus).
The barber pole worm is a blood-sucking nematode that causes anemia (blood loss), bottle jaw (sometimes), and sometimes more generic symptoms, such as loss of weight and body condition. Sudden deaths are not uncommon.
While there are many practices that can minimize exposure to infective worm larvae, the only way to treat a clinically-parasitized animal is usually with a drug (dewormer).
Unfortunately, there is considerable resistance to the drugs designed to kill worms in sheep/goats.
Resistance tends to be highest among the benzimidazoles: fenbendazole (SafeGuard) and albendazole (Valbazen).
High levels of resistance are also common with the avermectins: ivermectin (Ivomec), doramectin (Dectomax), and eprinomectin (Eprinex). Efficacy is usually better with moxidectin (Cydectin). Levamisole (Prohibit, Leva-Med) is usually the most effective dewormer.
Resistance varies by farm.
Due to drug resistance, it is now recommended that clinically-parasitized animals be given combination treatments.
A combination treatment is when you give dewormers from different drug families to the same animal. The purpose is to kill as many worms as possible.
Besides delivering a more effective treatment, this strategy helps to slow the development of resistant worms.
It is recommended that the most potent drug from each class be given: albendazole + moxidectin + levamisole. Give one drug after the other, full dose, don’t mix.
With combination treatments, you need to observe the withdrawal period for the drug with the longest withdrawal (usually moxidectin).
Goat (and camelid) producers need to seek the advice of a veterinarian when giving combination treatments, since none of the recommended drugs are FDA-approved for them and higher doses of the drugs are usually advocated for goats (versus sheep).
With a few exceptions, animals that are not showing clinical signs of parasitism should not be given dewormers.
There are various criteria that can be used to determine if an animal is clinically-parasitized and needs deworming. These include FAMACHA score,
Five Point Check©, and performance indicators, such as ADG.
Fecal egg counts can help determine deworming need but should not be used as the sole (or main) criteria when making deworming decisions.
Another important recommendation to follow is oral dosing. Small ruminants should always be given dewormers orally.
This does not mean squirting an injectable dewormer into an animal’s mouth or drenching it with a pour-on.
Only drench (oral) formulations should be used in small ruminants.
It is important that the drugs be delivered over the tongue into the animal’s gullet using an oral dosing syringe with a long metal nozzle and bent end.
Dosage should be based on accurate weights.
For more information about worm control in small ruminants, be sure to visit the web site of the American Consortium for Small Ruminant Parasite Control at www.wormx.info.