Magnesium Oxide for Horses

Magnesium oxide. It’s one of those ingredients people love to disagree over, should we use it, shouldn’t we use it, is it bioavailable or not for horses??

Part of this contention is due to the fact that magnesium oxide is a created ingredient… it is cooked in a process called calcination, that reacts magnesite with oxygen to create magnesium oxide.

Like all things, it can be made well, or it can be made poorly, and this then impacts on whether it will be bioavailable or not. So it’s not like limestone (calcium carbonate) that is mined for example and is generally always the same.

So when reading about magnesium oxide for horses, keep in mind that most studies do not report the conditions under which it was manufactured OR its final particle size, both of which have a huge impact on final bioavailability.

I still believe that quality magnesium oxide is a very useful source of magnesium for horses, but then I am very fussy when it comes to where it comes from and how it is produced!

We have information on various sources of magnesium for anyone who would like to read some more here:

And for anyone who loves details, this is a now old but still informative paper on this subject (Beede et al 1992). It is a Dairy paper but talks in detail about factors affecting magnesium oxide bioavailability.


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Too Much Salt Might Be Killing Gut Bacteria

The last two weeks has seen extreme weather conditions for us in my local area in Australia. In the last 14 days, 7 days have been 40 degrees celsius or higher (104 F +) and of the other 7 days only one was below 37 degrees C (99 F). To make things worse, the nights will not cool down, with most nights remaining over 20 degrees C (68 F) and a couple of nights being 26 + degrees C (79 F). On more than one occasion I have checked temperatures between midnight and 3 am and it has been 30 degrees or more in the middle of the night! It is HOT!!!

My horses are crusted in salt from continuous sweating. I took pity on them today and instead of having them out grazing with muzzles on they have hay in their hay pillows so they can at least stay in the shade.

But back to salt. I normally just let my horses eat salt free choice. Their balancer pellet gives them about 5 grams of salt per day and the rest of what they need they eat as loose rock salt.

BUT, the last couple of weeks I have been adding it to their feeds so I know they are getting enough to keep sweating. If horses run low on sodium or chloride they can’t sweat, and that, in these conditions is life-threateningly dangerous.

There is a trend at the moment though for people to add large amounts of salt to their horse’s daily feeds, despite actual requirements or what may be coming from the rest of their diet. Blanket recommendations like ‘add 10 grams of salt per 100 kg of bodyweight’ seem to be commonplace, yet don’t seem to take into account a horse’s specific situation.

Take Poet’s diet for example, shown in the graph below. If I add 10 g/100 kg of BW to his diet his sodium intake is well over 200% of what he needs. In these extreme conditions this may well be accurate, but once it cools off a little this is way more sodium than he needs.

While I was out just now giving them hay I had the thought ‘I wonder what this excessive salt might be doing to the bacteria in their gut’?? Salt is, after all one of the best known and most widely used anti-bacterial agents in the world.

So I did a little research… and while not much came up, there is a recent paper, published in ‘Nature’ (i.e. one of the most reputable journals in the world, so we can trust it) showing that in both mice and men adding more salt than normal to a diet affected the gut bacterial populations, in some cases it entirely wiped out certain strains of bacteria! Eek!

What is really interesting (from a human perspective) is that the researchers were then able to link those shifts in gut bacteria to high blood pressure, which may help to explain (the as yet poorly understood) link between high salt diets and hypertension.

Back to your horses though… feeding excessive salt is unlikely to have any benefit and may be negatively affecting the good bacteria in your horse’s gut. So when using FeedXL, just meet your horse’s requirement for sodium with salt that is added to the diet. Then leave free choice salt (preferably as easy to eat loose rock salt) out so they can top up any extra requirement they may have.

The paper is here if anyone would like to read it in more detail:

Questions? Comments?

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Iron for Horses: Could Forage Be Enough?

Comparison of equine dietary iron requirements to iron concentrations of 5,837 hay samples

N. Richards and B.D. Nielsen, 2018


Iron is essential for the production of red blood cells. According to the 2007 Horse NRC, Fe requirements are 50 ppm for growing foals, lactating and pregnant mares, and 40 ppm for all other classes of horses. The 2005 NRC suggested a maximum tolerable Fe concentration of 500 ppm using data from other species. It is claimed that excess dietary Fe is causative of horses becoming insulin resistant.

