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OSU Extension

College of Food, Agricultural, and Environmental Sciences

July 21, 2018 - 3:31pm -- lewandowski.11@...

          One of the biggest challenges to raising sheep and goats on a pasture-based production system is managing internal parasites.  For sheep and goats, the internal parasite of greatest concern is Haemonchus contortus, otherwise known as the barber pole worm.  This is a blood-sucking worm that ends up in the gut of the animal after ingestion off pasture grass.  High numbers of the parasite result in poor weight gains or weight loss, general thriftiness, anemia, and in severe cases, death of the animal. The Haemonchus contortus female is capable of producing upwards of five thousand eggs per day that are deposited on pastures with sheep and goat feces. 

          During the summer months, and under optimal conditions, the entire life cycle from egg to egg can occur in as few as twenty-three days.  Pastures can quickly build up extremely high numbers of the infective L3 stage larvae, just waiting for ingestion by grazing sheep/goats.  As if the sheer numbers of parasites on the pasture was not bad enough, research indicates that in our Ohio climate, these infective larvae can survive for 60 to 90 days so pasture rotation is not a good option to avoid infection.  The production stages most susceptible to parasite infection are lactating ewes/does and young lambs/kids. 

            Going back to the 1960’s, parasite control depended upon the regular and consistent application of anthelmintics, commonly known as dewormers.  However, over the past 10 or more years, the issue of parasite resistance to all chemical classes of dewormer on the U.S. market have made parasite management much more difficult.  Current parasite management focuses on a multi-prong approach that utilizes the concept of parasite refugia, “safe” pastures, and the identification of parasite resistant and resilience in animals to slow down the chemical resistance process and maintain chemical effectiveness.

            The refugia concept is dependent upon treating only selected animals rather than the entire flock/herd and planning pasture moves after any dewormer treatment to insure there is a susceptible worm population on the pasture.  Selective treatment is effective because research has demonstrated that 20 to 25% of the animals in a flock/herd are responsible for 70 to 80% of the parasite egg output.  One easy to use tool to identify those animals is the FAMACHA eyelid score.  The FAMACHA system was developed in South Africa.  It uses a 1 to 5 numerical rating of lower eyelid color to determine which animals in a flock/herd need a chemical dewormer rescue treatment.  The eyelid color chart is correlated with anemia and works only for the Haemonchus contortus parasite.  An eyelid score of 1, a dark red color, indicates no anemia or parasite related issues, and an eyelid score of 5, a pale white color, is an indication that death is knocking.  Typically, animals that score a three or higher need a rescue treatment with an effective chemical dewormer.

            Safe pastures are those where the Haemonchus contortus L3 larvae numbers are very low after a grazing pass or where enough time has passed since the last rotation that L3 larvae have died off.   Tillage of an infected pasture can kill and remove L3 larvae.  On some farms, the use of annual forages established with tillage provides safe pasture for at least one grazing pass. 

            Focusing on the genetics of the animal is another tool of parasite management.  Some animals have resilience to parasite infections, that is, they can tolerate parasite levels that would cause other animals to display symptoms of anemia and poor performance.   Some animals have true resistance.  These animals display very low or no parasite infection levels in conditions where other animals are displaying high parasite infection levels.

            For more information about small ruminant parasite management, contact the Wayne County Extension office at 330-264-8722.