Use of Rate-of-Gain and Dry Lot to Maintain Parasite Anthelmintic Susceptibility in Bluefaced Leicester Maryland Lambs

Final report for FNE18-900

Project Type: Farmer
Funds awarded in 2018: $13,658.00
Projected End Date: 02/29/2020
Grant Recipient: Vista View Farms
Region: Northeast
State: Maryland
Project Leader:
Andrew Keller
Vista View Farms
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Project Information


The purpose of this project was to verify an alternative means for determining anthelmintic need and evaluate the use of dry lots for improved healthy and profitability of lambs.  Identification of which lambs to drench is critical so that the susceptible lambs receive the care that they need, and so that the parasites in otherwise healthy lambs are not unnecessarily exposed to anthelmintics. Using rate of gain can be a valuable tool for large flocks where analysis of each individual animal may not be practical. To implement this method, producers will first need to know their expected rate of gain for both ram and ewe lambs.  Lambs that require anthelmintic treatment rather than being returned to pasture (control) were put on dry lot. Almost every animal that was treated and returned to pasture (the control group) required a second treatment and only one lamb requiring treatment survived to market. In contrast, the survival rate of treated lambs increased by 40%, from 17% to 57% when lambs that required treatment were moved into a dry lot.  In addition, even with the increased cost of feed by taking lambs off pasture, this system was more profitable.  This study showed producers can use pasture and dry lot to their advantage to raise healthier, more profitable lambs.  

Outreach was accomplished by way of article in sheep producers newsletter, "Wild and Woolly" published on the U. Maryland Cooperative Extension small ruminant website, and by a farmer panel at a small ruminant workshop.

Project Objectives:

Our proposed solution is using a rate-of-gain measurements and a dry lot to promote the health of susceptible lambs and reduce the proliferation and spread of anthelmintic resistant parasites.

There are four objectives.

1.Compare the number of treatments between co-located pastured lambs (control group), and lambs on pasture with those needing treatment moved into a dry lot (treatment group).

2.Compare parasites resistance to anthelmintics at weaning to lambs in the control group at market time.

3.Compare parasite resistance to anthelmintics at weaning to lambs in the treatment group that remained on pasture at market time.

4.Provide a cost benefit comparison for the purchase of feed versus the added value from reduced lamb loss and/or higher rates of gain in dry lot lambs.

We anticipate that if lambs needing treatment are immediately placed into a dry lot then the number of treatments required will be lower and parasite resistance will be lower in the treatment group than in the control group or at least remain the same as a resistance rates at weaning. We also anticipate that the increased income from a higher rate of gain and reduced lamb losses will mitigate the cost of purchasing feed while improving animal health.


The most common health problem of domestic sheep, particularly pastured young lambs, is internal parasites.  Parasites at sufficient levels result in anemia, bottle jaw, and can result in death.  Sick animals are not only an animal husbandry concern, but may substantially impact farm profitability.  Direct costs of parasites are veterinary costs, drugs to treat sick animals, animal losses due to death, and disposal expenses.  Indirect costs include increased farm labor time, increased feed costs/unrealized lamb growth for input, decreased wool quality, and the potential for delayed lambing for retained ewe lambs. 

Throughout the U.S., particularly in the mid Atlantic and southern states the barber pole worm, Haemonchus contortus, causes many deaths in sheep each year.  Lambs with parasites can be treated with drugs that kill the parasites known as anthelmintics. There are currently only three classes of anthelmintic drugs approved for use in sheep in the United States.  Appropriate use of anthelmintics is important to ensure effective treatment and slow the rate at which the worms become resistant to the drugs. One strategy to slow anthelmintic resistance is to target treatment to symptomatic lambs rather than treating the entire flock.

As sheep are prey animals, visible symptoms may not be evident to a producer until the animal has become sufficiently ill and reduced productivity is occurring.  Anemia diagnosis by current means requires physical handling of each animal to view the eye up close which can cause stress to the animal and producer, requires adequate training, may be physically challenging, and is time consuming for large flocks.  An alternative to assessing visible symptoms is looking at performance-based criteria.  This methodology requires intensive record keeping and often occurs after animals have been worked and data is subsequently analyzed. 

Targeted treatments are not always used due to misinformation, guidelines that recommend drenching on a schedule, and producers lacking confidence, ability, and efficiency in determining which animals should be treated.  Without methods for producers to rapidly distinguish animals in need of treatment, many will continue treat all animals in their flock, contributing to resistance.  The inability to control multiple-drug-resistant H. contortus seriously threatens the future viability of small ruminant farming (Kaplan 2004).    

