Podcast #71
When it comes to fuelling performance, muscle glycogen and grain feeding get most of the attention, but that’s only half of the story.
In this episode, Dr Nerida breaks down the dual fuel tank theory of performance horse nutrition: the finite store of muscle glycogen used for speed and high-intensity work, and the continuous supply of energy in the form of volatile fatty acids (VFAs) produced via fibre fermentation in the hindgut.
We explore how these two fuel systems work together, how forage is an essential performance fuel, how the VFA acetate contributes directly to working muscle energy, and why overfeeding grain can undermine the hindgut fuel system that helps horses conserve glycogen for when they really need it.
If you feed a racehorse, eventer, polo horse, endurance horse or other high-level athlete, this episode offers a different way to think about the way you structure your diets around forage and grain, to maximise muscle glycogen, gut health and performance.
This episode is proudly brought to you by EquiGI's microbiom analysis, order a test kit at https://www.equigi.com
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71. Rethinking Performance Horse Nutrition: Forage, Grain and the Dual Fuel Tanks
[Nerida McGilchrist] 14:54:08Hello, hello, and welcome to the Happy Horse Nutrition Podcast. I'm Dr Nerida, PhD equine nutritionist, founder of the My Happy Horse Nutrition app, and longtime equine nutrition consultant in the performance horse and racing sectors of our horse industry.
[Nerida McGilchrist] 14:54:23
And today we are talking about…
[Nerida McGilchrist] 14:54:27
performance horse. Because what I have come to realize, just in the last five years or so, and it sounds really obvious now when I say it out loud, is that horses don't have one fuel tank, they have two.
[Nerida McGilchrist] 14:54:40
This fuel tank is…
[Nerida McGilchrist] 14:54:43
The one we have traditionally all obsessed over. The second fuel tank is the hindgut, and it still gets very little attention from a high-level performance perspective. But when we understand these two fuel systems, and feed in a way that allows them to work together.
[Nerida McGilchrist] 14:55:00
It completely changes performance, and changes the way we think about how to feed grain, forage, and feeding the performance or racehorse in general.
[Nerida McGilchrist] 14:55:11
So, without any delay, let's dive into the dual fuel tank theory of feeding performance horses.
[Nerida McGilchrist] 14:55:20
So, to give you a little bit of historical background on feeding performance horses, I went digging back through some old textbooks and the old NRC publications to have a look at.
[Nerida McGilchrist] 14:55:36
where, essentially, the obsession of feeding grain to performance horses comes from, because if you go and have a look in any high-level, um, performance horse, so I'm thinking, when I say high-level, I'm thinking horses like polo horses, polo cross horses.
[Nerida McGilchrist] 14:55:52
venters, horses that actually do work hard, and also our thoroughbred and standard-bred racehorses. If you go and look through old textbooks about how to feed them.
[Nerida McGilchrist] 14:56:06
what you'll notice is that as workload increased, the recommendation for feeding all of those horses was to increase the amount of grain that was being fed. And in fact, in… as recent… I don't know, can we call the 80s recent anymore? It feels recent to me. Um…
[Nerida McGilchrist] 14:56:26
Well, sort of. I was a kid, I guess, in the 80s, but the 90s still feels recent to me, and then my kids love to tell me how long ago the 90s… the 90s were, but the 1989 National Research Council feeding and nutrition requirements of horses.
[Nerida McGilchrist] 14:56:44
specifies that…
[Nerida McGilchrist] 14:56:47
Horses should be fed, when they're in intense work, a ration that is 0.75 to 1.5% of their body weight in forage, which for a 500kg horse would be equivalent to 3.75 up to 7.5kg of.
[Nerida McGilchrist] 14:57:03
forage per day, but the concentrate recommendation started at 1% and went up to 2% of body weight. So that's 5 to 10 kilograms of concentrate per day.
[Nerida McGilchrist] 14:57:17
The Equine Nutrition and Feeding textbook, which was a David Frape publication, and you'll have to excuse me while I just open its front cover again. So it's the version that I've got, which says second edition was published in 1998.
[Nerida McGilchrist] 14:57:35
The only, um, actual diets I could find in there for performance horses were for Aventus, and it said 7 to 7.5 kilograms of haylage, and you have to remember that haylage is quite high moisture content, so the dry matter value of that would be, you know, anywhere from 3.5 to 5.
[Nerida McGilchrist] 14:57:52
maybe a little bit more than 5 kilograms of dry matter per day in forage, and then 5 to 6 kilograms of concentrate per day. There was a published paper, Southwood et al. Southwood and colleagues went through 25 standard bred and 25 thoroughbred racing stables.
[Nerida McGilchrist] 14:58:12
And they found on average that racehorses were fed 3.3, surprisingly difficult to say, kilograms of roughage per day and 7.8 kilograms of concentrate per day. So a roughage to concentrate ratio that is way in favor of concentrate, which is what?
[Nerida McGilchrist] 14:58:36
What these publications were recommending and advocating, so the 1989 NRC that I mentioned, it gives a forage to concentrate recommendation of 35% forage to 65% concentrate for a racehorse or high-level performance horse.
[Nerida McGilchrist] 14:58:55
I actually, as part of my PhD in the early 2000s, went through… it was about 75 racing stables, and I… I'm kicking myself now when I look back. I don't know why, but I didn't… we did record whether the horses were fed hay, but we didn't actually weigh the hay, because I was… I was very fixated on the grain.
