A study to determine if anthelmintic-resistant internal parasites exist in Vermont sheep flocks

2006 Annual Report for ONE06-061

Project Type: Partnership
Funds awarded in 2006: $10,000.00
Projected End Date: 12/31/2007
Matching Non-Federal Funds: $1,305.00
Region: Northeast
State: Vermont
Project Leader:
Chet Parsons
University of Vermont Extension

A study to determine if anthelmintic-resistant internal parasites exist in Vermont sheep flocks


This study was carried out to determine if internal parasites (IP) of sheep were resistant to dewormer medications (anthelmintics) on four Vermont sheep farms. These farms were chosen based on deworming results from the previous year. Twenty sheep on farm A and B and ten sheep on farm C and D were weighed in June of 2006 and a fecal sample was collected from each sheep. One half of the sheep were treated with fenbendazole and one half of the sheep were treated with ivermectin as recommended by the Vermont State Veterinarian. Fecal samples were sent to a parasitology lab to determine fecal egg counts (FEC). Fecal samples were obtained from the same sheep two weeks later and sent to the same pasasitology lab to determine FEC. The results of the FEC were compared to determine if the dewormer was effective in reducing the number of IP eggs in the sheep feces. From these results, farm A, B and D, did not appear to have IP that were resistant to anthelmintics. The results from farm C would suggest that some IP on that farm were resistant to anthelmintics. Future studies need to be done during the month of August to determine if a higher incidence of IP infectivity exist latter in the summer and if there is greater resistance to anthelmintics at that time.

Objectives/Performance Targets

Objectives/Performance Targets

•Identify four sheep producers who indicated that they could have internal parasites of sheep that are resistant to chemical dewormers.
•Weigh a sample of their sheep and take fecal samples to determine the number of internal parasite eggs that they are shedding.
•Treat the sampled sheep with chemical dewormers.
•In two weeks, take fecal samples from the sample sheep to determine the number of internal parasite eggs that they are shedding.
•Compare the results of the two fecal egg counts to determine if there was a reduction in the number of internal parasite eggs.
•If there was not a reduction in the number of internal parasite eggs, conclude that resistant parasites existed.


Four farms participated in the study. Fecal samples were taken twice, with animals treated after the first fecal samples were taken. The fecal samples were tested for internal parasite eggs at a parasitology laboratory. The Vermont State Veterinarian review the results of the laboratory reports and concluded that one of the farms had internal parasites that were resistant to chemical dewormers.

Impacts and Contributions/Outcomes

Results of the parasitology lab reports were shared with each respective farmer. Internal parasite management was discussed with each of the participants. Due to scheduling conflicts, the sheep producer meetings were not held and the grant was extended for another year to allow these meetings to take place. Other producers experienced sheep with parasite problems during the month of August. It is recommended that another study be done during that time and that the scope of the project be expanded to include a larger number of farms


Harvey Levin

Sheep Farmer
P. O. Box 164
East Charleston, VT 05833
Office Phone: 8027234283
Dave Martin

Sheep Farmer
Sheep Farmer
416 Irish Settlement Road
Underhill, VT 05489
Office Phone: 8028992104
Kerry Rood

Vermont State Veterinarian
Vermont Agency of Agriculture
116 State Street, Drawer 20
Montpelier, VT 05620
Office Phone: 8028282421
Kathryn Morse

Sheep Farmer
Sheep Farmer
732 Old West Chruch Road
Adamant, VT 05640
Office Phone: 8022235401
Erica Zimmerman

Sheep Farmer
1820 Center Road
Montpelier, VT 05602
Office Phone: 8022236930