Equine, PhD

The hay net research has caused quite the stir on social media this past week! For those of you interested in reading the full article on hay nets, you can find the article at this link!

Effect of hay nets on horse bodyweight, body condition score, hay usage, and dental health in mature adult horses Hay nets are a commonly used management practice to increase intake time and reduce hay waste but may impact horse health. The objectives were to comp…

PART TWO: Do hay nets impact bodyweight, body condition, and hay usage in horses?

The post you have all been waiting for!

If you missed part one evaluating hay nets on equine dental health, I encourage you to visit the first post as that may fill in some of the missing pieces. But here I am, back again, to relay some information on the other goal of the study, to evaluate how hay nets impact bodyweight and body condition of the horse as well as your pocket book when it comes to hay use.

Introduction: We do have some previous studies that exist evaluating hay waste and different hay feeders, including hay nets. These are short term studies but have found hay nets have the ability to reduce hay waste, however, little changes to the bodyweight (BW) and body condition score (BCS) of the horse were observed. We believe this finding can be attributed to these studies providing hay based on horse BW (around 1.5% BW) rather than free choice access. So we set out to look at how hay nets could impact horse BW, BCS, and hay usage throughout our study when horses had free choice access to round bales over the course of a year.

Materials and Methods: Thirteen mature geldings were used in a 2-year crossover design where each treatment lasted one year. Horses were blocked by weight at the beginning of the study and assigned to a no hay net control (CON) or a hay net (NET) treatment. The average starting BW for all horses was 1,210 pounds with an average BCS of 6 (on a 1 - 9 Henneke scale). These horses lived in identical neighboring pens with the only difference being if their hay was placed in Hay Chix hay nets with 1.75”/4.45 cm openings or not. All hay was provided in a ring round bale feeder regardless of hay net use. For 6 to 7 months of each treatment year, hay bales were weighed prior to being placed in the pens and monthly hay used was recorded based on BW of horses in the pen. This means hay usage is the combined weight of hay that was consumed AND wasted. Our equine veterinarians also took BCS on the horses at the beginning and end of each treatment year and horses were also weighed on a digital scale at these times.

Results: The CON horses gained an average of 44 lbs (20 kg) over the course of the year while the NET horses lost an average of 51 lbs (23 kg). This is a 95 lb (43 kg) weight difference based on hay net use when free choice access to round bales was provided. Similarly, CON horses went up 0.46 on the 9-point BCS scale while NET horses went down 0.88. I also want to note that all of our horses were at a healthy weight/BCS and stayed at or above healthy levels throughout the duration of the study. So while weight loss was observed, it had a positive impact on their health based on their starting condition. These changes in BW and BCS align with hay usage where CON horses used 3.23% BW on a DM basis while NET horses used 2.56% BW.

Discussion: These results show that horses with free choice access to hay without hay nets may gain weight, increase body condition, and also use more hay. In comparison, hay nets have the ability to control BW and BCS when free choice access to hay is provided. Additionally, if you are feeding a 1,110 (500 kg) horse and they are using an additional 0.67% BW in hay, this would equate to 7.37 lbs (3.3 kg) additional hay each day (on a DM basis) or 2,690 lbs (1,225 kg) additional hay per horse each year. I will let you do the math based on hay prices in your area but I know that is extra money I would rather spend elsewhere.

I also want to note that some horses may require weight gain, and in those instances you should consult with your nutritionist or veterinarian about the best options for your specific horse!

Conclusion: Hay nets have the ability to control horse bodyweight and body condition as well as reduce hay usage when free choice hay access is provided.

I do want to note that while Hay Chix funded this study, the PhD researchers and equine veterinarians (who were blinded to the treatment groups throughout the study) are in no way affiliated with the product or company. The research was published prior to sharing results with Hay Chix and the paper is peer reviewed and has been accepted for publication in the Journal of Equine Veterinary Science in their May edition. We greatly appreciate partners like Hay Chix who are willing to fund research projects, especially as they are taking a risk as well since we publish the results regardless of the outcome!

