Progress 10/01/08 to 09/30/13
Outputs
Target Audience: Results from this project have been of particular interest to livestock producers throughout the northern Great Plains. Because of our clear demonstration for the development of anthelmintic resistance (AR) in a population of Haemonchus contortus nematodes parasitizing a closed sheep herd from eastern South Dakota, our early results were especially important to regional sheep and goat producers. Our findings that many commercial cow-calf herds from eastern South Dakota are infected with Haemonchus placei has created concerns among cattle producers that the conditions leading to AR in Haemonchus from sheep might also drive the development of AR in cattle infected with H. placei. Changes/Problems: At the beginning of this project, the primary objective was to begin evaluating the level of anthelmintic resistance (AR) currently present in trichostrongyle nematodes from South Dakota beef and sheep herds. While we were able to make significant progress in the overall objective, experimental opportunities provided by a sheep herd with significant AR to the 2 major classes of anthelmintics resulted in a refocusing on the identification of factors that likely contributed to this resistance in the Haemonchus contortus population from this herd. This refocus significantly limited the number of sheep herds evaluated for AR. In addition, we had originally planned to use a commercial in vitro bioassay for AR evaluations performed in the sheep herds, but challenges with acquiring the bioassay materials also contributed to our refocusing away from a more extensive survey for AR in multiple regional sheep herds. We had also hoped that a similar bioassay for use in cattle would become available, but technical problems have prevented it's availability. For this reason, we chose to focus exclusively on the proposed alternative method for evaluating the possibility of AR in cattle herds by using a molecular method to identify cattle herds that are predominately infected with Cooperia species. Previous studies have shown that members of this genus are more resistant than the other trichostrongyle genera, and that the primary genus present in herds showing significant AR was Cooperia. Our unexpected discovery of Haemonchus in many of the initial cattle herds tested coupled with the determination that H. contortus was the cause of AR in the sheep herds with AR motivated us to add additional cow-calf herds to the survey (i.e. 8 herds that were frequently treated and 5 herds that had not been treated in the past 10 years). The most significant departure from the initial objectives proposed in this project was the inclusion of bison in the genus-level trichostrongyle survey. We included bison in this project because bison fecal samples became readily available (through the efforts of the Minnesota Buffalo Association) and Haemonchus was also identified in a herd of bison showing clinical parasitism. What opportunities for training and professional development has the project provided? During the summer of 2013, I attended the first International Conference on Integrated Parasite Management (IPM), sponsored by The American Consortium for Small Ruminant Parasite Control (ACSRPC), which is an organization dedicated to development and on-farm validation of non-chemical methods of parasite control in sheep, goats, and other livestock. The conference was held at Fort Valley State University (FVSU) in Fort Valley, GA, on May 20-22, 2013. This was a “Train-the-Trainer Conference” to train animal health professionals (Veterinarians, County Extension Agents, University personnel) in IPM principles, who will then train individual farmers in these principles throughout the country. In addition to providing opportunities to hear presentations given from international authorities in IPM parasite treatment and control approaches, the conference also provided “hands-on” training in performing fecal egg counts and FAMACHA scoring. The FAMACHA scoring workshop was conducted by the South African professors who invented the system, and I was certified in this scoring system by them at that time. How have the results been disseminated to communities of interest? In addition to publishing our various results in peer-reviewed journals, we are also describing our concerns for anthelmintic resistance in all our presentations given to stake-holders within the livestock industry from this region. During the project period, our results have been presented at 10 cattle producer/large animal veterinary meetings, 2 sheep producer meetings and a single meeting involving bison producers. From these meeting, we are seeing livestock producers alter their management systems in response to these developing problems. What do you plan to do during the next reporting period to accomplish the goals?
Nothing Reported
Impacts
What was accomplished under these goals?
