Progress report for ONE22-429
Project Information
This project will develop and test essential oil-based formulations for the control of winter cattle lice.
Objective 1: Identify essential oils of known insecticidal activity against lice, and carrier oils already approved for organic cattle production. Essential oils will be evaluated for suitability with partner farmers, show high louse mortality at low concentrations, and be safe to apply to cattle based on previous literature and safety data.
Objective 2: Test the efficacy of combinations of essential oils and carrier oils against lice and eggs in the laboratory using contact and vapor bioassays. The final formulation developed for the field trial (objective 3) will show ≥90% louse mortality at a concentration of ≤10%.
Objective 3: Test the efficacy of the formulation against lice in an on-farm field-trial using the self-groomer/scratcher oil-dispenser. Cattle will be housed in two groups to compare the impact of the essential oil formulation against the carrier oil control.
Impact: The results will demonstrate the efficacy of a new tool for farmers to control cattle lice using a time and labor-saving application technique, for use across diverse management systems. Reduced economic, environmental, animal health burden of winter cattle lice in the Northeast and increased confidence for farmers
Lice infestations during winter housing represent a significant challenge for cattle producers in the Northeast, particularly for organic producers wishing to raise cattle without using chemical inputs. Lice are the most important winter parasites of cattle, spreading easily between animals during housing, causing intense irritation and scratching which can impact welfare, reduce feed intake, and damage hides, resulting in production losses for farmers (Currin, 2008). The USDA estimated that US livestock producers lose $125 million a year to cattle lice (Campbell, 1992). Cattle in the Northeast can be infested with biting lice (Bovicolla bovis) which feed on skin debris and secretions, and sucking lice (Linognathus vituli; Solenopotes capillarus; Haematopinus eurysternus) which pierce the skin and suck blood from small vessels near the surface (White et al., 2007). The lifecycles are similar and take 3-4 weeks from egg to adult during cold weather, with 1-2 eggs laid per day, resulting in severe infestations if not managed correctly (Campbell, 1992).
Clinical disease is usually prevented though the routine application of chemical insecticides. Injectable formulations are only effective against sucking lice which ingest blood, so topical (pour-on) formulations are required to treat biting lice. None are effective against lice eggs so must be reapplied after 2-3 weeks to kill newly hatched lice (Currin, 2008). For organic producers, treatment options are extremely limited: diatomaceous earth, soap, and plant (e.g. canola) and mineral oils may be used, and Neem and Pyrethrin must be approved before use (Pedretti, 2014). Furthermore, there are growing concerns over the development of resistance to conventional insecticides (Levot, 2000; Sands et al., 2014; Mckiernan et al., 2021), as well as the off-target environmental impacts of veterinary parasiticides on beneficial insects due to residues in manure and water (Sands and Wall, 2018; Mooney et al., 2021; Sands and Noll, 2021). After treatment of livestock, a large proportion (often >90%) of the dose is excreted unmetabolized in the urine and/or manure, representing a significant source of environmental contamination (Mooney et al., 2021).
This project has been co-developed with Vermont organic cattle farmers in response to their expressed need for alternative control strategies during winter housing, when lice populations regularly reach unacceptable levels resulting in animal health and production concerns (personal communication, Sands and partner farmers). In a 2022 survey of Vermont cattle producers (n=55), 84% reported external parasites as an important issue on their farm and 73% wanted to find alternative methods of control (Sands, unpublished data). Other farmer surveys surrounding pest and parasite control methods further highlight this need, with cattle lice ranked second (after internal parasites) as the most important problem for beef cattle producers (Ferguson et al., 2006) and 80% of producers regularly treating for lice. In a survey of organic dairy producers in the Northeast, Integrated Pest Management (IPM) was unequivocally the highest priority animal health challenge, identified by 89% of respondents (Pereira et al., 2013).
