Water-soluble carbohydrates (WSC) or Ethanol-soluble carbohydrates, that is the question
There is ongoing debate within the equine community regarding whether water-soluble carbohydrates (WSC) or ethanol soluble carbohydrates (ESC) hold greater significance when evaluating the safety of forages and feeds for horses prone to laminitis. When discussing or calculating non-structural carbohydrates (NSC) in a diet, FeedXL opts for the inclusion of (WSC) along with starch to determine NSC.
Here’s the rationale behind this choice. WSC encompasses simple sugars as well as fructans, whereas ESC solely represents the measurement of simple sugars. Previously, it was believed that hindgut acidosis, resulting from fructan fermentation, was the primary cause of pasture-associated laminitis, similar to the effect of starch in grain overload. However, through research, it has been discovered that sustained high insulin levels are responsible for pasture-associated laminitis. Nevertheless, can we conclude that the absorption of simple sugars, as measured by ESC, is solely responsible for the insulin response? While simple sugars directly impact insulin levels, there are two potential ways in which fructans could also influence the insulin response.
Firstly, fructans are carbohydrates with varying chain lengths, consisting of fructose sugar molecules joined together with a glucose molecule at the end. Although most of these fructose bonds are not broken down by a horse’s enzymes, it is believed that some fructans, particularly the shorter chain ones, may undergo acid hydrolysis in the stomach or microbial fermentation in the small intestine. This process produces simple sugars, namely fructose and glucose, which can be absorbed by the horse and contribute to an insulin response.
Secondly, undigested fructans pass into the hindgut, where they undergo rapid fermentation. This fermentation leads to a significant increase in bacteria that preferentially ferment fructans, resulting in the production of lactic acid. The change in hindgut environment, becoming more acidic, causes a shift in microbial populations and reduces the diversity of microbes, including the desirable fiber-fermenting ones. While research in this area is still in its early stages, it is plausible that hindgut microbes can influence the insulin response, similar to humans.
The FeedXL Difference
Using ESC to calculate NSC may underestimate NSC and ignore fructans, potentially putting your horse at risk.
Hence, FeedXL recommends and uses the more conservative approach by considering WSC when examining the NSC component of forages (NSC = WSC + Starch). This approach is more conservative because WSC values are consistently higher than ESC values and still aligns with the principle of minimizing insulin spikes by limiting dietary simple sugars. Additionally, by maintaining low fructan levels in the diet, the negative impact on hindgut microbial populations caused by fructan fermentation is minimized, indirectly influencing the insulin response.
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We all know that forage should be a key component of your horse’s diet, but not all pasture is created equally. With pasture sometimes forming the majority, if not all, of our horse’s diets, it’s important to enter pasture quality as accurately as you can in FeedXL.
Pasture quality corresponds with the amount of digestible energy, crude protein, macro minerals and vitamins your pasture is providing. Therefore, pasture quality determines what else you may (or may not) need to supply in your horse’s diet to meet their nutritional requirements.
We like to keep it simple when it comes to deciding pasture quality – by looking at colour and presence or absence of seed heads (this is basically the stage of maturity of your grass). Be sure to note that when pasture is overgrazed (less than 1 inch in height), it’s unlikely you’ll see any seed heads, therefore colour is your major guide.
So, next time you’re entering your pasture use the definitions and images below to help you determine quality.
Pasture Quality
Overgrazed
Excellent
Green
Actively growing
Very leafy
Virtually no flowers or seed heads visible
Good
Green
May or may not be actively growing
Flowers and/or seed heads are present
Plants are beginning to mature and become stemmy
Average
Green to yellow or brown
Most plants are stemmy and/or have visible flowers and/or seed heads present
Poor
Completely brown
Plants are stemmy and/or have visible seed heads present
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Grazing muzzles are useful for reducing your horse’s pasture intake. They can be used for easy-keepers when you are trying to reduce energy levels within the diet. Or when your horse suffers from a health condition which requires a reduction of non-structural carbohydrates (starch + sugar) in their diet. Grazing muzzles have gained popularity with many horse owners as they allow their horse to socialise, exercise and be continually stimulated through grazing.
Studies have shown grazing muzzles can reduce forage intake by as much as 80%. There are many factors which affect intake including acclimatization to the muzzle, pasture height and type of muzzle used and your individual horse’s tenacity when it comes to getting grass to poke through the hole.
