parasite questions

[Haystack Hollow]

A number of our sheep seem to develop messy butts around this time of year. I always figured it came from the new grass with its high moisture content. This year it seems to be a little worse than usual. I would take this as a sign to worm, but at the same time, our county extension office is recommending that we cut down on worming, because of resistance developing. So I can't really decide whether to worm or not worm. Any advice? We did worm at lambing, and our lambs are already weaned and gone.

 

Another question: There's going to be a FAMACHA course offered next month. It's going to last a day and cost $20, I think. Has any one taken one of these? Is it worth doing?

 

Thanks.

 

Margie at Haystack Hollow

[Rebecca, Irena Farm]

That's the one where you learn how to manage internal parasites using a high-management approach rather than a scheduled worming regime, right? Basically worming when they look sick? I haven't been to one but I've heard about it and would be interested to know what you think after you've taken it.

 

This year we will be moving sheep around at a rate that I hope will deter the parasite population somewhat. So far it seems to have worked well. I usually get my first outbreak by now and it's been the right weather for it, but nothing so far.

 

I think I'm going to stick to the scheduled wormings, however - I don't think I can handle one more task around here!

[Debbie Crowder-BaaramuLuke]

Our sensational extension service scheduled a FAMACHA workshop, 10 dollars, worth the time and just another tool to keep from too quickly ruining any more wormers by resistance. (take everything I say with a grain of salt, I'm no expert). Only helps with identifying anemic animals, supposedly from the parasite (okay, this is going to be spelled wrong---)homonchas contortis. Go do it.

[Jordi44]

Don't know anything about the course - never heard of it, but as for worming, why not see if your vet can do a fecal sample? Wouldn't cost as much as the worm medicine, a lot easier, and at least then you know if and what kind of worms you're dealing with. If you do worm, switch classes/types of wormer to help prevent resistance.

[Bill Fosher]

FAMACHA is a system in which the farmer is trained to identify anemic animals by inspecting eyelids of sheep and comparing them to cards showing different levels of anemia in the sheep or goat.

 

I have grave misgivings about FAMACHA from both humane and practical standpoints. I'll start with the practical problems.

 

First, FAMACHA will identify only Haemonchus contortus (barber pole worm) infestations. There are plenty of other parasites that cause damage to and kill sheep. Ostertagia would be the main one of concern in my part of the world. FAMACHA will never pick up an ostertagia infestation because it doesn't cause anemia. In fact, Haemonchus contortus is the only bloodsucking internal parasite of sheep, and hence the only one that causes anemia.

 

Second, FAMACHA only detects infested animals that are anemic, which is a fraction of those who are actually infested with HC. Hyperacute infestations, in fact, can kill an adult ewe before she shows any symptoms. These hyperacute infestations usually take place in heavily stocked pastures where conditions coniside with grazing pressure and ewes take on a very heavy load of larvae at the same stage of development. They can literally have a clear fecal one day and be dead two days later, as 30,000 HC have hatched out and attached to their bloodstream overnight. But even in normal acute infestation, HC does not necessarily produce anemia.

 

Third, FAMACHA reveals anemia, not HC infestation. There are probably scores of potential causes for anemia, ranging from cobalt deficiency to caseous lymphadenitis.

 

So a positive result on a FAMACHA test doesn't mean that the animal has worms, and a negative result doesn't mean that it doesn't. As a practical matter, this seems like a pretty useless test.

 

Fourth, I think FAMACHA is incredibly labor intensive, compared to collecting a randomized fecal sample and then worming at certain trigger thresholds on a FEC.

 

From a humane standpoint, it seems to me that by the time an animal is anemic, it is very sick indeed. Absent a looming problem with wormer resistance, I don't think you can justify allowing an animal to go until its blood is unable to properly oxygenate its muscles before offering it relief.

