Reproductive performance is an important factor in determining profitability in the sheep flock. Most breeds of sheep have seasonal breeding patterns and the majority of flocks in Ohio are spring lambing.  In this scenario, the peak fertility of the ewe is from late September through November.  The breeding season will extend somewhat beyond peak fertility for the late spring lambing system and begin somewhat before peak fertility for the late winter lambing system.  Some management attention given to the ewes and rams prior to the breeding season can pay dividends in terms of increased conception and lambing rate.

A primary consideration regardless of the lambing production system and timing used is nutrition of the flock.  The nutritional status of the ewe and ram at breeding is probably the primary factor that influences reproductive performance.  The nutritional status of the flock is also a factor that a flock manager has a lot of control over.  Evaluation of the body condition of the ram and ewe before breeding can tell the manager whether nutrient consumption should be increased or decreased.  Based on a scale of 1 to 5, with 1 being very thin and 5 being fat, the goal should be to have the ram and ewe enter the breeding season somewhere around a 3.5 body condition score.

One practice that is helpful with ewes that are below the target body condition score is to provide them with a diet high in energy that allows them to gain weight.  This practice is termed flushing and should be done 2 to 4 weeks before breeding.  The high energy diet can be provided by supplementing a high energy grain such as corn at a rate of one-half to one pound per ewe per day, or by providing a high quality pasture. Flushing can result in an increased lambing rate and a decreased number of open ewes.

One caution that is generally given if ewes are to be flushed using a high quality pasture is to keep them off pastures with a high content of legumes (clovers and alfalfa) and use grass pastures.  The reason given is that these legumes contain estrogen that leads to infertility and decreases the conception rate and pregnancy of the ewes.  Does this caution mean that ewes must graze pure grass pastures? Legumes typically help to boost the energy content of a pasture sward and generally are considered as a positive to improve pasture quality. What does high content of legumes mean?

Clovers and alfalfa contain compounds known as phytoestrogens.  In clover species the specific compounds are isoflavones.  These isoflavones exhibit estrogen like behavior in sheep, while cattle do not seem to be affected by them to the same degree.  I reviewed some of the scientific literature about this topic and it appears that sheep are more susceptible to the effects of isoflavones because as they are metabolized in cattle they are rapidly excreted in the urine, whereas in sheep they are not rapidly excreted and remain in their system longer.  In addition, the estrogen receptors in sheep appear to be more sensitive to these compounds as compared to cattle.

There are also other factors that influence the level or concentration of phytoestrogens in legumes.  The specific variety is one such factor.  Improved cultivars have been found to have lower phytoestrogen contents.  Environmental factors such as drought can increase the phytoestrogen content.  Finally, soil phosphorus levels can influence the amount of phytoestrogens in legumes.  Legumes grown in soil phosphorus deficient conditions have contained higher phytoestrogen concentrations as compared to legumes grown in non-deficient soil phosphorus conditions.

Still, the question remains, what is considered a high level of legumes with regard to this condition?  In the literature that I reviewed, the legume stands that produced a negative effect upon reproductive performance were either pure stands or predominantly legume stands.  I had a sheep farmer raise this question with me back in 2008 as he wondered about including clover in a grass pasture.  I wrote an email to Dr. Shulaw asking him about this issue.  He sent me some of the literature that I reviewed and summarized in this article and he also wrote, in part, “At this point in time, unless ewes are grazing pure stands of clover near breeding season I don’t have much evidence to make me concerned about infertility.”  As I am out and about on sheep farms and looking at pastures it is rare that I ever see a pasture that contains more than 35 to 40% clover.  The bottom line is that unless you have a pasture that is well over 50% clover, it should be fine to use in a flushing pass before the breeding season.

Some attention should also be given to the ram(s).  In addition to making sure that they are in good body condition, it is recommended that a breeding soundness exam (BSE) be conducted prior to breeding season.  The BSE consists of a physical examination, a reproductive tract examination and a semen evaluation.  Waiting until after the breeding season to discover a problem with your ram that shows up in the form of an extended lambing season or open ewes is costly.  Contact your veterinarian to schedule a BSE.  It is money well spent.

Finally, I need to close with a word about internal parasites.  One practice that use to be recommended was to deworm all the ewes and rams in the flock before the breeding season.  This practice is no longer recommended due to the resistance that parasites have developed to chemical dewormers.  Deworming all ewes and rams at one time is a method that will select for resistance.  Instead, deworm with a chemical dewormer based upon individual animal need.  This can be determined by using the FAMACHA eyelid color scoring system.  Those animals scoring a 3 or higher on this 1 to 5 scale should be dewormed with a chemical dewormer.  Animals scoring a 1 or a 2 should not be dosed with a chemical dewormer.  For more information about parasite control and use of the FAMACHA system, contact a member of the OSU Sheep Team.