The "gold-standard" method for documenting anthelmintic resistance (AR) in trichostrongyles from herds of cattle and goats or flocks of sheep is the Fecal Egg Count Reduction Test (FECRT). During the initial year of this project, significant anthelmintic resistance (AR) was identified using the FECRT within trichostrongyle nematodes from a closed herd of sheep located in Brookings County, SD. This was the first documented case of avermectin (AV) and benzimidazole (BZ) resistance in sheep from the Northern Plains, and molecular analysis revealed that Haemonchus contortus was virtually the only species of trichostrongyle present in this aggressively-treated herd. Haemonchus contortus infections have been increasingly reported in ungulates from cold climates even though past studies have shown that the free-living juveniles from this species survive poorly under freezing conditions. Studies of the overwintering strategies used by this population of H. contortus revealed that winter survival depended almost entirely on the drug-resistant, hypobiotic J4s because few (if any) free-living H. contortus juveniles survived the winter in the pastures. Without the refugia from juveniles surviving each winter on the pasture, it is likely that AR developed more quickly in this aggressively-treated Haemonchus population due to the very high selective pressures for resistance in this cold winter climate. Fortunately, the population of Haemonchus had not yet developed resistance to moxidectin (MX); this anthelmintic class differs slightly from the AVs, but resistance to this last remaining class generally occurs within 2 years of usage in worm populations already resistant to the AVs. Therefore, a limited treatment strategy was developed for this herd based upon treating only animals that were showing clinical symptoms of haemonchosis (i.e. severe anemia based upon a visual scoring method). With this strategy, there has not been any significant increase in MX resistance among these sheep during the remaining time-period of this project. Due to the challenges of acquiring paired fecal samples (before and after treatment) for the FECRT involving commercial cow-calf herds, we focused all of our remaining efforts on using a molecular method to identify cattle herds that are predominately infected with Cooperia species as an indication that AR might be present in these herds. Previous studies have shown that members of this genus are more resistant than the other trichostrongyle genera, and that the primary genus present in cattle herds showing significant AR was Cooperia. While we didn’t find any cow-calf herds with a particular predominance of Cooperia, we unexpectedly found Haemonchus in 10 of the 13 cattle herds tested. Because Haemonchus has not been a common parasite of cattle from this region, and because of the AR identified in H. contortus from the aggressively-treated sheep herd, we have become particularly interested in the prevalence of this genus in various livestock from this region. Haemonchus also emerged as a very common parasite in bison based upon results from a parasite survey involving 30 herds from 7 north-central states. Prior to this study, there had been no studies to identify the most common gastrointestinal parasites in bison herds from the U.S.A. In 96 fecal samples containing large numbers of trichostrongyle eggs, PCR analysis identified at least 1 trichostrongyle genera in virtually all samples. Cooperia and Haemonchus were found in the vast majority of samples tested, and Ostertagia and Trichostrongylus were slightly less common.
Publications
- Type:
Conference Papers and Presentations
Status:
Published
Year Published:
2012
Citation:
Acharya, J., Hildreth, M.B., Holler, L.D., Holler, S., Eljaki, A.A., NandaKafle, G., and Reese, R.N. In Vitro and In vivo anthelmintic activity of Ericameria nausoesa and Rhus aromatica from the United States Northern Great Plains with quantification of condensed tannins for both plants. 96th Annual Meeting of the South Dakota Academy of Science Annual Meeting. Vermillion, South Dakota.. April 14, 2012.
- Type:
Conference Papers and Presentations
Status:
Published
Year Published:
2011
Citation:
Grosz, D.D., Eljaki, A.A., Holler, L.D., Holler, S. and Hildreth, M.B. Overwintering strategies of a population of anthelmintic-resistant Haemonchus contortus within a sheep flock from the U.S.A. Northern Great Plains. 56th Annual Meeting of the American Association of Veterinary Parasitologists, St. Louis, MO, July 16-19, 2011.
