How long should a pasture be rested to ensure that Barber Pole Worm has died off?
About 80% of the Barber Pole Worms live outside the host (either a lamb or a ewe) as larvae in the pasture grass. They are shed as eggs in the fecal pellets, then after four to nine days hatch out as larvae and crawl up the grass leaves. They are mostly in the two- to four-inch height range on the grass leaves. So, sheep can be on a pasture for about four to nine days before they can ingest the new larvae and re-infect themselves. Four days is a safe number to use. The hotter and wetter it is, the faster this egg-to-larvae transition takes place.
The length of time a pasture should be rested before regrazing depends upon the ambient temperatures. Australian research has determined that 90% of the Barber Pole Worm larvae die in 45 days of 90-degree highs. Barber Pole Worm larvae have been known to live for six months in cool temperatures in the 40-degree range. The reason is that BP larvae do not eat; instead, they have a fixed source of fat stored up. They also “wiggle” to swim through moisture droplets. The warmer it is, the more they wiggle, expending this fat energy.
It is very convenient that irrigated, cool-season grasses generally take at least 30 days to fully recover from a grazing event. This roughly coincides with the time it takes for about 75% of the BP larvae on the pasture to die in our summers. You should always let your grass fully recover before regrazing. You can tell when grass has fully recovered by checking the bottom leaf on a grass stem. It will be brown or have about one to two inches of brown on the leaf edge when the plant is fully recovered. This is its sign. For a demonstration of this, see the ATTRA video Intensive Grazing: One Farm’s Setup, Chapter Two, Sizing Your Paddocks.
Our experience has been that if you rest irrigated pastures for 35 days, you will be avoiding most of the BP larvae deposited from the last grazing.
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