Developing Sustainable Internal Parasite Control Programs for Small Ruminants

Final Report for OS02-007

Project Type: On-Farm Research
Funds awarded in 2002: $14,995.00
Projected End Date: 12/31/2004
Matching Non-Federal Funds: $15,000.00
Region: Southern
State: Virginia
Principal Investigator:
Joseph Tritschler
Virginia State University
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Project Information


A detailed phone survey was conducted with small ruminant producers in the Mid-Atlantic region (n=77 farms). Survey questions covered farm demographics, farm management, anthelmintic usage and perceived anthelmintic problems. Farm trend analysis did not reveal any significant or suggestive differences related to anthelmintic problems. This may be attributed to difference response patterns between goat and sheep producers, particularly those who had beef cattle. One-noted differences were that goat producers tended to overstock their acreage, which would be expected to exacerbate parasite problems. Anthelmintic testing with a more detailed survey was continued on-farm by comparing fecal egg counts prior to and following treatment. Results for fenbendazole, albendazole and ivermectin indicated moderate to severe resistance. In contrast, levamisole and moxidectin were still moderately effective, but signs of resistance were noticed. Data suggest anthelmintic resistance is a serious problem. The third year of the study emphasized producer education on alternative parasite control methods, which is ongoing.


Control of gastrointestinal nematodes is a major factor limiting small ruminant production, especially in humid warm climates. Since the development of modern broad spectrum anthelmintics, treatment programs have relied heavily upon their use. Commercial release was followed quickly by the occurrence of anthelmintic resistant nematodes. The purpose of this study was to explore management practices used to control gastrointestinal nematodes and the prevalence of resistance in the Mid-Atlantic region.

Project Objectives:

The following are the six main objectives or targets from the proposal:

1) Survey development and implementation
2) On-farm survey and testing
3) Fact sheet development and distribution
4) Outreach workshop and presentations
5) Follow-up survey
6) Veterinarian survey and agent training


Click linked name(s) to expand/collapse or show everyone's info
  • Ursula & Tony Burgess
  • Michaela Dismann
  • Allen & Renee Dyer
  • Jessy Hodges
  • Mike & Nancy Holland
  • Marilyn Sanford
  • Ned & Donna Strange
  • Dorthy & Harold Walker
  • Carl & Andra Wurzer
  • Steven Yoder


Materials and methods:

Regional small ruminant producers were solicited for a detailed phone survey, which collected data on farm demographics, management, parasite control, and anthelmintic efficacy. Farms were separated based on selected responses and analyzed using the General Linear Models procedure of SAS. The survey was completed with detailed 30-minute phone conversations with 77 small ruminant producers. In addition, some 30 farms were visited, and detailed surveys and on-farm anthelmintic testing trials we conducted. This may be attributed to difference response patterns between goat and sheep producers, particularly those who had beef cattle. On-farm anthelmintic efficacy was evaluated for the five compounds most used by surveyed producers: albendazole, fenbendazole, levamisole, ivermectin and moxidectin. Fecal Egg Count Reduction Tests (FECRT) were conducted by comparing fecal egg counts (FEC) prior to and 7-14 days following treatment, adjusted to an initial level of > 50 eggs per gram of feces and a minimum of zero percent FECRT.

Research results and discussion:

Of the common anthelmintics, ivermectin was the most used (40%) and levamisole was the least used (6%). Pharmacologically goats require a higher dose than sheep (or cattle), but this difference is not expressed with labeling information. This may help explain the observations that goats receive higher dosages but are also more likely to be treated at subtherapeutic levels (principally with benzimidazole compounds). Although a purpose of the phone survey is to investigate differences in demographics or management practices that might be associated with perceived anthelmintic failure, analysis did not reveal any significant or suggestive correlatives. The survey results suggest that producers who had only sheep or goats, worm less frequently and use less anthelmintic classes than those who have both species. Those with both species had fewer animals and were less likely to have beef cattle. Goat producers were more likely to have discontinued using some product, suggesting more problems. More sheep producers rotated pastures and among more paddocks, and they had more acres in grass and less in woods. Small ruminant producers who also had beef cattle have considerably more land in all agricultural categories. Even thought they had a comparable number of small ruminants, the larger land base permits lower stocking densities. Improved pasture management as measured by rotation among five pastures or more was associated with more sheep but not more goats or cattle. Increased frequency of anthelmintic treatment was also associated with this increased pasture management. In spite of popular press to the contrary, this agrees with the scientific literature that suggests that most pasture rotation does not improve (and may hamper) parasite control. In this survey increasing stocking density was clearly associated with increasing quantity of goats (but not sheep or cattle) compounded by decreasing pasture acres. Similarly, perceived anthelmintic failure was associated with goats (treated more frequently) but not sheep.