[Nerida McGilchrist] 14:59:14
And looking at how do we process cereal grains for racehorses to make them more digestible in the small intestine so that we had more starch digestion in the small intestine and less starch going into the hindgut. So by that stage, we did have an understanding that feeding too much grain, and especially feeding too much grain that was not very digestible, wasn't a good thing.
[Nerida McGilchrist] 14:59:35
But I found in… in my paper, which was published, um, it'd be published under Richards, which was my, um, surname back then, and, um…
[Nerida McGilchrist] 14:59:48
I can't even remember the journal or the year that it was published now, I should have looked that up, but the… the average amount of grain that we found trainers were feeding was 7.3 kilograms per day, but I vividly remember some stables feeding, you know, 10 to… there was one stable that was feeding.
[Nerida McGilchrist] 15:00:05
13 kilograms of grain to their racehorses per day. So there's this… there's been this… there's been this fixation on feeding grain, and it's for really good reason. So…
[Nerida McGilchrist] 15:00:20
Grain has got starch, so if you break a cereal grain, and really any cereal grain, barley's probably the nicest one to do it to, because the starch in barley is really bright in colour and contrasts quite well with the seed coat.
[Nerida McGilchrist] 15:00:35
If you break any cereal grain open or cut it straight down the middle with a knife, you'll see all this white stuff in the middle, and that white stuff is starch. And the middle part of the grain is called the starchy endosperm, so where all the starch is kept.
[Nerida McGilchrist] 15:00:52
And stat is just glucose molecules that are all joined together.
[Nerida McGilchrist] 15:00:56
And the reason we feed cereal grains, predominant reason we feed cereal grains to performance horses, is so that they can digest that starch, absorb the glucose, and then store that glucose in their hindgut.
[Nerida McGilchrist] 15:01:11
as glycogen. And then glycogen is this really valuable source of muscle fuel for performance horses.
[Nerida McGilchrist] 15:01:22
So, glycogen, when… when a performance horse's muscles need energy.
[Nerida McGilchrist] 15:01:27
They will mobilize glycogen and use that, the energy generation areas of a cell, so the mitochondria will take the glucose and put it through a metabolic pathway and produce ATP, and ATP is the ultimate muscle fuel. That's the fuel that actually powers muscles.
[Nerida McGilchrist] 15:01:50
muscles are always looking, when we're asking them to do work, they're looking for this ATP energy. Now, if a horse takes a glucose molecule, and in the presence of oxygen, so, um, when horses are exercising, up to the most intense.
[Nerida McGilchrist] 15:02:08
forms of exercise. So, you know, even galloping, not absolutely flat stick galloping, but galloping, they can still get enough oxygen to their muscles to allow them to have oxygen present when they're burning.
[Nerida McGilchrist] 15:02:23
glycogen inside their cells. And when there is oxygen present, they take a glucose molecule.
[Nerida McGilchrist] 15:02:32
And they can create 30 to 32 ATP from that one glucose molecule. So it's incredibly… it's an incredibly efficient way for them to generate this ATP muscle energy. And the other advantage that glucose gives a horse's muscles is.
[Nerida McGilchrist] 15:02:50
When the horse puts its foot flat to the floor and is doing something that is very intense, so we're either asking them to jump, or we're asking them to accelerate, or we're asking them to jump from a standing start and then accelerate very quickly, or, say, at the end of.
[Nerida McGilchrist] 15:03:10
a race for harness races or thoroughbreds when they are working as hard as they possibly can and going as fast as they possibly can.
[Nerida McGilchrist] 15:03:20
they can no longer get enough oxygen to their muscles to use oxygen in that energy generation process. And so their muscles have to flick to what we call anaerobic energy generation, so anaerobic just being in the absence of oxygen, no oxygen is available.
[Nerida McGilchrist] 15:03:37
And glucose is the only form of energy that a muscle can use in that state.
[Nerida McGilchrist] 15:03:44
But the really interesting thing is, when there is no oxygen present, for every one glucose molecule, you get two ATP. So when there's…
[Nerida McGilchrist] 15:03:55
When there's oxygen present, so in all other levels of intensity other than the highest levels of work. Sorry, that's not coming up very well, is it? So when a horse is working hard, but not the hardest it can work, and it can still get oxygen to its muscles, it's producing that 30 to 32 ATP for every one glucose.
[Nerida McGilchrist] 15:04:19
when they're working as hard as they can, and the oxygen disappears, they're only getting 2 ATP for every 1 glucose. But the important point is…
[Nerida McGilchrist] 15:04:29
they can still get ATP from that glucose when there is no oxygen present. They can't do that with any other fuel source. So…
[Nerida McGilchrist] 15:04:39
we have a fixation with grain in performance horse diets, because grain provides starch. Starch is broken down in the small intestine to glucose. The glucose is taken up by the muscles and stored as glycogen.
[Nerida McGilchrist] 15:04:52
And then when they're exercising, they can break that glycogen down, either in the presence of oxygen or without oxygen, and create muscle energy. So the glycogen, or the glucose in the muscles, is the energy that allows horses to work at the highest intensity, and if they… if they.
[Nerida McGilchrist] 15:05:12
don't have that glycogen available. They act… they can't work at those really high, um, intensity levels. They can only…
[Nerida McGilchrist] 15:05:20
generate energy back down at the level where they can have oxygen present. So it's an incredibly valuable source of energy for a performance horse because it allows them to generate muscle energy at all levels of exercise intensity.