Feel free to ask questions, in fact, I encourage it! But I do ask that you do so respectfully.

There may be a part 3 coming in the somewhat near future! But we are just wrapping up the manuscript now so you will have to wait a little longer for these results to go public.

We can't wait to share!

PART ONE: Hay nets and horse teeth, what do you think? Should we use them or forgo them?

Well I am excited to announce we have some research-based answers for you! We set out to evaluate this in a 2-year study and we found out this weekend that our manuscript, titled "Effect of hay nets on horse bodyweight, body condition score, hay use, and dental health in mature adult horses" was accepted by the Journal of Equine Veterinary Science! I am so excited to share the results in a two part post. This one will focus on dental health but stay tuned for part 2 where we will focus on bodyweight, body condition score, and hay usage!

Introduction: Hay nets are a common management practice used in the horse industry. They have been shown to slow down intake rate, so hay is available longer, and they reduce hay waste, which can provide financial benefits and reduce labor at horse farms. While studies have shown 73% of horse owners report using hay nets, there are still some unanswered questions regarding how they can impact the dental health of the horse, which has made some horse owners hesitant to try this management practice.

Materials and Methods: Thirteen mature geldings were used in a 2-year crossover design. During year 1, they were blocked by weight and seven were on the no hay net control (CON) and six were on the hay net (NET) treatment. These horses lived in identical neighboring pens with the only difference being NET horses had their hay placed in hay nets with 1.75”/4.45 cm openings (graciously provided by Hay Chix) while CON horses did not. At the beginning of the trial, blinded equine dentists (blind meaning they did not know which treatment each horse was on to prevent any bias) performed dental examinations on the horses where abnormalities and conditions were documented, followed by dental correction (horse teeth were floated). Incisor tooth length and the presence of bevels (slants on the incisors) were recorded before and after dental correction as well. Horses remained on these treatments for one year and digital images were taken of their mouth monthly and provided to two equine dentists so they could assess and assign a rostral oral cavity score. After the first year, horses had their dental examination and correction with the same measurements taken and they switched to the other treatment for an entire year before their teeth were evaluated a final time at the end of the study. We chose our timing so horses could be used as their own control and one year is often the recommended length between dental corrections for horses.

Results: Incisor length, the presence of bevels, dental abnormalities and conditions were the same regardless of hay net use after one year. Additionally, rostral oral cavity scores that were assessed based on factors including gingiva color and margin, chips, cracks, abrasions, feed stasis, among other things, were the same for both treatments at 47%.

Discussion: These findings suggest hay nets do not impact dental health in the horse when evaluated over the course of a year. While I have spoken with equine dentists who have reported the same anecdotal evidence to support these findings, it is important to monitor your horse's dental health regularly as there are some rare instances in which horses may eat aggressively and should be monitored with any type of feed restriction.

Conclusions: These results demonstrated that hay net use does not result in negative impacts to dental health in horses.

Funding: This research would not have been possible without funding from Hay Chix and we are so grateful for their support!

Wishing you all the best!
Dr. DeBoer

How do you handle drastic weather changes? 💨❄️💧🌧️☀️

Right now we are experiencing some major temperature swings in the Upper Midwest. Yesterday we had temperatures nearing 70°F and overnight they will fall to 4°F with wind and snow before climbing back up to the mid-60’s by Saturday. I know many horse owners are keeping an eye on these drastic changes in the weather, very fearful that these conditions will create the perfect storm for colic. But sometimes our precautions can cause more harm than good. Here are a few things to keep in mind when managing weather swings with your equine friends:

🏠 Make sure horses have access to shelter, clean (not frozen) water, and hay. Many healthy horses are able to adapt if we give them the tools to do so.

📦 Confining your horse for long periods can cause more harm than good. While we may like the idea of being in a nice cozy stall, allowing your horse to move around can actually increase gut motility which is an important factor in reducing the risk of colic.