To enter pasture intake in FeedXL when your horse is wearing a grazing muzzle, subtract up to 80% from the time your horse spends grazing. For example, if your horse is allowed to graze muzzled for 15 hours and is dry-lotted the remainder of the time, you might enter ‘3 hours’ as the amount of time your horse ‘grazes’ into FeedXL (80% of 15 is 12 hours; 15 x 0.8 = 12 hours: 15 – 12 = 3 hours of ‘grazing time’.
Observe your horse grazing pasture while muzzled and watching his body condition over time. This will allow you to get a better estimate of actual intake by your horse. You may find that reducing the ‘time’ grazing in FeedXL by 80% is too much, so adjust it as you see fit.
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This is something we often hear… and 99% of the time it is WRONG!
Forages are (almost) always too low in trace minerals to meet a horse’s requirements and leaving them un-supplemented on forage only diets usually results in problems with their hooves, joints, immune system, muscles … everything really!
They may look OK, but there is usually a bunch of stuff going on inside that you can’t see until a deficiency is quite pronounced.
BUT, there are always exceptions to the rule and here is one example. This is a pasture from New Zealand that is able to meet all trace mineral requirements without any additional supplementation.
Even for selenium, which is something we don’t expect in New Zealand!
Sodium is a bit low (nothing unusual there) and iodine was not tested, but the fact is it is actually a pasture that horses would do OK on without extra supplementation. Just need a bit of iodised salt!
The horses on this pasture were being fed a selenium-containing balancer pellet and recently tested with blood selenium levels just in the high range (nothing scary, just high).
The lesson in this, forage analysis is a wonderful tool when assessing your horse’s diet and FeedXL makes it so super easy to really see what forage is providing and what you need to add, which in this case is very little.
If you’d like to have your forage tested, we love to recommend Equi-Analytical.
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Have you ever got the results back from a pasture or hay analysis and been left scratching your head trying to figure out what the numbers mean? Frustrating isn’t it!?
That is unless you have a tool (like FeedXL) to interpret the numbers for you.
The analysis below shows the analysis result numbers a pasture, but they are kind of meaningless unless we look at them in terms of how much of that pasture a horse eats and how much nutrient is provided compared to the amount of nutrient the horse actually needs.
Take phosphorus for example, the pasture contains 1.45 g/kg of phosphorus, which is only enough to meet 39% of a late pregnant (month 11) mare’s requirement if she was given full time access to this pasture.
This pasture is native pasture, and the soils are low in phosphorus, so the pasture is lower in phosphorus than most pastures. BUT point is 1.45 g/kg of phosphorus was only a number until we put it in terms of what our late pregnant mare needs each day to meet her requirement.
You will also see from the diet readout from FeedXL below that the pasture only diet (bar graph with the green and red bars) is not meeting requirements for multiple other nutrients for this late pregnant mare, which also would have been difficult to determine just from reading the analysis numbers alone.
So with FeedXL we can see what is not in your pasture that your horse needs. You can then also add other feed ingredients to the diet to meet those requirements.
The second bar graph with the green and blue bars shows a diet for a late pregnant mare on this pasture. The diet uses 2 kg of prime lucerne hay (shown in the darker green) and 3 kg of a commercial broodmare feed (shown in the blue). All requirements are now nicely met!
Pasture analysis made that bit more useful! Using FeedXL to assess your forage analysis also means you will only supplement with the nutrients you need to add, potentially saving yourself a lot of money by not adding unnecessary products and nutrients.
You can upload as many pasture and hay analyses as you like into your FeedXL account, just click the ‘Add my own forage’ link in the Create Forage section of the diet wizard, or directly from the Feeds list (see below). Click here to log in and give it a try!
If you’d like some help finding a forage analysis lab, you can click here to download our free ‘Lab List’ with laboratories in Australia, New Zealand, United States, Canada and the UK.
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Grazing muzzles are a really, really useful tool. A muzzle means horses can be out grazing 23+ hours per day. Without them they would be strip grazed (trashing pastures in the process) or locked up for extended periods, which for gut and mental health is not ideal either.
But they come with their challenges. They can rub if they don’t fit properly. If you don’t have one that your horse is OK with, they can create behavioral issues (rearing while trying to put them on or being impossible to catch to put them on) and certain brands can be too hot to wear in hot climates.
And of course, there is always that unknown of how long you should leave one on in your particular muzzle+horse+pasture combination (which can cause a bit of angst for a while until you get it figured out!).