[Eileen Stein]

I went to a FAMACHA workshop last year and found it very interesting. Bill makes some good points (his slant is pretty different from the person who gave the workshop!), which are certainly worth keeping in mind. The instructor was very upfront that the color scale only relates to Hc, and that other parasites may be present at problematic levels and will not be detected. But if Hc is your principal parasite problem, and if you can rule out most other causes of anemia, it seems to me FAMACHA is of some value.

 

Speaking as someone who has been moderately to severely anemic at times in my life, it wasn't really a painful condition, so I don't think it's inhumane to defer worming until animals are somewhat anemic. (They won't lose weight from it either, if my experience is any indication!) The sheep and goat specialist who gave the workshop strongly impressed on us the increasing ineffectiveness of available wormers as a result of developing resistance. Seems to me it only makes sense that if you can minimize the use of wormers, you minimize the development of resistance in your worm population. And one way of reducing use is by not dosing sheep in your flock who are not showing ill effects from worms, either because their individual worm burden is lower, or because they have more natural resistance. The specialist made the point that fecal samples generally don't help at all in distinguishing the vulnerable sheep from the ones who are not in need of treatment; they are more a measure of pasture infestation.

 

Of course, Bill is right that FAMACHA is somewhat labor intensive, but if you don't mind rounding up your sheep and putting them through the chutes and checking their eyelids every couple of weeks, then that disadvantage won't seem too great -- or may even be an advantage at some stages of dog-training. With the number of sheep Bill has, the workload is much more of a consideration for him than for me.

 

Even if you don't think much of the FAMACHA system itself, the workshop I attended was worthwhile for the other subjects it covered. It gave a good overview of the families of anthelmintics and which ones are most effective for which parasites, had some instruction in doing your own fecals and recognizing different parasites and eggs under the microscope, and just in general covered a lot of ground about sheep and goat parasites. It was a one-day thing -- I forget the cost, but it was in the $10-20 range.

[Rebecca, Irena Farm]

Interesting. I'm always interested in more information on sheep management, so maybe it would be worthwhile even if I do agree with Bill for the most part. My experience with haemonchus has been similiar to Bill's - sometimes it strikes without warning, though I've found it more of a lamb problem than an adult one. One big thing is that anaemic sheep are extremely heat and exercise intolerant. It's the reason one of my daily chores is to go out and walk the flocks briefly at about 1:00 or 2:00. Sometimes lambs that are slightly sluggish are obviously losing color, sometimes not.

 

But I can often pick out the wormy lambs without moving them as I watch them begin grazing first thing in the morning. The heavily infested lambs tend to be the last to start grazing and the first to lay down as the sun climbs. While the healthy lambs then will get up and graze at intervals through the day, these lambs will keep their activity levels low.

 

It makes me really glad to have a good dog when I spot one of these. When I started years ago, I'd have to wait until Patrick had time to help and then it would take half an hour to worm one sheep! Now I just go out and worm the little critter right when I see it - it usually takes longer to find my supplies than it does to do the job!

[Bill Fosher]

There are places and situations where FAMACHA is needed and justified. My concern is that it is being touted as a silver bullet to parasite problems. It is not, and I don't believe that the people who developed it think it is either.

 

There are also other ways of delaying the onset of resistance. Using the proper amount of wormer, rotating families, using two families at a time, leaving a few sheep untreated, and practicing clean grazing techniques are all very effective tools that have fewer negative consequences for animal welfare.

 

Parasite control is probably the single most challenging aspect of keeping sheep or goats, and since FAMACHA is The Latest Thing it's getting a lot of attention. It was just 15 years ago that ivermectin was The Latest Thing, and now it basically doesn't work south of the Mason-Dixon line, from what I've been told.

 

I just wish that integrated parasite control was the topic of the workshops, rather than FAMACHA itself. In some cases, I think they are. And if the presenter is up on small ruminant parasitology, it will be the best $20 or $30 you've ever spent for your sheep. But I've heard of "seminars" that consist of someone sitting behind a table collecting the fee and handing people the FAMACHA card -- which is a violation of its license.