[Nerida McGilchrist] 15:05:37
Which they can't do with other energy sources, so fatty acids from oils, or volatile fatty acids that come out of the hindgut. So we do tend to get fixated, and certainly, traditionally, we tend to get fixated on feeding grain to performance horses, because we know that.
[Nerida McGilchrist] 15:05:54
the grain increases the…
[Nerida McGilchrist] 15:05:57
glycogen content of the muscles, or at least it allows performance horses to have a ready access to glucose from the diet so that they can build glycogen stores in their muscles.
[Nerida McGilchrist] 15:06:12
But the thing that I think we've all missed and it's not that we haven't been aware of the second fuel tank. It's more that I don't think we've really realised how important the second fuel tank is.
[Nerida McGilchrist] 15:06:28
Um, so we've missed…
[Nerida McGilchrist] 15:06:32
The… the hindgut fuel tank, and how much it supports a performance horse by allowing the performance horse to conserve its glycogen for when it actually really needs it.
[Nerida McGilchrist] 15:06:43
So, the first fuel tank that a horse has is that glycogen in their muscles, but their second fuel tank is their hindgut, and the fuel that comes out of the hindgut is the volatile fatty acids that the microbes produce when they ferment fiber.
[Nerida McGilchrist] 15:07:00
So we have to remember, and for anyone who has listened to any more than a couple of Happy Horse Nutrition podcast episodes, you'll know that I often will take nutrition back to an evolutionary basis for horses.
[Nerida McGilchrist] 15:07:15
So horses have been evolving for 55 million years and they have evolved as animals who are monogastric hindgut fermenters. So they have a small single stomach, long small intestine and these very large in hindgut.
[Nerida McGilchrist] 15:07:34
this very enlarged hindgut. And in that hindgut, there are trillions of microbes. And essentially what happened millions of years ago is the horse has said to these microbes, hey, if I give you somewhere warm and safe.
[Nerida McGilchrist] 15:07:48
To leave?
[Nerida McGilchrist] 15:07:51
Will you help me digest fiber? And so these microbes live in the horse's hindgut and they help the horse break down fiber because the horse, like humans, we have no endogenous enzymes, so we have no enzymes that we create for ourselves that are actually capable of digesting fiber. We rely on, and the horses definitely rely on, the microbes, so the bacteria and the fungi predominantly, that live in their hindgut to break down fiber.
[Nerida McGilchrist] 15:08:19
So, a horse's entire gastrointestinal system is built around the digestion of fibre, which means their entire muscle physiology is built around utilising the energy that comes out of the hindgut.
[Nerida McGilchrist] 15:08:36
So cereal grains and very starchy ingredients are only really recent additions to a performance horse's diet. And when I say really recent, humans have been in horses' lives for about 4,500 years, which is 0.01% of the time they have been on Earth. I love that statistic because it blows my mind every time I say it. It is just the blink of an eye.
[Nerida McGilchrist] 15:09:00
It's the tiniest little amount of time and their gut has not had anywhere near enough time to adjust to the diets that we now feed them, so we always get the best performance out of horses when we feed them in a way that honours their gastrointestinal system.
[Nerida McGilchrist] 15:09:20
And one of the most important things to remember in doing that is that their body is set up to use the fuel that flows constantly out of their hindgut.
[Nerida McGilchrist] 15:09:30
So when a horse eats fiber, so it can be fiber from pasture, or hay, or, um, you know, chopped hay and chaff, um, and it can also be fibers from high-energy fiber ingredients like sugar beet pulp and lupin holes, and there's lots of, you know, alternate fibers, copper meal.
[Nerida McGilchrist] 15:09:50
Um, that we can feed to performance horses as well. So… so when those high-fiber ingredients go into the hindgut, the fiber-fermenting bacteria and fungi then literally eat the fiber, and the… and then they ferment it.
[Nerida McGilchrist] 15:10:06
And… which is their digestion process for fiber. And the byproduct of that fiber fermentation.
[Nerida McGilchrist] 15:10:14
is compounds called volatile fatty acids. And there's 3 main volatile fatty acids that will be produced in a horse's hindgut.
[Nerida McGilchrist] 15:10:26
They are acetate, propionate, and butyrate. And when a horse ferments fiber, the predominant volatile fatty acid that the microbes will produce is acetate. And the really funky thing is, acetate gets absorbed, and it is used as a direct source of.
[Nerida McGilchrist] 15:10:46
energy by the horse's muscles. And in fact, it slots in to exactly the same metabolic pathway as glucose, but just a little bit further along in the metabolic pathway, so glucose has to enter a few steps before where acetate can come in. So.
[Nerida McGilchrist] 15:11:04
Horses are so beautifully wired up to use acetate as a muscle energy source, and they're, um…
[Nerida McGilchrist] 15:11:15
The big advantage that that acetate gives to a performance horse is even when they are working, so even when they're racing, even when they're out on the cross-country course, even when they're on the polo field, the hindgut continues to produce.
[Nerida McGilchrist] 15:11:32
volatile fatty acids, and they continue to absorb those volatile fatty acids. And so, it's literally handing the horse energy as the muscles are burning it during exercise, which is in contrast to their muscle glycogen fuel tank, which.
[Nerida McGilchrist] 15:11:48
We can fill that muscle glycogen fuel tank up, but when a horse starts.
[Nerida McGilchrist] 15:11:55
any kind of event. So, you know, be it a cross-country course or a race.
