Control of Haemonchus contortus in northern New England sheep and goats through manipulation of its winter ecology

Control of Haemonchus contortus in northern New England sheep and goats through manipulation of its winter ecology

Summary

In 2016, we completed data collection for our on-farm comparisons of parasite loads and management efficacy during the grazing season, with over 120 ME, NH, and VT producers participating. We initiated a new, more intensive monitoring scheme for regional producers, with 10 farms participating in intensive, individual monitoring of post-lambing ewes to detect and treat animals with large post-parturient increases in Haemonchus contortus egg counts during the early Spring of 2016.

One aspect of this project was to identify the effectiveness of dewormers that were in use on the participating farms. We found that nearly all of the chemical dewormers in current use did not effectively reduce parasite loads, and recommended that producers switch to other, more effective drugs. The intensive spring monitoring, plus the use of effective dewormers by these farmers resulted in significantly lower parasite counts and lower use of dewormers throughout the 2016 grazing season on these farms when compared to the 2015 grazing season.

We developed preliminary data that suggested a positive effect of fall deworming for the control of Haemonchus contortus in sheep during the following grazing season. Our Haemonchus contortus cold-tolerance study was completed in 2016, and we found that parasites originating from sheep living in a northern climate were more tolerant of cold conditions than parasites from sheep on farms in the Deep South (Louisiana). These results are consistent with our hypothesis that H. contortus larvae are becoming increasingly competent to survive winter on pastures in northern climates, and indicate that we may need to adapt our winter management strategies in northern New England to accommodate increased overwintering of this parasite.

We presented basic parasitology information and data generated during the first years of this project to several producer groups in 2016. Overall, we reached >200 producers during 4 separate events. We also taught 40 producers to use microscopy to measure fecal egg counts in their sheep.

Objectives/Performance Targets

One hundred NNE sheep and goat producers adopt more effective parasite management strategies, including routine monitoring of Haemonchus levels in their sheep through FAMACHA and fecal egg counts (completed).

Sixty producers will adopt at least three of the following cold weather management techniques to reduce or eliminate the shedding of Haemonchus ova on winter and spring pastures: 1. Winter dewormer treatment (in progress); 2. Hasten Spring rise through earlier lambing or increased photoperiod (planned for 2017); 3. graze weaned lambs separate from dams on ‘clean’ pastures (planned for 2017, if possible); 4. Use appropriate pasture stocking rates and practice rotational grazing (completed); 5. reduce egg shedding on early spring pastures through the use of a ‘mud season’ paddock (completed).

These management changes will positively affect the productivity of 2000 sheep and goats on 1000 acres of pasture, resulting in additional profits of $200 per year in the northern New England region.

Accomplishments/Milestones

In late 2015 we completed monitoring of pooled fecal egg counts from pooled samples during three critical periods during the early-, mid-, and late-season grazing. Over 120 farms submitted data for an entire grazing season and also completed a survey of their farm metrics and management practices.

We provided hundreds of veterinary consults to producers based on farm-specific data. Many of these farms decreased their Haemonchus counts between the first and second year of monitoring. We changed our field study emphasis in 2016 to more intensive monitoring and treatment of a small subset of farms that were willing to collect individual manure samples from each of their animals at multiple times during early spring, a period that is critical for parasite success in northern New England.

Ten farms from Maine, New Hampshire and Vermont participated in this study. Our plan was to identify, at the time of spring lambing, ewes that had carried heavy burdens of Haemonchus larvae through the winter and were at risk of anemia as these larvae matured into feeding adults. Furthermore, we wanted to identify heavy shedders of Haemonchus ova during the spring, since these ova were likely to develop into infective larvae during early June and increase exposure of ewes and lambs to Haemonchus during the upcoming grazing season.Highly parasitized ewes were identified and communicated to producers, and then were treated with a chemical anthelmintic. Manure samples were again assayed for parasites at 10 to 14 days post-treatment to assess the efficacy of treatments.

