Using real-time generated rate-of-gain to determine anthelmintic need in pastured Blue Faced Leicester Maryland lambs

Final report for FNE17-875

Project Type: Farmer
Funds awarded in 2017: $9,104.00
Projected End Date: 12/31/2018
Grant Recipient: Vista View Farms
Region: Northeast
State: Maryland
Project Leader:
Andrew Keller
Vista View Farms
Expand All

Project Information


The purpose of this project was to evaluate a time efficient method to determine need for anthelmintic administration in lambs.  Lambs were tagged with EID tags which allowed their rate-of-gain to be determined real time using RFID technology.  The rate-of-gain and FAMACHA score (a “gold standard” for determining anthelmintic application) were collected bi-weekly and the rate-of-gain collected each week.  Rate-of-gain only measurements took less than half the time of conducting FAMACHA analysis.  The results, decision if the lamb required anthelmintics, was the same 70% of the time when comparing the rate-of-gain threshold to FAMACHA scores of 4 or 5.  On average the decision to drench based on rate of gain was 3 times per growing season while it was only 2 times using FAMACHA scores. Since the goal is to reduce drenching unless necessary, it is evident that more work needs to be done to see if the rate of gain values can be modified to reduce the potential for any non-necessary drenching.  We used 66% of expected ROG and may now decrease that to 60%.

Fecal samples collected from a subset of the most frequently and least frequently drenched lambs were analyzed for parasite resistance but did not demonstrate refugia being maintained in the co-located lambs that were not drenched as frequently.  Thus, both groups showed the same resistance to dewormer in the parasites they carried or shed in their feces.

This information was shared in an on-farm demonstration with the Maryland Commercial Sheep and Goat Producers, a presentation for the Maryland Sheep Producers Seminar attended by 20 local sheep farmers and 2 local veterinarians, and has been incorporated into a “Decision Tool for Drenching” presentation that our technical advisor created which is available online.   


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. 

One hurdle to targeted treatment may be producers lacking confidence 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).    

Parasitic gastro-intestinal worms in sheep are not a new problem. Research has found that it is common for 20-30% of animals in sheep and goat flocks to harbor 70-80% of the worms (Kaplan 2004). While there are multiple parasitic worms, including Trichostrongylus, Ostertagia, and Cooperia, the barber pole worm, Haemonchus contortus, is generally recognized as the single most important sheep and goat pathogen in the United States.  H. contortus causes many sheep deaths per year (Zajac, 2016).

The life cycle of these parasitic worms has been researched and is well understood.  Understanding their life cycle, we know that worms cannot be eradicated from sheep as long as sheep are on pasture (Zajac, 2016). H. contortus are particularly difficult to control as they are prolific.  Female worms lay 5,000 to 10,000 eggs per day, and are capable of going into a "hypobiotic" or arrested state when environmental conditions are not conducive to their development and resuming their life cycle once environmental conditions improve (Schoenian, 2016).

Anthelmintic development is an important first step in providing a solution to this important health problem.  Three classes of anthelmintics (three categories of drugs that work in different ways to kill parasitic worms) are available to treat sheep with parasitic worms.  With treatment, however; the worms are becoming resistant to these drugs, rendering them ineffective.

Figure 1: Illustration of Refugia

Different theories on how to use anthelmintics to slow the rate at which worms become resistant have been proposed.  These theories are based on maintaining refugia.  Refugia is maintaining a “refuge” of parasitic worms that are not exposed to anthelmintics.  Figure 1 provides an illustration of refugia (FDA, 2013).  To maintain refugia, research has been conducted to study how to differentiate between animals that should be treated, and animals that should not (i.e., those that will serve as a refuge). 

Techniques for how to conduct Targeted Selective Treatment (TST) include FAMACHA©, faecal egg count (FEC), or production traits such as liveweight (The Happy Factor™), body condition scores (BCS) or milk production (McBean et al. 2016).  A comparison of these identification techniques found that there is no “one size fits all” approach for TST and the indicators should be calibrated to farm-specific conditions to increase their efficacy (Chylinski, 2015). 