- Type:
Conference Papers and Presentations
Status:
Published
Year Published:
2011
Citation:
Eljaki, A.A., Grosz, D.D. and Hildreth, M.B. PCR survey of trichostrongyle genera
present in a heavily-infected bison herd from eastern South Dakota. 56th Annual Meeting of the American Association of Veterinary Parasitologists, St. Louis, MO, July 16-19, 2011.
- Type:
Conference Papers and Presentations
Status:
Published
Year Published:
2010
Citation:
Grosz, D.D., Pike, K. and Hildreth, M.B. Effects of fecal floatation solutions on the binding of peanut agglutinin lectin to the surface of Haemonchus contortus eggs. 94rd Annual Meeting of the South Dakota Academy of Science Annual Meeting. Spearfish, SD. April 10, 2010.
- Type:
Conference Papers and Presentations
Status:
Published
Year Published:
2010
Citation:
Eljaki, A.A., Knutsen, J.A., and Hildreth, M.B. Absence of Haemonchus contortus and other abomasal nematodes in eastern South Dakota whitetail deer during the 2010 winter season. 94rd Annual Meeting of the South Dakota Academy of Science Annual Meeting. Spearfish, SD. April 10, 2010.
- Type:
Conference Papers and Presentations
Status:
Published
Year Published:
2010
Citation:
Boswell, B.R., Bierle, J.D., Grosz, D.D., Holler, L.D., Holler, S. and Hildreth, M.B. Marginal benzimidazole resistance in trichostrongyles from a South Dakota sheep herd previously found to be resistant to the avermectins. 94rd Annual Meeting of the South Dakota Academy of Science Annual Meeting. Spearfish, SD. April 10, 2010.
- Type:
Conference Papers and Presentations
Status:
Published
Year Published:
2009
Citation:
Haas, J., Chandle, A.C., Holler, L.D., Holler, S. and Hildreth, M.B. Genus-level PCR analysis of a population of avermectin-resistant trichostrongyles from a South Dakota sheep herd.. 93rd Annual Meeting of the South Dakota Academy of Science Annual Meeting 2009, Aberdeen, SD. April 2009.
- Type:
Conference Papers and Presentations
Status:
Published
Year Published:
2009
Citation:
Pike, K., Chandler, A.C. and Hildreth, M.B. Use of Calcofluor White and image analysis for quantifying trichostrongyle eggs from sheep fecal samples. 93rd Annual Meeting of the South Dakota Academy of Science Annual Meeting 2009, Aberdeen, SD. April 2009.
- Type:
Book Chapters
Status:
Published
Year Published:
2012
Citation:
Hildreth, M.B. and A. Harmon. 2012. Haemonchus. In "Molecular detection of human parasitic pathogens" (Dongyou Liu, eds.) pp. 571-582., CRC Press.
- Type:
Journal Articles
Status:
Published
Year Published:
2013
Citation:
Grosz, D.D., A.A. Eljaki, L.D. Holler, D.J. Peterson, S. Holler, and M.B. Hildreth 2013. Overwintering strategies of a population of anthelmintic-resistant Haemonchus contortus within a sheep flock from the United States Northern Great Plains. J. Vet. Parasitol. 196(1-2):143-52
- Type:
Conference Papers and Presentations
Status:
Published
Year Published:
2011
Citation:
Acharya, J., Hildreth, M.B., and Reese, R.N. In vitro screening of extracts from twenty-one native South Dakota plants for anthelmintic activity against the sheep Nematode, Haemonchus contortus 95th Annual Meeting of the South Dakota Academy of Science Annual Meeting. Oacoma, South Dakota.. April 9, 2011.
- Type:
Conference Papers and Presentations
Status:
Published
Year Published:
2011
Citation:
Grosz, D.D., Eljaki, A.A., Holler, L.D., Holler, S. and Hildreth, M.B. Efficacy of Cydectin� in a South Dakota sheep herd infected with an anthelmintic resistant population of Haemonchus contortus. 95th Annual Meeting of the South Dakota Academy of Science Annual Meeting. Oacoma, South Dakota.. April 9, 2011.
