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No More Deworming Rotation Chart?

Looking for the 3 way rotation chart. Had it saved to my favorites and it shows up for 1/2 a second then goes to this page. Can you repost this on your website? PLEASE bring this back. Or, is there someone out there who has it saved and can send it to me? Thanks, Ann

From: 5 Things You Need to Know About Dewormer

Dear Ann,

Actually, we specifically removed the rotation chart from our website and catalog because experts now agree that switching between classes of dewormers based on the calendar is neither the best way to protect our horses from parasites or to prevent resistance from developing in the worms themselves. While rotating between the three chemical classes of dewormers made sense when it was first introduced almost 40 years ago, for a number of reasons it is no longer the best defense against parasites and in fact, may be doing more harm than good.

First, each of the three chemical classes of dewormers (benzimidazole/pyrantel/ivermectin) has a different egg suppression period. That is, each class prevents eggs from being laid by adult female worms for a different amount of time. When benzimidazole is used, it only takes a month for strongyles to mature into egg-laying adults. It takes six weeks for this to happen after a pyrantel-containing product is given. For ivermectin, the egg-suppression period is the full eight weeks or two months that is commonly recommended in rotation charts. Moxidectin, the newest dewormer we have, suppresses egg laying for 84 days, or almost three months. So a parasite control program that rotates between these classes every eight weeks isn’t taking into account the differences in how long each dewormer “lasts.”

Second, experts have detected resistance to almost all of the chemical classes of dewormers. Throughout the country, there are pockets of parasite resistance where the benzimidazoles or the pyrantels are no longer effective against small strongyles in adult horses. Scientists have also found that, on some farms, ivermectin is ineffective in controlling ascarid (roundworm) infections in young horses. Therefore, it’s important to use a chemical class on your farm that you know works through fecal egg counts.

Third, parasites have life cycles that depend on external environmental cues like temperature and moisture. When it’s below about 40 degrees, eggs continue to be laid in manure (and onto your pasture) but they are no longer able to hatch into infective larvae. So there’s no need to deworm after the first hard frost in the fall in northern climates because horses aren’t picking up any new parasites. However, when temperatures begin to warm up in the spring, eggs that were lying dormant on your pasture all winter now hatch, which is why you should begin deworming again when temperatures remain consistently above freezing (it’s the opposite for southern climates). This is also why it’s a good idea to deworm your herd in the spring before they go out on pasture and deposit even more eggs that can then hatch and infect the horses.

As my parasitologist friend Craig Reinemeyer, PhD, says “you don’t get any points for going through the motions.” I encourage you to sit down with your veterinarian and develop a parasite control program that is appropriate for your horse, in your geographic area, that takes into account whether he is a low, medium or high egg shedder and incorporates other parasite control measures like manure management.

Read more about deworming methods here: 5 Things you need to know about dewormer




Lydia F. Gray, DVM, MA SmartPak Staff Veterinarian and Medical Director Dr. Lydia Gray has earned a Bachelor of Science in agriculture, a Doctor of Veterinary Medicine (DVM), and a Master of Arts focusing on interpersonal and organizational communication. After “retiring” from private practice, she put her experience and education to work as the American Association of Equine Practitioner’s first-ever Director of Owner Education. Dr. Gray continues to provide health and nutrition information to horse owners through her position at SmartPak, through publication in more than a dozen general and trade publications, and through presentations around the country. She is the very proud owner of a Trakehner named Newman that she actively competes with in dressage and combined driving. In addition to memberships in the USDF and USEF, Dr. Gray is also a member of the Illinois Dressage and Combined Training Association (IDCTA). She is a USDF “L” Program Graduate and is currently working on her Bronze Medal. Find Dr. Gray on Google+

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29 comments on “No More Deworming Rotation Chart?
  1. Brenda Miller says:

    I have been told you can mail a fecal sample and have it analyzed for which wormers would be most effective. I would think you need to do this a couple times a year. Does this process work well and in the Northeast is there a place that can be recommended?

    • Jessica Sanders says:

      I’ve used the fecal tests before. You can give samples to your vet and he/she can send them to a lab to be tested. Or you can purchase a test kit, which is what I did. I think I paid about $18 for it, and I ordered it from Just follow the directions that come with it. The kit recommends testing before giving any dewormer to see just what your horse may be harboring. Then you can medicate for the specific species of parasite. Then they recommend you test again about 2 wks after medicating.

      I decided to rotate my dewormers and then I’ll retest in the spring. Our fall and winter here in PA have been very mild so far with bugs still flying around. My rotation, which I started in Nov after the fecal test, is as follows: Nov – ivermectin + boticide, Jan – pyrantel pamoate, Mar – Oxibendazole. (My horses’ test came back positive for strongyles.) Hope this helps.

  2. Susan Kirkland says:

    I have asked my vet and even did a fecal egg count during annual check-up. He recommended the rotation you had on your site, wo wish you wouldnt have removed it. You seem to offer a lot of problems, but I didn’t read a real solution.

