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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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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Teff Hay seems to be gaining popularity as a hay option for many horse owners and because it is sold as a low starch low sugar hay it is starting to be recommended in place of Rhodes Grass Hay.
BUT, if you are lucky enough to have access to Rhodes Grass Hay, here are some things to think about before considering a swap:
1. Rhodes Grass Hay is low in oxalate, containing approximately 2.5 to 3 g/kg of oxalate.
Teff Hay is moderate to high in oxalate at 10 to 12 g/kg. This means Teff needs careful supplementation of calcium, phosphorus and magnesium to prevent it from causing Bighead Disease. With Rhodes being so low in oxalate Bighead is not an issue (though you do still need to make sure you correctly balance the diet for minerals and vitamins as forages rarely contain enough to meet a horse’s requirement).
2. Rhodes Grass Hay is more reliable and consistent when it comes to the low starch, low sugar characteristic.
From the analyses we have seen coming through here at FeedXL, Teff can be high in starch, with one analysis sent through showing an as-fed starch content of 7.1% and total NSC of 13.7% which, for a laminitic horse, is going to be too high. While soaking would more than likely bring this non-structural carbohydrate (NSC) level back down to safe levels it makes for much more time-consuming feeding… so if you have access to Rhodes Grass it would be much easier to use this.
3. Teff Hay causes some odd behavioural issues in some horses and this is normally associated with an alkaline fecal pH.
We have no way of explaining this, and it doesn’t happen with all horses on Teff so I don’t know if all Teff Hay is the same or if there is a certain variety that causes this issue.
So, while Teff gives people in cooler climates a low NSC option which is welcome, it is not yet well understood and not without its issues. If I had a choice between Teff and Rhodes I would go with Rhodes Hay every time.
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Following on from our article Identifying Pastures Part 1 that looked at how to identify grasses that could cause mycotoxin problems for horses, this blog will help you to identify grasses that have the potential to cause Nutritional Secondary Hyperparathyroidism, also known as ‘Bighead Disease’. Bighead Disease is a severe calcium deficiency and one way it can be caused is by grazing subtropical or C4-type pastures without appropriate calcium supplementation.
Subtropical or C4-Type pastures like kikuyu, bermuda grass (couch grass), buffel grass, setaria, green panic, pangola grass, guinea grass, purple pigeon grass, para grass and signal grass contain a compound known as oxalate. The oxalate in the grass binds most of the calcium available in the grass making it unavailable for absorption when the horse eats it.
So even though these grasses may contain plenty of calcium, horses cannot access it, meaning over time they will develop a severe calcium deficiency. The oxalate appears to also bind some of the calcium coming from other feed ingredients in the diet, rendering it useless to the horse as well. The more oxalate the pasture contains, the more rapidly a horse will develop bighead. Setaria, and specifically Kuzungula Setaria is the most dangerous high oxalate grass for horses, with severe bighead appearing in horses grazed on this grass species within one to 3 months.
Where do these “bighead” grasses grow?
Bighead Disease caused by pasture has traditionally been thought of as a disease of the subtropics and tropics as this is where the high oxalate pastures were first introduced for grazing cattle (cattle don’t experience the problem as the bacteria in their rumen are able to break the oxalate/calcium compound so they can absorb the calcium). However, some of the grass species that readily cause Bighead, like Kikuyu and Bermuda Grass, can grow in a wide range of environments and due to their popularity as a hardy lawn species, they are spread well into temperate climate areas.
So don’t be complacent: even if your horse lives in a temperate environment, the grasses that can cause bighead disease are widespread. Being able to identify them is important! Use this newsletter to have a wander around your paddocks to see if any of the 4 most common problem species are in your pasture.
Identifying your grasses
Now it is time for you to look at some grasses to see if you have any of the 4 most common pasture species that may cause Bighead lurking in your paddocks. Use the information in Identifying Pastures Part 1 as your plant physiology reference guide (you can find this here).
Kikuyu (Pennisetum clandestinum)
The characteristics of Kikuyu are as follows:
Emerging leaves are folded
Leaves have a prominent mid vein with many smaller veins running in parallel
Leaves are light to bright green and moderately hairy on top and underneath.
Leaf tip is slightly keeled, though leave flatten as they get older.
Auricles are absent
Ligules are hairy
Grows using both underground rhizomes and vigorous over ground stolons (so it has an obvious matt of runners above ground).