Clean pastures (rotational grazing) and dry lots are management practices used to reduce the need for treatment by reducing the intake of larvae during grazing.  Because 3 months of rest time is necessary for a worm population to decrease significantly, this can be difficult to achieve on farms with limited acreage.  Dry lots are not picturesque and require purchasing feed.  While not the natural environment, dry lots can provide multiple benefits including: no parasite pressure, no need to rotate pastures, increased rate of gain (Berger).  Producers may assume that expensive barns and slated floors are necessary for a dry lot in a humid climate such as Maryland.  Limited information is currently available on dirt dry lots for sheep.

Description of farm operation:

I have been involved with farming my entire life. I now have a 45-acre farm producing hay, small grains (on rented ground), vegetables, and includes a flock of approximately 80 sheep. To manage the sheep we utilize a sheep handling system, electronic scales, electronic ID reader and stock recorder and software for data management which will be used for this project. Half of the flock are Bluefaced Leicester (BFL), a breed with fleeces highly valued by hand spinners. In addition to selling raw fleeces, value-added wool products (e.g. socks, blankets) are sold. The remaining flock, and BFL wethers, are marketed for meat including direct to consumers, meat lockers, and other farms.


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  • Susan Schoenian - Technical Advisor (Educator and Researcher)


Materials and methods:

This research was done to look at early Spring born lambs, but is applicable to lambing at any time the lambs would be on pasture at an early age.  At birth, ewes and their lamb(s) were moved into individual lambing jugs.  Standard lamb data was recorded: dam tag number and sire, if the lamb was a single, twin or triplet, birthweight, and sex. Lambs were also tagged using Radio Frequency Identification Device (RFID) tags.  Standard protocols for vaccinations and tail banding were followed. 

For the purpose of this study, lambs were divided into two groups (control and treatment) and kept in separate pastures.  For the first group, the control group, lambs remained as a single group from the time they were put on pasture until were are marketed (mid-August).  For the treatment group, lambs that failed to meet the pre-determined rate of gain, requiring anthelmintic treatment, were moved into a dry lot and the remaining lambs in the treatment group returned to pasture. 

Water, hay and a grain ration (via self feeders) were provided ad libitum.  For the purpose of this study, a record of the quantity of hay and feed provided to each group was maintained.  Feed expenses were then calculated using cost per bale of hay and pound of feed.  This was done to evaluate if the feed cost associated with pulling the lambs off pasture would be recovered by increased rate of gains and decreased lamb losses. 

Initially the “dry lot” was intended to be an outdoor area to maintain the environment as close to the pastured lambs as possible.  To maintain the area devoid of vegetation a flame weeder was used.  We found that this method was not as effective as desirable against perennial grasses and weeds.  The shade structures installed may have been too high as they were not utilized by the lambs in either group.  Thus, lambs taken off pasture were placed in a barn and also benefitted from more shade and protection from the rain than the lambs that remained on pasture. 

Beginning at weaning, lambs were weighed bi-weekly and FAMACHA scores recorded.  Lambs that did not meet our pre-determined rate-of-gain threshold (discussed below) and had a FAMACHA score of 4 or 5 were treated with anthelmintics.  When lambs required treatment, they were treated simultaneously with all three classes of anthelmintics.  This is the most recent recommendation from our local sheep/goat specialist and the American Consortium for Small Ruminant Parasite Control. 

Producers will need to determine the appropriate threshold for their breed and management style.  Our predetermined rate-of-gain threshold to determine which lambs should be treated with anthelmintics was 0.34 lbs./day for ram and 0.30 lbs./day for ewe lambs.  To arrive at this number we used data collected in 2017 from this group of sheep where the average rate of gain was 0.52 and 0.46 lbs/day for wether and ewe lambs, respectively.  We then reduced this value by 66% of the expected rate-of-gain based on similar studies in the United Kingdom. 

To ease handling, the farm was equipped with a sheep handling system and the technology to drench based on rate of gain.  As lambs moved through the raceway they entered a scale and the RFID tag was read with a handheld stock recorder (Shearwell).  The scale and stock recorder were connected via Bluetooth. The daily rate of gain (using weaning weight as a baseline weight) was displayed automatically (“real-time”) on both the scale head and stock recorder.  Lamb weights and treatments were stored electronically in the associated FarmWorks software. 

Fecal samples were collected and analyzed by two means in order to study resistance.   As able, samples were collected from each lamb at weaning, and then thereafter if the lamb required drenching, and two weeks following drenching.  Two pooled fecal samples were collected and sent to the University of Georgia College of Veterinary Medicine for DrenchRite analysis at the conclusion of the study in mid-August (market).   These pooled samples were homogenized fecal samples from 10 lambs that had not received anthelmintics in the last 2 weeks.    One sample was collected from the control group and one from the treatment lambs that remained on pasture.  