Athletic horses, and particularly those in Thoroughbred racing, are often supplemented with Fe in an attempt to improve performance. Supplementation is commonly carried out without any formal analysis of the diet to determine if additional iron is required. Forages are typically high in iron and supply a majority of iron in all equine diets.

This study looks at the iron concentration in forages typically fed to equines and whether iron from forage is enough to meet the iron requirement of an athletic horse.


Nutrient concentrations from hay samples submitted for analysis in 2017 and for which Fe was measured were obtained from Equi-Analytical, representing 3,060 grass, 1,193 legume, and 1,584 mixed hay samples.

Iron concentration was measured using inductively-coupled plasma mass spectrometry (ICP). Analysis methodology is available from Statistical analysis was performed using Proc MEANS of SAS.


Iron was highest in Legume and Mixed Mainly Legume Hays and lowest in Grass Hay (Table 1). All hay types had a mean iron concentration more than five times that required by athletic horses and a median iron concentration more than three times.

From all hay samples (n = 5,837), 707 contained Fe at or above the suggested tolerable threshold of 500 ppm, while only 81 contained Fe at less than 50 ppm. Further, only 15 contained Fe at less than 40 ppm.


A 500 kg horse in heavy work has an iron requirement of 500 mg/day (NRC 2007; based on a daily feed intake of 2.5% bodyweight and a requirement of 40 ppm). Forage intake is often restricted by Thoroughbred trainers. But even when fed at 1% of bodyweight to a 500 kg horse, these hays will supply an average 1,060 mg to 2,230 mg of iron per day, supplying more than 200% of daily iron requirements in the forage component of the diet alone.

Fortified grain concentrates are fed at an average 2.5 kg/horse per day in Australian Thoroughbred racing stables (Richards 2003). These concentrates have an average iron concentration of 190 ppm (, adding an additional 475 mg/day of iron to the diet of these horses. Almost 60% of Australian Thoroughbred trainers then add an iron supplement to their horses’ diets (Richards 2003). It is expected similar trends would be found in the USA.

Based on this broad diet analysis, forage is able to meet the daily iron requirement of athletic horses. When iron from fortified feeds and supplements is added, there would be few racehorses receiving less than 300% of their daily iron requirement. It’s not unexpected that many horses would be receiving in excess of 500% of their daily iron requirement

What About Insulin Resistance

Given the dearth of Thoroughbred racehorses that are insulin resistant, despite Fe supplementation in combination with diets that can easily supply amounts beyond requirements, it seems unlikely excess Fe causes insulin resistance. However, it is recognized insulin resistant horses may have elevated serum ferritin.


Council NR. Nutrient Requirements of Horses: Sixth Revised Edition. Washington, DC: The National Academies Press, 2007.

Richards N, Hinch G, Rowe J. The effect of current grain feeding practices on hindgut starch fermentation and acidosis in the Australian racing Thoroughbred. Aust Vet J 2006;84:402-407.

FeedXL Nutrition Software,, 2018.

HUGE THANKS to Equi-Analytical for providing the data to write this paper, which was presented as a poster at the recent International Conference on Equine Exercise Physiology (ICEEP).

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Vitamin C for Horses?

Did you know Vitamin C is not an essential nutrient in your horse’s diet? Unlike we humans, who will get scurvy and die if we don’t eat vitamin C, horses make their own vitamin C in their liver! Clever right!!

There are some situations, like when a horse is very ill, really stressed or has liver damage where supplementing with vitamin C may be useful. Just be mindful that when you want to stop supplementing you should remove the vitamin C from the diet gradually so the horse has a chance to ramp its own production up again.

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Diet Lacking in Vitamin E?

We are frequently asked about how to add Vitamin E to a horse’s diet when all other nutrient requirements are being met. Vitamin E is abundant in fresh green forages and many horses will meet their daily requirement of Vitamin E with adequate intake of good quality pasture. Vitamin E declines over time in stored feeds including preserved forages. Most commercial pre-mix feeds and vitamin & mineral supplements account for this and are formulated with supplementary Vitamin E.

At times when pasture is average or poor quality, overgrazed or simply not available, diets which previously had adequate Vitamin E may become low as a result. Sometimes even with a good quality pre-mix feed or vitamin & mineral supplement, the Vitamin E levels may still not be adequate within the diet.