[Nerida McGilchrist] 15:12:03
They've got… whatever they've got on board for muscle glycogen, that's essentially it for that.
[Nerida McGilchrist] 15:12:10
Particular event and if they burn through all of their muscle glycogen they will hit fatigue because if they, if they, they will hit fatigue at really intense levels of exercise and we see this, you can literally see this happening in racehorses and I've been, I've actually been watching way more racing than what I would normally watch as we've been trawling through lots of race footage trying to find good examples of.
[Nerida McGilchrist] 15:12:38
horses who have got plenty of energy on board from both their fuel tanks and horses who appear to, in a race, be really reliant on their muscle glycogen fuel tank, because you'll see those horses that are overly reliant on their muscle glycogen.
[Nerida McGilchrist] 15:12:52
they'll race well, but then when their jockey asks them to give extra at the end of the race, they can't, because they don't… they've run out of muscle glycogen. Or, what can happen when they burn muscle glycogen?
[Nerida McGilchrist] 15:13:08
in the absence of oxygen, so they'll take one glycogen and produce two ATP, and then the byproduct of that process is actually lactic acid. So they'll get to a point where they've created so much ATP without any oxygen there that their muscles produce a heap of lactic acid.
[Nerida McGilchrist] 15:13:27
and then the pH of the muscles drops too low, it gets too acidic, and that metabolic pathway will shut down to protect the horse. So, if you…
[Nerida McGilchrist] 15:13:39
send a horse out to perform.
[Nerida McGilchrist] 15:13:44
And you've got them predominantly running on their muscle glycogen fuel tank, you risk getting to the point where they either run out of energy or where they acidify their muscles to the point where that metabolic pathway shuts down and they have to slow down.
[Nerida McGilchrist] 15:14:01
their speed enough or their effort enough that they can get oxygen back to their muscles so that they can continue to burn either glycogen with oxygen present so that they're producing a lot more ATP per glycogen molecule that they're using up.
[Nerida McGilchrist] 15:14:16
or that they are able to use the acetate as the volatile fatty acid coming out of their hindgut again to fuel performance. So, they don't run out of muscle glycogen and stop dead. They have to slow down enough to allow them to get oxygen.
[Nerida McGilchrist] 15:14:32
back to their muscles so that they can they can burn other fuel sources.
[Nerida McGilchrist] 15:14:49
So with that, and I hope I've managed to explain the two fuel tanks to you. I'll just recap them really quickly. So the first fuel tank is the glycogen that they have stored in their muscles, and they can burn that glycogen to produce the ATP, either with oxygen present or without oxygen present. So super useful source of fuel.
[Nerida McGilchrist] 15:15:10
And then the second fuel tank is the hindgut and the volatile fatty acid, acetate, that is produced when the bacteria and fungi who live in the hindgut ferment fiber. So, actually interesting, and we'll get to that in a minute, I was going to say interesting point.
[Nerida McGilchrist] 15:15:28
We might have to cut that bit out, David. Sorry. I hope you can. I hope you can cut that bit out. Sorry, I was going to say something and then I thought better of it. So, with that understanding of the two fuel tanks, it starts to make a difference to at least how I think about fueling performance horses, because.
[Nerida McGilchrist] 15:15:45
What I want to achieve is I want a hindgut fuel tank that is absolutely pumping out volatile fatty acids to the muscles when the horses are working. And I also want them to start whatever event or race they're about to start.
[Nerida McGilchrist] 15:16:03
with a muscle glycogen fuel tank that is brimming full. So we have to feed them in a way that supports both of the fuel tanks.
[Nerida McGilchrist] 15:16:14
And the way we do that is to make sure we feed plenty of forage, because that fills the hindgut fuel tank, and it gives the bacteria and fungi lots of fibre to ferment, so that they're producing lots and lots of acetate. And in…
[Nerida McGilchrist] 15:16:30
Performance horses like thoroughbred racehorses who travel at high speeds and do have a heavy reliance on muscle glycogen, we also use cereal grains in a very specific way to make sure that we're also giving them that easy source of glycogen.
[Nerida McGilchrist] 15:16:50
Sorry, the easy source of glucose that then they can absorb and use to top up their muscle glycogen energy supplies. It's interesting, I'm working at the moment on presentations to give to Northern Farm and their racing barns in Japan in October.
[Nerida McGilchrist] 15:17:11
And I was trawling back through some older presentations that I'd given to the farms that I worked with in Japan.
[Nerida McGilchrist] 15:17:19
And the very first time I went up there was in 2020, and I'd been asked to give a presentation about feeding their performance horses, their racehorses. And when I looked through that, it was really interesting for me, and I realized how much I'm constantly evolving as a nutritionist.
[Nerida McGilchrist] 15:17:36
Because that… that presentation that I'd written back in 2020 was completely focused on grain and grain processing and using enzymes to help with the digestion of grain, but it was… it was solely focused on the muscle glycogen fuel tank. And, you know, my thinking and…
[Nerida McGilchrist] 15:17:55
is partly come out of the fact that, you know, my PhD was on cereal grains, and how do we process cereal grains to make sure that the horses are getting maximum starch suggestion, and therefore maximum glucose out of these cereal grains. But there was nothing… I said nothing in this presentation about fibre.
[Nerida McGilchrist] 15:18:12
And it's completely different to the way that I would present racehorse nutrition now, because so much of fueling a racehorse and getting the best performance out of them comes from the hindgut. And in fact, if you go back and listen to episode 68 of the Happy Horse Nutrition podcast.