The breeding season is upon the majority of flock owners in Ohio.  Some pro-active management action can insure that it is a successful and profitable breeding season.

July – September are critical times to closely monitor the internal parasite burden of lambs and kids. Preferably monitoring would start in June. The internal parasite of principal concern during the summer months is Haemonchus contortus, the barber pole worm. Lambs and kids grazing on pastures that are contaminated with large numbers of infective Haemonchus contortus larvae can go downhill very rapidly in July and August. It would not be uncommon that within a 7 to 10 day period a lamb or kid could go from a perky animal with energy to bounce around a pasture to an animal that is on the threshold of death, lethargic and with little energy to move about. Unless an effective rescue treatment is applied at this stage, the chance of survival is very low.

I sometimes hear sheep and goat owners say that parasites are not a concern to them because they are using rotational grazing or because they have an effective chemical deworming schedule. Neither of these strategies is going to totally prevent high worm burdens from accumulating or do away with the need to monitor lambs and kids during the critical July – September period.

Although rotational grazing is a good strategy to manage pasture health and provide quality forage, it does not prevent Haemonchus contortus from building up to very high levels on pasture. Let’s do a brief review of the life cycle of the worm during the grazing season. Adult worms attached to the stomach of an infected animal lay eggs that are passed in the animal’s feces. Under the favorable temperature and moisture conditions that exist in most summer pastures, eggs hatch to the infective larval stage in 4-7 days. Newly hatched larvae remain near the fecal pellet and pass through 3 stages of larval development termed L1, L2 and L3. The L3 stage is termed the infective stage because this larva will climb up blades of grass and wait to be ingested by grazing animals. Once the L3 stage has been ingested, it molts into an L4 larva stage and then molts in to an immature adult. When adults reach about 14 days of age in the stomach of the infected animal, they begin laying eggs. The entire life cycle from egg to egg can occur in as little as 24-25 days.

In a recent conversation with Dr. Shulaw, an OSU Extension Veterinarian who has considerable experience working with this problem of internal parasites, I asked about the life span of an infective Haemonchus contortus larva on pasture. Dr. Shulaw replied that L3 larvae can live up to 90 days on summer pastures given our climate and general pasture conditions. So, within the grazing season if a pasture is being re-grazed within that time frame and assuming our ewes and does were shedding Haemonchus contortus eggs in their feces on the first grazing pass, then those larvae are there waiting to be consumed in subsequent grazing passes. Since a mature female Haemonchus contortus worm can lay up to 5000 eggs/day, it does not take long for a pasture to accumulate very high levels of infective L3 larvae.

Depending upon chemical de-wormers and a regular deworming schedule is, at best, a short term fix. By now, sheep and goat owners who are serious about long-term production know that chemical resistance is an issue and that there is documented parasite resistance to all classes of currently available chemical dewormers. No chemical dewormer is 100% effective. Used repeatedly over time, the chemical will loose its effectiveness as the percentage of worms resistant to the chemical increase in the worm population on the farm. It’s important to understand that every time a chemical de-wormer is used, there is some selection for resistant worms. Deworming every animal in the flock or herd on a regular schedule is a formula for developing a resistant worm population and chemical failure. Selective deworming of only those individuals that really need some help will help to sustain the effectiveness of a chemical dewormer. That brings us back to the opening statement that animals need to be monitored.

How should lambs/kids be monitored during this critical period? There are two main tools that livestock owners can use; the FAMACHA eyelid score system and fecal egg counts. Both require time and regular application to be effective. Since few producers have the time, expertise and equipment to do fecal egg counts, they will have to depend upon their local veterinarian. The local vet may not have the time and/or staff to get fecal egg counts done in a timely and consistent manner and producers may not want to fork over $10 to $15 per fecal egg count test. That leaves the FAMACHA system.

The FAMACHA eyelid color score system uses a scale of 1-5 to grade eyelid color. The color of the lower eyelid is correlated with anemia caused by Haemonchus contortus burden within the animal. A chart with eyelid color and scores is matched to the live animal’s eyelid color. A bright red color score of 1or 2 indicates low levels of anemia and pale pink to white (scores 3-5) increasing levels of anemia. Generally an animal scoring a 3 or higher would be treated with an effective chemical dewormer. The value of the FAMACHA system is that it allows animals that are most affected by Haemonchus contortus to be identified and selectively treated without using a chemical dewormer on the entire herd/flock.

