How can I raise lambs on irrigated pasture without having to use chemical wormers?

Answer: It is important to test for the amount and species of parasites that you may have on your pastures through fecal egg counts. Your veterinarian or your state veterinary diagnostic laboratory should be able to run these tests for you. Haemonchus contortus (Barber Pole Worm) is by far the predominant sheep parasite in the United States.Successfully raising lambs on irrigated pasture while minimizing parasite infections can be accomplished through a three-pronged grazing-management approach:1. Pasture rest period of 30 to 35 daysThe rest, or pasture recovery, period is the time elapsed between the grazing of one paddock or pasture and its subsequent re-grazing. It is sometimes referred to as the grazing cycle time. On irrigated pastures in the dry Intermountain West, the infective larval populations of Barber Pole Worm tend to diminish after 30 days. Grazing periods that take advantage of this will limit the amount of parasite infection.2. Paddock grazing periods of less than four days (one to two days is ideal) The amount of time that livestock are in a particular paddock is the grazing period. The Barber Pole infective L3 larvae take four to five days to migrate out of a fresh fecal pellet and up the grass stem. Paddock grazing periods of less than four days minimize fresh ingestion of the L3 larvae.3. Exit each paddock with a residual height of five to six inchesIn general, most of the Barber Pole L3 larvae populate the first three inches of the grass stems. Leaving at least the bottom six inches of the grass plant intact when exiting paddocks results in less ingestion of the infective larvae. This practice also results in the trampling of residual grass, which will increase soil organic matter and soil fertility. This should be one of the primary objectives of any well-managed intensive-grazing system.For more information on sustainable pasture management and parasite control, see the following ATTRA publications:Integrated Parasite Management for Livestock Internal Parasites in Sheep and Goats for Managing Internal Parasites in Small Ruminants: Pasture Management Intensive Grazing on Irrigated Pastures? Pastures: Setting Up an Intensive Grazing System That Works