Rory Lewandowski, OSU Extension Educator, Athens County
The biggest enemy of pasture based sheep and goat production has got to be internal parasites and especially, Haemonchus contortus, or the barber pole worm. Its incredible reproductive capacity, an adult female can lay up to 5,000-10,000 eggs/day, combined with the fact that the infective third stage (L3) larvae can survive 60 to 90 days or more on pasture during the growing season, make it almost impossible to avoid production robbing and/or life threatening infection levels in grazing kids and lambs. In previous editions of this newsletter I have covered some of the strategies and tools small ruminant livestock owners need to use to manage parasite infection levels through the dangerous summer period.
As we get in to the fall of the year and temperatures begin to cool down and are less favorable for rapid progress through the parasite’s life-cycle, many small ruminant owners give a sigh of relief that they have survived another year. Especially in the late fall, most of the pasture larvae L3’s that become stage 4 (L4) larvae in the sheep’s abomasum (true stomach) do not continue to molt into the adult stage, but rather enter period of arrested development or dormancy that is termed hypobiosis. These L4 larvae will remain inactive in this state and not cause any harm to their host until emerging from hypobiosis in early spring. Surely now the small ruminant owner can take a break from thinking about parasite management and concentrate on some other management issues. As you can probably surmise from the title of this article, I don’t believe fall is the time to let parasite control fade from your management efforts, and here is why.
There is at least anecdotal evidence that infective L3 larvae can survive our winters and provide a source of early spring infection that can serve to jump start serious parasite burdens in sheep and goats in the coming season. A Purdue Extension fact sheet entitled “Managing Internal Parasitism in Sheep and Goats” says that L3 larvae can survive on pasture “…up to 180 days in the fall or winter.” Some on-farm research that was done here in Athens County in 2008 and 2009 that utilized short duration pasture rotations support the concept of surviving overwintered larvae as a source of some significant spring and early summer lamb parasite infections. However I am not aware of any research studies that have focused specifically on how long Haemonchus contortus L3 larvae from the fall of the preceding year might remain viable into a new grazing season, although there is published research that shows other parasite species do survive over the winter to infect lambs and ewes.
Responding to a question posed to him in May of this year (2009) regarding how “safe” a pasture might be that was last grazed in September of 2008, Dr. Shulaw, OSU Extension Veterinarian, replied that “I think there will be some surviving larvae on those pastures, but the number depends upon how many eggs were deposited there last fall when there was still moisture and temperature conditions favorable to development to the L3 stage.” Dr. Shulaw continues, “The number today (May 21) is much less than there was April 1 and the number June 15 will be considerably less than now. L3 larvae rely on stored energy. Every day it warms up to where they try to migrate in a moisture film on a grass blade, they use some of that stored energy. Eventually they “run out of gas.” However, it is likely that the number of L3 larvae available on April 1 was fairly low.” This reply was based on Dr. Shulaw knowing that the producer asking the question had tried to manage for low parasite numbers on fall pasture. Other management schemes could certainly result in higher numbers of overwintered L3 larvae on an April pasture.
There are a couple of points I want to emphasize here. One is that it matters where you are grazing in September and October, especially if those are pastures that will be used for early spring grazing. Second, the population level of surviving, overwintered L3 larvae is related to how heavy a worm burden your animals have in this late summer and fall period. If the worm burden is heavy, then a lot of eggs are being deposited on that fall grazed pasture.
A practical application of all this is to have a plan in place to protect those pastures you want to use early next spring from potentially high numbers of surviving overwintered L3 larvae. Avoid creating an early season worm infection. This might be done by not using those pastures grazed by lambs in September and October for April/May grazing or ewes and their lambs. The longer fall grazed pastures can be delayed from use in the grazing rotation the next year; the lower will be the potential number of infective L3 larvae. If the flock or herd has been managed throughout the entire grazing season with strategies to keep parasite infection levels low, then even the fall grazed pastures will not have large numbers of potentially surviving overwintered larvae. This, of course still leaves the producer with having to manage the periparturient rise in the early spring as the L4 larvae come out of hypobiosis, but that is the subject of yet another article.
The bottom line is that small ruminant owners that want to be pasture focused as a production system can’t take a season off from parasite management. Pasture management is parasite management within an integrated system.