Additional vitamin E can be safely added to diets and can be found in FeedXL’s blue ‘Balancers & Supplements’ tab under ‘Antioxidants’. Antioxidant supplements commonly contain both selenium and vitamin E. Unless the diet requires additional selenium, look for supplements which contribute only vitamin E to your horse’s diet.

To find vitamin E only supplements, click on ‘Complete Data’ which is located below the ingredient name when editing diets or browsing ingredients and FeedXL will show you which nutrients that product contains. (See the image in this post).

Another consideration when choosing a suitable Vitamin E supplement is the form of Vitamin E to supplement with. Natural vitamin E is reported to be more effective in raising plasma  Vitamin E concentrations when compared with a synthetic source. To know which is which you will need to read the manufacturer supplied information for each product on their website or product labels.

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Vitamin B6 for Horses

This little vitamin is not talked about much in equine nutrition, mainly because we still don’t know exactly what a horse’s dietary requirement is. We also assume a large part of their requirement is fulfilled by the Vitamin B6 produced by the bacteria in their hindgut.

We do know B6 is important for building muscle. I just saw a very recently published paper looking at Vitamin B6 supplementation and muscle development in rabbits. (…)

I know a rabbit is very different animal to a horse, but from a gut physiology and nutrition perspective they are actually really similar, so I thought I would take a look to see what the researchers found.

Vitamin B6 supplementation was shown to significantly alter protein metabolism and increase the ratio of fore + hindleg muscle weight to body weight (i.e. supplemented rabbits had more leg muscle). Interesting!

We do track B6 intake in our Pro FeedXL plans … this just reinforces to me though how important a horse’s base diet is when it comes to achieving specific outcomes. For example, if you are wanting your horse to build muscle but you aren’t meeting basic nutrient requirements (like vitamin B6) you could add all the fancy muscle building supplements you like to the diet and they won’t help!

You can’t build muscle unless you get your basics right first! Here at FeedXL, we can help you with that! Take a look at our plans and pricing here.

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Find Supplements to Fix This Diet – It’s Here!!

‘Find supplements to fix this diet’ has (finally) made it to FeedXL Beta! We are just a bit excited about this as finally we have the beginning of a feature that will help so many of you answer the difficult question of ‘OK, so FeedXL has found a few gaps in my horse’s diet… what on earth do I add now to fill them?’

In its current state it is suggesting some very neat and useful diets, BUT it is pretty ugly, doesn’t do any sort of decimal place rounding, presents options to you in a boring spreadsheet format and can’t fix or provide options for all diets … think of it as seeing someone first thing in the morning right out of bed. Mostly functional but not so pretty to look at!

With time over the next few months we will brush FeedXL’s hair, give it a coffee and put on its day clothes so this new feature is more presentable. BUT, for now we really need you all to help us to refine the actual functionality… in particular to tell us about diets it is unable to give you any options for so we can make it a little bit smarter 

Have fun… and we take no responsibility for the possible addictive nature of this new feature!! 

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Chickpeas For Horses: Should They Be Cooked First?

There has been a little bit of discussion of late about chickpeas and whether they need to be cooked prior to being fed to horses. Big apology from me (Nerida) as it seems I have confused the issue and created some angst. So, to clear the waters I have muddied, here is some better information:

4 things to consider when feeding chickpeas to horses

  1. Chickpeas do contain anti-nutritional factors including trypsin inhibitor, which is the same as the main anti-nutritional factor found in soybeans. Trypsin inhibitor does exactly as its name suggests, it inhibits/stops trypsin, an enzyme in the small intestine which chops up protein into smaller pieces so it can be absorbed. Too much trypsin inhibitor in the gut can reduce protein digestion to such an extent that protein deficiency will become apparent. This doesn’t sound good for chickpeas!
  2. BUT, on reading about the amount of trypsin inhibitor in chickpeas it is much, much lower than soybean. I can find published values of 15 TUI (Trypsin Units Inhibited – reflects quantity of trypsin that has its activity inhibited) for chickpeas while values for soybean are more like 80 TUI. Reading papers and interpreting units is proving exceedingly difficult as it seems everyone likes to express their TUI units in slightly different ways so just be careful with this!
  3. Chickpeas have been fed raw to pigs at levels of up to 88% without affecting measured parameters to determine growth and feed conversion. A pretty good indication the anti-nutritional factors aren’t too anti-nutritional as growing pigs will show us very quickly if something is not right. This study did however find that adding additional methionine improved growth performance in chickpeas.
  4. Chickpeas are routinely used uncooked in pig diets in Australia at levels up to 20% of the diet without any ill effect. They typically aren’t fed to younger pigs less than 20 kg bodyweight.