    • Susan Kirkland says:

      I spoke to my other vet today. He does my dog and cat, but has done horses also. I’ve known him for 14 years and he is the most outstanding vet I’ve ever known. He stays on top of all the latest research and treatments. He said he believed it would be irresponsible not to do quarterly deworming, with two rotations being ivermectin. He said the horse can have damage to the messentery if you do nothing but fecal egg counts until you find a problem. I will continue my rotation after being told this by two excellent vets. I really wish you would include the chart again as now I have to go to another site and prefer yours.

      • SmartPak SmartPak says:

        Hi Susan-Thanks for sharing your experience! We agree that only deworming when fecal egg counts rise to a certain number (say 200 or 400 eggs per gram) is not a sound method of controlling parasites in horses because worms don’t lay eggs all the time. The beauty of fecal egg counts is that every horse on the farm gets dewormed at least twice a year (spring and fall), then only the identified “high shedders,” horses whose fecal counts are above 400 epg, get dewormed in between, following the egg suppression schedules of four, six, eight or twelve weeks, depending on which dewormer chemical class was used. The other beauty of fecal egg counts (when did fecal exams become beautiful?) is that it helps farms know which dewormer classes are still working and which are no longer effective.

    • Brian says:

      I agree with Susan. My vet recommends the same rotation schedule and they have kept our horses happy and healthy for 15+ years. Ug. Time to call and complain.

  3. Judith says:

    A fecal test is only good IF the worms are laying eggs at the time of collection. A fecal test looks for eggs, not the worm.

    A horse can have worms, and still have a negative fecal test. I hope Smartpak didn’t remove the calendar so customers feel inclined to buy the fecal kit.

  4. Marina says:

    I agree completely with Dr. Gray. Resistance is a huge concern. It is already happening at high rates in small ruminants and could become a problem in horses as well if we continue to misuse dewormers. Yes, some vets may be really good vets and have years of experience but if they have not kept up with current literature then they are doing your pets a diservice. Times have changed. I just graduated from veterinary school and this is what we learn now: fecal eggs counts and targeted deworming programs. Gone are the days of rotational worming. It is not a scam by Smartpak. It is the responsible thing to do. Older vets just need to get with the times.

    • Brian says:

      There is nothing wrong with using the latest and greatest tools available to us. The word Vet for me refers to the staff of 5 highly trained individuals that take care of our horses. They also work tightly with the local New Bolton Center and keep up on the latest finds. So if they tell me to stick with the old rotation, I stick with the old rotation. The nice would have been to keep the old chart up but reference the new findings. Old information is not necessarily bad information.

    • Christine says:

      Thank you! I wish everyone would keep up on the new research and get on board with the fecal testing method as it’s going to affect all of our horses when the parasites become resistant to the drugs we have.

  5. DEE says:

    Here it is the end of February and still no rotation charts – I agree that putting the most current information and thoughts out via the SmartPack website and catalog would be beneficial WITH the rotation charts for worming….my horses have done well in the past and look great – I guess I’ll have to go elsewhere for a basic rotation grid. I cannot afford to have a vet do egg counts and the like every so many weeks or months….I’m lucky to remember to flip my calendar over!

  6. Carol Plett-Henryson says:

    Related question: what is good de-worming program for a busy boarding facility? The fecal testing routine seems excellent for a closed herd, but what does one do when horses are coming & going, due to owners changing barns, or showing?

  7. Michelle says:

    The link to “5 things you need to know about dewormer” at the bottom of the article is broken. Given the controversy, it might be helpful info to add. It would also be helpful to explain if no eggs are present in a fecal test, can you skip worming altogetherfor as long as that remains true? I’ve had several fecal tests run over the years on my horse and they’ve always been negative which makes me wonder about their efficacy. As a result of trusting they’re true, I rarely worm my horse (1-2 times/yr only as a precaution). He lives around 15 other horses that are on all on their owners’ different worming schedules, btw.

  8. Lauren says:

    I was actually just talking with my vet (had them out for spring shots!)about worming and she told me that because we have them on the rotational charts and are worming them so much, they’re seeing horses becoming immune to the wormers, so she is having us do a fecal sample for spring and fall and having us deworm then and only then so that they don’t develop a resistance.

  9. Anne says:

    This is the old rotation calendar everyone is looking for. I don’t know if they will let it stay up though.

    I’m in the South and we do a bi-annual rotation in Spring/Fall due to the hot summers. My vets will do a fecal egg count, but are happy with the current rotation. The final word on the efficacy of using the egg count isn’t out yet, but resistance certainly is a problem, just like antibiotic resistance in humans.

  10. Christie M says:

    What do you recommend for boarded horses where everyone is doing their own thing with wormers? I don’t have any control over possible “high shedders”. How would I treat my horse?

  11. JP in Texas says:

    I never hear the vets talk about daily Strongid C 2X anymore???
    I have used on my horses for years and only paste with Ivermectin 2-3 times year for bots, etc. This is what vets here told me if using Strongid daily, but none call tell me if wasting money for using daily or why they no longer talk about it. Seems like they quit talking about it when it was made available at all equine places instead of thru the vets like when first started.
    Anyway, I never hear or read anything from vets talking about worming, rotation, etc and use of daily Strongid 2X.
    I still use it but would like to know what they say about it today since changing on the rotation of wormers.

