Battle continues to wage against parasitic worms

By MINDY POEHL | Central Texas Edition

Pale mucous membranes on a goat indicate that the goat has anemia, caused by internal parasitic worms, called Haemonchus contortus. -Staff photo by

April 28, 2005 - One of the biggest problems for sheep and goat producers is effective internal parasite control of Haemonchus contortus, or Barber Pole Worms. In fact, many sheep and goats have built up a resistance against dewormers.

On April 19 the Comanche Extension Livestock and Range Committee held a program called "Internal Parasite Control in Goats: New Techniques to Try." Dr. Joan Burke, research animal scientist, USDA, Agricultural Research Service explained the problems of parasitic worms in sheep and goats.

"Abomasal and intestinal worms are the most important pathogens of sheep and goats," Burke said. "Worm control has relied almost exclusively on the use of anthelmintics (medicine that kills worms). You must do your research on sheep and goats to find control methods for parasites."

H. contortus is the most abundant worm found in the stomach, that affects sheep, goats, deer and exotic ruminants, Burke said. The blood sucking of the worms causes anemia and is highly pathogenic.

The worms in the stomach lay eggs, which eventually come out in the animal's feces, where they hatch. The larvae can get in drops of dew on the grass and other animals that eat the grass will contract the worms.

"H. contortus evolved in the tropics and has a short life cycle. It lives less than three weeks out in the pasture," Burke said. "Immunity is slow to develop in sheep, and the background to the problem of resistance is overused anthelmintics."

Worms that are resistant survive and pass on their "resistant" genes.

"So, I don't recommend putting them out to a clean pasture," Burke stated. "Underdosing, treating all animals at the same time and moving animals to a clean pasture is where we have gone wrong in treating the worms."

Benzimidazoles, Ivermectin, Doramectin, Levamisole and Moxidectin helped create the prevalence of resistance of H. contortus, Burke said.

"It doesn't seem as bad as it sounds because not all worms are resistant," Burke said. "Killing some of those worms may relieve the animals for a few weeks."

But, resistance is inevitable. The rate of selection for resistance can be greatly reduced by using two processes: FAMACHA and Smart Drenching.

FAMACHA is a selective treatment that monitors the parasites and helps to identify severely parasitized sheep and goats. FAMACHA provides a tool to identify anemic animals.

"FAMACHA is basically a selective deworming based on the level of anemia determined by the color of the lower eyelid," Burke explained.

FAMACHA provides an eye color chart with five color categories. The chart allows producers to compare the chart with the color of the mucous membranes of the sheep or goats. To find the mucous membranes, pull down the lower lid of the animal's eye and study the color. The redder the membrane, the healthier the animal is. The more pink or white the membrane is, the more anemic the animal is.

Smart Drenching is an approach in which the current knowledge of host physiology, anthelmintic pharmacokinetics, parasite biology, dynamics of selection for resistance and resistance status of worms on the farm are known and recorded.

"Goats metabolize anthelmintic drugs much more rapidly than other livestock," Burke said. "Goats should be given a dose of 1.5 to 2 times higher than for sheep or cattle. Administer drugs orally, because pour-ons are absorbed poorly. And, make sure to use the proper dosage- no less or it will not work- and the proper technique."

For more information on H. contortus, visit the Southern Consortium for Small Ruminant Parasite Control website at www.scsrpc.net.