The other thing you need to be really aware of is how they limit normal behavior. Horses love to groom one another, but with muzzles on all the time they can’t do this. So, make time to let them have muzzle free time together so they can do some mutual grooming.
Just something to keep in mind for those of you with muzzled horses.
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Setaria should really be classified as toxic for horses. It is a subtropical pasture with such high levels of oxalate that it makes it almost impossible to prevent Secondary Nutritional Hyperparathyroidism (Bighead disease) in horses grazing this grass.
Grasses like kikuyu and buffel grass readily cause bighead disease with an oxalate content of around 15 g/kg. Setaria contains anywhere between 30 and 80 grams of oxalate per kg of (90% dry matter) pasture… which translates to HUGE amounts of calcium being needed to balance the calcium to oxalate ratio to prevent bighead.
We have seen horses go from normal to severely affected in a matter of months on setaria. So if you have setaria in your pasture you need to be very aware of what you are feeding and how well this is meeting calcium (as well as phosphorus and magnesium) requirements.
FeedXL will help you in calculating the calcium to oxalate, calcium to phosphorus and calcium to magnesium ratios to keep your horse healthy. BUT, the first step is identifying that you have this grass in the first place so you know you need to be on your game with managing nutrition!
Here are some photos (below) of setaria on the NSW mid-north coast… setaria everywhere! Please take a look at the photos and then in your paddocks to see if you have setaria. And if you do, please do something sooner than later to prevent severe and often life-threatening calcium deficiency.
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There has been a lot of talk in recent years about the effect pasture mycotoxins are having on our horses and whether or not mycotoxin binders are an effective solution. While the extreme cases of staggers and pregnancy complications from grasses like perennial ryegrass and tall fescue are well documented it appears that pasture mycotoxins may be having more subtle effects on our horses that until recently have not been well recognised.
In an attempt to reduce the impact of the mycotoxins present in pastures many horse owners have been using mycotoxin binders. But do they work?
The problem with pastures
Some species of ryegrass and tall fescue are inoculated deliberately or infected with wild endophyte fungi. These fungi live within the plant in a symbiotic relationship where the plant provides the fungi with food and a place to live, and the fungi provide the plant with protection from insect and nematode attack by producing toxic chemicals or mycotoxins which cause a disease in some grazing animals called a mycotoxicosis. So, while the endophyte infected pastures are desirable from a pasture production perspective, the toxins they may contain can cause health problems for your horses. Horses grazing these pastures may exhibit some or all of the following clinical signs:
Reduced appetite
Weight loss or reduced growth rates
Inability to correctly regulate body temperature
Diarrhoea
Excitable, unpredictable, irritable or uncharacteristic behaviour
Over-reaction to common stimulus they would normally be OK with
Muscle twitching or twitching of the face, lips and eyelids
Prolonged pregnancy and thickened or retained placenta
Aborted or small, ‘undercooked’ foals
Dramatically reduced milk production by mares in early lactation
Loss of coordination, especially in the hind end, and staggering
Severe lameness
Bleached and/or rough coat
These possible symptoms are obviously very broad and many of them can be caused by any number of other factors, so you need to be very, very careful not to jump to conclusions and assume that the problems you are seeing in your horses are caused by mycotoxins in your pasture. if you have ruled out other possible causes and your horse is grazing a pasture that is potentially ‘poisoning’ them, then chances are what you are seeing is a mycotoxicosis.
Which mycotoxins are present in pasture?
Potentially, there could be any number of mycotoxins in your pasture as common moulds or fungi like Aspergillus, Fusarium and Penicillium can produce mycotoxins when growing on pasture. However, the mycotoxins most likely present in perennial ryegrass and tall fescue pastures that will cause issues are ergovaline and lolitrem B.
What are mycotoxin binders?
A mycotoxin binder is a compound that can be added to a horse’s ration in an attempt to grab hold of a mycotoxin that may be present in feed or pasture, binding it strongly enough to prevent absorption from the gut of the animal.
There are many materials that can be used as mycotoxin binders including activated carbon, aluminosilicates like zeolite, cellulose, polysaccharides that are found in the cell walls of yeast and some bacteria (eg glucomannans) and even some synthetic materials.
Do all binders bind all mycotoxins?