  12. Barbara says:

    I think we are all over worming our horses, just as doctors have us over medicating our families. They need to be able to build their immune systems to handle worms and other things and we are killing those natural antibodies. Horses have survived in the wild for many years without wormer and they build their antibodies and find other natural alternatives for worming. They know what they need to eat!! I always wormed my horses 1 to 2 a year and they were all happy fat and healthy, until I had babies and everybody (vets included) said you have to follow this worming schedule, so I did religiously and my beautiful stud colt died at 2 1/2 anyway! The bigger problem we have is pigeon fever that has mutated so bad that it is now killing our animals!!!!

  13. Debbie Sharp says:

    I went to a seminar given by Pfizer, and they make most of the wormers, told us the same thing. We are over-worming and not getting the results we think we are. When I joked with him that he was going to cost his company alot of money because us old school owners were worming every six weeks (when the farrier came so we didn’t forget…lol)he said Pfizer was more concerned with the fact that there are NO NEW STUDIES for new wormers (and it would take years to develop a new wormer)so if the resistance/immunity of the worms continue….”the strong will survive and the weak will die off.” I will never forget him saying that….scary stuff and if people won’t listen to change…they will just be contributing to this health issue. I actually heard this over a year ago and have had several heated discussions with people who absolutely would not research it themselves, just continuing with the schedule they THINK works. Glad this info is coming out from different places to reach more owners. Pfizer also told us we could throw out Strongid and Safeguard as they are ineffective and short lived.

    • Kaitlyn says:

      Hi Debbie,

      Did Pfitzer say why Strongid and Safeguard are ineffective and short lived? Is it those two brands or is it the active ingredients?

  14. Joanne says:

    After reading the article and all the comments I am more confused than ever. So I will keep on rotating for now.

    Has anyone done the 5-day SafeGuard power dose?

    • SmartPak SmartPak says:

      Hi Joanne, thank you for reading our blog article and please know that we can totally appreciate someone still scratching their head when it comes to deworming. The recent evolution of equine deworming has been complex, but will ultimately help us all take better care of our horses now and in the years to come. We would love the chance to chat with you in person and talk through this very complicated but important issue! Please always feel free to give us a call at 1-888-572-5171, and we would be happy to chat parasites with you (what could be more fun!?). I also encourage you to check out the Zoetis website, as they also do a fantastic job of explaining individualized deworming, and I’ve included a link to their site below. I hope that’s helpful! – SmartPaker Casey


  15. Joy says:

    My vet has told me to rotate my horses worming

  16. YIKES! I’m defiantly confused and don’t know what to do now. My horses are now at a boarding facility and we are in Florida where bugs never die. Help!

    • SmartPak SmartPak says:

      I know it can seem like a lot of information to take in at once, but the new recommendations are so much more effective in controlling parasites that it’s worth the time to understand them! First of all, know the parasite transmission season for your location so you can test fecals and administer dewormers during peak worm time. For Florida, the bugs actually DO die–in the heat of the summer. Parasites in southern climates begin to get busy in the fall, are active all winter, and start to become dormant in the spring. So you want to deworm everyone in the fall, deworm only the high shedders throughout the parasite transmission season, then deworm everyone in the spring. Of course, as with any change in your horse’s health care routine, it’s best to work closely with your veterinarian, as they know your horse and the local conditions best. Good luck! – Dr. Lydia Gray

  17. Nancy says:

    I just checked out the Zoetis website. I found the chart to be confusing, it was more confusing because it was too small to read. Any suggestions? I could not figure out how to zoom it in to make it easier to read. Thanks for the suggestion anyway. – Nancy

  18. Terry says:

    I just got done reading an article on summer sores which stated because many new vets are taking this approach and because of the light or tropical winters California has had this is the main cause of summer sores returning and being a Medical Assistant we do not deal with worms very often but do deal with different types of viruses that shed, you can not always know when a worm, egg etc. is going to shed so doing the test once or even twice does not always show larvae. I disagree with this approach and I believe new medications of wormers need to be developed but pretty much keeping to the schedule that you had posted.

  19. Laurie Mooney says:

    It’s time to get with the times we live in people. Overuse and abuse of wormers has brought us to the place where we are….just like overuse and abuse of antibiotics in people. It’s no different. The wormers are ineffective because the worms have built up a resistance. It’s time to put on your big girl or big boy panties and start testing fecal matter so you can treat the issue at hand instead of over worming your horses. The next thing people will want is STRONGER wormers and newer medications that will be even more harmful. It’s a downward spiraling mess if we continue in this manner. SmartPak is just way ahead of the game and is being RESPONSIBLE about what is in the best interest of horses.

  20. Sue says:

    What about quest? I am scared to death after reading horror stories of horses dying but it is a different chemical correct? Should we be using it?

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