- Type:
Journal Articles
Status:
Published
Year Published:
2012
Citation:
Smith, S.J., A.A. Eljaki, J. Acharya, R.F. Daly, and M.B. Hildreth. 2012. Effect of Safe-Guard� Free-Choice Mineral Blocks on trichostrongyle nematodes in pastured cattle from eastern South Dakota. In Press: Proc. S.D. Acad. Sci. 91:131-143.
- Type:
Journal Articles
Status:
Published
Year Published:
2009
Citation:
Harmon, A.F., B.C. Lucas and M.B. Hildreth. 2009. PCR comparison of trichostrongyle genera present in South Dakota cattle with and without springtime deworming. Proc. S.D. Acad. Sci. 88:147-154.
- Type:
Journal Articles
Status:
Accepted
Year Published:
2014
Citation:
Acharya, J., Hildreth, M.B. and Reese, R.N. 2014. In vitro screening of forty medicinal plant extracts from the United States Northern Great Plains for anthelmintic activity against Haemonchus contortus. In press J. Vet. Parasitol.
- Type:
Conference Papers and Presentations
Status:
Published
Year Published:
2011
Citation:
Hildreth, M.B. 2011. Internal Parasite Treatment and Resistance in South Dakota Cattle. Proceedings of the 120th Annual Meeting of the South Dakota Veterinary Medical Association. pp. 3-9.
- Type:
Conference Papers and Presentations
Status:
Published
Year Published:
2013
Citation:
Eljaki, A.A., Acharya, J., Bowron, J. D., Grosz, D.D. and Hildreth, M.B. Gastrointestinal parasites in commercial Bison bison herds from the U.S.A. central Great Plains. 58th annual meeting of the American Association of Veterinary Parasitologists, Chicago, IL July 20-23, 2013
- Type:
Conference Papers and Presentations
Status:
Published
Year Published:
2012
Citation:
Eljaki, A.A., Grosz, D.D. and Hildreth, M.B. Fecal egg count reduction test to evaluate the effectiveness of doramectin against trichostrongyle nematodes in bison from eastern South Dakota. 96th Annual Meeting of the South Dakota Academy of Science Annual Meeting. Vermillion, South Dakota. April 14, 2012.
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Progress 01/01/12 to 12/31/12
Outputs
OUTPUTS: During the previous year, a fecal egg count reduction test (FECRT) and a PCR-based diagnostic test to identify the genera of trichostrongyles represented by the eggs in the FECRT was used to identify anthelmintic resistance (AR) in the flock of sheep from South Dakota. This strategy was again used during the fourth year of this project to evaluate the efficacy of a free-choice anthelmintic delivery system (i.e. Safe-Guardr Free-choice Protein Blocks) on trichostrongyle nematode populations in a stocker cattle herd managed under normal pasture conditions in eastern South Dakota. A group of 42 heifers (treatment) were given one free-choice SafeGuardr Protein block for 4 days, starting on September 7. A similar group of 22 steers (controls) were given similar, but non-medicated protein blocks. The 2 groups were grazing on adjacent pastures throughout the summer, and therefore naturally infected with trichostrongyle nematodes from the pastures. Prior to treatment, the mean trichostrongyle egg output were numerically higher in the steers (35.8 eggs/g) than the heifers (22.6 eggs/g), but not statistically different. Representative samples from the heifers were analyzed to determine the genera of trichostrongyles represented by the eggs, and these results indicated the presence of Haemonchus (81% of tested animals), Cooperia (75% of tested), Ostertagia (63% of tested) and Trichostrongylus (13% of tested) in the heifer herd. Based upon the calculated consumption rate of the free-choice SafeGuard Block, the average dosage consumed was lower than that recommended by the manufacturer. However, after treatment, egg output dropped significantly to 1.5 eggs/g (greater than 93% reduction) in the treatment group, but increased significantly in the untreated group to 69.0 eggs/g (greater than 92% increase). The same PCR/FECRT strategy was used to evaluate the genera of trichostrongyles present in a herd of bison from eastern South Dakota, and the effectiveness of yearly Dectomaxr treatments and altered pasture management on the level of trichostrongyle parasitism in these bison. Initial focus was given to this commercial bison herd because some of its animals had shown signs of clinical parasitism in 2010. Using molecular techniques used to identify the genera of trichostrongyle eggs harvested from sheep and cattle, we were able to identify the following 5 genera in this bison herd: Haemonchus (29% or 26% of the herd depending on the primer used), Cooperia (26% of the herd), Ostertagia (17% of the herd), and Trichostrongylus (2% of the herd). Prior to initial treatment of this herd with Dectomax injectable (doramectin) at the recommended dosage for cattle), trichostrongyle egg output was 10.5 eggs/g for 33 cow samples and 186.1 eggs/g for the 15 calf