The periparturient egg rise
Susan Schoenian
Sheep & Goat Specialist Emeritus
University of Maryland Extension
The periparturient egg rise is a well-documented phenomenon in small ruminants. It is the temporary reduction in the naturally-acquired immunity to gastro-internal parasites that begins around the time of lambing and kidding. It can occur approximately two weeks before and continues for up to eight weeks after. During this period, the ewe or doe has a reduced ability to deal with worms. Coccidia oocyst counts also increase during this period.
The intensity and distribution of the periparturient egg rise varies by breed, individual, and season. While the exact mechanism is not fully understood, the periparturient egg rise is believed to be the result of various nutritional and hormonal factors. When lambing and kidding occur in the spring, the eggs deposited during the periparturient egg rise are largely responsible for the infections that lambs and kids acquire during summer grazing. For this reason, the periparturient egg rise has also called the “spring rise.” In an indoor lambing and kidding environment, the effect of the periparturient egg rise is minimal because the eggs are not being deposited onto pasture and females are not continuously ingesting new larvae.
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Several strategies can be implemented to minimize the effects of the periparturient egg rise. The traditional approach was to deworm ewes and does prior to lambing/kidding (within 1 month) or shortly thereafter (within two weeks). A pre-breeding treatment to eliminate hypobiotic (arrested) larvae was another commonly used strategy. These strategies are no longer recommended due to the widespread development of drug-resistant worms. Instead targeted selective treatment (TST) is recommended for small ruminants.
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Targeted selective treatment is when only those animals that require (or would benefit) from treatment are dewormed. In the case of the periparturient female, this means only deworming those ewes/does which display clinical signs of internal parasitism. This would include ewes/does with bottle jaw (submandibular edema), those with FAMACHA© scores of 4 or higher (3 for goats), and/or any female with a body condition score of 2 ( on a scale of 1 to 5) or less. Another strategy would be to deworm dams with larger litters, 3 or more lambs for a ewes and 2 or more kids for a doe. Ewes/does with larger litters are under greater production stress and usually have higher fecal egg counts. It is a good idea to deworm yearlings, especially if they are raising more than one offspring. Their immunity to parasites is not as good as mature females. In dairy animals, a common strategy is to deworm the heaviest producing females, as they are the ones under the most lactation stress.
Leaving some females untreated will leave more refugia. Refugia are worms that have not been exposed to the dewormer(s). Refugia-based strategies are considered essential to maintaining dewormer efficacy. This is because If all the animals in a group are dewormed, all of the surviving worms will be resistant to the dewormer(s). This is especially problematic if the treated animals are put onto a clean paddock.
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Strategic nutritional supplementation, especially protein, is another way to counteract the effect of the periparturient egg rise. Research has shown that ewes fed higher protein
diets in late gestation have reduced fecal egg counts. Feeds rich in by-pass protein are considered especially advantageous. Nutritional supplementation makes sense, since the loss of resistance is occurring at the same time the female’s nutrient requirements are increasing. Current NRC requirements probably encompass an influence of low levels of parasitism (all recommendations are for confined animals), but there are no clear recommendations available for the effects of subclinical levels of parasitism on metabolizable protein requirements of sheep and goats.
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Another strategy to manage the periparturient egg rise is to lamb or kid at a time of the year when worms are less active. There is less risk of parasitism when birthing occurs in the winter or fall months. Obviously, there will be geographical differences and pros and cons to lambing and kidding during different seasons. As already mentioned, lambing and kidding in confinement (or dry lot) will greatly reduce the impact of the periparturient egg rise since pastures are not being contaminated with worm eggs and larvae. Since animals get infected with parasites when they consume infective larvae when they graze on pasture plants, there is little risk of worm infection in confinement (dry lot or deep bedded barns). The risk of coccidia; however, is usually greater. Hygiene is of utmost importance for controlling outbreaks of coccidiosis. A coccidiostat can be fed to ewes/does in late gestation to lessen the amount of coccidia oocysts that are shed into the birthing environment.
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A relatively new strategy for managing the periparturient egg rise is to feed BioWorma® to periparturient females. BioWorma® is a naturally occurring fungus that traps and kills worm larvae in the manure, resulting in less contamination of pastures with infective worm larvae. However, it is important to understand that BioWorma® has no effect in the animal and that clinically-parasitized animals will still require deworming with effective drugs. Moreover, BioWorma® has to be fed daily to have maximum effect. The manufacturers recommend feeding it whenever temperatures are above 40 degrees F. Research is currently on-going in the US to determine the best strategies for incorporating BioWorma® into parasite control programs.
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Selecting sheep/goats that are more resistant to internal parasites is probably the best long-term strategy for controlling internal parasites, including the periparturient egg rise. The best way to do this is to use estimated breeding values (EBVs) for fecal egg count. EBVs are mathematical estimates of an animal's genetic value. Using sires with strong EBVs (high negative values) for parasite resistance will gradually improve the parasite resistant of the flock. Other less accurate ways to select for parasite resistance are central performance (ram or buck) tests and on-farm selection. Culling animals that need deworming will help, but it is important to understand that resilient animals (those not requiring deworming) may still harbor heavy infections and be shedding a lot of worm eggs onto the pasture. The CarLA saliva test measures antibodies in the sheep's saliva and may eventually be used to select animals with more parasite resistance, but until the test is commercially available, fecal egg counts remain the method of choice for identifying resistant animals.
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***Originally published December 2012. Reviewed and updated May 2024.***
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Relevant fact sheets in the Best Management Practices Series
Genetic selection: using crossbreeding and estimated breeding values
Nutritional