The most effective use of the FAMACHA system is consistent, regular application. During the critical July- September period, this means checking lamb/kid eyelids every 7 to 10 days. Keep track of scores for individual animals and use this as a record to notice trends that are developing. This is advice that was learned the hard way and here’s the story.

In 2008, I was involved in a small on-farm research project examining early weaning and pasture management to try to control Haemonchus contortus infection levels in lambs. Lambs were FAMACHA scored on a regular basis beginning in May. Towards the end of June over 90% of the lambs were scoring a 1 or a 2 and I thought parasites might not be a big issue. Then, doing FAMACHA scoring on July 8, over 40% of the lambs had to be treated with a chemical dewormer based on FAMACHA scores and backed up by high fecal egg counts. How did the situation change so quickly?

Ever notice how once something goes wrong you have time to go back and correct the mistake or take the time to think through what led to the error? We went back and looked at the FAMACHA scores and Dr. Shulaw did an analysis of FAMACHA percentages over time in the study. Here are some of the results: May 5: 77% of the lambs scored a 1, 23% scored a 2. June 5: 36% of the lambs scored a 1, 64% scored a 2. June 23: 29% scored a 1, 65% scored a 2, 5% scored a 3 and 2% scored a 4. July 8: 9% scored a 1, 42% scored a 2, 42% scored a 3, 5% scored a 4 and 2% scored a 5. Notice the trend toward higher scores over time. The distribution of FAMACHA scores was changing. Once the scores were looked at from this perspective, it was clear that lambs did not go downhill as suddenly as we perceived. The information was there, and a warning bell was sounding. The FAMACHA system can be used as an early warning system, but only if it is used regularly, records are kept and then those records are looked at for trends after each scoring of lambs/kids.

The last point I need to make in this article is that a farm needs an effective chemical dewormer to serve as a rescue option. How do you know if your chemical dewormer is effective or if resistance is developing? One way is by examining worm egg counts in the manure of treated animals, but this involves sampling relatively large groups and having your veterinarian do quantitative egg counts. Another way involves collecting some representative fecal samples and then exposing the eggs to the various chemical dewormers. One such assay is called the DrenchRite assay and is performed by a lab at the University of Georgia. The cost of this test is about $400, but resistance to all three chemical dewormers is evaluated on one composite sample. This makes this method very attractive for small flock/herd owners, and the assay results are available in about three weeks.

Beginning in June, but especially in the July-September period, is a critical time to monitor lambs and kids for internal worm burdens. Livestock owners need to recognize that early season pasture management will have an effect on parasite burdens. If lambs and kids can’t be moved to a safe pasture or feedlot system, then monitoring by use of the FAMACHA system, combined with an effective chemical dewormer, can help to reduce lamb/kid mortality.

For more information about the FAMACHA system or management of internal parasites, contact a member of the OSU Extension Sheep Team. Additional information about worm control and pasture management is also available on the Extension Sheep Team website at www.sheep.osu.edu .

A FAMACHA training session will be held at the Great Lakes Fiber Show at
the Wayne County fairgrounds in Wooster, OH, on May 23. The schedule and
more information about the event can be found at
http://www.greatlakesfibershow.com/shows-sales.htm
For information about registering for the FAMACHA training contact Marlene & Carl Gruetter: 740-256-1866 or e-mail at trf@trfohio.com.

Bill and Susan Shultz will be scanning their 2009 lamb crop on Friday, June 20, 2009 at their farm in DeGraff, Ohio. They have contracted with Bonnie Bradford, a skilled technician, to do the scanning of loin eye and back fat as she has done the past three years for the Shultz’s.

For any sheep breeder who is interested in scanning their lambs, the Shultz’s are willing for you to bring your lambs to their farm during the late morning on the 20th. Due to health concerns all lambs will need to be unloaded, processed and reloaded onto the truck or trailer as there will be no penning of animals at the site. The procedure for scanning is that a weighing scale will be available, and personnel will be available to shear each lamb between the 12th and 13th rib to provide adequate contact for the scanner. Bonnie charges $5.00 per head for scanning. For best results, lambs should weigh between 120 and 180 pounds.

If you are interested in scanning lambs please contact Bill or Susan at bunkerhillfarm@gmail.com and they will schedule you in for the morning of June 20th.

The 2009 Appalachian Grazing Conference will be held at the Lakeview Resort in Morgantown, West Virginia on March 6&7. For more information and registration details, log onto http://www.wvca.us/grazing_conference.