🍎 Do not make sudden major dietary changes. While you can soak the feeds you currently give each horse to increase hydration, don’t introduce an entirely new feed or mash suddenly as the quick change can upset the microbes in the GI tract and put your horse at a greater risk of colic.

💦 Hydration is very important during these weather changes. To encourage a horse to drink, you can add salt to their feed (I just buy mine at the grocery store!). You can also use electrolytes but regular old salt does the trick.

❤️ Just keep an eye on your horse and their behavior to make sure they are comfortable and acting normal. The sooner you can catch a potential problem, the better!

This post is meant to be informational and does not replace veterinary care or recommendations. Every horse is different and there is not a ‘one size fits all’ solution. It is very important to be able to recognize what works for you and your equine friend(s)!

I hope this helps and that you and your four-legged friends stay healthy!

Dr. DeBoer

If you still haven’t gotten enough of podcasts and blanketing, check this one out! I had a great time diving into more science around winter blanketing!

Horse Talk - Do you blanket your horse? Why or why not?

Leave your answer in the comments below! Then, if you haven't yet, go and listen to our latest episode which discusses this exact topic with a scientific, evidence-based approach.

Listen here:

How do you decide if you are going to blanket your horse? ❄️🥶

Blanketing is a management practice not everybody uses and not every horse needs. But it can come in very handy!

I have included some factors I consider when I decide if I should use a blanket (based on science of course).

💧Precipitation is a big deciding factor for me. If it is going to rain or sleet, or if there is a wet, dense snow, I often opt for a blanket. When their hair coat gets wet, the water can impact the hair and increase heat loss for the horse. When I have seen horses shiver, most of the time it is when their coat becomes wet which I can try to prevent with a proper fitting blanket.

💨Wind is another weather condition I pay attention to for my horses. While a horse uses piloerection to trap warm air next to their skin, wind can remove that warm air to increase heat loss. Wind has been shown to increase shelter use and blanket preference for horses.

❄️What about snow? While research has shown horses seek shelter or prefer to wear a blanket when precipitation is present, there have been mixed results regarding these behaviors/preferences with snow. I wouldn’t be surprised if these differences are related to the type of snow as a wet, dense snow is not very insulating in comparison to a more fluffy snow with a lot of aiir pockets which can act as an insulating layer! So if it is a nice day out with a fluffy snow, I will let them be most of the time. But if the snow is wet or accompanied by wind or a drop in temperatures, then I will usually pull out the blanket!

🏠Shelter also plays a role. A horse should have a access to a 3-sided shelter . However, using the shelter should not compromise other important needs for the horse such as safety. So you need to consider if the horse feels trapped in the shelter or if other horses won’t let them in. Research has also found certain factors related to shelter design and placement may reduce the use of the shelters including placing them low in the terrain, having entrances that are narrow and/or away from activity, the presence of mud in front of the openings, a small indoor area, and alternative natural shelter in the same enclosure. So make sure you consider these things when deciding where your shelter should go and how you design them!

I also choose to throw extra hay in their shelter so they can eat to stay warm while not having to leave their area of protection. I figure eating hay and keeping their coat dry are two important things that help a horse stay warm so I like to ensure both can be done at the same time!

Another thing to note is that blanketing does not make shelter use redundant. While they may use the shelter less when wearing a blanket, they do still use it, so a blanket shouldn’t be a substitute for adequate shelter for horses who stay outside in inclement weather.

🌡️In all honesty, ambient temperature is not a main consideration I make but I do use it to guide my decisions. That is because a cold day where the sun is out and no wind may feel fine compared to a more moderate day that is overcast and windy. So I prefer to look at the whole picture regarding the weather rather than just the temperature. I also find it interesting that most recommendations put forth by blanketing companies are primarily based on ambient temperature when there are so many other factors involved!

⚖️Body weight and body condition score of the horse also needs to be considered. While many horses do fine without a blanket, staying warm will require additional energy expenditure which could lead to weight loss. While this might not be a concern for some horses, a horse who is thin or a hard keeper can benefit from blanket use to reduce the energy expenditure needed to stay warm to help them maintain their weight.