[Nerida McGilchrist] 15:18:32
I dig in detail into the research around how the hindgut microbes affect performance, and the research showing that the more diverse the microbiome in a horse's hindgut, and also the more, um, set up a horse's hindgut microbiome is for.
[Nerida McGilchrist] 15:18:49
fiber fermentation, the better the performance.
[Nerida McGilchrist] 15:18:52
But I didn't have any of that understanding, and that research around the hindgut microbes has sort of come out after 2020. I think all of the papers that I cover in that episode were from 2024. So our understanding of performance horse nutrition is constantly evolving, and I now put so much more, as a nutritionist, I personally put so much more emphasis on the fibre portion.
[Nerida McGilchrist] 15:19:21
of a horse's diet, while also recognising still that the grain portion is really important. But if we fed in the way, or if we feed in the way that the previous NRC recommendations would have us believe was the right way to feed a performance horse, so with a ratio of forage to grain of 35% to 65% and feeding up to 10 kilograms of grain per day.
[Nerida McGilchrist] 15:19:47
It has some pretty negative consequences on the overall fuel system.
[Nerida McGilchrist] 15:19:53
So, the ideal way, in my current opinion, and who knows, this might change in another 5 years' time, and I'll be looking back at this episode and saying, you know, don't listen to that episode of the Happy Horse Nutrition podcast, because we've had to rethink it all again.
[Nerida McGilchrist] 15:20:09
With what we know at this point in time, it's really important to get enough forage into performance horses. It does so many things, and, you know, it reduces the risk of gastric ulcers, and keeps their hindgut full, reduces the risk of colic, all of those things. So there's all of those benefits of forage.
[Nerida McGilchrist] 15:20:28
in the diet. But what it does is it fills up their hindgut with fiber, and it gives the fiber-fermenting microbes lots and lots of fiber to ferment, and then they are.
[Nerida McGilchrist] 15:20:43
pumping out masses of acetate into the horse's body, even during an event. So if you… I imagine the hindgut fuel tank a little bit like the gas knob on a stove. So if you don't feed very much forage.
[Nerida McGilchrist] 15:21:00
you… it's like having the gas knob turned right down. So it's… it's there, there is some energy, there's some heat, but not very much. But a horse that is getting fed enough forage and enough fibre, you crank that gas knob up to full, and all of a sudden you've got big flame and lots of heat, lots of energy coming out.
[Nerida McGilchrist] 15:21:19
That's what you can achieve when you feed plenty of forage in a performance horse's diet. So, plenty of forage would be an absolute minimum of 1.5% of their body weight per day. So, that used to be the upper end of what the NRC recommended. So, it's 7.5 kilograms of.
[Nerida McGilchrist] 15:21:38
hay or other forage and fibres per day.
[Nerida McGilchrist] 15:21:43
Um, and, and that amount, and I, I should say here, my preference is always to give horses 24-7 access to forage. So, um, don't, don't meter it out to them, just give them, give them access to as much forage as they want to eat. There's always exceptions to the rule, so if anyone's listening, going, oh my goodness, my horse would explode if I did that.
[Nerida McGilchrist] 15:22:03
This is why we use slow-feeding hay nets or slow-feeding barrels, but as much as you can keep the forage in front of performance horses all of the time. So, part of that old theory around feeding lots of grain, and I think part of the reason why, you know, papers like Southwood et al in 1993 report an average of 3.3 kilograms of roughage per day. What used to happen, and unfortunately still happens in some.
[Nerida McGilchrist] 15:22:33
sectors is that trainers or riders would restrict the amount of forage a horse had access to to force them to eat more grain because we were convinced back in the day that it was the grain that was actually fuelling.
[Nerida McGilchrist] 15:22:50
the high-level performance. But we know now that that's not the case. The grain is important, and I'll get to that in a moment, but, um…
[Nerida McGilchrist] 15:23:00
You have to have the volatile fatty acids coming out of the hindgut, because otherwise.
[Nerida McGilchrist] 15:23:06
What happens is you put, and I'm using racehorses as examples here a lot because it's so easy to see with them. So with something like an Aventa, there are so many other factors that come into play that will affect that horse's performance. With a racehorse, it's much more clear cut and it's a lot easier to see when they hit the wall, they hit fatigue and, you know, go from.
[Nerida McGilchrist] 15:23:31
From leading a race often to just not doing well. And in fact, a couple of races I watched a few days ago looking for videos for our current Racing Queensland project, there was one horse who was about 20 lengths in front, which we could argue that this is a behavioural issue as well, and that contributed to his demise, but then finished dead last and you could see him.
[Nerida McGilchrist] 15:23:58
Um, hit the wall because he'd burnt through all of the energy that he had, and then he had to slow his speed right down so that his muscles could actually access oxygen again and generate energy in the presence of oxygen.
[Nerida McGilchrist] 15:24:12
So what happens with a racehorse is that if you start a race with a hindgut that is not functioning well because you are not feeding enough forage, or it could be because you're feeding too much grain or feeding raw grain, especially cracked corn, and putting a lot of starch into the hindgut and.
[Nerida McGilchrist] 15:24:35
essentially destroying your fiber fermentation capacity. And you also, when you do that, you reduce the production of acetate, which is the volatile fatty acid that they can burn as a direct muscle energy source. And…
[Nerida McGilchrist] 15:24:49
you'll start to produce more propionate, so the bacteria and fungi will create more propionate. And that propionate can still be used for energy, but it has to go to the liver, and then be converted to glucose, and then gets burnt as energy. So acetate just goes straight to the muscles, and propionate has to do this detour through the.