Log on and get registered soon as the reduced lodging rate of only $76.00/single occupancy coupled with the conference registration of $75.00 is only available until February 2.

This O.S.U. Extension Coordinated Program is an effort to provide outreach programs in several areas of sheep production. We invite sheep and goat producers from around Ohio to come to one or more of the educational sessions to learn more about different areas of sheep and goat production.

Programs Sponsored by: Ohio Sheep Improvement Association, Roger A. High, Executive Director, contact (614) 246-8299 or rhigh@ofbf.org or visit our website at www.ohiosheep.org for more information. Contact Extension Educators for possible meeting fees.

When, Where and What?

Wednesday, January 14, 2009 “Mt. Victory Program”
Location: Mt. Victory Plaza Inn, Mt. Victory, OH
Time: 6:00 p.m. – PAID RESERVATION IS REQUIRED FOR MEAL
7:00 p.m. – Program begins
Registration for meal: $15.00/person: Paid Registration due by: January 5, 2009
Speaker: Bob Hendershot, USDA/NCRS Grazing Specialist, “Pasture Management”
Contact: Wesley Haun, Logan County Extension Educator at (937) 599-4227

Tuesday, January 27, 2009 “Springfield Program”
Location: Clark County Extension Office, 4400 Gateway Blvd., Suite 104, Springfield, OH
Time: 7:00 p.m.
Speaker: David O’Diam, OSU Meat Lab Manager, “Lamb and Goat Carcass Evaluation”
Contact: Jonah Johnson, Clark County Extension Educator at (937) 328-4607 or
Tim Fine, Miami County Extension Program Assistant at (937) 440-3945

Monday, February 9, 2009 “Burton Program”
Location: Geauga County Extension Office – Patterson Center, 14269 Claridon-Troy Rd, Burton, OH
Time: 7:00 p.m.
Speaker: Roger A. High, OSU Sheep Extension Specialist, “The Management Continuum”
Contact: Les Ober, Geauga County Program Assistant, (440) 834-4656

February 25, 2009 “Bryan Program”
Location: Williams County Extension Office -
Time: 7:00 p.m.
Speaker: Dr. Bill Shulaw, OSU Preventive Veterinarian, Beef and Sheep, “Internal Parasite Management”
Contact: Flo Chirra, Williams County Extension Educator at (419) 636-5608

Wednesday, March 4, 2009 “Fostoria Program”
Location: Ag Credit Services Corporate Office, 610 West Lytle St., Fostoria, OH
Time: 7:00 p.m.
Speaker: Dr. Steve Loerch, OARDC Ruminant Nutritionist”, “Ruminant Nutritional Programs utilizing Dried Distiller’s Grain’s (DDG’s)”
Contact: Ed Lentz, Seneca County Extension Educator, (419) 447-9722 or Gary Wilson, Hancock County Extension Educator, (419) 422-3851

Monday, March 16, 2009 “Licking/Muskingum Program”
Location: Licking Valley High School, Haynesview Drive, Hanover, OH
Time: 7:00 p.m.
Speakers: Roger A. High, OSU Sheep Extension Specialist, “What Market are You Breeding For?”
Katherine Harrison, General Manager, Blystone Farms, “Marketing to the Ethnic Population”
Contact: Howard Siegrist, Licking County Extension Educator, (740) 349-6900 or
Mark Mechling, Muskingum County Extension Educator, (740) 454-0144

Thursday, March 19, 2009 “Barnsville Program”
Location: “New” Farm Bureau Building, 100 Colonel Dr., Barnsville, OH
Time: 7:00 p.m.
Speaker: Roger A. High, OSU Sheep Extension Specialist, “Sheep Nutrition”
Contact: Steve Schumacher, Belmont Co. Extension Educator, (740) 695-1455 or
Mark Landefeld, Monroe County Extension Educator, (740) 472-0810

Wednesday, March 25, 2009 “Lisbon Program”
Location: Crestview Local School, 44100 Crestview Rd. , Columbiana, OH
Time: 7:00 p.m.
Speaker: Roger A. High, OSU Sheep Extension Specialist, “Lamb and Goat Quality Assurance”
Contact: Julie Herron, Columbiana County Extension Educator, (330) 424-7291

UNKNOWN DATE AT THIS TIME! 2009 “Bryan Program”
Location: Unknown at time of release – More details later
Time: 7:00 p.m.
Speaker: Dr. Bill Shulaw, OSU Preventive Veterinarian, Beef and Sheep, “Internal Parasite Management”
Contact: Flo Chirra, Williams County Extension Educator at (419) 636-5608

We are setting these programs up as “district” programs to reach as many sheep and goat producers around the state of Ohio as possible. We encourage you to come and to get your sheep and goat production questions answered.