Botanical insecticides are naturally occurring insect toxins which degrade rapidly in the environment and generally have low mammalian toxicity. For example, essential oils are volatile plant secondary metabolites, consisting of up to 80 compounds such as terpenes and aromatic hydrocarbons. Many of these have cellular or neuronal targets which elicit an insecticidal effect, deterring insect herbivory on the plant. The value of essential oils as control agents against veterinary ectoparasites, particularly lice, mites, and ticks, are well documented (Ellse and wall, 2013). Laboratory tests showed that 5% tea tree and lavender oils resulted in >80% mortality of donkey lice Bovicola ocellatus after 2 hours of exposure (Ellse et al., 2013). When formulated with emulsifiers (SLS and PVP) efficacy increased to 100% mortality after 2 hours (Sands et al., 2015) and, unlike many chemical insecticides, they were highly ovicidal meaning lice eggs were also killed. Field trials were conducted with formulations of 5% tea tree or lavender oil as a solution that was groomed into the coats of winter-housed donkeys (Ellse et al., 2015). After 2 applications there was a 78% reduction in louse abundance, suggesting that essential oils can be used to manage louse populations successfully in the field.
Plant based ethno-veterinary medicine is used in the sustainable management of livestock ectoparasites worldwide (Tesfaye et al., 2015; Gemechu et al., 2019) but represents a form of traditional knowledge that has been under-represented in Northeast agriculture. The volatile nature and short half-life of essential oils are desirable for low environmental toxicity but means they must be applied regularly and penetrate the coat to reach lice next to the skin. This is less problematic for companion animals such as donkeys which are groomed regularly but has been an obstacle for their use in livestock management. As a result, large scale field trials with livestock, building on the promising results from laboratory investigations, have been limited (Ellse and Wall, 2013). To address these challenges, this project will develop essential oil formulations with high insecticidal activity against cattle lice in the laboratory, and then investigate their efficacy in a field trial with winter-housed cattle using a novel application technique - a cattle self-groomer/scratcher oil-dispenser. Essential oils will be formulated with carrier oils already approved in organic production, at the lowest concentration that can achieve ≥90% lice mortality in the laboratory.
The self-groomer/scratcher has a tank which wicks oil-based solution into the brushes as cattle rub against them, facilitating coat penetration and offering a time and labor-saving route of administration for farmers. This research will develop and test an environmentally sustainable alternative for winter cattle lice control, which could be widely adopted by diverse farming communities in the Northeast, providing additional tools, particularly within organic and traditional systems, for producers wishing to avoid chemical treatments. The project will contribute towards the Northeast SARE’s outcome statement by diversifying management options for cattle producers to reduce the economic, environmental, and animal health burden of winter lice infestations. This will increase resiliency, sustainability, and quality of life by providing additional tools to farmers amid rising concerns over the impacts of resistance and climate change on pest and parasite transmission.
Cooperators
- - Producer
- - Producer
- - Technical Advisor
Research
Objective 1 [year 1]: A literature search of peer-reviewed research will be conducted (Web of Science, Google Scholar) to identify essential oils of high insecticidal activity against lice. To be considered for testing in this study, essential oils must result in high louse mortality (≥90%) at low concentrations (≤10%) so that formulations can be developed that are cost effective and safe to apply to livestock. Further requirements will be the absence of mammalian toxicity, and essential oils will be shortlisted following a review of safety data sheets and toxicological information. The insecticidal activity and safety data, along with physical samples of the essential oils, will be discussed and evaluated with the partner farmers so that they can identify the most suitable to be tested in the laboratory (objective 2). Preferred carrier oils from those already approved in organic production will be selected for use in the essential oil formulations. Finally, safety, efficacy, and formulation of chosen oil combinations will be discussed in consultation with ectoparasite control expert Richard Wall via video teleconferencing.