[Denise Wall]

This may not go over well but I'm going to say it anyway. I've started culling heavily for parasite susceptibility. The way I do this is after the lambs were weaned, I don't worm the ewes until something starts showing symptoms. (I try to pick up on the symptoms as soon as I possibly can.) I earmark those sheep, worm, and after slaughter withdrawal, cull those ewes. I plan on culling the bottom 10-20% each year this way. It didn't take but about two to three cycles of the above last year before I wasn't needing to worm much at all. Not only had I gotten rid of the susceptible sheep, I had removed many of the sheep that were increasing the worm burden in the others.

 

I understand parasite resistance isn't very highly heritable but I can certainly increase the overall resistance in the flock I have now by culling this way. I think I read it takes about five generations before you start to see increased genetic resistance to worms in the lamb crop due to selection. I'm sticking with the plan and hope I'll see some results by then.

 

Why am I doing this? Because there's only one wormer that really works here anymore and that's moxidectin. Soon that won't work either and I doubt they can keep discovering new wormers to keep up with the resistance. Two years ago I saw the writing on the wall and started this program. I really felt like I had no choice.

[Howdyjabo]

Heres my theory---

FAMANCHA is useful-- but......

 

It still needs to be used in a three pasture rotation system.

If you just worm the anemic animals then keep them with the more resistant animals they just get reinfected.

But..... if you move the anemic animals to a new pasture after you worm them- they are on clean pasture for longer. The more resistant animals are left on the contaminated pasture till they need worming too- or its time to get them all together again.

Eventually everything is on the second pasture.

You start again.

 

I try to use each pasture once a year- but usually ended up useing one twice.

 

When lambs or kids were around I would keep the wormed animals in a pen overnight-- seperated pairs would usually get together on each side of the seperating fence. I would worm them too and put them back together on a clean pasture.

 

On top of that I would remember which ewes and lambs were the last to leave the contaminated pastures and they went to the top of the list for which replacements I kept.

 

I had to worm less, used less wormer overall,I successfully used the cheapest wormer on the market,and it used both FAMANCHA and worm and move to clean pastures techinques. And I used alternative species grazing to help clean pastures where I could. If I needed hay I would have also used a crop of hay to clean a pasture.

 

Checking eyelids was no big deal because I had a chute to run them thru and sort out of. It was cheap and easy to make- and the way I set it up the sheep and goats flowed thru pretty fast.

On the goats it was easy to tell when I should check... their vulva and anal area would get pale and with the goats tails sticking up it was easy to spot.

 

I read somewhere that useing Ivomec was just shooting yourself in the foot---- It stays in the manure and kills beneficial dung beetles that are there to eat the worms.Making the pasture stay contaminated longer- and selecting even more for ivomec resistant worms to propogate.

 

There was a research paper out about seeding pastures with suseptable strains of worms- to try and out compete the resistant ones.

[Rebecca, Irena Farm]

Denise, I hope your plan will work because I've been following it for seven years now! I keep throwing in a monkey wrench by not selecting rams for worm resistence, but eventually I will add that in also.

 

I think that while possibly parasite suseptibility/resistence might not be heritable, there seems to be something that contributes that CAN follow lines. I've gone down to just one worming on my ewes in the summer. My lambs are another story but this year I'm trying to keep them on clean pastures.

 

Can you tell I'm just a wee bit obsessive about this? Ever since I had a vet tell me after a PM, my ewe was the cleanest sheep he'd ever opened up, I've tried to maintain that standard. Some years are better than ever for sure.

 

The last step in my obsession will be to get equipped and trained to do my own fecals. Been meaning to do it for a couple years but life has sort of gotten in the way.

[Bill Fosher]

Denise,

 

Identifying susceptible individuals is a great first step in a strategic parasite control plan. The next step is to identify the "typhoid Marys" in your flock. These are the sheep that tolerate parasites exceptionally well, but still carry a heavy load. This is a matter of individual FECs.