Figure 2: FAMACHA© Card

The FAMACHA© technique enables clinical identification of anemic sheep at the farm. Having completed training, an individual can compare the ocular mucous membranes of sheep or goats to the color on the laminated scoring card (As shown in Figure 2).  The lighter color, a sign of anemia, would indicate an animal that should be treated with anthelmintics.  This method is effective for H. contortus as anemia is a primary pathological effect.  A study on the accuracy with which sheep and goat producers found that failure to identify an anemic animal (false negative) occurred less than 5% of the time in sheep (Burke 2007). FAMACHA© has been suggested to be a useful tool for the long-term genetic selection of resistant and resilient animals; however, it is necessary to maintain thorough records, which has been a significant hurdle to its implementation (Periera 2016). 

The Happy Factor™ relies upon lambs meeting expected individual weight targets to determine if treatment is necessary. Farms in Scotland using a 66% of maximum weight gain cut-off to determine treatment need saw an 8.7% to 52.3% reduction in the number of treatments compared to the traditional routine treatment of all animals (McBean 2016).  “In the Scottish climate, the predominant parasite genera detected on farms are Teladorsagia circumcincta and Trichostrongylus spp (Busin et al. 2013).” One major constraint for the use of bodyweight gain is the requirement for individual identification of animals.  Use of an electronically readable ear tag (EID) system and automated weigh systems is recommended and allowed the Happy Factor™ to be implemented with little extra effort (Busin et al 2014, McBean 2016). 

No studies using rate-of-gain as an indicator for treatment could be found in regions in which H. contortus is the primary parasitic worm of concern in lambs.  One study comparing indicators in France did find reductions in weight to be a sensitive indicator in Blackbelly and Romane sheep; however, the study questioned the accuracy of their results (Chylinski 2015).    


Burke, J.M., Kaplan, R.M., Miller, J.E., Getz, W.R., Mobini, S., Valencia, E., Williams, M.J., Williamson, L.H., A.F. Vatta. (2007) Accuracy of the FAMACHA system for on-farm use by sheep and goat producers in the southeastern United States. Vet. Pathology 147: 89-95

Burke, J.M. and J.E. Miller. (2008) Use of FAMACHA system to evaluate gastrointestinal nematode resistance/resilience in offspring of stud rams. Veterinary Pathology 153: 85-93

Busin, V., Kenyon, F., Parkin, T., McBean, D., Laing, N., Sargison, N.D., Ellie, K. (2014) Production impact of a targeted selective treatment system based on liveweight gain in a commercial flock.  The Veterinary Journal 200: 248-252.

Chylinski, C., Cortet, J., Neveu, C., J. Cabaret. (2015) Exploring the limitations of pathophysiological indicators used for targeted selective treatment in sheep experimentally infected with Haemonchus contortus. Veterinary Parasitology 207: 85-93

FDA. (2013) Antiparasitic Resistance in Cattle and Small Ruminants in the United States: How to Detect It and What to Do About It. Last accessed 11/4/16

Kaplan, R.M., Burke, J.M., Terrill, T.H., Miller, J.E., Getz, W.R., Mobini, S., Valencia, E., Williams, M.J., Williamson, L.H., Larsen, M., Vatta, A.F., Validation of the FAMACHA© eye color chart for detecting clinical anemia in sheep and goats on farms in the southern United States. Veterinary Pathology 123: 105-120

McBean, D., Nath M., Lambe, N., Morgan-Davis, C., F. Kenyon. (2016) Viability of the Happy Factor™ targeted selective treatment approach on several sheep farms in Scotland.  Veterinary Pathology 218: 22-30

Papadopoulos, E., Gallidis, E., Ptochos, S., Fthenakis, G.C. (2013) Evaluation of the FAMACHA© system for targeted selective anthelmintic treatments for potential use in small ruminants in Greece.  Small Ruminant Research 110: 124-127