✂️A clipped horse will also require a blanket. If you take away their natural form of protection, it only makes sense that they will need a substitute.

———————————————————————————

There are many other considerations to make but these are some big ones!

And if you are wondering if this pony was blanketed after this picture, the answer is yes. While all looks good in this picture (plenty of hay and a shelter available), my horses wouldn’t let her in the shelter and we had snow as well as wind gusts up to 35 mph with temperatures expected to drop to -9°F over the next 4 days and we are expected to get to -29°F overnight including wind chill. She probably would’ve been just fine without a blanket but I feel more comfortable knowing that she has some protection when she can’t get into the full shelter and I will continue to keep an eye on all of my horses closely and pull blankets when it warms up middle of next week! I also hope to build a pony shelter this summer so this doesn’t become a recurring problem!

Now with all of that being said, very few of our school horses ever wear blankets (although there are a few exceptions). They also have shelter, 24/7 hay, and are at a healthy weight and body condition score and we monitor their health regularly. The issue blanketing does pose is that the horse becomes dependent on humans for their thermal comfort as blanketing interferes with their natural thermoregulation. As a result, it becomes the responsibility of the caretaker to ensure blanket use is being used to increase comfort rather than create discomfort through improper fit or overheating.

At least this weather means we have been able to squeeze in some fun mini blanketing projects! And hopefully the more reseach we have on this subject, the better informed we can become to make the best decisions for our horses. Stay tuned for some updates!

Dr. DeBoer

This review paper does a really great job discussing horse care when it gets cold! However, there are some interesting studies that have been published since that I also use to make decisions.

Mejdell CM, Bøe KE, Jørgensen GH. Caring for the horse in a cold climate—Reviewing principles for thermoregulation and horse preferences. Applied Animal Behaviour Science. 2020 Oct 1;231:105071.

If you are looking for something to listen to on your holiday travels, check out part 2 of this Podcast!

In part two of episode 72, we continue the discussion of blanketing horses. Some of the conversation topics are:

• How horses keep themselves warm, and ways we can support them.
• The most important factors to consider while choosing to blanket or not.
• How often blankets should be removed to evaluate the horse for body condition, rain rot, rubbing, etc.

Head on over to www.standleeforage.com/podcast to listen now!

Or subscribe and download on your favorite podcast platform.

Equine, PhD

All of our blankets are now labelled and organized in alphabetical order by horse name and blanket weight as we get ready to start another research project! I am super stoked about this one!

Now we just need the weather to cooperate. While I love these tropical 40 degree days we have been enjoying lately, I could really use a cold front and some frigid temperatures right about now so we can get this project rolling (and this is the ONLY time I will ever beg for the weather to be cold, I can promise you that!).

But even more good news is that this is only one of two blanketing studies we are working on this year. I can’t wait to share what we find!

Do you know how to properly fit a blanket for your horse?

If not, or if you would just like a reminder, then take a look at this infographic I was asked to make for Extension Horses!

And it you haven’t yet, go follow them! Their content is created by a bunch of amazing and knowledgeable equine scientists who provide great information about horses (which is science-based)!

🥶🐴❄️🐴🌨

I was invited to give a webinar on winter blanketing for Penn State this Friday, December 15, from 12 - 1 pm EST! I am super excited about this opportunity and hope you can join. In the talk, I will be highlighting the physiology involved in thermoregulation for horses and how blanketing may impact it - specifically focusing on the research that has been published on the topic.

If you are interested, you can register at the link below. The event is free and even if you cannot attend, you will get access to the recording after the event is finished as long as you register ahead of time.

See you there?

The Science Behind Blanketing Horses In this webinar, we'll delve into the effects of blankets on horse hair growth, hay consumption, shelter preferences, and the ideal environmental conditions for blanket use.

I was invited to chat with Katy Starr and Dr. Tania Cubitt with Standlee Premium Western Forage about blanketing! Check out the first installment of their podcast here!