Rory Lewandowski, Extension Educator, Athens County

July and August are critical months to control the internal parasite, Haemonchus contortus in pasture based sheep and goat production. Often producers may find that lambs and kids seem to “stand still” during the summer, with little or no weight gain. There can be several reasons for this situation. One is that the nutrient level needed for good gains is not being provided, in other words, pasture quality is low. Another reason is that the animals have a parasite burden that prevents them from gaining weight. Finally, for those animals born in the February/March period, a natural immune response to internal parasites may be starting to develop. While this is important in the long run, this immune response exerts an additional nutrient demand upon the animal. In addition, the immune response can be overwhelmed by heavy parasite infections. In many cases, poor weight gain is a result of a combination of these factors.

Pasture management and monitoring of animals for parasite infection must be practiced as part of an internal parasite control strategy. The old saying, “know thy enemy” is appropriate since it is hard to make good pasture management decisions or know how to properly use monitoring tools without understanding the biology and lifecycle of Haemonchus contortus.

Haemonchus contortus survive and begin their life cycle each year through larvae that overwinter on pasture and/or through larvae “hibernating” in a process called hypobiosis in the abomasum of the host animal. This hypobiosis is actually an arrested development stage of the L4 larvae. In early spring, generally around lambing/kidding time, these L4 larvae resume the normal lifecycle, become adults and start laying eggs that are passed in the feces of the animal. So in the spring, adults and lambs can begin to accumulate Haemonchus contortus from consuming overwintered larvae, or from larvae emerging from newly deposited eggs.

Once an egg is deposited on pasture, if there is moisture and warmth, the egg hatches and a larva emerges, termed an L1 larva. Larvae need to go through a couple of growth stages to reach an L3 larva, which is the infective stage. L3 larvae migrate up and down grass blades in films of moisture. The time to go from egg to L3 infective larvae can be as short as 4 to 5 days under ideal temperature and moisture conditions. Once L3 larvae are ingested by grazing animals they travel to the abomasum or true stomach of the host animal. Larvae attach to the abomasum wall and begin to feed on blood. Within 2-3 days L3 larvae develop into L4 larvae and then adults. Once adulthood is reached, about 14 days are required before egg laying begins. The entire life cycle from egg to egg can be completed in as little as 21 days. Once egg laying begins, the female Haemonchus contortus can lay up to 5000 eggs per day. As life cycles are completed, pastures can become heavily contaminated.

It is important to realize that the L3 infective larva can survive on pasture for up to 90 days in the summer, and up to 180 days when they develop in the fall. This obviously presents some difficulties in a rotational grazing system. For example, let’s say a pasture was grazed by ewes or does in October. This means that eggs being deposited at that time could result in some overwintered larvae still being around in April. By April ewes and does will have resumed shedding eggs, and in many years, pastures managed under rotational grazing are ready to graze by early April. New eggs are being deposited, infective larvae are being ingested, and here we go. By time that paddock has been rotationally grazed a couple of times, watch out! This is what would be termed a “hot” pasture. It might look like good green, succulent grass, high in quality, but it can be teeming with infective L3 larvae. Even a pasture paddock that started out more than 180 days removed from a previous season grazing pass can become a hot paddock after a couple of grazing passes with ewes, does, lambs and kids shedding eggs.

What are management options? They must revolve around trying to keep parasite levels low. Keep a pasture log/record of when paddocks were grazed and the length of time pasture paddocks were grazed. Start the grazing season on pastures that are likely to have very low levels of overwintered larvae. Rotate to a new paddock within a 5-day period to insure animals are not ingesting infective L3 larvae. A critical piece is to have some safe pastures that have very low or no parasite larvae on them to graze in July and August. This could be a pasture that has not been grazed since the previous fall, a paddock that might have had a grazing pass but then been allowed to grow for hay harvest, or a summer annual forage. Weaning time can also play a role in how pastures are used. Once a lamb or kid has been weaned from the ewe or doe, and the stress of lactation removed, the ewe or doe can tolerate some parasite infection. The immune response provides some protection. So keep some safe pasture for weaned lambs/kids and then the ewes and does can go back and graze some of those pasture paddocks that contain infective L3 larvae.

The other management piece is monitoring animals. There are several tools available, including the FAMACHA eyelid color system and fecal egg counts. Both of these tools should be used on a consistent and regular basis to be effective. Used regularly, they provide trends that tell the livestock owner what is happening on the pastures and within the animal regarding parasite levels. Contact a member of the OSU Extension Sheep Team for more information about using these parasite-monitoring tools.