Research results and discussion:

This study originally had four objectives designed to measure the need for anthelmintic treatment, feed cost, and anthelmintic resistance differences between the control (all lambs collocated on pasture) and treatment (treated lambs placed into a dry lot) groups. We found that during this year of unusually high precipitation, creating a dry lot with the use of shade cloth was not practical. We also found that the use of flame weeding was not solely sufficient at controlling perennial grasses and weeds. As we anticipated a long season we had attempted to use flame weeding to avoid repeat use of herbicides and potential resistance issues. Producers that do not have a barn or other enclosure may need to first use chemical methods or thick layer of non-herbaceous material (e.g. sand or mulch) to “clean-up” an area. Since the objective of the dry lot was to avoid exposure to parasites through grazing, we were able to use our barn for this purpose.

The first objective was to compare the number of treatments between co-located lambs (control group), and lambs on pasture with those needing treatment being placed into a dry lot (treatment group). Each group began with 18 lambs. There was not a significant difference in the numbers that required treatment; however, the number of total treatments and the health outcomes did vary. Almost every animal that was treated and returned to pasture (the control group) required a second treatment and only one lamb requiring treatment survived to market. In contrast, the survival rate of treated lambs increased by 40%, from 17% to 57% when lambs that required treatment were moved into a dry lot.


n = 18 # of Animals Treated Total # of Treatments Average # of Treatments per Animal # of Treated Animals that Died % Survival of Treated Lambs
Control Group 6 11 1.83 5 17%
Treatment Group 7 9 1.29 3 57%

We were not able to complete the second and third initial objectives as the DrenchRite analysis was not available at the time of weaning. They were to compare parasite resistance to anthelmintics at weaning to lambs in the control group at market time and to compare parasite resistance to anthelmintics at weaning to lambs in the treatment group that remained on pasture at market time. As the DrenchRite analysis was available in late August, we were able to compare parasite resistance to anthelmintics at market time between lambs in the treatment group and control group. There was no difference found in the resistance to the benzimidazole and ivermectin class with parasites being resistant. The slight difference in levamisole and moxidectin is likely due to the loss of most of the lambs that were treated in the control group. The results were consistent with the findings from 2017 and 2016. Despite the high percentage of lambs that were treated, refugia on the farm was likely maintained in the ewe population where drenching was done on a single ewe ‘as needed” basis with very few ewes requiring drenching.

CONTROL ESTIMATED EFFICACY ~0% ~90-94% ~ ≤50% ~≥95%
TREATMENT ESTIMATED EFFICACY ~0% ~≥95% ~ ≤50% ~≥ 70-94%
2017 RESISTANCE STATUS R (High) R (Low) R (High) LR


In the absence of the DrenchRite analysis in the Spring of 2018 samples were collected for fecal egg count analysis. Using the three classes of drenches simultaneously reduced the fecal egg count to zero in all 13 lambs that were drenched. In the one control group lamb that was treated and made it to market the fecal egg count at week 6 had increased back to the pre-treatment levels. In contrast, the lambs in dry lot maintained a zero egg count from 2-weeks post drenching (first post treatment analysis) until the conclusion of the study.

The final objective was to provide a cost benefit comparison for the purchase of feed versus the added value from reduced lamb loss and/or higher rates of gain in dry lot lambs. For the purposes of this study we used $15.00 for a 50 lb. bag of 16% feed and $5.00 for a 40 lb. bale of hay. The total feed cost for the treatment group was higher than when all lambs were kept on pasture in the control group. The sum weights figure below demonstrates that for both the treatment rams and ewes, the final sum weights were higher for the treatment group than the control group. The decrease in weight between 7/31 and 8/14 was due to multiple casualties which coincidentally of not coincided with a heat wave. When the total pounds of lamb available for market was taken into account, the feed cost per pound of lamb was substantially lower for the lambs in the treatment group.



Control (lambs returned to pasture) Treatment (lambs sent to dry lot)
Feed Use (lbs) 2178  2623
Feed Cost  $653.40  $786.90
Hay Use (lbs)  120 240
Hay Cost $15 $30
Lbs. lamb for market 793 1070
Feed cost per lb. $0.84 $0.76


Research conclusions:

This study sought to investigate if using a dry lot could maintain parasite anthelmintic susceptibility in Bluefaced Leicester Maryland lambs.  The anthelmitic susceptibility testing results indicated that there was no difference in susceptibility between lambs kept in a convention management style (co-locate on pasture) from lambs where those requiring treatment were placed into a dry lot.  Despite this, the data revealed important information about the management style differences and the potential savings for farmers.   