In a word… NO! And this is where a major key lies to whether mycotoxin binders will work to prevent pasture associated mycotoxin poisoning or not. For example, it has been shown that glucomannan from the yeast Saccharomyces cerevisiae is very effective at binding aflatoxin (one of the most important and prevalent mycotoxins present in grain-based livestock feeds) and good ability to bind the fumonisin and zearalenone mycotoxins, but it is ineffective when it comes to binding other important mycotoxins like T-2 (trichothecene), DON (deoxynivalenol) and ochratoxin.
Why don’t all binders work on all mycotoxins?
One of the reasons some binders can bind some mycotoxins and not others is dependent on the mycotoxin itself and whether it is polar (possessing an electrical charge) or not. Aflatoxin for example is a polar mycotoxin and is very easily ‘picked up’ by a yeast derived glucomannan based binder (which are the most common mycotoxin binders on the market for horses). The pasture-based mycotoxins ergovaline and lolitrem B on the other hand are non-polar (no charge) so trying to pick them up with a yeast cell wall-based toxin binder is sort of like trying to pick up a piece of paper with a magnet … it just won’t work.
Where does that leave us with pasture mycotoxins and my horse?
Well… unfortunately there is very little research to show what may or may not work with regards to pasture toxins. None of the companies that manufacture or sell the yeast-based binders have (from what I can see) ever released data to show their products are effective against lolitrem B and ergovaline in any animal species, let alone horses. Research at the University of Melbourne is showing promising results with a new mycotoxin binder in reducing the impact of ergovaline and lolitrem B in sheep. This toxin binder as well as one or two others now on the market for the more common mycotoxins are a new type of ‘binder’ that combines the ability to bind mycotoxins with the ability to also break them down and deactivate them – presumably it is this double mode of action that is enabling them to be somewhat effective in reducing the impact of the endophyte toxins like ergovaline and lolitrem B.
What do you do now?
If you believe your horse is affected by pasture mycotoxins and you are using a mycotoxin binder, it would be a good idea to contact the company you are buying the binder from and asking them what the binder is and whether they have data to show it actually binds the endophyte mycotoxins affecting your horse. If it is a yeast-based binder it is unlikely to be reducing the effects of ergovaline and lolitrem B but you may still be seeing a positive effect if your other feed, hay or chaff is contaminated with one of the common mycotoxins that these yeast-based binders are good at binding.
Really the best way to reduce the impact of ergovaline and lolitrem B is to either remove the horses completely from the pasture, especially during late summer and autumn when endophyte mycotoxin levels are likely to peak. Alternatively, manage your pastures well by preventing both overgrazing and underutilisation of pasture (allowing pastures to go rank/long with many seed heads) so that the risk of ergovaline and lolitrem B ingestion is reduced. Providing mycotoxin free hay to reduce pasture intake will also help.
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As the seasons change so does the amount of pasture available to your horse. And as the amount of pasture changes, the other aspects of your horse’s feeding regimen also need to change. Failure to adjust your horse’s feeding regime correctly with changing seasons could result in an overweight, hyperactive horse or an underweight, tired mount. But is it as simple as just changing the amount of feed you are giving? We explore this in detail in the following article.
Controlling Energy
As the amount and quality of pasture changes in your paddocks, so does the amount of digestible energy (calories) available to your horse. During cold seasons like winter or periods of drought when very little pasture is available, performance horses often need to be provided with additional energy in the form of hay, haylage, chaff and/or pelleted, extruded or sweetfeed concentrates to ensure their daily energy requirements are met.
In the reverse, when large amounts of high-quality pasture is available, the pasture alone can often go close to meeting a performance horse’s requirement for energy. When these high-quality pastures are available, there is little to no need to feed additional hard feed. In the middle of those two extremes is a situation where either the quality or quantity of available pasture means additional hard feed or forages needs to be supplied to meet energy requirements.
The table below shows the energy deficit left in a working horse’s diet when excellent, fair or poor-quality pasture is the only feed provided in the diet. Excellent quality pasture is able to meet 100% of this horse’s energy requirement, while the poor-quality pasture leaves a 26 MJ/day energy deficit.