Notice that nothing has been said in this article about regular use of a chemical de-wormer. That is a road we don’t want to travel due to limited chemical options and big problems with parasite resistance to chemical de-wormers. Every sheep and goat farm that is serious about long-term production needs to know which of the chemical de-wormers, if any, work in their flock/herd and then save the use of that chemical for rescue treatments and selective de-worming as determined by regular monitoring.

REFERENCES:

Managing Internal Parasitism in Sheep and Goats

Kate Hepworth, Mike Neary, Terry Hutchens

Parasite Control in Sheep: Biologic Approaches for the New Millennium

William P. Shulaw and Clifton M. Monahan

(Originally Published in Sheep Team Newsletter June 2004)

Wet weather may contribute to fly infestations on livestock. Young lambs and sheep are particularly vulnerable. Wet soiled wool, wounds and dying tissue attract blow and bottle flies in the spring. Young animals may become infested very quickly. Flies usually deposit eggs on wet navels or around the rear end of the animal. Infected animals appear lethargic, walk with a limp, tail twitch, and generally appear depressed. If not treated immediately maggots may enter animals through the rectum, vagina or navel area.

Examine animals frequently this time of year. Closely inspect animals which are soiled or exhibit the clinical signs mentioned above. If maggots are found, look the animal over closely for spreading populations. In addition to the locations above, maggots can often be found between the hooves and in the flank region. Shearing and crutching helps to control outbreaks on mature animals. It may be necessary to clip wool to determine the extent of the infestation, remove the maggots and spray on a wound healing dressing such as screw worm spray. Fly larvae that have entered the body of animals can be encouraged to leave by coating the area where they entered with petroleum jelly. Once the wound is treated and larvae killed, there are many products approved for sheep containing Permethrin which will kill flies and provide some residual protection. Severe infestations may require antibiotic treatment, contact your veterinarian for assistance.

(Originally Published in Sheep Team Newsletter September 2007)

Peak worm transmission season has been with us for a few weeks already, and some shepherds in Ohio have already experienced episodes of clinical disease and poor growth caused by worm burdens.  For most people, the blood-sucking worm, Haemonchus contortus, or the “barber pole worm” causes this loss.  Although the FAMACHA system can be very effective in controlling this worm, it must be properly and regularly applied, and it is extremely critical that the drug being used to treat the individual animals selected be effective.

Because this worm is a very prolific egg layer, worm larvae burdens on pasture can build to dangerous levels very quickly and persist for several weeks.  For this reason, and perhaps unfortunate past experiences with severe parasitism, many shepherds have approached parasite control by routine treatment of grazing lambs, and sometimes ewes, with dewormers given every twenty-one to twenty-eight days.  If the drug is an effective one, this will usually prevent severe parasitism and may allow for maximal growth.  However, it is a prescription for selecting worms that are resistant to the drugs used.

There are other recommendations from the past that are still being advised and used but which, in light of newer information about parasite biology and development of drug resistance, should be abandoned.  One of these recommendations is the so-called “treat and move” strategy.  This technique is especially useful for young growing lambs, and its effectiveness was demonstrated by research here in Ohio in the early 1980s.  It involves treating all the lambs in a group and then moving them to a “safe” or “clean” pasture which is defined as one with no, or very low numbers of, worm larvae on it.  This can be a hayfield that has been harvested and allowed to regrow, a pasture that has had cattle on it earlier in the grazing season, or one that hasn’t yet been grazed by sheep.  Lambs with very low worm burdens that are placed on pastures that have no worm larvae on them will remain relatively uninfected for several weeks to several months.  This is an ideal situation for the lambs and for the shepherd, but unfortunately, we now know that it too can be a powerful force for selecting for drug resistant worms.

It works like this:  No dewormer is truly 100% effective and some worms survive treatment.  In addition, we now know that genes for drug resistance exist in the important worm species in virtually all domestic sheep populations across the world.  The proportions of worms carrying these resistance genes vary from flock-to-flock; but they are there and we can select for them.  Treating all the lambs in a group and then moving to a safe pasture allows the survivors of treatment to enjoy a reproductive advantage.  In most cases, it is likely these survivors will be the ones carrying the resistance genes.  Their progeny will then develop on the new pasture with little or no competition from worms that do not have the resistance genes.  Depending on the season and weather, the immune status of the sheep, the stocking density, and length of time the new pasture is grazed, the resistant worms in those animals can build to significant numbers and create a pasture capable of making considerable change in the gene pool of the farm’s total worm population.