On Episode 71 of the Beyond The Barn podcast, co-hosts Dr. Tania Cubitt and Katy Starr and guest Dr. Michelle DeBoer discuss the hotly debated topic of whether or not horses actually need blankets in the winter, based on scientific research, including:

•Changes in hair coat length and diameter in blanketed and non-blanketed horses
•How body weight, body condition score and dry matter intake are impacted in blanketed horses
•The next scientific research project in the works to evaluate whether horses should be blanketed or not

Can horses actually TELL us if they want a blanket or not? Dr. DeBoer (Equine, PhD) also shares the results from a fascinating research study answering this question.

This is only part one of our interview! The second part of this conversation, releases December 5 as Episode 72.

➡️ Head on over to www.standleeforage.com/podcast to listen now!

Or subscribe and download on your favorite podcast platform:

Apple - https://podcasts.apple.com/us/podcast/beyond-the-barn/id1541221306
Spotify - https://open.spotify.com/show/3dmftQmwLKDQNueUcCJBZa
Google Podcast - https://podcasts.google.com/feed/aHR0cHM6Ly9mZWVkcy5zaW1wbGVjYXN0LmNvbS9rR1FQdkJoRg==

Tapeworms (Part Two)

This is a continuation of another post that discussed the basics of equine tapeworms. Check it out on my page if you missed it! But now we will discuss how to determine if your horse has them and how to manage them accordingly!

How do I know if my horse has tapeworms?

Common methods of f***l egg counts are an unreliable way to determine if your horse has tapeworms (Tomczuk, 2014). However, research has evaluated ways to modify these tests including using more f***s and centrifugation. While these tests are considered to be more time-consuming and laborious, they are very reliable and can be used to evaluate a tapeworm infection in your horse (Nielsen, 2016).

Depending on the country you live in, there are also blood and saliva antibody tests that can be used to help determine infection pressure and exposure. This can help horse owners shape their parasite control practices based on what they find.

How do we combat tapeworms?

Preventative measures are an important part of any parasite control program. Because eggs are passed in the f***s, manure management is key for a lot of parasite control and timely removal and proper disposal are critical.

Additionally, the recommended fall deworming following the grazing season is recommended to combat tapeworms. The reason for this is because horses will pick up tapeworms in the summer while grazing pasture, and health problems associated with tapeworms are often observed over the winter. As a result, deworming them going into winter can combat the tapeworms to reduce the health risks of harboring this parasite. A dewormer containing praziquantel (often combined with an ivermectin or moxidectin) is recommended or a double dose of a pyrantel dewormer (Reinemeyer et al., 2006). However, recent research demonstrated a lack of efficacy of these dewormers in treating tapeworms and needs to be evaluated further to determine if this lack of efficacy is widespread enough to conclude resistance is present (Nielsen, 2023).

So what is the bottom line?

When horses are on grass, they are exposed to tapeworms but it does not mean every horse is infected by the parasite. And even if a horse is infected, it does not mean they will have clinical signs although certain types of colic are associated with a tapeworm infection.

Edited: Lack of dewormer efficacy has been observed when treating tapeworms with both pyrantel and praziquantel in horses. This means it is important to further evaluate efficacy and figure out alternatives to maintain horse health in the future. F***l egg count reductions can be used with modified tests designed to detect tapeworm eggs to determine if these dewormers are effective for your horse herd.

If your horses have pasture access, deworm them in the fall after they are removed from pasture with a dewormer containing praziquantel or a double dose of pyrantel to reduce the risk of health concerns related to tapeworms over the winter months.

Follow preventative measures, including manure management, to reduce the spread of parasites in general.

Happy parasite control!
Dr. DeBoer

Nielsen, M.K. 2016. Equine tapeworm infections: Disease, diagnosis and control. Equine Vet. Educ. 28: 388-395. https://doi.org/10.1111/eve.12394

Tomczuk, K., Kostro, K., Szczepaniak, K.O., Grzybek, M., Studzinska, M.,Demkowska-Kutrzepa, M. et al. (2014) Comparison of the sensitivity of coprological methods in detecting Anoplocephala perfoliate invasions. Parasitol. Res. 113:2401–2406.

