Jerusha (Jessie) Lay, DVM, Assistant Professor of Animal Health
Fecal Egg counts are a quantitative diagnostic tool that determines the number of parasite (Haemonchus, Ostratagia, Trichostrongylus) eggs that are in 1 gram of feces. This can be a useful tool for managing parasites in livestock herds. Within a herd of animals, a few susceptible animals may harbor the greatest numbers of parasites because they are less genetically resistant to parasites. By comparing fecal egg counts within a group of animals, these less resistant animals can be identified and removed from the breeding herd, which will in turn decrease the overall parasite burden on farms and pastures and, through selective breeding, create a herd that is more resistant over time.
Current recommendations for treatment are to only treat animals when they display clinical signs of parasitism. Fecal egg counts should not be the only tool used to determine when to deworm animals because other factors may affect which animals need to be treated. Some individual animals will have a higher resilience. Animals with higher levels of resilience can have higher parasite levels but not show the symptoms. This is also a good trait for the animals, as they have less clinical problems, but shedding eggs on the pastures can still increase the parasites loads in the environment. According to the American Consortium for Small Ruminant Parasite Control, deworming is recommended to deworm bucks/rams or does/ewes that are not nursing kids at 2,000 eggs per gram of feces, and young kids/lambs, yearlings or does that are lactating at 1,000 eggs per gram. Due to the stress of milk production, dairy breeds should be dewormed at 750 eggs per gram. Individual animals may vary from these numbers, so you should also consider the FAMACHA score (based on the color of ocular subconjunctival membranes), the animal's body condition score and any other health or stress factors to determine if treatment is needed.
may vary from these numbers, so you should also consider the FAMACHA score (based on the color of ocular subconjunctival membranes), the animal's body condition score and any other health or stress factors to determine if treatment is needed.
As resistance to multiple classes of dewormers are very common, it is not only important to monitor parasites in the animals, but also to determine the effectiveness of treatments. In many herds, producers will find a product they are comfortable with and use it exclusively for several years until the parasites on that farm become resistant. Once parasites are resistant to that class of dewormer, even when given