Current strategies to prevent this from happening and to help maintain the long-term effectiveness of available dewormers revolve around the concept of retaining a portion of the worms that do not have the resistance genes and allowing them to reproduce preferentially.  This is a difficult concept to “sell” to many sheep farmers; especially those who have enjoyed the benefits of modern dewormers these past 40 years or so.  However, it is quite clear that we are approaching a time when we will no longer have that luxury.

The first of these strategies involves a targeted approach to treatment such that only the animals that are shedding the highest numbers of eggs and which may be the most burdened by worms are treated.  The FAMACHA scoring system does this using a patented color chart that reflects the amount of red blood cell loss in an animal.  It is specific to Haemonchus contortus only, but is quite useful here in Ohio.  When this system is used, typically only 20-40% of animals will need treatment; unless they are already experiencing severe parasitism before the planned move.  This allows the untreated animals, which are usually carrying relatively low worm burdens, to repopulate the next pasture with worm genetics that are similar to those before treatment.  (for more information on FAMACHA see http://scsrpc.org and articles from past issues of the Sheep Team Newsletter at http://sheep.osu.edu/category/parasites/) Another approach is the so-called “delay the move after the dose” strategy.  This allows the treated animals to become lightly re-infected before going to the clean pasture.  This helps ensure that contamination of the new pasture will occur with larvae from worms that have not had drug selection pressure put upon them.  This may be especially useful if signs of parasitism, such as anemia or bottle jaw, have already appeared in lambs before moving to the clean pasture.  The number of days to graze the infected pasture before moving depends on how heavily infected it is and the relative susceptibility of the animals (lambs versus less susceptible non-lactating ewes), but in general 4-7 days of grazing offers a useful compromise.  It is important to note that deworming with moxidectin will not allow this strategy to work because of its persistent activity in killing incoming larvae from pasture that can be as long as 35 days.

A variation of this strategy is to “move then dose.”  This means grazing the new pasture a few days before deworming to allow some contamination to occur.  Less information is available to recommend the length of time to graze before treatment and it will depend on the level of egg shedding when the animals are moved.  Animals with severe parasitism caused by Haemonchus can be shedding tremendous numbers of eggs so the pasture can be come contaminated relatively quickly, and they may suffer more stress from the move.  In most cases it should be safe to wait a week before treatment if the animals are apparently healthy.

Other strategies researchers have studied include using weight, weight change over time, or body condition score as a determinant of which animals need deworming.  Details for using these strategies may become clearer with time, and they may be most useful for parasite infections that are not predominantly caused by Haemonchus.  Because Haemonchus infections can build to dangerous levels quickly and animals (especially lambs) can die when they are still in good body condition, weight or weight change may not be reliable in areas where this parasite is the predominant one.

With the rather widespread occurrence of drug resistant worms across the world, and the specter of having no new chemical classes available in the foreseeable future, parasitologists and forage specialists are working diligently to devise new strategies that do not rely heavily on chemical dewormers to assist sheep producers in achieving sustainable control of parasitism.  Please consider how you might integrate some of this newer information into your management plan.  You can contact your veterinarian or a member of the OSU Extension Sheep Team for more information.

(Originally Published in Sheep Team Newsletter September 2007)

The single biggest threat to animal health and welfare on sheep and goat farms that use pastures as a significant part of lamb and ewe nutrition (and doe and kid nutrition) is internal parasite infection.  Although for the past 40 years producers have been able to minimize this threat with the routine use of highly effective dewormers that became available in the 1960s, it is now clear that on many farms most, if not all, of these dewormers are no longer highly effective as a result of the appearance of drug resistant worms.  As we learn more about how resistance to dewormers develops and the how the genes determining it are transferred, it has become clear that some of our older recommendations for dewormer use are no longer valid or perhaps even dangerous.

One of these, the “treat and move” strategy for lambs was discussed in an earlier article.  This approach involves sending treated lambs to a pasture that is free of, or nearly so, worm larvae.  The treated animals will stay relatively uninfected for several weeks, but this approach is a powerful force in selecting for drug resistant worms.  Treating all the lambs in a group and then moving to a safe pasture allows the survivors of treatment to enjoy a reproductive advantage.  In most cases, it is likely these survivors will be the ones carrying the resistance genes.  Their progeny will then develop on the new pasture with little or no competition from worms that do not have the resistance genes.  Depending on the season and weather, the immune status of the sheep, the stocking density, and length of time the new pasture is grazed, the resistant worms in those animals can build to significant numbers and create a pasture capable of making considerable change in the gene pool of the farm’s total worm population.