Periera, J.F.S., Mendes, J.B., DeJong, G., Maia, D., Teixeira, V.N., Passerino, A.S., Garza, J.J., Sotomaior, C.S. (2016) FAMACHA© scores history of sheep characterized as resistant/resilient or susceptible to H. contortus in artificial infection challenge.  Veterinary Pathology 218: 102-105

Schoenian, S. (2016) Sheep 201: A Beginners Guide to Raising Sheep. Last accessed 11/4/16

Zajac, A. Managing the worms in your sheep (or- is there life after drugs?). Last accessed 11/17/16

Project Objectives:

Our proposed solution is using real-time generated rate-of-gain measurement to determine if anthelmintic treatment is necessary. Rate-of-gain is a performance measure that can be easily calculated requiring little additional equipment and training. For larger producers, use of Radio Frequency Identification Device (RFID), corresponding readers and software can be used for real-time decision-making (following an initial baseline weight). Overcoming training obstacles, reducing time inputs, and demonstrating efficacy may increase the number of producers who choose to selectively treat animals and slow anthelmintic resistance.

This research has three objectives. First, the study will compare the number of lambs treated using the rate-of-gain versus lambs that would be treated using a FAMACHA© score, a currently commonly used identifier. Second, the time to record FAMACHA© scores versus rate-of-gain decision-making will be recorded to demonstrate producer timesavings. Third, fecal samples from the co-located lambs will be pooled from animals needing treatment, and pooled from animals not requiring treatment, and tested for parasites resistance to anthelmintics to compare resistance rates.


Click linked name(s) to expand/collapse or show everyone's info
  • Susan Schoenian - Technical Advisor


Materials and methods:

28 Blue Faced Leicester ewes were bred using 3 rams beginning on December 1, 2016 for an expected lambing start of May 2017.  At birth, ewes and their lamb(s) were be moved into individual lambing jug’s.  The following lamb was recorded: dam tag number and sire, if the lamb is a single, twin or triplet, birthweight, and sex. Lambs were tagged using Radio Frequency Identification Device (RFID) tags.  Standard protocols for vaccinations and tail banding/castration were followed. 

After approximately 5 days, dams and their lambs were moved into a group pen.  On May 29, 2017, lamb weights and FAMACHA scores were recorded and lambs weaned and moved as one group onto pasture with access to shelter.  Water and hay were provided ad libitum and lambs had creep feed access to 18% lamb starter.  Due to a change in availability lamb feed containing BVT (a coccidiostat) was not provided as initially intended.   

Lambs were weighed weekly following weaning.  Twice monthly, in addition to weighing the lambs, the lambs were evaluated for their FAMACHA score.  Lambs that do not meet our pre-determined rate-of-gain threshold, and lambs that score a 4 or 5 using the FAMACHA© scoring system were treated with anthelmintics (discussed below).  By analyzing the rate-of-gain and FAMACHA© on the same animals at multiple time points we were able to compare if the techniques identify the same sheep, or a similar number of sheep, for treatment (Objective 1). 

Our predetermined rate-of-gain threshold to determine which lambs should be treated with anthelmintics was 0.33 lbs./day.  To arrive at this number we considered that the expected rate of gain for lambs fed a higher percentage of grain is 0.5 to 0.8 lbs/day while pastured lambs have an expected rate of gain of 0.25 to 0.5 lbs/day (Neary 1998).  Studies in the United Kingdom using rate-of-gain set their threshold at 66% of the expected rate-of-gain.  Thus, by providing creep feed to lambs on pasture our expected rate-of-gain is approximately 0.5 lbs/day, 66% of which is 0.33 lbs./day. 

Lambs remained as a single group from the time they were put on pasture until they were marketed or the study is complete.  We also considered the timesaving’s (Objective 2) by the difference in the amount of time required to work the lambs on days when just the rate-of-gain was analyzed with the time required to perform both rate-of-gain and FAMACHA©.   