 

The problem with selecting against susceptibility based on clinical signs is that you aren't really selecting for resistance, you're selecting for tolerance, and you could end up with a flock of typhoid Marys. I think this is what has stymied the search for the holy grail of genetic parasite resistance: it's simply too hard to really identify the problem sheep if you have more than 20 or 30 individuals to track.

 

So far parasite resistance has not been transferrable from one flock to another, so the theory is that what's actually being seen in the flocks that appear to have it is good managment that minimizes the burden on the sheep, and adaptation to the particular worm population on that flock's property.

 

Two rays of hope: there's some evidence that resistance to levamasole is a recessive trait that nematodes lose after a number of generations. If you wait a few years, levamasole may work again. So if you zap everything with levamasole, you may start to see some effectiveness in the other other wormers because you'll essentially be starting with a fresh (or much fresher) set of dice.

 

Secondly, the Moredun Institute in Scotland is working on developing a vaccine that would make the sheep's gut and bloodstream inhospitable to Haemonchus. I'm not sure what stage that's at, and even less sure whether it will be available in the US, but with the passage of the Minor Use/Minor Species law last summer, it seems at least possible.

[Debbie Crowder-BaaramuLuke]

All of this is very good info. I'm a novice at sheep-keeping, and sadly enough, a 4H leader, BUT what I lack in experience, hopefully I balance that with an open mind and curiousity. Our FAMACHA workshop was held at a wonderful seminar on forage management. Morning session was on forage, with speakers from VATECH and VA State on things like grasses, rotational systems and weed control. The afternoon sessions were divided for equine, cattle and small ruminants. We're lucky to have a small ruminant group in central VA, meet periodically and have speakers. Our FAMACHA workshop was a field trip to a nearby sheep operation AFTER an hour long talk (try THAT one on 9-19 year-olds!) on parasitology and products in use, along with current resistances in our area. Our 4H project is with Hog Island sheep, supposedly parasite-resistant by virtue of their feral heritage. They are better than average. They also flock miserably, also probably a feral trait (no predators on that island), just an aside because I have rotten results working them with the dogs.

 

I only offer this as a suggestion for a great Extension offering in whatever areas ya'll are in.

[Denise Wall]

Hi Bill,

 

Lots of good information in your post.

 

I understand about the high worm burden tolerant sheep but have decided to try removing the symptomatic ones for now. Although I know how to do fecals, and have all the equipment, I try to avoid it if possible.

 

I've been holding off on the levamasol for just the reasons you stated. I hope it'll work again in a few years.

 

So far parasite resistance has not been transferrable from one flock to another, so the theory is that what's actually being seen in the flocks that appear to have it is good managment that minimizes the burden on the sheep, and adaptation to the particular worm population on that flock's property.

I'm not sure I follow what you mean here. Do you mean genetically, or that new sheep introduced with worms that are wormer susceptible don't help the wormer susceptibility of the flock, or both?

 

In my experience, the introduction of one sheep (a ram) with ivermectin resistant worms apparently knocked out the effectiveness of that wormer for me within months. I had been so careful over the years so I would have that wormer as a fail safe and that was gone just like that.

 

A vaccine would be great.

 

I forgot to list a big part of my 'war on worms' plan which is the introduction of border cheviot blood into my flock. I'd say this is working, maybe best of all.

[Eileen Stein]

Bill wrote

 

>

 

One thing I wish I'd asked more about at the workshop is the mechanism of resistance (or tolerance) in sheep. I don't think I really understand it. Is it a quality of the lining of the GI tract that makes it harder for the parasites to penetrate? I guess that's what I assume it is, since tolerance apparently develops during the lifetime of an individual, but if so, then a resistant sheep almost couldn't have a heavy worm load, since its worms by and large wouldn't be getting nourishment. Or is it an especially vigorous blood supply that can support a heavy worm load and support the sheep too? Or does anybody really know?