Another recommendation from the past that is now considered potentially dangerous is the routine treatment of ewes “in the jug” or at lambing time in the barn before turnout to pasture.  This practice can also select for drug resistant worms, especially Haemonchus contortus.  It is somewhat like the “treat and move” strategy in that survivors of treatment are more likely to be the resistant ones, and they are the ones that will serve to repopulate the next pasture with worm larvae.

In our climate where we often have some cold dry winters, Haemonchus contortus survives the winter primarily as larvae in a state of arrested development (sort of a suspended animation) embedded in the wall of the sheep’s fourth stomach, the abomasum.  It doesn’t survive as well over the winter on pastures as some other species of worms.  These arrested Haemonchus larvae resume development to the adult stage in the spring, especially around lambing time, and their eggs then seed the pastures for the next season’s life cycles.  This is the principal source of this worm for lambs, and because Haemonchus is a prolific egg layer, the buildup can become sufficient by June to cause severe parasitism and death even in ewes.

If all the ewes are treated in the barn before turnout, then most of the farm’s Haemonchus population is the survivors of the treatment in the ewes’ abomasum.  If the ewes then go to typical pastures where there are some other over wintered worm larvae, but few or no Haemonchus larvae, those surviving worms are the ones who repopulate the pastures with their larvae.  To the extent that these survivors of treatment in the barn carry resistance genes for dewormers, the farm’s worm population becomes shifted toward resistance.

Avoiding this problem requires implementing some strategy that will allow a few worms that have not had exposure to the dewormer to survive in order to produce eggs and larvae that will compete with those of the survivors of treatment.  As an alternative to deworming, ewes and lambs can be placed in a clean pasture and then moved to a second pasture before a severe buildup occurs.  This usually takes at least 4 weeks during the spring in our climate.  If additional clean pastures are available to move the ewes and nursing lambs to at the time a buildup is expected, this will break the cycle of buildup and protect both lambs and ewes.  However, many producers do not have this luxury and are somewhat unwilling to allow untreated ewes to go to pasture with their lambs because they are aware of the dangers.  Some strategies they could use that help avoid selection for drug resistant worms include treating only a portion of the ewes such as just the thin animals.  Some work in Europe and Australia suggests that leaving only 5-10% of the animals untreated may provide a large enough source of unselected worms to repopulate the pasture and still not heavily contaminate it.  This author is unaware of similar work in the USA but similar proportions may be sufficient.  Alternately, ewes could be moved to pasture and deworming delayed 4-7 days to allow some contamination to occur from unselected worms before treatment.

Another recommendation from the past that has recently come under scrutiny is the practice of deworming all the ewes during flushing or just before breeding.  Usually this is done in the late summer or early fall for winter lambing ewes.  The concern about his practice is as follows.

For most of the year, adult ewes have relatively high levels of acquired immunity to worms as a result of exposures during the grazing season. The exception is around lambing time and during lactation when this immunity is relaxed, or weakened, as we have discussed.  Normally, this immune response returns quickly after the lambs are weaned, and egg counts and worm burdens fall rather dramatically.  At breeding time, most ewes will have low worm burdens and low fecal egg counts because of their immune response.  New larvae acquired from grazing an infected pasture may not become egg-laying adults in ewes with this strong immune response which helps maintain this low worm burden.  Treatment of these ewes at this time tends to destroy the susceptible parasites leaving the resistant ones.  Because the ewes’ immune system may inhibit the establishment of new worms they ingest from pasture, the survivors of treatment will enjoy a prolonged period in which they are the principal producers of eggs that become infective larvae on the pasture.  This has the effect of selection for resistance on the farm worm population. Larvae developing from eggs deposited in late summer and fall are better able to survive over winter than older larvae, and they will be available when weather favorable for transmission begins again in the spring.

Well-fed ewes in relatively good body condition will probably not receive much of a benefit to a deworming at this time.  Therefore, some parasitologists now recommend that only thin ewes, immature ewes, or ewes with evidence of clinical disease be de-wormed at breeding time. Like the FAMACHA system, this is a targeted, or selective, deworming approach that allows some worms that have not been exposed to dewormers to survive in order to reduce selection pressures that lead to increased resistance.

It should be obvious from these two articles that if we are to effectively combat the increasing threat of drug resistant worms and prolong the effectiveness of those dewormers available to us, we must rethink how we use them in light of basic parasite biology and new knowledge of how resistance develops.  Sustainable parasite control will undoubtedly involve some use of dewormers for the foreseeable future, but we must be careful with them and integrate other management strategies in our control programs.