Pasture Conditions
Energy requirement for a 500 kg horse in moderate work
Amount of energy supplied by 24 hours access to pasture
Energy Deficit that needs to be filled with supplementary feed
Excellent
104 MJ
104 MJ
Nil
Fair
104 MJ
88 MJ
16 MJ
Poor
104 MJ
78 MJ
26 MJ
The key to knowing when to adjust the amount of feed you are feeding according to pasture conditions is regularly body condition scoring your horse to detect changes in body fatness and taking careful note of your horse’s behaviour (see FeedXL Newsletter #1). If your horse is starting to get too fat or is feeling full of itself, this may indicate you are feeding too much. If your horse is losing condition or feeling flat during work pasture quality may have dropped and you may need to feed more supplementary feed.
What about minerals?
While adjusting the amount of extra feed you provide may seem simple and is something a majority of horse owners do instinctively very well, there is a catch … you need to adjust what you are feeding to control energy intake WITHOUT unbalancing your horse’s diet from a vitamin and mineral perspective.
Let’s look at an example; A horse is grazing poor quality pasture and being supplemented with 2 kg/day (4.4 lb) of alfalfa/lucerne hay and 3 kg per day (6.6 lb) of a complete feed. As spring approaches and pasture conditions start to improve the horse starts to put on some weight so its owner (wisely) reduces the complete feed being fed from 3 kg/day to 1.5 kg/day (3.3 lb) and the horse’s weight stabilises. Once the warm weather arrives, the pastures improve to excellent quality and again the horse starts to put on some weight and feels a bit fresh in its work, so the complete feed and lucerne hay is now completely removed from the horse’s diet.
This feed reduction strategy is perfect with respect to controlling energy intake and is absolutely what should happen to avoid an overweight, hyperactive horse. However, simply reducing the amount of a complete feed in a horse’s diet leaves that horse wide open to mineral deficiencies, because in reducing the amount of complete feed in the diet to control energy intake, you are also going to reduce the amount of supplementary minerals in the diet and create some mineral deficiencies. The table below demonstrates how these mineral deficiencies develop as the amount of complete feed in the diet is reduced.
Energy
Copper
Zinc
Selenium
Iodine
% of recommended daily intake provided by the diet*
Poor quality pasture + 2 kg Lucerne Hay + 3 kg Complete Feed+
100%
129%
127%
110%
107%
Fair quality pasture + 2 kg Lucerne Hay + 1.5 kg Complete Feed+
100%
89%
108%
82%
73%
Excellent quality pasture only
100%
44%
73%
36%
29%
*RDIs from FeedXL.com +Well formulated commercial feed for performance horses
What is the solution?
Obviously continuing to feed the same amount of complete feed all year round to meet mineral requirements is not a feasible solution as while this will prevent mineral deficiency, it will oversupply energy requirements when pasture conditions are good, causing horses to get overweight and hyperactive. So, what should you do?
You need to learn to feed your horse seasonally. The best solution is to always have a complete feed and a compatible low dose mineral supplement or balancer pellet on hand so that as you reduce the amount of complete feed to control energy intake you can add some supplement or balancer pellet to meet mineral requirements without adding unwanted calories to the diet.
Let’s look at the diets above, this time with a balancer pellet added to meet mineral requirements:
Energy
Copper
Zinc
Selenium
Iodine
% of recommended daily intake provided by the diet*
Poor quality pasture + 2 kg Lucerne Hay + 3 kg Complete Feed
100%
129%
127%
110%
107%
Fair quality pasture + 2 kg Lucerne Hay + 1.5 kg Complete Feed + 200 g Balancer Pellet++
100%
116%
130%
106%
103%
Excellent quality pasture + 550 g Balancer Pellet++
100%
124%
153%
103%
111%
+ Well formulated commercial feed for performance horses ++Well formulated balancer pellet
Adding the balancer pellet at different rates according to pasture conditions and the amount of complete feed being fed means you can control energy intake without causing a mineral deficiency.
Of course, not all complete feeds and balancer pellets are created as equal, so use FeedXL (FeedXL.com) to work out which ones do actually meet all of your horse’s requirements. Also stick with products that fully disclose the nutrient analysis of the feed on the label so you can make informed choices on the best complete feeds and supplements to use for your horse.
Take Home Message
As seasons and pasture availability change, you also need to change what you feed your horse. In order to control your horse’s body condition and behaviour the amount of energy (calories) in the diet needs to be kept in check. To do this, the amount of supplementary feed you give will increase during times of poor quality pasture and in the reverse the amount you feed will need to be decreased when there is high quality pasture available.