[Nerida McGilchrist] 15:25:11
through the liver before it can be turned into a form of energy that the muscles can use. So, if you start a racehorse with a hindgut that is not fully functional and doesn't have enough fibre and is not pumping acetate.
[Nerida McGilchrist] 15:25:27
From the moment those horses jump, and potentially even before then, you know, when they're loaded onto the truck, when they're in the parade ring, if they don't have that beautiful supply of acetate energy flowing from their hindgut that their muscles can just take up and.
[Nerida McGilchrist] 15:25:45
burn, when there's oxygen present, they will be starting to dip into their muscle glycogen supplies. And remember, the muscle glycogen is limited, so they can fill their muscles up with it, but once that glycogen fuel tank is full, they can't actually put any more glycogen.
[Nerida McGilchrist] 15:26:02
in, and, um, if they start burning it too early in a race, they'll run out, and that's when they hit fatigue at the end of the race. Versus…
[Nerida McGilchrist] 15:26:14
A horse that, if you start a race with a horse that has got a hindgut absolutely brimming full of fermentable fibres and has got a really healthy hindgut microbe population that are set up.
[Nerida McGilchrist] 15:26:29
to ferment fibre and produce acetate, those horses are going to be relying on that acetate coming out of the hindgut for a majority of that race. And one of the most fun things for me to watch in racing.
[Nerida McGilchrist] 15:26:44
is when a horse is racing, and the jockey or the driver say, okay, go now, and they put their foot down, and that horse just picks up a couple of gears, and… and just flies home, um, and finishes the race. And, you know, they… they… they look happy when they do that. It doesn't even look like they're… they're working hard.
[Nerida McGilchrist] 15:27:03
But essentially, what they've been able to do is conserve their glycogen fuel, so they've conserved all of that glucose in their muscles until they put their foot flat to the floor and need to accelerate. And when they do that, and they go looking for that muscle.
[Nerida McGilchrist] 15:27:19
fuel that they can use when there's no oxygen present. There's still heaps of it there, and they haven't really burnt any up to this point, um, and so they haven't… they also haven't acidified their muscles too much.
[Nerida McGilchrist] 15:27:34
So, there's all of these, um, although, in saying that, even if they are burning muscle glycogen early in the race, if there's still oxygen present, they won't acidify their muscles, so that's, um, not as much of a consideration, unless the horse is unfit.
[Nerida McGilchrist] 15:27:49
But what we want to happen is that horses will rely on their most natural fuel source, so the fuel source that their whole body has been wired up over millions of years to use, being the acetate that comes out of their hindgut.
[Nerida McGilchrist] 15:28:04
And then when we ask them for the extra effort, they flick over to using muscle glycogen, and they've got a full tank of glycogen.
[Nerida McGilchrist] 15:28:14
there. I was trying to think of an analogy to… to sort of demonstrate this a little bit more clearly. I was thinking, okay, if we… if we take a car, as an example, with a 60-liter fuel tank.
[Nerida McGilchrist] 15:28:27
And let's say it's a V8 supercar in a race.
[Nerida McGilchrist] 15:28:34
If… if that car was only able to operate, um…
[Nerida McGilchrist] 15:28:43
under anaerobic conditions, so no oxygen available, just as an example, I'm just making up these analogies as I go along.
[Nerida McGilchrist] 15:28:53
For every litre of fuel.
[Nerida McGilchrist] 15:28:55
So remember that a horse, when there's no oxygen, they can only make two ATP for every glucose that they burn, versus 30 to 32 ATP when there is oxygen present. So if you imagine this car, if there was no oxygen present, as an analogy, that would mean that it's only able, out of every liter of fuel, it's only able to actually use 66 mils.
[Nerida McGilchrist] 15:29:18
of that fuel, and the other 934 mils gets locked away in a fuel tank that it actually can't access. So this is the same. So when a horse burns glucose and only gets two ATP, it hasn't actually destroyed the other energy, but it can't access it until the oxygen comes back.
[Nerida McGilchrist] 15:29:39
Um, so it essentially just gets locked away somewhere else that the horse can't access. So, if a V8 supercar was operating like that, that would mean out of its 60-liter fuel tank, it's only going to be able to burn just under 4 litres of that fuel, and those things use about 3 litres.
[Nerida McGilchrist] 15:29:56
every minute when your foot's flat to the floor. So, you know, you'd get just over a minute's worth of energy if you were burning that fuel. And it's the same for horses. So that's how fast your muscle glycogen disappears. So when you put your foot flat to the floor at the end of a race.
[Nerida McGilchrist] 15:30:17
And they flick into that anaerobic energy metabolism and they start only getting two ATP for every piece of glucose that they're burning. They burn through their muscle glycogen supplies so fast because they're using so much of it to get the energy that they need to fuel the speed and performance that you're asking them to give you.
[Nerida McGilchrist] 15:30:41
So if you imagine a horse that, let's imagine 2 horses. One horse has got a very healthy hindgut full of fiber and lots of volatile fatty acid or acetate coming out of the hindgut to fuel it in the first part of the race. Another horse has been fed a classic low forage, very high grain diet, so it's got plenty of glycogen. It starts the race with plenty of glycogen because it's been fed heaps of grain.