samples. Following 3 yearly Dectomaxr treatments, egg output diminished by more than 95%, indicating the absence of AR in this bison herd, With treatment and improved pasture management (mainly lower stocking rates), egg-out remained below 5 eggs/g in the cow, and below 20 eggs/g in the calves. PARTICIPANTS: Dr. Michael Hildreth is a professor in the Departments of Biology & Microbiology and Veterinary & Biomedical Sciences. He served as the PI for this livestock parasitology project. Russ Daily (in the Department of Veterinary & Biomedical Sciences) assisted with various aspects of the overall project, but was particularly involved in identifying the herds used in this study. Technical assistance was provided by two masters and one PhD graduate students. The SafeGuard project served as a major portion of Stephanie Smith's (Department of Veterinary & Biomedical Sciences) masters project and Jyotsna Acharya is from the Department of Biology & Microbiology. Another PhD student, Abdelhakim A. Elsadek Eljaki, provided significant assistance with the PCR analysis portion of the project. TARGET AUDIENCES: Results from this study and from the general anthelmintic resistance project are particularly important to cattle, sheep, goat and bison producers and veterinarians from the northern Great Plains. In addition to publishing our various results in peer-reviewed journals, we are also describing our concerns for anthelmintic resistance in all our presentations given to stake-holders within the livestock industry from this region. This past year, that included 7 different presentations. We are also working on an extension fact sheet for Haemonchus that is focused on issues specific to this region. PROJECT MODIFICATIONS: Nothing significant to report during this reporting period.
Impacts
Administering anthelmintics individually to cattle is an inconvenient and expensive process when treating cattle on pasture. Free-choice anthelmintics were developed to improve the ability of beef producers to effectively deworm cattle without passing them through a cattle chute. The convenience of free-choice anthelmintics outweighs those of traditional deworming practices; however, there have been surprisingly few published studies evaluating the effectiveness of this delivery approach, and no studies involving pastured cattle from the Northern Plains. In spite of the lower that recommended intake of anthelmintic from the blocks, access of the heifers to this product significantly decreased trichostrongyle nematode loads in the treated cattle during the study period, and demonstrated the validity of this treatment option. While the Safe-Guard Mineral Block showed good efficacy within the herd, decreased labor costs, and reduced the stress on treated animals, egg reductions did not occur in every heifer. This variability indicates that not every animal received a proper dosage of the fenbendazole. When inadequate dosages of anthelmintics are used (especially over a long period of time), there is a risk for increased AR problems. Future studies should monitor the development of benzimidazole resistance in herds treated with free-choice anthelmintics during extended time periods. Very little is known about the gastrointestinal helminth communities in bison from this area, in spite of the growing number of bison herds throughout the northern Great Plains. There have been no published studies evaluating doramectin as a treatment for trichostrongyles in bison, and our study clearly demonstrated its efficacy when injected at a dosage similar to that used in cattle. The pre-treatment prevalence of Haemonchus among the bison evaluated in this study was rather surprising given the inability of its free-living juvenile stage to survive well at temperatures typically present in South Dakota soils during the winters months. Not only was Haemonchus present in this bison herd, but it was also very common in the beef heifer herd studied this year. Haemonchus was also previously reported in 9 of 13 cow-calf herds from eastern South Dakota. The pathogencity of this genus, and the demonstration of its anthelmintic resistance in a flock of sheep from eastern South Dakota illustrates the potential danger that this trichostrongyle genus might represent to the livestock industry from this region. Fortunately, in this region there is no evidence yet for resistance in Haemonchus from livestock groups other than sheep, but clearly it is important to start evaluating this problem among the cattle and bison herds, especially those that have implemented aggressive deworming practices. It is also important that the findings from this project be disseminated to the livestock producer-groups in the region so that they can alter their management systems in response to any developing problems.