However, in adjusting feed amounts up and down to match pasture conditions, be aware of the diet’s mineral balance because controlling energy intake by reducing the amount of complete feed you are giving may be inadvertently causing mineral deficiencies that will affect your horse’s health. Feeding a complete feed, together with specific amounts of a mineral supplement or balancer pellet will allow you to control energy intake whilst always meeting mineral requirements. FeedXL.com can help you to work out which products are best to use for your horse and will show you when you are or are not meeting mineral requirements as you adjust amounts of feed in the diet.
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As temperatures warm up heading into spring or cool down heading into autumn you will start to notice your pastures changing as temperature and moisture conditions change. In spring you will usually see a rapid growth of lush pasture while in autumn, depending on the climate you may see a flush of growth similar to that of spring in warmer climates, or you may simply get a slower growth of lush pasture in cooler areas with possible early frosting. While this new growth is usually a welcome sight and means horses are able to return to or remain out on pasture, this new growth pasture can present some unique problems for horses.
Spring and autumn are well known as ‘danger times’ for laminitis and it is not uncommon to find more horses with diarrhoea, behavioural problems and colic during these periods. So, what is it about pastures growing during these seasons that make them unique and how can they be managed?
Weight loss, diarrhoea, and colic
Lush spring and autumn pastures can contain as little as 15% dry matter meaning they are up to 85% water. Because of the extremely high water content of these pastures, horses need to graze for long periods and eat large amount of pasture to ingest their required amount of 90% dry matter feed. For example, a 500 kg horse grazing a 15% dry matter pasture would need to eat over 60 kg of this pasture in order to consume 10 kg of 90% dry matter feed (equivalent to 2% of bodyweight). If pasture quantity is low (for example your pasture is overgrazed) this is a major challenge for any horse and can result in horses doing poorly on lush new pastures, even though on a dry matter basis they are very high in digestible energy and crude protein.
There is also very little fibre present in pastures during these early growth stages. Fibre that remains undigested to some extent as it passes the whole way through the digestive tract is important for the normal functioning of the gastrointestinal tract and the formation of manure. Horses that are not given an additional source of fibre when on lush young grass may experience diarrhoea and are at a higher risk of colic associated with a low gut fill.
Young, lush pastures can be high in nitrates. Nitrate is irritating to the gut and one of the most common symptoms of high nitrate intake is diarrhoea that may also be associated with mild to severe colic.
Dehydration and respiratory irritation
Grasses in the very early vegetative stages of growth can contain as much as 25 to 30% crude protein on a dry matter basis. While for most healthy horses this doesn’t present a problem, horses in very heavy work may find that the high crude protein level adds to their digestive heat load and will also increase urine production as the body works to rid itself of the excess nitrogen. In situations where water balance is important and water isn’t always readily available (for example in endurance horses during competition), the combination of more digestive heat and increased urination can lead to an increased risk of dehydration.
Horses that are stabled overnight or during the day and allowed to graze the remainder of the time may also experience problems associated with these high levels of protein. Excess protein causes the distinct ammonia smell often detectable when mucking out stables, which in poorly ventilated areas can cause respiratory problems for the horse.
Spookiness, aggression, and muscle problems
Rapidly growing pastures contain high levels of potassium and low levels of magnesium. While not proven in horses, excessive potassium can reduce the absorption of magnesium (possibly through its effect on the DCAD, or cation, anion difference of this diet which can then affect tissue sensitivity to parathyroid hormone) and increase magnesium excretion from the body. This effect is observed in other animal species including humans. This reduced magnesium absorption, increased magnesium excretion and an already low level of magnesium in the pasture is thought to cause chronic magnesium deficiency in horses. Young rapidly growing pastures can also contain high levels of nitrate which also increases magnesium excretion from the body. Other factors associated with some pastures including low levels of selenium and a high phytoestrogen content in clover dominant pastures can also exacerbate magnesium deficiency.
Magnesium deficiency (and the resulting active vitamin B1 deficiency) can cause normally quiet, calm horses to become ‘spooky’, behave erratically and become excited easily, show signs of incoordination, muscle tenseness, soreness or twitching and in severe cases may become dangerously aggressive and exhibit unusual herding behaviour. For more information on pasture induced magnesium deficiency, read our post ‘Is pasture affecting your horse’s behaviour?‘
Laminitis
Perhaps the condition that has received the most attention in association with spring and autumn pastures is laminitis. Green pastures use the process of photosynthesis to create non-structural carbohydrates (NSC) from sunshine, water and carbon dioxide. Under good growing conditions the plant uses these NSCs as fuel for its own growth. However, if the plant is stressed in any way or subjected to temperatures too low for growth to occur over several days, these carbohydrates will continue to be produced and will accumulate in the plants leaf and stem tissue for later use.