Farms with high levels of resistance to multiple classes of anthelmintics should review their management styles, but may also be able to use drenches simultaneously to increase their overall efficacy.  In this study, fecal egg counts demonstrated that this was an effective treatment regimen.  There was still loss of lambs indicating that further care may need to be taken to overcome the loss of nutrients and possible gastrointestinal damage done by the worms prior to treatment.   

The use of a dry lot for lambs requiring anthelmintic treatment is a management style that will be adopted.  Use of the dry lot increased the survival of treated lambs and decreased the number of times that lambs required drenching, reducing overall exposure to anthelmintics.  While using a dry lot increased feed costs, the overall profitability was higher due to an increase in marketable lambs and rates of gain.   

Participation Summary
1 Farmers participating in research

Education & Outreach Activities and Participation Summary

1 Curricula, factsheets or educational tools
1 Published press articles, newsletters
1 Webinars / talks / presentations

Participation Summary:

56 Farmers participated
3 Number of agricultural educator or service providers reached through education and outreach activities
Education/outreach description:

PastureBasedGrazingFieldDay2019.docx_The first method of outreach was through an article in the Wild and Woolly Newsletter.  This newsletter is available electronically for free on the Maryland Small Ruminant Page (  As the newsletter is in pdf form, there isn't a great mechanism in place for continued discussion or feedback, so it is difficult to gauge how many framers may change their farming practices as a result of the information shared. WildWoolyArticle

The second method of outreach was through participation on a producer panel at the Maryland Small Ruminant Pasture, Grazing, & Browsing Conference.  Here, despite most producers in attendance being focused on being pasture based, several producers mentioned that they would consider a dry lot for some lambs to help them control their parasite problems.  The conference participants received a USB drive that contained the information from the Wild and Woolly article so they could see the changes in survival and economic benefit.  

Technical advisor, Susan Schoenian, in her role as Sheep and Goat Specialist, talk frequently to groups about parasites.  She mentions this SARE work in her talks when discussing anthelmintic need and considering the benefit of dry lots.  

Learning Outcomes

5 Farmers reported changes in knowledge, attitudes, skills and/or awareness as a result of their participation
Key areas in which farmers reported changes in knowledge, attitude, skills and/or awareness:

Feedback was primarily received through conversation at the grazing conference.  Farmers in attendance were largely proponents of 100% pasture based operations.  After hearing the option to maintain healthy lambs on pasture and sequester lambs that are not thriving, many participants took an interest in using the combined approach in order to increase flock health and improve profitability.  The attitude change learned was looking at dry lots as a tool to promote animal health and not consider them a cruel means of animal husbandry.  

Project Outcomes

1 Farmers changed or adopted a practice
Project outcomes:

There were two changes in practice and a benefit that were implemented during the 2019 lambing season:  

a.    Using rate of gain: The predetermined rate of gain, adjusted from the 2017 study to account for sex differences, were consistent with the FAMACHA scores indicating a need for drenching with one exception.   In one two week interval the temperature was over 90 degrees for greater than a week.  Thus, rate of gain was used to determine drenching needs.

b.    Putting lambs in a dry lot.  Lambs that required anthelmintic treatment were placed onto a dry lot until marketing.

Assessment of Project Approach and Areas of Further Study:

In a year of record breaking rainfall the use of an outdoor dry lot was not feasible.  It still may be possible in different climates or through the use of other material such as sand.  One consideration through was that the lambs in the barn also fared better during the heat waves as they had more shade and were likely a few degrees cooler.  Overall this study supports not being afraid to put animals in a barn (with adequate water and feed).   

The unforeseen inclusion of adding fecal egg counts to this study was a great enhancement that should be included in the future for similar studies.  While the big picture of this study was to reduce the use of anthelmintics by using a dry lot, the fecal egg counts demonstrated that anthelmintics may be being used in lambs where the parasite has been controlled.  In these situations producers should be treating that physiological state or addressing the nutritive needs as additional anthelmintics will not provide any further support for the lamb.   

The use of the fecal egg count was also able to demonstrate that the use of the combined anthelmintics was effective at controlling parasites.  For farms that are experiencing resistance, this could be a viable option.  As the parasites could still develop resistance, the use of anthelmintics should still not be used in lieu of other animal husbandry practices.   

From this one year study the question of if using a dry lot for lambs could help maintain refugia could not be answered.  Taken with the other years of selectively treating lambs and ewes there may be a slight increase in overall efficacy, however the difference is likely not significant.  For producers that would like to maintain at least a partial pasture based operation, these results do indicate that lambs that do not require treatment may still thrive on pasture, but it would be best to take those that were more susceptible to parasites off pasture for their wellbeing and the producers profitability. 

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.