Objective 2 [year 1]: To test the efficacy of essential oils against lice in the laboratory, they will be formulated with the carrier oils at concentrations of 2.5%, 5% and 10% and used in contact and vapor filter paper bioassays. Lice and eggs will be collected from naturally infested winter-housed Belted Galloway beef cattle with partner farmers at Philo Ridge Farm, Vermont (supporting materials 1). Cattle will be passed through an Arrowquip chute and examined for lice at aggregation sites on the body (face, head, neck, withers, brisket, inner legs, and base of the tail). Lice and eggs will be removed using a small, hard bristled brush, collected in specimen tubes, and returned to the laboratory. Four species of cattle lice are found in the Northeast, one biting and three sucking (Rutz and Waldron, 2016), and the species present will be identified using a dissecting microscope and morphological keys (Price and Graham, 1997). If both biting and sucking lice are found, bioassays will be performed separately on each group to test efficacy. Lice will be maintained in an incubator at 20 °C and 75% RH in darkness prior to use, and bioassays will be conducted the day following collection.
Alongside the formulations of carrier and essential oils, the carrier oil alone will be used as a control. A 1-mL aliquot of each formulation will be applied to a 90-mm-diameter filter paper resting in a 90-mm polystyrene Petri dish to fully saturate the filter paper. Ten adult lice will be placed onto each filter paper, ensuring that lice cannot avoid contact. Lids will be placed on the Petri dishes, and maintained at 30 °C and 75% RH in a constant temperature incubator. Louse survival will be recorded at 10-min intervals for 30 min, at 1 h, hourly for a further 3 h and finally at 24 and 48 h. For this the Petri dish will be removed from the incubator and the lice inspected for movement; lice will be considered dead if they are immobile and fail to show any movement even after agitation with a pin. Three replicates of each essential oil formulation concentration, and each carrier oil only control, will be performed. A non-contact assay will be used to determine whether lice must be in direct contact with the formulations or whether the inspiration of the vapor phase results in mortality (supporting materials 2). Filter papers will be impregnated as described above and ten adult lice will suspend on a layer of muslin between the Petri dish and lid.
Ovicidal activity of the formulations against lice eggs will be investigated using contact assays with filter papers treated in the same way as described above. Twenty lice eggs will be placed onto each filter paper using a fine paint brush and forceps, lids placed on the Petri dishes, and maintained at 35∘C, 75% RH. Egg hatch will be recorded on days 1, 4, 8 and 12 and 14 after their introduction (cattle lice are known to hatch within 1-2 weeks). Petri dishes will be removed from the incubator and the eggs inspected under 10×magnification. Three replicates for each essential oil concentration and control will be performed.
The resulting mortality data will consist of three replicates of 10 lice for each essential oil formulation concentration and the carrier oil only control. For statistical analysis, louse mortality will be used as the dependent variable in a three-way analysis of variance (ANOVA) with essential oil type, concentration, and carrier oil as factors. Tukey multiple range tests will be used for post hoc analysis. Egg hatch data will be analyzed using chi-squared analysis. Data will be summarized, presented graphically, and in a farmer-friendly information sheet which will be distributed during outreach workshops and field days.
Objective 3 [year 2]: The results from objective 2 will be used to take forward a final essential oil formulation to be tested in field trials using a cattle self-groomer/scratcher dispenser (supporting materials 3). The essential oil – carrier oil combination with the highest efficacy at the lowest concentration to achieve ≥90% mortality in the laboratory will be chosen in consultation with partner farmers. On-farm trials will take place with partner farmers at Philo Ridge Farm, Vermont, where all animals have a history of persistent lice infestation during housing. Cattle will be housed in two groups, one barn with 30-60 steers and the other with 30-60 cows plus yearlings. Prior to setting up the self-groomer/scratcher oil-dispensers, lice on the cattle will be counted by passing them through the Arrowquip chute. Ten body sites on each animal will be examined: around the eye, neck, withers, inner leg, and base of the tail on either side. Hair will be parted five times in 5 cm lengths and the total number of lice at each site will be recorded using a click counter. To administer the essential oil formulations, two cattle self-groomer/scratchers will be set up in each barn and the trial will commence at the time of highest louse abundance in January 2024. One barn will receive the essential oil formulation, and the other the carrier oil alone as a control (supporting materials 4). All animals will initially be passed through the self-groomer/scratcher via the chute, after which they will have free access for 2 weeks, and then louse numbers will be re-counted as described above. All animals will then be passed through the self-groomer/scratcher again, given free access for a further 2 weeks, and a final lice count will be made.
