It seems likely that most sheep and goat producers with high pasture stocking densities will eventually experience difficulties with internal parasite control.
In all cases of animal health concern, it is essential producers work closely with their veterinarian to unravel this issue.
Egg counts
Fecal egg counts can provide useful data in assessing dewormer effectiveness if used properly.
Understand that a fecal egg count is ever changing in an individual, and within a flock. Therefore, it represents a mere picture in time.
One must also consider factors which naturally occur when using fecal egg counts to evaluate drug resistance.
At any time in the Ohio grazing season, one may see individuals within the flock having very high egg counts and others with very low egg counts.
As fall approaches, one will begin to see a decline in the number of eggs shed, due to the seasonal life cycle of the parasite itself.
Immunity within an animal can also change when stressors, such as lactation are removed.
With these factors in mind, one must question whether enough individuals were sampled to represent the flock and whether the resultant egg counts were due to the dewormer or other naturally occurring factors.
When evaluating the effectiveness of a dewormer using fecal egg counts, it may be prudent to evaluate egg shedding from a control group “untreated,” and at the same time evaluate shedding of a treatment group “receiving dewormer.”
Fecal egg counts should be taken at the start of the trial and be high enough to evaluate, then 10 to 14 days later following the deworming counted again.
Afterward, one can compare the treatment group to the control group.
In large flocks, Bill Shulaw, former OSU Extension veterinarian, recommended the sampling size should represent 15 individuals per group.
If the drug has worked effectively one would expect to see at least a 95 percent reduction in the average fecal egg count from the treatment group.
Testing
Another valuable tool used to evaluate drug resistance in Haemonchus contortus, (Barber pole worm), is the DrenchRite® Assay.
This specialized test can be used to determine parasite resistance status for all of the drug classes commercially available. Livestock producers who work with their veterinarian and use this tool can expect to learn what internal parasites the flock has, and which drugs are effective on their farm.
For information related to using this assay, contact Dr. Kaplan’s laboratory at the University of Georgia College of Veterinary Medicine, 706-542-0742.
Effective gastrointestinal parasite control in small ruminants should be considered a multi-pronged approach and will involve learning if one’s dewormer is effective. Working with a veterinarian and using the tools above may help in starting to unravel the parasite issue.