[Nerida McGilchrist] 15:31:07
But its hindgut is going to be all but, um… it depends how much grain and how bad it is, but… and there's levels of this, but its hindgut is not going to be producing the same amount of acetate as the horse with the very healthy hindgut, and so it will be more reliant on muscle glycogen at.
[Nerida McGilchrist] 15:31:25
The start of that race, so if you imagine the horse with the healthy hindgut gets most of the way through the race still with all of its muscle glycogen or a majority of its muscle glycogen on board, the other horse has had to start using that glycogen almost as soon as the race started.
[Nerida McGilchrist] 15:31:41
So when you start to burn through three litres of fuel per minute in the car analogy, you're always going to be able to sustain that effort for longer when you've been able to conserve the glycogen that you do have on board for longer. And if you've still got most of your glycogen towards the end of the race because you've been able to fuel that horse with volatile fatty acids.
[Nerida McGilchrist] 15:32:06
then that horse is going to do a lot better. And you can see these horses, they get all the way through a majority of a race, and then the jockey or the driver says go, and they just go. And they do it, they make it look easy when they do it. And I love, it's so much fun to watch horses when they're racing like that. But it really, really comes down to making sure that.
[Nerida McGilchrist] 15:32:33
that both of their fuel tanks are functioning. So, like I said, the traditional diets and the, you know, the old recommendation of not very much forage and lots of grain.
[Nerida McGilchrist] 15:32:46
Feeding that way does give you lots of muscle glycogen, but it really compromises the high gut fuel tank, and then you start to burn your muscle glycogen a lot earlier, and you don't get nearly that…
[Nerida McGilchrist] 15:33:02
glycogen-sparing effect of a healthy hindgut, and you don't have as much to fuel the final sprint to the finish.
[Nerida McGilchrist] 15:33:37
So, it's been fascinating for me over the last few years working closely with Kirima Racing, and watching them sort of transition their feeding towards feeding more forage and less grain, and more digestible grain. And we do talk about it in detail, if you want to have a listen.
[Nerida McGilchrist] 15:33:55
to, you know, the process of going through that change with them. I think it's back on episode 25, or somewhere around there on the Happy Horse Nutrition podcast. But what's, um, so cool.
[Nerida McGilchrist] 15:34:08
about working with a stable of that size is that you get so much data, and we have been measuring faecal pHs with those racehorses over years now, and there's a paper that we have submitted to the ICIP conference, which is in Tokyo in October, next month.
[Nerida McGilchrist] 15:34:29
which is the International Congress on Equine Exercise Physiology. And one of the papers that we submitted is looking at grain processing and starch load in a diet and how that changed faecal pH and also performance in racehorses.
[Nerida McGilchrist] 15:34:46
And the really cool thing is we can see that when a horse has got…
[Nerida McGilchrist] 15:34:53
too low a pH, so too much acid in their hindgut, which is indicative of too much starch going into the hindgut. We can see that they… so if the pH was less than 6.
[Nerida McGilchrist] 15:35:03
Those horses would race less times throughout a preparation and were also 14% less likely to finish in the top 3 placings of a race, so this is indicative of a horse that is being fed either too much grain or grain that has starch that is reasonably indigestible, and a lot of that starch was getting dumped in the hindgut and then being rapidly fermented to acids, so more propionate and lactic acid as well.
[Nerida McGilchrist] 15:35:32
Um, and compromising the hindgut. So if we go below pH 6.2, that's when we start to negatively affect our poor little fiber-fermenting microbes, um, and start to really negatively affect the hindgut.
[Nerida McGilchrist] 15:35:46
The other interesting bit of data is that if a horse's pH was above 6.5, their performance also suffered. So there's this sweet spot between 6.2 and 6.5, where we've got a healthy hindgut.
[Nerida McGilchrist] 15:36:01
But we've also got plenty of fuel in the hindgut to fuel performance, so when the pH is higher than 6.5, it's indicative of less volatile fatty acid, less muscle fuel in the hindgut, and horses were not performing as well when they had those.
[Nerida McGilchrist] 15:36:20
higher pHs either. So it's just…
[Nerida McGilchrist] 15:36:25
it's just really, sort of, um, stamped for me that the hindgut is so important when we feed performance horses. And in fact, for a lot of performance horses, so outside of thoroughbred racehorses.
[Nerida McGilchrist] 15:36:38
Even for standard bred racehorses to a large extent because their muscle types are different and the speed of work is quite different, we can get away with feeding so little grain to a lot of performance horses, and the less grain in a performance horse's diet, the more chance you've got of being able to keep the hindgut healthy. And then when you can keep the hindgut healthy, everything works better because the hindgut and its microbes are so tied up with immune function and gut-brain axis communication.
[Nerida McGilchrist] 15:37:07
There's also gut-lung axis and there's a gut-bone axis. They're integrated pretty much into every aspect of a horse's health. So thoroughbred racehorses are the exception for me. They need a little bit more grain than every other performance horse that I work with.
[Nerida McGilchrist] 15:37:27
you can get away with less grain in a lot of performance horses' diets. And it's useful to remember, too, that the muscle glycogen fuel tank has a limit. So, once you feed enough grain and provide enough starch that gets broken down into glucose.
[Nerida McGilchrist] 15:37:45
and goes in to replenish muscle glycogen stores, you can't really push that system anymore. So feeding more grain, I mean, they'll still use the energy, they'll convert it and store it as fat, and some of it will inevitably flow into the hindgut, and it does get turned into volatile fatty acids, and they can use it, but it's not without doing damage to the hindgut when you feed too much.