When horses with insulin dysregulation who are prone to laminitis graze these pastures with the high levels of accumulated NSC, laminitis can develop. Other characteristics of spring and autumn pastures may also increase the risk of laminitis for prone horses. For example, a study in cows and calves by Lentz et al (1976) found that high levels of potassium (infused as potassium chloride) caused significant elevations in plasma insulin and in the calves, this response was further exaggerated in magnesium deficient animals. So, it is possible that the high potassium content of lush pastures coupled with an induced magnesium deficiency is contributing to laminitis by causing prolonged elevations of insulin, which presumably would be worse in insulin dysregulated animals.
High levels of nitrate have also been suggested as a cause of laminitis in horses and dairy cattle, though the role of nitrates in laminitis is not clear. Pastures that are subjected to frosts or those that contain capeweed are of particular risk for nitrates, especially following application of nitrogen fertiliser.
Feeding to reduce the impact of spring and autumn pastures
There are some simple management techniques you can use to reduce the negative impact of spring and autumn pastures on your horse’s health, including:
Provide your horses with a supplementary source of fibre in the form of hay, chaff or haylage. Give them access to free choice hay or provide them a meal of hay, chaff or haylage equivalent to at least 0.5% bodyweight (2.5 kg for a 500 kg horse) every 24 hours. This amount should be increased if pasture availability is limited. The extra fibre in these feeds will improve gut fill and manure consistency reducing the risk of colic and diarrhoea and also help your horse to consume the calories he needs when pasture water content is very high.
If high protein intake is an issue, provide your horse with a meal of lower protein grass or meadow hay or chaff before being turned out onto pasture. You may also need to restrict your horse’s pasture intake by using a grazing muzzle, strip grazing or extending the period of time your horse is kept off pasture with access to lower protein hay.
Have your spring or autumn pasture tested for mineral content and use this information together with FeedXL to rebalance any potassium and magnesium imbalance. Care must also be taken to provide enough salt to meet sodium requirements as a sodium deficiency reportedly increases the likelihood of a magnesium deficiency in some horses.
Manage grazing times to reduce the risk of laminitis. If NSCs are suspected as causing issues for your horse you should restrict grazing to only the very early hours of the morning, removing the at-risk horse from pasture by 2 hours after sunrise. If nitrates are suspected (for example on post-drought pastures or capeweed infested pastures) horses should only be allowed to graze in the late afternoon and into the early evening. A grazing muzzle can be used at any time to reduce pasture intake while allowing the horse to move freely around the pasture. If a muzzle is used for limited periods of grazing, care must be taken to provide additional forage in the form of hay or haylage to ensure minimum forage requirements are met. FeedXL will help you to calculate your horse’s minimum forage requirement and how much additional forage must be fed each day in order to meet the minimum requirement.
Don’t overgraze your pasture. Pastures that are constantly very short and in the early stages of growth are the ones that are highest in potassium and nitrates and lowest in fibre and magnesium. Use good grazing management and rotational grazing strategies to allow pastures to stay at a healthy height and stage of growth. As a general rule of thumb don’t graze your pastures until they are at least 6 inches (15 cms) in height and then allow your horses to take half of the pasture and leave the other half there to photosynthesise and provide fuel for further pasture growth.
Pasture analysis is the key
Spring and Autmn pastures are a valuable source of nutrients for your horse and managed correctly they can be fed without any issues. But to know exactly what you are dealing with and to allow you to correctly balance your horse’s diet to avoid problems you should have your pasture tested to assess energy, protein, nitrate, NSC and mineral levels (a sample should be taken in the late afternoon for the NSC analysis and in the early morning for the nitrate analysis).
Armed with a full analysis you can then use this information together with veterinary advice and a ration analysis from FeedXL that uses your pasture analysis data to come up with a ration and a feeding strategy that will lessen the risk of any problems occurring. As they say, information is power and knowing exactly what you are dealing with in your spring and autumn pastures is no exception.
If you’d like some help finding a forage analysis lab, you can click here to download our free ‘Lab List’ with laboratories in Australia, New Zealand, United States, Canada and the UK.
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