 

BTW, I was lucky -- although I called the workshop I went to a FAMACHA workshop, it truly was an IPC workshop.

 

KillerH,

 

The single most counter-intuitive thing they told us at the workshop -- even more counter-intuitive than refugia -- was that you should NOT turn newly-wormed stock into a clean pasture. What they said was that this would lead to having ONLY resistant parasites in that pasture. I still can't quite buy it -- maybe I misunderstood it.

[Pipedream Farm]

Like Debbie, I too am really enjoying this post. Lots of interesting stuff. I've always wormed based on slight swelling under the jaw (I have hair sheep, so it's easy to see). With the lambs, if I see one like that, then I worm all the lambs. I have a small flock so it's easy for me to keep a close eye on things. I'm not talking about waiting until it looks really bad, just a slight swelling. I was wondering though if that might not be the best method since like the eyelid check it's not accounting for some types of worms.

What are your thoughts on changing wormers? Some say to change every time and others say only if it doesn't seem to be working. I use the second approach because from a practical standpoint, I would have wormers expiring before I used them all. I really haven't noticed a resistance problem so far.

Renee

[Pipedream Farm]

Eileen,

 

I guess this is what they mean....

 

sheep has an ensemble of parasites

treat sheep with drug A

sheep is left with only parasites resistant to drug A (assuming 100% killing of non-resistant parasites)

turn sheep with only drug A resistant parasites into "clean" field

sheep sheds drug A resistant parasites into "clean" field

 

If this theory is correct then it would counter act the theory of seeding a field with non-resistant parasites (assuming one turns treated sheep loose on that field).

 

Too bad there's isn't a way to make parasites sensitive to UV light, that way the load in the field would be reduced.

 

Mark

[Howdyjabo]

Eileen--- ALL the worms are damageing- so turning freshly wormed sheep onto a dirty pasture is just a waste of time. And yes turning sheep on to a clean pasture just seeds the pasture with the resistant worms that survived a worming.

 

That is why you also rotate, take a hay crop or use alternative stock grazing-- so that the environment has a chance to knock them down.

 

That is the issue that the research paper was trying to address. After you take the sheep off a pasture- they seeded it with the susseptible worms to compete with the resistant worms- but not have any stock around to reinfect.

 

There is some other research around about useing liquid nitrogen to make a clean pasture. If the application is timed properly and the majority of the worms are hatched and climbing the grass(ie damp)- the nitrogen kills them. As a bonus the grass gets a boost .

 

 

And there has been some sucess by useing a dry dirt lot or barn and only allowing access to the pastures after the morning dew has been dried off.

The worms are in the ground unless there is moisture on the grass.

 

Basically worming is a waste of time long term-- unless you also use other means of controlling the environment.

[Bill Fosher]

Denise,

 

I'll see if I can try to explain it a little better. My own understanding is a little vague anyway, so I may do more harm that good.

 

When I use the phrase "worm-resistant sheep" I mean sheep that for whatever reason do not get infested with worms despite exposure to larvae. There are such individuals, and within some flocks it seems to travel in families, raising great hopes that we would be able to select for such sheep. Over time, the theory goes, there will be fewer and fewer worms on the pastures used by resistant sheep since they must parasitize a sheep in order to continue their life cycles.

 

Apparently, this is exactly what happens. So, if you take a ram from parasite resistant families on farm A and put it over ewes on farm B, there's no significant transferrance of that resistance to his offspring. The ram himself sometimes continued to show resistance on farm B, and sometimes did not.

 

What was probably happening on farm A was that by selecting for parasite-resistant ewes, they over time reduced parasite burdens on their own fields to the point where even susceptible sheep could handle the load. But why some of this trait doesn't go through the male side of the equation remains a mystery.

 

Lots of money has been spent on this in New Zealand, and they still haven't found the key, as far as I know.

 

When I use the term "parasite-tolerant sheep" I mean the ones that for whatever reason are able to thrive despite heavy burdens. As far as I know, Eilieen, no one has been able to determine what the mechanism is that allows some sheep to tolerate parasitism better than others, even when management is the same.