Updates in FeedXL…

Based on all of this we have now updated our information in FeedXL to read:

Chickpeas are classified as a pulse, which is a seed from a leguminous plant. Chickpeas are rarely included in horse diets but can be fed as a protein and energy supplement in much the same way lupins or faba beans are used. The protein is of moderate to good quality with good concentrations of the essential amino acid lysine. They may however be too low in methionine for some classes of horses.

Like most pulses, chickpeas appear to contain some anti-nutritional factors including a trypsin inhibitor, which blocks the activity of the protein digesting trypsin enzyme in the gut and can negatively affect protein digestion. The anti-trypsin activity of chickpeas is however much lower than that of soybean, with chickpeas expected to ‘block’ around 15% of trypsin enzyme activity in the gut compared to more than 80% of trypsin activity being blocked when raw soybean is fed.

Chickpeas should therefore be safe to feed without any form of heat treatment to mature horses at levels of no more than 20% of their ‘hard feed’. If larger amounts were to be fed, heat treatment is recommended. Chickpeas would be best heat treated prior to feeding if being fed to horses younger than 12 months of age.

As always our information is quite conservative, but we prefer to play it safe with so many people using our service with so many varied scenarios.

I hope that helps everyone who has had a recent interest in the use of chickpeas in horse rations.

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Joint Supplements: Are They Beneficial?

Joint supplements! A lot of you use them, and while there is theoretical justification for their use there is still very little science that actual shows a proven benefit in feeding them.

A study just published does however lend some nice information in this area. It is both blinded (i.e. the people feeding the horses, the people assessing the horses for various measures of movement and levels of comfort don’t know if the horses was on the joint treatment or not at the time of assessment so it couldn’t influence what they ‘saw’ and recorded. And the author who analyzed the data was blind to which horse was on what treatment so they too could not be influenced) and is also a crossover study where each horse in the study was on both the joint treatment and the placebo and assessed on both so you could see changes in the same horse as opposed to changes between two different groups of horses where one group is treated and one group given a placebo.
This study also used ‘objective’ measurements of gait using high speed motion capture to assess movement of the hind legs at the trot.

The results are interesting, with significant improvements in lameness scores (less lameness in treated horses), less response to flexion tests and improvements in muscle tone reported (plus many other results).

The full paper is available here for full download for the next week or so (…/article/pii/S0737080616304749) for those of you interested in reading it.

A good time to remember too that not all joint supplements are created equally as far as the ingredients and amount of ingredient per dose they contain. The supplement used in this study was ‘FlexAbility’, from Science Supplements, UK; it contains chondroitin sulfate 162 g/kg, glucosamine 190 g/kg, vitamin C 80 g/kg, methyl sulfonyl methane 256 g/kg, docosahexaenoic acid 66 g/kg, eicosapentaenoic acid 34 g/kg For those of you who use FeedXL, if you look in the ‘Health’ tab in your results you will see a breadown there of the various joint nutrients and how much of each are in your horse’s diet when you use a joint supplement.

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Oil for Horses: Good or Bad?

Hard working horses have enormous requirements for energy that are traditionally filled using high grain rations fed together with chaff and hay. However, feeding large amounts of grain does come with its own set of issues which can include colic, hindgut acidosis, nervous or fiery behaviour, tying up and loss of appetite. Oil has gained popularity in recent years as a substitute source of energy for working horses, but is it effective, how much can be fed, are all oils equal in the benefits they can provide and do they cause any health issues of their own?

A little bit goes a long way

The biggest benefit oils provide working horses is their very high energy content relative to grains. Oils contain nearly 3 times more energy than oats, with 400 mls of vegetable oil providing as much energy as 1 kg of oats. The real benefit in this is you can reduce the size and sheer bulk of feed a horse has to consume without reducing calorie intake, allowing you to get enough ‘feed’ into horses with poor appetites. The end result being these horses can hold their weight and continue to train and compete for longer than they otherwise would on a more traditional diet.