Publications
- Hildreth, M.B. and A. Harmon. 2012. Haemonchus. In "Molecular detection of human parasitic pathogens" (Dongyou Liu, eds.) pp. 571-582., CRC Press.
- Grosz, D.D., A.A. Eljaki, L.D. Holler, D.J. Peterson, S. Holler, and M.B. Hildreth 2013. Overwintering strategies of a population of anthelmintic-resistant Haemonchus contortus within a sheep flock from the United States Northern Great Plains. J. Vet. Parasitol. (in press)
- Smith, S.J., A.A. Eljaki, J. Acharya, R.F. Daly, and M.B. Hildreth. 2012. Effect of Safe-Guardr Free-Choice Mineral Blocks on trichostrongyle nematodes in pastured cattle from eastern South Dakota. In Press: Proc. S.D. Acad. Sci. (in press).
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Progress 01/01/11 to 12/31/11
Outputs
OUTPUTS: During the third year of this project, we continued characterizing the anthelmintic resistance (AR) of Haemonchus contortus, particularly in an eastern South Dakota (SD) flock of sheep that periodically exhibits clinical parasitism, and is monospecifically infected with H. contortus resistant to benzimidazoles (i.e. albendazole: Valbazen) and to avermectins (i.e. doramectin: Dectomax). This year, we also evaluated their resistance to the milbemycin class of non-avermectin macrocyclic lactones (i.e. moxidectin: Cydectin) using a fecal egg count reduction test (FECRT). Results showed no AR to Cydectin (100% efficacy) in adult H. contortus adults treated in the fall. Prior to treatment, fecal egg counts (FEC) for 27 ewes averaged 317.1 eggs/gram, but 21 days after Cydectin treatment, no eggs were found in any of these ewes. The next spring, only 2 of the 27 Cydectin treated ewes showed any post-lambing egg output (5.9 eggs/gram for all treated ewes), whereas, the FEC for the Cydectin control ewes was 1,422 eggs/gram. This data indicates that Cydectin treatment in the fall also killed virtually all of the tissue-dwelling H. contortus J4 juveniles. Because of their known benzimidazole (BZ) resistance, this group of sheep is being also used to establish and evaluate a molecular assay to more-sensitively measure BZ resistance in H. contortus. This assay actually measures the allele frequency of a single-nucleotide mutation at the 200 codon of the β-tubulin isotype 1 gene. A DNA extraction protocol based upon digestion in proteinase-K was used to extract DNA from individual third-stage juveniles cultured from eggs recovered from individual ewes. Previously, this protocol had only been used to extract DNA from groups of multiple juveniles. A nested amplification (non-specific to the resistant or susceptible isotypes) of the β-tubulin gene was performed prior to the allele specific PCR. Preliminary results indicated that DNA was only detected in 63.6% of the samples, suggesting problems in the extraction method for individual juveniles. Of the samples with extracted DNA, 77.8% showed the resistant allele and 22.22% showed the susceptible allele. These results were considerably higher than the roughly 20% resistance to BZ measure in H. contortus adults, but may be similar to that measured for juveniles. During this time, we also helped evaluate methanol extracts from 40 plants native to SD for anthelmintic activity based upon an egg hatch assay for H. contortus. Extracts were initially screened at 50mg/ml diluted in 0.5% dimethyl sulphoxide (DMSO) or 3-(N-morpholino)propanesulfonic acid (MOPS buffer). Of the 40 extracts,12 showed anthelmintic activity in DMSO, and 7 showed activity in MOPS buffer. Extract from Ericameria nauseosa (rubber rabbitbrush) in both diluents and Rhus aromatica (fragrant sumac) in DMSO exhibited maximum inhibition (100%) even at the lowest concentration of extract (1.5mg/ml). When eight plant extracts were further evaluated with a larvae migration assay, extracts of E. nauseosa (ED50 =4.5mg/ml) and R. aromatica (ED50=7.3mg/ml) exhibited strong activity (p <0.001) against H. contortus third stage larvae. PARTICIPANTS: Dr. Michael Hildreth is a professor in the Departments of Biology & Microbiology and Veterinary & Biomedical Sciences. He served as the PI for the sheep project. Neil Reese (also in the Departments of Biology & Microbiology) was a CoPI on the project measuring anthelmintic resistance in South Dakota plants. This project was added in this year. Dr. Larry Holler (in the Department of Veterinary & Biomedical Sciences) provided valuable collaboration on the sheep project. Technical assistance was provided by two masters graduate students: Drew Grosz is from the Department of Veterinary & Biomedical Sciences and Jyotsna Acharya is from the Department of Biology & Microbiology. These projects are serving as major portions of their masters thesis. Another PhD student, Abdelhakim A. Elsadek Eljaki, provided some labor support for the sheep project, but received very valuable sheep parasitology experience from that project, which will be very useful when he returns to Libya. Two undergraduate students also received valuable research experience through these projects. TARGET AUDIENCES: Results from this study are particularly important to sheep and goat producers and veterinarians from the northern Great Plains. The ability to identify AR in commercial flocks of sheep and herds of goats will enable producers alter their management systems in response to developing problems. Perspectives developed during the sheep phase of the project will be useful in establishing AR monitoring approaches in cattle and bison. PROJECT MODIFICATIONS: Nothing significant to report during this reporting period.
Impacts
Historically, AR has not been a problem in South Dakota cattle and sheep. There is still no evidence for AR in cattle, but a growing number of clinical observations are suggesting that AR is becoming a significant problem in sheep and goats from this region. In addition, Haemonchus contortus should not be a common parasites in South Dakota sheep and goats because the free-living juvenile stage does not survive well at soil temperatures typically found in South Dakota pastures. Our discovery of a flock of sheep in South Dakota that was exclusively infected with H. contortus, and that these worms are resistant to the two major classes of anthelmintics provides the need to determine the distribution of this problem within the region, but also provides the opportunity to evaluate methods for diagnosing AR in ruminants that are more efficient and effective than a FECRT. Ongoing evaluations of molecular assays for BZ resistance suggest that this is the most accurate approach because increasing frequency of the resistant alleles can be directly monitored over time. Because only one fecal collection is necessary, this also can be the most convenient approach if the molecular resources are available. If avermectin resistance is firmly established in flocks from southern climates, significant moxidectin (MX) resistance usually develops two years after producers switch to this compound. Management changes have been implemented in the eastern SD flock to limit the development of MX resistance; by monitoring the efficacy of MX in this flock during the next few years, it will be possible to determine the extended usability of MX in avermectin-resistant sheep. By identifying SD plants that possess anthelmintic activity and are palatable to ruminants, it might be possible to use these plants to support organic production of cattle, bison, sheep and goats, or to limit the need for commercial anthelmintics, and thereby, slow the development of resistance. In vitro efficacy results from both rubber rabbitbrush and fragrant sumac indicate that they should be further evaluated in vivo with Haemonchus-infected sheep.
Publications
- No publications reported this period
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