Kikuyu does not get visible seed heads but at flowering time, long, white, thread like stamens will sometimes be visible.
The leaf sheath of kikuyu (where the new leaves emerge from) is pale and light green in colour, turning brown as the grass matures. It is obviously hairy.
These images show kikuyu when it is green and growing and also almost completely dried off. Note the distinctive almost lime green colour of the grass when it is green and the dense, thick matt of stolons once it has dried off.
Bermuda Grass/Couch Grass (cynodon Dactylon)
The characteristics of Bermuda Grass/Couch Grass are as follows:
The seed/flowerheads are a digitate panicle with 3 to 7 thin branches 2 to 6 cm long.
Emerging leaves are rolled.
Leaves have a prominent mid vein with many smaller veins running in parallel.
Leaves are relatively short, green and hairless to sparsely hairy with more hairs underneath.
Leaf tip is flat.
Auricles are absent.
Ligules are short hairs on a membranous rim with a tuft of longer hairs on each end.
Grows using both underground rhizomes and over ground stolons (so it has visible runners above ground, but they are not nearly as thick as seen with klikuyu).
Buffel Grass (Cenchrus ciliaris)
The characteristics of Buffel Grass (also known as African Foxtail, Black Buffel Grass or Rhodesian Foxtail) are as follows:
The seed head is cylindrical (like a small bottle brush) and can be straw, grey or purple in colour.
Emerging leaves are rolled
Leaves are flat, hairless except for some sparse long hairs near the sheath and green to blue in colour.
Leaf edges are rough and tip is flat.
Auricles are absent
Ligules are hairy
Grows in a tussocky or bunch growth habit but it can sometime have stolons and rhizomes.
Setaria (Setaria sphacelata)
Setaria is the most dangerous of all the sub-tropical grasses for horses, so if you have it, it is important that you identify it. The characteristics of Setaria (also known as South African Pigeon Grass and African Bristle Grass) are as follows:
Spike like, panicle seed head that can be 8 – 25 cm long and varying in colour from purplish brown to brown to orange tinged.
Leaves are broad, flat, grey-green in colour and generally hairless.
Auricles are absent
Ligules are hairy
Grows in a dense tussock with short underground rhizomes.
If you think you have these pastures but aren’t 100% sure, pot some of the plants you suspect are Buffel or Setaria and let them grow and go to seed. The seed head will help you to positively identify the species.
So you have these grasses … what now?
If you have accurately identified that Kikuyu, Bermuda Grass/Couch Grass, Buffel Grass or Setaria are present in your pasture, you will need to take this into account in your horse’s diets in FeedXL. First of all, determine what percentage of the pasture each of the species comprises, and then use the Advanced Pasture Builder feature to create a pasture that is comprised of these pasture types.
For example, if your pasture is 25% Kikuyu, 10% Setaria and 65% native grasses, use the Pasture Builder in FeedXL to create a pasture that is ‘C4-Type Grass – 25%, Setaria – 10%; and Native Grass – 65%. It is important to be accurate so FeedXL can calculate an accurate calcium to oxalate ratio for you and keep your horse out of harms way!
Once FeedXL knows these pastures are present in your diet it will warn you if the calcium to oxalate ratio of the diet is too low, putting your horses at risk of bighead, and guide you in adding additional calcium to achieve the minimum ratio required of 0.5 parts calcium to 1 part oxalate. For more information on this, please read our blog: Bighead Disease.
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Bighead is a disease resulting from long term calcium deficiency in the diet. Bighead has severe effects on your horse, making movement painful and lameness a constant issue. Luckily though, it is a condition that is easily avoided by carefully balancing your horse’s diet.
What is Bighead?
Bighead, correctly known as nutritional secondary hyperparathyroidism, is a severe calcium deficiency resulting from a horse not absorbing enough calcium from its diet. During these periods of calcium shortage, horses will mobilise calcium (and phosphorus) from their bones to keep blood calcium levels ‘normal’.
When this state of calcium deficiency occurs for prolonged periods of time horses mobilise so much calcium and phosphorus from their bones that their bones become fibrous and weak.
What are the symptoms?
As its name suggests, Bighead results in the horse’s facial bones becoming fibrous and swelling to give the horse a ‘bighead’ appearance as shown in this photo. This facial swelling appears most commonly in young horses whose facial bones haven’t fully formed and hardened, though it is possible for it to occur in mature horses as well.