Data on the efficacy of the essential oil formulations in the field will therefore consist of lice numbers infesting cattle before, during and after application of the treatment (essential oil formulation) and control (carrier oil only). A percent louse reduction for each group will be calculated. For statistical analysis, the number of lice on each animal will be the response variable in a repeated measures ANOVA comparing the average louse abundance at each inspection between treatment groups. Data will be summarized, presented graphically, and in a farmer-friendly information sheet which will be distributed during outreach workshops and field days.
Education & Outreach Activities and Participation Summary
Participation Summary:
The project results so far have been shared through the UVM Extension Organic Dairy Conference held each year in VT. The 2023 Organic Dairy Conference was held in Randolph VT and attracted 111 organic dairy producers and stakeholders. The conference was attended by Jeffrey Sanders and Bryony Sands who reported on the project. The work was also discussed with participants at the UVM Extension NWCS field day in Alburgh VT in July 2023 which attracted 181 participants including farmers, educators and service providers.
Information gained through the project was used to develop a factsheet series which are posted at www.uvm.edu/extension/nwcrops:
- Factsheet 1 – Cattle Lice – provides information on the biology and lifecycle of winter cattle lice and the economic, environmental, and animal health importance of effective lice control.
- Factsheet 2 – Control of lice in cattle – provides a summary of the various treatment and IPM options for controlling cattle lice in conventional and organic production systems
In 2024 a final fact sheet will be produced that specifically focuses on the essential oils and project results.
- Factsheet 3 – Essential oils for the alternative control of cattle lice – will use the results of the laboratory and on-farm field trials to provide information on the efficacy and benefits of using essential oils in the cattle self-groomer/scratcher.
In the summer of 2024 a day-long parasite management workshop will be held to provide education to stakeholders on livestock pest and parasite management. The workshop will include information on identifying livestock pests, understanding lifecycles, and Integrated Pest Management. Information and data from the research will also be shared. The workshop will educate cattle producers and service providers on the considerations associated with lice management strategies in the Northeast and introduce and demonstrate the benefits of essential oil formulations applied using the cattle self-groomer/scratcher. Farmers will host the field day and participate in a farmer panel. Project team members will present data collected from laboratory studies (year 1) and on-farm field trials (year 2).
To reach a broader audience the project results and benefits and considerations associated with lice management strategies will be shared in a webinar series. The webinars will be hosted live to allow for participant interaction but will be archived and posted at www.uvm.edu/extension/nwcrops to reach a wider audience.
Learning Outcomes
Identifying lice on cattle - when lice are present vs other skin conditions. When lice become active, which months they start to increase in the fall/winter. Examining cattle for lice, body areas they are found on, which types of lice are present (sucking or biting). Efficacy of essential oil treatments on lice - why they work, how long they might last, when they need reapplying based on the lice lifecycle. How to apply essential oil treatments, and time, labor, and financial costs and benefits compared to cydectin treatments.
Project Outcomes
We developed a formulation based on lavender, clove, and thyme oils with a mineral oil base, and applied it by hand to two groups of animals who were housed in different barns. We used one group and a treatment and one as a control, and reversed these groups later in the season to account for confounding factors between barns. We counted lice before and after treatments. Early in the winter, the group who were treated with essential oils did not develop any lice, whereas the untreated barn developed heavy infestations and several animals had to be treated with Cydectin. Later in the winter when lice populations were established, the treated group had significantly reduced lice numbers compared to the untreated group.
The animals were a herd of approximately 60 certified organic Belted Galloway beef cattle with known problematic seasonal winter lice infestation and were housed in 2 separate barns grouped as cows with their calves, and mainly steers with some young heifers. Barns were situated 350 ft apart and some animals (such as the herd bull) were moved between the groups during the season. Twenty cattle from each barn were randomly selected by their ID number, and lice were counted by passing them through an Arrowquip chute system (Manitoba, Canada). Each animal was examined at 8 body sites including the neck, shoulder, back, and rump, on each side. The hair was parted in 50 mm sections and the skin observed for the presence of lice. Five partings were made at each body site giving a total of 40 counts per animal.