The farm was equipped with a tub and raceway corral system.  As lambs move 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 allowing the weight to be captured automatically. The daily rate of gain (using 2 week weight as a baseline weight) was also displayed automatically (“real-time”) on both the scale head and stock recorder.  This allowed the farmer to make a decision quickly whether to give anthelmintic treatment to an animal prior to it leaving the scale.  In addition, the FAMACHA© test score (1-5) was recorded into the stock recorder. 

Anthelmintic treatment for lambs was based off of a Fall 2016 DrenchRite Report from sheep on the farm and recommendations from our extension sheep specialist.  Resistance was found to the Benzimidazole and Ivermectin classes of anthelmintics.  Cydectin and Valbazen, at full strength according to the label directions, will be given simultaneously as the anthelmintic treatment.  This avoided the use of the “last resort” class for this farm, the Levamisole class. 

Pooled fecal samples were collected and sent to the University of Georgia College of Veterinary Medicine for DrenchRite analysis.  Pooled fecal samples were collected at two time points, in July and September.  These pooled samples were homogenized fecal samples from 10 lambs that had not received anthelmintics in the last 2 weeks.  One pooled sample was collected from lambs at weaning (approximately 7 weeks of age).  This sample was intended to provide a baseline of the worm species present and their resistance status to the three classes of anthelmintics.  Two pooled samples were be collected in September (wether lambs were finished for market).  The first sample collected was from the 10 lambs receiving the most treatments.  The second sample collected was from the 10 lambs receiving the least number of treatments.   The fecal egg count, part of the DrenchRite test, provides insight into the resilience versus resistance of the lamb treatment groups.  The resistance status of the worms provides insight if fewer treatments helped to preserve refugia when lambs are co-located in the same pasture (Objective 3).  Due to the cost of analysis only these three pooled fecal samples were analyzed and a statistical analysis will not be feasible. 


Research results and discussion:

The first objective was to compare the decision outcome (i.e., whether or not to dose a lamb with anthelmintics) would be the same using rate-of-gain versus the FAMACHA© score system.  The determination to drench using rate of gain was consistent with drenching animals with a 4 or 5 FAMACHA© score 70% of the time.  Since the FAMACHA© system is the gold standard this is promising result for a preliminary study.  The lamb rate of gain and FAMACHA© scores are attached: LambData9.19.17.  On average the decision to drench based on rate of gain was 3 times per growing season while it was only 2 times using FAMACHA scores.  Since the goal is to reduce drenching unless necessary, it is evident that more work needs to be done to see if the rate of gain values can be modified to reduce the potential for any non-necessary drenching.

Reviewing the data there are a few changes necessary to the protocol to make this an ideal program for my farm.  First, when lambs needed drenching they tended to need two weeks to recover, so checking the animals every week  lead to non-necessary drenching.  In the future, the interval between checking for rate of gain should be increased to two weeks.  Ewe lambs were also drenched more frequently, sometimes corresponding with a FAMACHA© score of 3 or better, indicating that the cut-off value was too high and the sex difference should be taken into account.  In the future, a slightly lower rate of gain will be used for a cut-off value.

The second objective was to evaluate timesavings by using RFID technology with rate-of-gain instead of FAMACHA for determining drenching needs.  Including the time to move the animals into the corral the timesavings using rate-of-gain was on average about half the time that it took when conducting FAMACHA scores.  We did not include the time to tag animals, but as scrapies tags are already required we did not consider this an extra time burden.

The third objective was to compare the anthelmintic resistance rates between a subset of the least and the most treated animals.  The results from the DrenchRite tests are in the attached forms.DrenchRite.Results1.  These results show the same parasite resistance rates for both sets of lambs.  Lambs requiring more treatments had an overall higher egg count indicating that they harbored more parasites.  While it is a common practice, maintaining lambs that require more treatment in the same management group as those not requiring as much treatment could be detrimental in that those susceptible lambs may accelerate parasite resistance in parasites which will spread throughout the entire group.  