The efficacy of ivermectin was tested in 16 farm location trials, involving 123 animals. The labeled dose of ivermectin for sheep or cattle is 200 ug/kg. At 400 ug/kg, the efficacy (adjusted % FECRT) ranged from 0%-55%, while at 600 ug/kg the ranged was from 74%-76% when administered orally. When limiting results to animals with high initial FEC, the values are improved slightly from 5%-75% at 400ug/kg and 71%-72% at 600 ug/kg. These levels of ivermectin efficacy point to severe and moderate parasite resistance ranges, even when administered at twice or three times the recommended dose. This would suggest that if administered at the labeled dose, efficacy would be even lower.

The efficacy of moxidectin was tested in 14 farm location trials, involving 93 animals. The oral labeled dose of moxidectin for sheep or cattle is 200 ug/kg. At 500 ug/kg, the efficacy (adjusted % FECRT) ranged from 20%-100%. When limiting results to animals with high initial FEC, efficacy improved to a range from 73%-100%. These levels of moxidectin efficacy point to moderate levels of parasite resistance in some cases, but no parasite resistance in others farm locations when given orally at 2.5 times the recommended labeled dose. Given the high efficacy on most farms, these data indicate that parasite resistance to moxidectin is low, but new data suggest or possibly not currently a problem.

The efficacy of levamisole was tested in 14 farm location trials, involving 100 animals. The labeled dose of levamsiole for sheep or cattle is 8mg/kg. At 12mg/kg, the efficacy (adjusted % FECRT) ranged from 67%-97%, while at 16mg/kg it ranged from 57%-98%. When limiting results to animals with high initial FEC, the values are improved from 83%-100% at 12mg/kg and 50%-100% at 16mg/kg. These levels of efficacy point to moderate to low parasite resistance ranges, when administered at twice the recommended dose.

The efficacy of fenbendazole was tested in 13 farm location trials, involving 97 animals. The labeled dose of fenbendazole for sheep, or cattle (and recently goats) is 5mg/kg. At 10mg/kg, the efficacy (adjusted % FECRT) ranged from 0%-75%, while at 15mg/kg it ranged from 52%-98%. When limiting results to animals with high initial FEC, the values slightly improved from 0%-76% at 10 mg/kg and 62%-98% at 15 mg/kg. These levels of fenbendazole efficacy point to severe, moderate, and low parasite resistance ranges, when administered at twice or three times the recommended dose.

The efficacy of albendazole was tested in 5 farm location trials, involving 34 animals. The labeled dose of albendazole for sheep or cattle is 10mg/kg. At 20mg/kg, the efficacy (adjusted % FECRT) ranged from 45%-59%. When limiting results to animals with high initial FEC, efficacy improved to a range from 40%-78%. These levels of albendazole efficacy point to moderate to severe levels of parasite resistance when given orally at double the recommended dose. Together, both studies indicate that parasite resistance to albendazole might be cross- related to the parasite resistance level in fenbendazole, which is in the same anthelmintic class, and may become increasingly prevalent. Data suggest anthelmintic resistance may be a serious problem in the Mid-Atlantic region.

Participation Summary

Educational & Outreach Activities

Participation Summary:

Education/outreach description:

Several parasite control outreach presentations were added in the second year, and outreach became the focus of the program in the third year. These were at Virginia State University (fall small ruminant expo 2003 and 2004, Virginia Tech, Blackstone AREC (fall tri-state small ruminant program for Central Extension District), University of Maryland, Keedysville AREC (fall tri-state regional ruminant nutrition conference), Mid-Atlantic Meat Goat and Lamb Marketing Cooperative (fall board meeting and program), Mid-Atlantic Meat Goat Symposium (annual meeting), Eastern Cashmere Goat Associatio (national show and meeting), Wisconsin Sheep Association (winter meetings), Virginia Meat Goat Association (annual meeting), Virginia Biological Farming Association (annual meeting), and numerous Virginia County Cooperative Extension Programs (Albelmarle, Bedford, Campbell, Caroline, Floyd, Fluvanna, Goochland, Hanover, Henrico, Louisa, Montgomery, New Kent, Patrick, Powhatan, Spotsylvania, Stafford).