Reinemeyer, C.R., D.E. Hutchens, W.P. Eckblad, A.A. Marchiondo, and J.I. Shugart. 2006. Dose-confirmation studies of the cestocidal activity of pyrantel pamoate paste in horses. Vet. Parasitol. 138:234-239.

Nielsen, M.K. 2023. Apparent treatment failure of praziquantel and pyrantel pamoate against anoplocephalid tapeworms. Int. J. Parasitol.: Drugs Drug Resist. 22:96-101.

Tapeworms (Part One)

We recently took the time to discuss stomach bots. And while completing a different necropsy this past week, I saw tapeworms for the first time and thought it would be a great idea to dive into these parasites next! This is a rather long read so I decided to put it in two parts and I will link them together when they are both up!

The Life Cycle of the Tapeworm

Tapeworms have a unique life cycle where they have not one but two hosts: an intermediate and definitive (final) host. The intermediate host is the oribatid mite that lives in the soil and herbage. This mite which will ingest tapeworm eggs while feeding on manure. Upon ingestion, the outer shell of the egg is mechanically destroyed and the larval development begins until the parasite reaches the final infective stage known as the cysticercoid. Eventually, the oribatid mite is accidentally ingested by the horse during grazing and the tapeworm larvae can be released within the gastrointestinal tract of the horse.

While there are three different species of tapeworm, the most common one is the Anoplocephala perfoliata. This tapeworm makes its home at the ileocecal junction in the gastrointestinal tract, which is the connection between the final portion of the small intestine (ileum) and the initial part of the hindgut, the cecum. Here, the tapeworms can mature to adults and lay eggs, which ultimately leave the body in the manure to perpetuate this life cycle.

How does it impact my horse?

Horses do not develop immunity to tapeworms and can harbor them at any age. And while tapeworms are common and widespread, their prevalence is dependent on housing and climatic conditions. Horses grazing green, lush pasture are at the greatest risk of exposure (this is where mites live!) and are most likely to harbor tapeworms in the fall (at the end of the grazing season). In comparison, horses without pasture access or living in dry and arid regions are unlikely to be exposed to these parasites (Nielsen/AAEP). It is important to note that just because a horse is exposed to tapeworms, it does not mean they harbor the parasite. Rather, the number of horses within a herd infected by tapeworms can vary significantly. But the bottom line is: if your horse has access to pasture, it would not be surprising to learn they have tapeworms.

Considering this and that the most common species of tapeworm persists at the ileocecal junction, a small opening connecting the foregut and hindgut, horses who are diagnosed with an ileocecal colic or ileal impaction are statistically more likely to also have an A. perfoliata infection (Proudman et al., 1998). HOWEVER, the risk of having these types of colic if a horse has tapeworms is unknown as many horses harbor tapeworm infections and do not display any clinical signs or discomfort (Nielsen, 2016). So the takeaway here is: if your horse has an ileocecal colic or ileal impaction, you are more likely to find they also harbor an A. perfoliata infection, but just because your horse has tapeworms, does not mean they will experience this colic.

Part two will focus on how to test your horse for tapeworms and how to combat them so stay tuned!

Dr. DeBoer

Nielsen, M. American Association of Equine Practitioners. https://aaep.org/horsehealth/tapeworms-horses

Proudman, C.J., N.P. French, and A.J. Trees. 1998. Tapeworm infection is a significant risk factor for spasmodic colic and ileal impaction colic in the horse. Equine. Vet. J. 30: 194-199. https://doi.org/10.1111/j.2042-3306.1998.tb04487.x

Nielsen, M.K. 2016. Equine tapeworm infections: Disease, diagnosis and control. Equine Vet. Educ. 28: 388-395. https://doi.org/10.1111/eve.12394

🪰Stomach Bots 🪰

Last month we did a necropsy and came across some bot fly larvae in the stomach. I thought this could be an educational opportunity as we are moving into fall, a time when horses may harbor these larvae if they have not been dewormed. So let's learn a bit more about them!