 

Obviously the researchers at Moredun think they have discovered something that makes Haemonchus dislike sheep, but I don't know what that is.

 

-----

 

Always move sheep to clean pasture after deworming has been dogma for generations. But if you think about it, returning them to "dirty" pasture makes a certain amount of sense from a population genetics standpoint.

 

Suppose that 4 percent of the worms survive treatment. If you put the ewes back out on clean pasture, then all of the eggs they deposit on that ground will carry the genes for resistance to that chemical. While there will be fewer of them, and hence fewer eggs deposited, the population there will be 100 percent resistant. The eggs hatch and mature into larvae, which are consumed by the sheep, and mature into worms in the gut. They start going to the wormy discos and picking one another up, and every potential breeding partner carries the genes for wormer resistance. This will further concentrate the trait in the following generation.

 

If you put the ewes back onto infested ground, the parasite discotheques are populated by both resistant and non-resistant worms, so the trait remains relatively diluted. The same logic applies to refugia -- leave a few sheep untreated so that the eggs from their worms don't carry the resistance factor in such a high proportion.

[Deacon Dog]

Renee, see page 8 of this article. Basically it says that alternating wormers doesn't slow resistance.

 

Apparently simultaneous dosing with 2 effective wormers and dosing with half the amount 12 hours apart has been shown to increase efficacy. Anyone tried these techniques?

[Pipedream Farm]

Thanks Tony!

[Rebecca, Irena Farm]

Bill, do you have more information about the refugia technique - it's not the SAME sheep each time, right? I wonder whether my program of having the ewes on a much longer worming cycle would have the same effect, since they normally graze about a month behind the lambs in the peak growing season?

 

What I'm doing is actually worming about three days before moving, on the advice of my vets, then moving them to clean pasture. So, today we will be worming the lambs, and Sunday we will move them to the next paddock.

 

Also, I wonder how "grazing forward" affects the parasite population in a pasture - where the nursing lambs are given creep access to new pastures before the ewe flock is moved? I had this in practice, though not on purpose, as there was a place in the old mothering paddock where the lambs could get over into the next pasture. We wormed everybody once during that time.

[Bill Fosher]

Hi Becca,

 

It's been a long time since I read up on refugia. I believe the idea is to simply withhold treatment from a few random sheep, not the same ones every time.

 

The vast majority of a parasite's life span is spent outside the sheep, so using the same sheep wouldn't have all that much benefit -- refugia is a means of managing the gene pool of the worm population on a farm, not inside the animal itself per se..

 

Where using the same sheep is important is if you are trying to identify wormer resistance. You take FECs from the same animals before and after worming and see what the difference is.

[Bill Fosher]

In parts of the world where we still have two effective wormers, treating sheep with two wormers at a time is probably the most effective way to delay resistance. Worms that are resistant to white drenches are probaby not resistant to clear drenches, and vice versa.

 

You should also do everything you possibly can to ensure that your worming is as effective as possible. The more you kill, the fewer are left to produce the next generation. While worming on an empty stomach is not considered necessary, it will increase the efficacy of all drenches. So simply standing your sheep in the barn for 6 to 12 hours before worming will increase the killing power of whatever wormer you're using.

 

Proper dosing is also very important and very much overlooked. I think most people would be surprised how much their ewes weigh.

[Rebecca, Irena Farm]

Proper dosing is also very important and very much overlooked. I think most people would be surprised how much their ewes weigh.

Most small farms don't have access to scales but it's an investment I'm looking into for the future. I have hopes of being able to take my lambs to a graded market in the future and I know I'm terrible at guessing live weights on lambs.

 

Fortunately for me, I've had a three different state post mortems. Since they weigh the ewe, I've been able to check the actual weight against the accuracy of the tape I use when I'm unsure. It's always been just slightly under so I feel confident in my vet's original direction to use the tape.