Research conclusions:

We believe that rate-of-gain could be adopted by sheep producers to evaluate drenching needs in lambs with less time commitment and physical handling than FAMACHA.  The overall result was positive that this method was consistent with FAMACHA scores 93% of the time.  We did recognize a few limitations and changes that we will make when adopting this to our farm.  First, measurements every week did not allow for the lambs provided treatment to recover and meet the pre-determined rate-of-gain, so we will use bi-weekly measurements.  Second, we will reduce the rate requirement for ewe lambs as they tend to grow a little slower and the established rate was where the rate-of-gain indicated treatment when FAMACHA scores did not always.  Third, there needs to be discretion used for animals that appear to have coccidiosis (dirty backsides).  Other producers would likely need to carefully establish the appropriate rate-of-gain for their animals given their breed(s) and management style.  

We did not meet our objective of demonstrating refugia in lambs that were not treated as frequently.  This is likely due to the lambs being co-located in the same pasture, a common management practice.  This has highlighted the potential for changing livestock management practices to prevent the spread of resistant parasites among lambs.  

Participation Summary
1 Farmers participating in research

Education & Outreach Activities and Participation Summary

3 Curricula, factsheets or educational tools
2 On-farm demonstrations
1 Published press articles, newsletters
2 Webinars / talks / presentations
1 Workshop field days

Participation Summary:

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

Two on-farm tours were conducted.  The tours provide a demonstration of the use of electronic identification (EID) tags and software system and FAMACHA scoring.  A handout was provided for the commercial group which included a summary of the results.  FNE17-875KellerSummary1

A short presentation was provided for the SARE IPM webinar, participants were mostly researchers.Keller.Anthelmintic11

A presentation including videos of tagging with EID's and using a stock recorder to read lamb information was presented at the MD Sheep Producers seminar.  This seminar was attended by 20 local farmers and 2 local veterinarians. Keller.MDSheepProducers41

An article was written for the local sheep newsletter.MDSheepProducersOutreach1

The outcome of this study has also been incorporated into educational materials online by our technical advisor.  Specifically the UMD small ruminant page "decision tools to worm or not" - .  It has been shared among different educational sheep groups on Facebook.

Learning Outcomes

60 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:

Limit drenching to animals in need. The concept of refugia. Awareness of EID's and software management systems.

Project Outcomes

1 Farmers changed or adopted a practice
1 Grant applied for that built upon this project
Project outcomes:

There has not been a lambing "season" subsequent to these outreach activities to gain feedback on the number of farmers that will adopt this technology.  This method will be adopted on our farm as we have experienced the timesavings and ease of use.  In addition, it has helped us to identify issues down to the specific lamb.  We hope to evaluate dam and sire over the course of time to see if there is a genetic component to select for more resilient lambs.  The past year using 3 different rams did not demonstrate a difference, not a formal objective of the study but one that we were able to analyze for in the data set.  There is more research to do combining this technology with other livestock management practices that we feel can help us reduce animal losses, preserve anthelmintic effectiveness, and improve quality lamb and wool gains.    

Assessment of Project Approach and Areas of Further Study:

The projects key success was to demonstrate with by using EID tags rate-of-gain is a time efficient way to determine if lambs require anthelmintics.  These were two questions that we set out to study.  We plan to modify the protocol by recommending drenching less frequently, biweekly, and modifying the rate-of-gain to account for sex differences.  

One lesson learned in this study is that the parasite population is field/pasture specific.  We would therefore no longer promote keeping lambs co-located as a management group if there is a subset that requires more drenching.  Care should be taken that pastures those lambs have been on are not re-populated with other sheep until the pasture is "clean" (e.g., mowed for hay).  

There is a lot more work that can be done in this area.  Breed and management style can be evaluated for variations in the appropriate rate-of-gain.  We hope to follow-up with an additional study where lambs requiring treatment are placed on a drylot to see if using the two management techniques can help slow resistance rates.  This knowledge would likely benefit medium to large producers and feedlot operations since there is an equipment expense to implement.  

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.