We found that many of the participating farms, plus about ten farms that were evaluated for dewormer effectiveness using the Fecal Egg Count Reduction Test (FECRT), did not achieve effective reductions in parasite burdens after the initial anthelmintic treatment. For farms with anthelmintic failure, we reviewed their history of dewormer use and made recommendations on alternative chemical dewormers that might be more effective on their farms. We then followed up with an additional FECRT to ensure that animals were carrying low burdens of parasites, including Haemonchus contortus, onto fields at the beginning of the 2016 grazing season.

A preliminary comparison of fecal egg count data from 2015 (pre-intensive monitoring) to to 2016 (post-monitoring and consultation) showed decreased parasite counts in 2016. In 2016 we completed development work on a quantitative in vitro assay to measure the cold tolerance of the L3 stage of Haemonchus contortus that persists on pastures and infects grazing sheep. We then conducted testing of prolonged (3 to 6 days of exposure) of L3 larvae obtained from farms in Maine, Virginia, Arkansas and Louisiana. We found that the Maine-sourced L3’s were tolerant of cold exposure down to at least 10 degrees C. Parasites from Arkansas and Virginia were not significantly different from the Maine L3’s in cold tolerance, but the Louisiana-based L3’s were killed by significantly warmer temperatures ranging between 20 and 25 degrees C. While these are preliminary results, they indicate that there may be an evolutionary adaptation of the infective L3 stage of Haemonchus to cold that would increase its overwinter survival on pastures in northern climates.

During the winter of 2015 / 2016, we performed a preliminary study, using our university flock, that compared the effectiveness of preventative anthelmintic treatment at different times during the non-grazing season. We found that fall deworming of adult ewes almost completely eliminated their subsequent spring rise. The fall 2015-treated animals were then placed on an aggressive rotational grazing system during 2016, and required no dewormer treatments. In contrast, all of the animals that did not receive a fall deworming experienced spring rise-associated parasitism and anemia that required one or more dewormer treatments, and that likely resulted in significant contamination of their paddocks / fields with Haemonchus ova during the spring of 2016. We are currently repeating this study using larger numbers of animals, and will continue to collect data through the grazing season of 2017.

During 2016, we presented basic parasitology information and data generated during the first years of this project to several producer groups in 2016. Overall, we reached >200 producers during four separate events. We also taught 40 producers to use microscopy to measure fecal egg counts in their sheep. All of these presentations and workshops occurred in northern New England.

Impacts and Contributions/Outcomes

Several potentially valuable outcomes have resulted from our 2016 work. First, we implemented a pre-grazing season monitoring and treatment strategy on ten northern New England farms that seemed to reduce Haemonchus contortus parasitism in sheep during the subsequent grazing season. We feel that an intensive period of parasite monitoring and targeted treatment during the immediate post-lambing period may be an effective tool for decreasing parasite burdens in sheep during the subsequent grazing season. Our detection of parasite resistance to ivermectin-type dewormers in multiple northern New England farms built on evidence from multiple published reports that Haemonchus contortus in U.S. sheep is becoming resistant to multiple chemical classes of dewormers. Preliminary results from 2015 / 2016 indicated that fall-based identification and treatment of a sub-population of ewes that are overwintering large burdens of Haemonchus larvae may result in reduced ewe anemia at the time of lambing, when ewes are already at high levels of nutritional stress. Reduction of egg-laying adults in the spring would also decrease spring contamination of pastures. Use of selective fall deworming, combined with delayed entry of sheep onto northern pastures until after “mud season” (2015 results) and effective rotational grazing, appear to reduce the impact of Haemonchus contortus on grazing sheep to levels that do not require interventional dewormer treatment of anemic animals during the relatively short grazing seasons in northern climates.

A cornerstone of effective parasite or pathogen management should be to reduce exposure of target animals to the infectious agent rather than treating them after they become ill. The U.S. sheep industry in northern tier states would certainly benefit from a reduction in the “salvage” treatment of heavily parasitized, anemic sheep and lambs that might result from implementation of our findings. Preliminary information from our in vitro cold tolerance study indicates that Haemonchus contortus may be evolving an increased tolerance of winter cold. if confirmed, this may translate into higher winter survival of infective larval stages on northern New England pastures. Higher overwinter survival on pasture may eventually reduce the effectiveness of winter treatments / management changes that target hypobiotic stages that overwinter in the sheep gut.

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