Big head (or Nutritional Secondary Hyperparathyroidism) is a common problem in our area and is due to low absorption of dietary calcium. In this region, buffel grass is the main cause, as it contains oxalates which bind up dietary calcium making it unavailable to the horse. With the spread of buffel into new areas, we are seeing cases on properties where it has never been seen before and people often have no prior experience in managing the problem.
The horse's body starts sourcing it's calcium requirements from bone, and lays down fibrous tissue in place of good mineralised bone.
Symptoms include lameness (which may be shifting), stiffness particularly in the "shoulders", weight loss and in some cases the classic swelling over the face. Any stiffness is worsened if the horse has to work. Horses with weak, fibrous bones will be prone to fractured legs or spines. We see these fractures most commonly in brood mares because of their high requirement for dietary calcium.
Diagnosis is often reached by looking at the history (exposure to buffel) and typical clinical signs. However, comparative Xrays can be very useful to show the degree of bone loss. The pony on the right below is a normal healthy 20 year old pony (she has run on buffel for 3 years but with correct supplementation). Notice the good density of bone. The pony on the left is affected by "big head" and shows a marked loss of density and also fluffy areas around the joints (most likely where ligaments have torn away from the fibrous bone). Treatment will increase this pony's bone density with time, but she may remain unsound due to permanent damage around the joints.
( ALSO SEE further down this page for some very important points about Buffel Toxicity)
***SOME VERY IMPORTANT POINTS***
* The oxalate level in buffel is at it's highest when the buffel is lush and green (not when it has seeded as some believe). The oxalate level can be so high as to bind up some of the calcium you supplement as well.
* There may be mixed grasses in the paddock but some horses will prefer buffel (perhaps even selectively eat buffel only). This makes it difficult to assess the level of supplementation each individual horse requires.
* Some horses may never recover, or may go sore again after a day's work.
* They will not always show the classical swellings on the face.
* Vitamin D injections do help with calcium uptake, however you do need to be careful when using it (speak to your vet). Vitamin D does not replace the need to give adequate calcium supplementation.
* It can be DANGEROUS to give analgesics (pain killers such as PBZs) to a horse that is or has been running on buffel, to mask even a mild lameness in order to work him. At best it will contribute to joint damage, and at worst could fracture his leg or your neck!
* There is no perfect solution. I have had two old horses die perfectly sound at 30 years and 37 years who had run on straight buffel for 20 years. However, I knew their grass intake was 100% buffel and could tailor their individual daily calcium dose accordingly. It is not always this simple. Some people have 12 horse running together on mixed grasses - all with different Buffel intakes and different calcium requirements (ie growing, pregnant or lactating). But do speak to your vet about your individual situation - they may be able to help.
BUFFEL RECIPE - Average 450kg horse running on Buffel.
A. Clinically affected horse:-
Mix ground limestone (or AG LIME) and Dical Phos (DCP POWDER) at a ratio of 1kg Ag Lime to 2kg DCP. *Do not use Brickie's Lime - it's toxic! Add 2 kg of this mix to 3kg of Molasses and feed this amount per horse per week. Must continue this for 4-6 months depending on severity of the condition.
B. Maintenance & Prevention (450kg horse running on Buffel):-
Feed 1 kg of the mixed Ag Lime/DCP mix in 1.5kg of molasses per horse per week.
Note: We feed the daily quota of this ration with a SMALL amount of bran in a mixed damp feed each evening as we find it more convenient than molasses in our situation. Bran is high in phosphorus and a high phosphorus intake will interfer with calcium uptake. However, pastures in our area are phosphorus poor, so a small amount of bran may be a good thing.