Because nutritional secondary hyperparathyroidism affects a horse’s entire skeleton it will also result in shifting lameness and generally sore bones and joints. In severe cases horses will be reluctant to move or may move with a ‘hopping rabbit’ gait.
Affected horses also tend to lose weight even though they have access to ample feed. Because of the swelling that occurs in the bones, the upper airways can become obstructed resulting in noisy breathing during exercise and it is also possible for teeth to fall out.
What causes Bighead?
Bighead is literally a severe and long term calcium deficiency. There are two major causes of bighead in horses. These are:
An incorrect dietary calcium to phosphorus ratio with more phosphorus in the diet than calcium. Phosphorus is able to block the absorption of calcium if there is more phosphorus than calcium in the diet eventually leading to a severe calcium deficiency. Diets that contain large amounts of high phosphorus ingredients like wheat bran and pollard (also called wheat middlings, millmix, millrun or broll), rice bran, copra and cereal grains have high levels of phosphorus and have the potential to cause an incorrect calcium to phosphorus ratio.
Grazing high oxalate pasture. Sub‐tropical or C4‐Type pastures like kikuyu, buffel grass, setaria, green panic, pangola grass, guinea grass, purple pigeon grass, para grass and signal grass contain a compound known as oxalate. The oxalate in the grass binds most of the calcium available in the grass making it unavailable for absorption when the horse eats it. So even though these grasses may contain plenty of calcium, horses cannot access it, so over time they will develop a severe calcium deficiency. The more oxalate the pasture contains, the more rapidly a horse will develop bighead. Setaria, and specifically Kuzungula Setaria is the most dangerous high oxalate grass for horses, with severe bighead appearing in horses grazed on this grass species within one to 3 months.
Fortunately, bighead is a disease that is easily avoided given the correct nutrition. The strategy to avoid bighead depends on its cause.
If the disease is occurring because of an incorrect calcium to phosphorus ratio, adding additional calcium to the diet to balance the calcium to phosphorus ratio will make sure you avoid this problem. Calcium can be added by feeding calcium supplements like limestone or a branded calcium supplement or calcium intake can be increased by adding high calcium forages like alfalfa/lucerne and clover to the diet. Dolomite is best avoided as a calcium supplement as its calcium bioavailability (the amount of calcium the horse can actually absorb) is low.
The calcium to phosphorus ratio must be kept above 1 part calcium to 1 part phosphorus for all horses. For young horses, the ideal calcium to phosphorus ratio range is 1:1 to 3:1. For mature horses the ideal range is 1:1 to 6:1.
If high oxalate grasses pose a threat to your horse, you must feed enough calcium in the diet to keep the calcium to oxalate ratio above 0.5 parts calcium to 1 part oxalate. The biggest difference between bighead caused by high oxalate pastures and bighead caused by an incorrect calcium to phosphorus ratio is that when adding calcium to the diet of horses on high oxalate pastures, phosphorus must also be added.
To correct the calcium to oxalate ratio of a horse’s diet, you should use a 2 parts dicalcium phosphate to 1 part limestone (calcium carbonate) mixture, adding enough of this to the diet to keep the calcium to oxalate ratio at or above 0.5 parts calcium to 1 part oxalate. Of course you must also make sure the calcium to phosphorus ratio remains balanced.
Are you groaning by now? So much math…
FeedXL to the rescue
Doing all the maths to work out correct calcium to phosphorus ratios and calcium to oxalate ratios can be tricky, but luckily FeedXL makes it very easy for you. The last section at the bottom of the Nutrient Table in the results section of the FeedXL report shows a number of ratios. The first two are the calcium to phosphorus ratio (shown for all diets) and the calcium to oxalate ratio which is shown only when a horse is grazing a high oxalate pasture or eating high oxalate hay.
FeedXL will warn you when your horse’s diet has an incorrect calcium to phosphorus ratio or if your horse’s diet has a calcium to oxalate ratio that is too low so that your horse is kept out of bighead harm’s way.
Do you have a question or comment? Do you need help with feeding?
We would love to welcome you to our FeedXL Horse Nutrition Facebook Group. Ask questions and have them answered by PhD and Masters qualified equine nutritionists and spend time with like-minded horse owners. It’s free!