[Nerida McGilchrist] 15:38:08
So you have to find that sweet spot of enough grain to fuel their performance, but not so much that you're going to start compromising your hindgut fuel tank. So you just, you need to find that balance depending on the horse and the type of work it's doing and the type of forage you're feeding. So obviously the higher the energy forage.
[Nerida McGilchrist] 15:38:32
you can feed, the less reliant you will be on starch. But I guess the key point to all of this is that.
[Nerida McGilchrist] 15:38:39
we've been so fixated on grain for performance horses for so long that we've kind of missed that the hindgut is actually really capable of providing a whole lot of forage, sorry, a whole lot of energy to performance horses, including thoroughbred racehorses. So, lots of horses that I've watched win big races over the last few years.
[Nerida McGilchrist] 15:39:06
have been on, like, around 4 to 5, um, no more than 5 kilograms for a 500 kilogram horse per day, which is a lot less than what has traditionally been fed. Um, and, and in fact, another, another paper that has been submitted, not to steal all of ICEP's thunder, but, um, and we'll give you a proper wrap-up on those papers after the conference, but it's showing that if you, if you go over that, you know, um, kilo per 100 kilos of body weight, you actually start to.
[Nerida McGilchrist] 15:39:35
negatively affect performance, which ties in beautifully with the faecal pH data and showing that if you drop faecal pH too low, then you do negatively affect performance. So, I hope all of that makes sense. Um, the really key takeaways are feed lots of forage to performance horses. They need it, and it's such an important, um, source of fuel for them, and, you know, think about it like you've just got, in fact, going back to the, to our race car analogy.
[Nerida McGilchrist] 15:40:05
The volatile fatty acids are kind of like having a fuel tanker hooked up to your V8 supercar and following it around the track, or somehow having some magical cord between a supercar and a fuel tanker. It's just this constant supply of energy that is flowing.
[Nerida McGilchrist] 15:40:26
the whole time. So if you keep that hindgut healthy, it is pumping energy out to those nozzles, and those horses are burning it. And it's funny for me watching races, because, you know, I know the horses that I work with, and I know that their hindguts are hopefully in pretty good shape, and that, you know, for the early parts of races, that that's the fuel.
[Nerida McGilchrist] 15:40:46
that they're actually racing on. And then you can see that at the end of the race when they kick up a few gears and you know that they've got so much muscle glycogen on board. So feed lots of high quality forage. Do feed as much as you can fibre diversity. So feed multiple different types of hay. Go back and have a listen to episode 68 because we do talk about that quite a lot in that episode.
[Nerida McGilchrist] 15:41:10
And then feed grain when you need to, but make sure you feed digestible grain, so grain that has been properly cooked, um, and… or oats, so oats is okay to feed without processing, although there is some research that shows very clearly that as soon as you feed oats.
[Nerida McGilchrist] 15:41:28
It does actually shift the microbiome, but it's a lot safer and a lot more digestible than every other cereal grain and can be fed unprocessed to horses. And it is a really nice source of starch. And also it has got quite a lot of fibre and oil, so it's providing these fatty acids and volatile fatty acids as well to fuel performance. So always, always think with a performance horse about both of their fuel tanks. Look after their hindgut.
[Nerida McGilchrist] 15:41:57
And also feed them whatever they need to top up their muscle glycogen. And that varies. I mean, lots of performance horses you can get away with very, very little grain. And I know successful Aventus and even some successful harness racing horses that have won at very high levels on almost no grain because we can use predominantly the hindgut to fuel those horses.
[Nerida McGilchrist] 15:42:24
So I hope that gives you some food for thought.
[Nerida McGilchrist] 15:42:29
do… there's… there's lots of ways you can… you can monitor hindgut health, and I think if you go back, there is a…
[Nerida McGilchrist] 15:42:36
at My Happy Horse… sorry, I'm confusing. We've got My Happy Horse, the nutrition software, and we have Happy Horse Nutrition Podcast, and occasionally I blend them together. Um, if you go back and listen to the Happy Horse Nutrition Podcast, it's around episode 9 or 10, somewhere around there. There's… there's ways of measuring.
[Nerida McGilchrist] 15:42:56
Hindgut health. So I've mentioned faecal pH a couple of times during this episode. That's definitely a good one to measure. And you're looking for racehorses, you're looking for that faecal pH between 6.2 and 6.5 and manure scoring and various other things. But there is a whole episode way back.
[Nerida McGilchrist] 15:43:16
Now, but, um, a whole episode on monitoring hindgut health.
[Nerida McGilchrist] 15:43:22
Uh, I would absolutely love for you, if you found this episode useful or just fascinating, would love for you to follow us. Um, it really does help us get found on whatever podcast platform you use, and if you have 10 seconds, um, please do give us a rating as well.
[Nerida McGilchrist] 15:43:42
And if you know anyone with a performance horse, please share this episode with them. It helps to, yeah, just starting to create, and I am seeing it shift, but it just starts to create a shift around the way we feed performance horses, and particularly the way we feed racehorses, and feeding them these higher forage, lower grain diets.
[Nerida McGilchrist] 15:44:03
is so much better for their welfare. So, it gives you better performance, and in this beautiful, um, double benefit, it is also so much better for their welfare. So, two, please share this episode.
[Nerida McGilchrist] 15:44:14
And with that, I will say thank you very much for being here, and I will catch you in the next episode.