Scientific publications include abstract, graduate student paper and poster at scientific meetings:

Dismann, MPL and JP Tritschler. 2003. Anthelmintic Resistance in Small Ruminants in Virginia. Association of Research Directors, 13th Biennial Research Symposium.

Tritschler, JP, MPL Dismann, and BL Sayre. 2003. Goat and Sheep Management in the Mid-Atlantic Region Obtained via Preliminary Telephone Survey. Association of Research Directors, 13th Biennial Research Symposium.

Tritschler , JP, MPL Dismann, and BL Sayre. 2004. Telephone survey of small ruminant parasite control and management in the Mid-Atlantic Region. Presented at American Society of Animal Science meeting, Midwestern Section.

Fact sheets and popular press publications:

Dismann, MPL and JP Tritschler. 2003. Fecal examination as an aid to parasite control. Fact sheet with presentation to Eastern Cashmere Goat Association, National Show, Virginia State Fair.

Dismann, MPL and JP Tritschler. 2003. Research controlling nematodes in small ruminants. Virginia Shepherd Vol 2: 7-9 (Jan 2003)

Tritschler, J. 2004. Internal parasites of grazing ruminants. 2003-04 Sheep Management Wisline Series, University of Wisconsin 15 pp

Tritschler, J. 2005. Strategies for non-chemical control of nematodes in grazing ruminants. Proceedings of the Virginia Biological Farming Association Conference (Feb 2005) 15 pp.

Tritschler, J and M Dismann. 2003. Strategic internal parasite control in grazing ruminants and horses. Proceedings of the Virginia Licensed Veterinary Technician Annual Continuing Education Program. Blue Ridge Community College 15 pp.

Project Outcomes

Project outcomes:

These results suggest that many small ruminant producers are aware of the difficulties of controlling gastrointestinal nematodes, but appear to have limited options in the face of increasing anthelmintic resistance and small acreage. The control issues include differences between species, lack of approved products, inadequate off-label use information, anthelmintic resistance, lack of land resources, and limited suitability / availability of parasite tolerant animals. Small, part-time producers appear to be having more control problems possibly due to lack of resource options and difficulty of the information.

The on-farm trial created an opportunity for collaboration in food safety. A subset of the fecal samples collected for parasite analysis has been tested for potential human pathogens (Salmonella and E. coli 0157:H7). These data indicate a low level of potential pathogens in small ruminants.

Several unexpected outcomes were the recognition that our SARE trial received. First, Southern Region SARE chose it for their annual Highlights (in press). Second, there have been several requests for popular press articles related to these trials. One of these has been published in the Virginia Shepherd (January) and another is pending Mid-Atlantic Meat Goat and Lamb Marketing Cooperative newsletter (drafted). Third, the paper and presentation of this work by Ms. Michaela Dismann received a second place in the graduate student competition the Association of Research Directors 13th Biennial Research Symposium (March). Fourth, enthusiastic producer response has spurred a desire for detailed parasite control programs. These programs are now emphasizing a selective reduction in the use of anthelmintics and non-chemical approaches.

Economic Analysis

There are direct and indirect cost savings to producers as a result of these trials. Direct savings are realized by discontinuing ineffective parasite control programs. In our survey, the average cost of anthelmintic was about $0.60 a treatment. Combined with on-farm testing results, it suggests that producers are spending between $1 and $3 per head annually on treatments that have little or no effect. With about 100 head per farm, this is a significant direct savings. In directly, parasite burden reduce weight gain and ineffective treatments would not remove parasites. Studies have suggested potential losses of 5 – 10 lbs per head for market lambs and kids. With current prices at $1 or more per pound, this represents considerable lost potential gain.

Farmer Adoption

Producer response has been excellent. The producers that have participated in the survey spurred an accelerated outreach effort. Over 30 outreach programs have now been given. There are numerous requests for addition programs, which will continue throughout the foreseeable future. This effort is not unique to Virginia, as similar efforts are underway in a number of southern and mid-Atlantic states.


Areas needing additional study

The results of this study indicate that anthelmintic resistance is widespread, and small ruminant producers are eager for alternative parasite control options. Unfortunately the options are complex and relatively untested. There is a serious need for additional research in two areas: epidemiological methods of control for grazing ruminants and immuno-genetics of parasite tolerance.

Any opinions, findings, conclusions, or recommendations expressed in this publication are those of the author(s) and do not necessarily reflect the view of the U.S. Department of Agriculture or SARE.