Essential oils of lavender (40/42 standardized), clove bud, and white thyme (Bulk Apothecary, Ohio, USA) were mixed into a mineral oil base at concentrations of 5%, 2.5%, and 0.25%, respectively. Lice counts were performed approximately every 2 weeks over the winter, depending on inclement weather. At the beginning of winter before lice numbers had increased, the cow-calf barn was given two applications of the essential oil formulation two weeks apart, with louse counts performed the morning before the application, and the steer barn was left untreated. Later in the winter when lice populations were established, the steer barn was given two applications of the essential oil formulation two weeks apart, and the cow-calf barn was left untreated. For adults, yearlings, and calves, a volume of 1000 mL, 500 mL, and 250 mL respectively was applied as a pour-on along the back topline, and brushed into the coat. Two cattle in the steer barn were removed from the study because they had very heavy lice infestations early on in the trial and received a moxidectin treatment.
Results
Cattle had mixed infestations of chewing lice and sucking lice. Lice numbers started off low or absent at the beginning of winter and then increased sharply. They remained high for the rest of the trial period (until 9th March 2023). Lice were seen in all of the observed body parts (neck, shoulder, back, and rump) however there were significantly fewer lice on the rump than the shoulder (Z720=3.621, P<0.001) and back (Z720=3.227, p<0.01). Adult cows had the fewest lice, followed by, steers and steer calves, and heifer calves were the most heavily infested with significantly more lice than steer calves (Z108=-2.260, P<0.05) and adult cows (Z108=-6.078, P>0.001).
At the beginning of winter, in the untreated steer group lice numbers significantly increased from an average of 0.7 lice per cattle on day 14 to an average of 32 lice per cattle on day 21 (Z38=7.562, P<0.001; Fig. 1). For the treated cow-calf group, lice numbers did not increase and were ≤1 for the duration of the trial period. On day 21, two heavily infested individuals in the untreated steer group with lice counts of >150 were treated with Cydectin.
Later in the winter when lice populations were high, for the untreated cow-calf group lice numbers did not significantly change over the trial and average lice numbers remained around 30±2. For the treated steer group, lice numbers significantly decreased from an average of 15 lice per animal to 0 after a single treatment and remained at 0 for the rest of the trial (F1=22.9, P<0.001; Fig. 1).
This has resulted in reduced chemical inputs for the farmers, who are pleased with the results and wish to continue using the essential oils. Farmers noted that applying the essential oil formulation was not much more effort than applying the Cydectin which they would have to use every year anyway, so the labor involved was acceptable to them.
The work so far has resulted in a new collaboration with a nearby farm who also have a problem with winter cattle lice in their beef herd, and who are interested in trialing the essential oil formulation as a way to reduce inputs with insecticide. We are now working with them to set up groomer-scratcher stations for cattle to self-administer the essential oil formulation this winter.
Further work this winter will involve testing essential oils against lice in laboratory assays to get specific mortality data and investigating the efficacy of cattle self-administering the essential oil formulation through the groomer-scratcher.
The methodology was revised to include a trial of the essential oil formulation in the first year, because the farmers preferred to try it out than to use Cydectin again. Laboratory trials will proceed this winter. The field trial involved applying the essential oils to each animal individually, and the results indicated that the treatment was very effective. We are setting up the cattle self-groomer scratcher with the essential oil formulation in it to evaluate whether lice numbers can be kept low with the cattle self-administering the treatment. This would reduce time and labor costs and improve the situation for the farmers further. We now know that the treatment is effective, and are continuing with additional work to improve the process of application, and to examine how regularly the treatment needs to be applied to keep lice numbers down over the winter. We have reported on the positive results at outreach events, and are now collaborating with other farmers who have winter lice issues and are interested in using the essential oil formulation. This is likely to benefit organic farmers and those wishing to reduce chemical inputs across the Northeast and anywhere cattle must be housed during winter.