The Life Cycle of the Bot Fly

First off, bots are not worms but rather the larvae of a bot fly. These infections within the horse often go undetected and do not result in obvious clinical signs, the adult flies can often be a nuisance to us as well as our horses. These flies begin their life cycle as eggs, which are yellow in color and are attached to horse hair, commonly found on the legs, neck, chest, withers, and mane hair. The egg will develop into the first larval stage which is triggered to emerge when the horse licks or bites at the fully developed egg. The larvae then burrow into the gums or lining of the mouth for about a month. At this point, the larvae will molt into the second stage and ultimately the third stage while it is attached to the lining of the stomach. Here, the larvae will remain immobile for 8 to 12 months. After the third larval stage is fully mature, the larvae will pass in the f***s where it will burrow into the soil or manure, often in late winter or early spring. In one to two months, the adult fly will emerge and live for less than a week to reproduce and lay eggs to continue the life cycle.

How do stomach bots impact my horse?

While bot flies can attach to the gums or lining of the mouth as well as the lining of the stomach, they do not cause significant damage. In the second picture on this post, an arrow is pointing to part of the stomach where a bot was previously attached. As you can see, the larvae sits on the surface of the stomach lining and has not been shown to cause ulcers or perforate the stomach. While there can be cases of stomach bots causing discomfort, this is pretty rare! Once they are removed, these areas tend to heal very quickly. As a result, bot fly control should not dictate your parasite control program!

So what should I do about bot flies?

Preventative measures are going to be valuable in managing many parasites, including bot flies. And interrupting the parasite's life cycle is a key way to do this! First, removing bot fly eggs from the horse can reduce the risk of ingestion. Bot fly eggs can be removed using a bot fly knife or by applying warm water to simulate the licking behavior of the horse. Additionally, timely manure removal from paddocks and pasture and then hauling it away, composting, or covering it with a dark tarp, the larvae can be removed or killed before it is able to fully mature to break the life cycle.

What about deworming?

Deworming with ivermectin or moxidectin will kill many different parasites including bot fly larvae. It is commonly recommended to use one of these products in the fall (alongside praziquantel to combat tapeworms) but exact timing will change based on climate so be sure to consult with your veterinarian. It is also important to note, while these dewormers will combat stomach bots, this is not the primary goal of your deworming as stomach bots are rarely harmful to the horse.

Should I wait until after the first killing frost to deworm?

Contrary to popular belief, the first killing frost is actually irrelevant to your deworming schedule. As mentioned previously, stomach bots do not impact horse health enough to alter your deworming schedule. Rather, it is important to focus on timing to prioritize combatting strongyles, tapeworms, and ascarids (for young horses). By making the suggestion to deworm after the first killing frost, there is this false sense of security that 1) the frost will kill all the parasites on pasture when in reality they are fairly cold tolerant and 2) that the dewormer is going to kill all parasites within the horse and they will be parasite free in the winter. Rather, we are deworming to reduce the risk of parasitic disease in our horses.

Since these parasites are often picked up while horses are grazing pasture, the current recommendation is to deworm at the end of the grazing season. This allows us to combat the parasitic burden that may have increased during the high transmission period and reduce the risk of parasitic disease that may be seen during winter months. While you will wait until the horse is done grazing, you DO NOT need to wait until after the first frost and it can often benefit the horse to be dewormed earlier in the fall! It is also rather convenient that the same dewormer that kills small strongyles and tapeworms also targets bot fly larvae so you will combat them even if that is not the primary objective.

So what is the bottom line?

Current recommendations often suggest deworming your horses in the fall with ivermectin or moxidectin (+ praziquantel) to combat different parasites (not just bot flies). But consult your veterinarian to make sure you have the best plan established for your horse and climate.

Bot flies may look gross but they rarely cause concern for horse health.

It is a great idea to follow preventative measures, including manure management, to reduce the spread of parasites.

Happy parasite control, everyone!
Dr. DeBoer