Reducing heat load

Oils generate less heat during the digestive and metabolic processes than an equivalent amount of grain or forage. Feeding oil also means that you can feed less grain and still meet energy requirements. Combined, this means that high oil diets place less of a heat load on working horses, reducing electrolyte losses and the amount they need to sweat to stay cool, a big bonus for hard working horses, especially those training and racing in hot environments or working over very long distances.

Saving glycogen

Fatty acids from oils are the preferred fuel for muscles during slow and medium pace work while glycogen is the only source of energy a muscle can use during sprints and strenuous exercise. Once a horse runs out of glycogen its muscles fatigue and the horse will slow down and lose the ability to perform at the level it is capable of. Feeding oil in diets provides a source of fatty acids for muscles to burn during the warm up and slower phases of a competition, meaning muscles are able to conserve valuable glycogen and avoid fatigue.

Problem solving

‘Problem horses’ and particularly those that tie up or get excited and nervous on high grain diets will often benefit from rations that provide a portion of the dietary energy from oils. It is thought that the positive effects seen in these horses on high oil diets is due more to the reduction in grain intake as opposed to the addition of oil, but using oil in the diet allows you to reduce grain intake without compromising energy intake and performance.

Oils aint oils

All oils contain virtually the same amount of digestible energy, but there are other differences you may want to consider when looking to purchase an oil, including:

Essential Fatty Acid Content: Horses need omega 3 and omega 6 fatty acids in their diet. Grains are naturally high in Omega 6, so for horses on a high grain diet, it is preferable to choose an oil with some omega 3 content. The table below shows the amount of omega 3 and omega 6 in some commonly used oils. Linseed and canola oil contains the highest omega 3 fatty acid content of the natural vegetable oils.

Ingredient Name Omega 3 (%) Omega 6 (%)
Linseed (Flax) Oil 57 13.9
Cod Liver Oil 25 2
Canola Oil 10 20
Soybean Oil 7 52
 Corn Oil  1  55
 Olive Oil  1  11
 Rice Bran Oil  1  39
 Sunflower Oil  0.3  60
 Coconut Oil  0.1  2

Some linseed oils and fish oil including cod liver oil are notoriously unpalatable for horses, so while these oils are useful for providing omega 3 fatty acids, they can’t be fed in large amounts as most horses simply won’t eat them.

Processing Method: Oil is extracted from oilseeds in two main ways; cold pressing where oil is squeezed out of seeds, often in a water cooled environment to keep the oil at less than 60C; and solvent extraction where a solvent like hexane is added to extract oil from seeds. The oil is then heated to remove the hexane. Cold pressed oils tend to be higher in quality as more of their essential fatty acids and natural antioxidants are left intact in comparison to solvent extracted oils.

It takes time

Horses need time to adapt to digesting and metabolising oils. Oils should always be introduced into a diet slowly, starting with ¼ cup of oil per day and increasing this by ¼ cup every 5 days until you reach the full amount you want to feed. Introducing oil into a diet too quickly can result in soft manure and reduced fibre fermentation in the hindgut.
It will take a minimum of 3 weeks before a horse starts to really benefit from the oil in its diet and it could take up to 3 months before the full benefits of oil are realised.

How much can you feed?

Horses can be fed up to 20% of their total energy intake as oil, which in real terms means just over 3 cups of oil per day for a 500 kg horse in full work. While this level of oil is useful for horses that tie up, very few horses are fed this much oil per day. Feeding between 1 and 2 cups of oil per day is enough to give horses the benefits discussed above without making diets messy, unpalatable or unnecessarily expensive.

Good Stuff

Oils are ‘good stuff’ for working horses. They reduce reliance on grains, make the amount of feed a horse needs to eat smaller, keep horses cooler, allow horses to conserve muscle fuel for sprinting, give horses that tie up a safer and more effective source of energy and provide essential fatty acids in the diet.

For the best results, introduce oils slowly into the diet and select oils based on the following: their omega fatty acid content with oils containing some omega 3 fatty acids preferred; palatability, be aware that some oils including linseed and fish oils can be unpalatable; and method of processing, with cold pressed oils preferred over solvent extracted oils.


Dr. Nerida Richards is FeedXL’s resident equine nutrition specialist. With a degree in Rural Science, a doctorate degree in equine nutrition and nearly 20 years of full time, on the ground experience in feeding all types of horses Nerida is able to help FeedXL members solve any problem they may come up against with feeding their horses. To learn more about Nerida and to ‘meet’ the rest of the FeedXL team, check out our About Us page here.


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