Equine Parathyroidism: Too Much Phosphorous

Equine Parathyroidism:  Too Much Phosphorous

Barbara Kinsey

Introduction

Equine Parathyroidism is a recognized disorder in horses (Little, Redding, Spaulding, Dupree and Jones, 2000). It is also known as Miller’s Disease, or Big Head (Petalia, 2009, Kentucky Equine Research, 2013).  It is caused by feeding cereal grains without balancing the phosphorous (Crabbe, 2013) The feeding of processed feeds rather than the stable manager mixing grains has decreased the incidence of parathyroidism in horses.  Research into feeding horses has helped educate the managers of horses so that they are aware of the necessity of balancing feeds (Little, Redding, Spaulding, Durpree and Jones, 2000).

Define the problem

Too much phosphorous in the horse’s diet which will result in health issues in a period of months.  Pastures may be high in phosphorous.  This may be a result of chemical fertilizer applied to the fields (Crandall, 2016)  Wheat bran contains ten times more phosphorous than calcium. (Lenz, 2016).  A diet low in Vitamin D is also attributed to causing Secondary Parathyroidism (Capen & Rossel, 1989;  Sojka, et al, 2014).  A low calcium:high phosphorous ratio  in the feeding of the horse (Veterinary Treatments and Medications for Horsemen, 1977;  David, et al, 1997;  Little et al, 2000;  Kentucky Research Staff, 2013) causes this problem.  Feeding cereal grain, which is high in phosphorous without balancing with a high calcium feed will cause  secondary  parathyroidism in horses. (Veterinary Treatments and Medications for Horsemen, 1977) 

Clinical Signs of an Excess of phosphorous/Secondary Parathyroidism

The bones become weaker as the calcium is depleted.  Lameness, swelling in the bones and bone formation issues.  The horse may have a stiff movement (David et al. 1997)  The horse may have many little fractures in the long bones (David et al. 1997).  

The skull of the horse will show changes, which is where the “Big Head” name comes from. (Little, et al, 2000).  The horse may have trouble chewing due to changes in the skull configuration (Norton, 2013, Petalia, 2009)

Diagnosis is only after a other causes are ruled out.  A feed analysis, x-rays, bone density, and other tests are done to determine that the problem is caused by too much phosphorous (David et al, 1997).  

Management Strategies

Feed a balanced diet.  Attention must be paid to the calcium:phosphorous ratio.

Balance alfalfa with wheat bran or grass hay (forageplus staff, equisearch staff).  Beet pulp is balanced with bran by adding twenty-five per cent bran immediately prior to feeding. (Equisearch staff)  Grass is balanced in most areas.  In the Prince George area  grass hay is analyzed at 1:1 calcium:phosphorous. (Best, 2016).  In the UK, grass analysis shows a high calcium content (forageplus.co.uk).  Another method for avoiding a calcium phosphorous imbalance would be to restrict cereal grain by feeding hay.  Most horses do not require cereal grain added to their diet as they are able to maintain their condition (a Body score of 4-6 would be good).  Adding bran to working, growing or lactating mare’s diets would ensure that the calcium phosphorous levels are close to the ideal. (forageplus.co.uk staff)

Wheat bran contains an average of 2.4 grams of phosphorous per 220 kilograms of weight. (minimum of 1.71 grams to a maximum of 3.5 grams per 220 kilograms).  (forageplus.co.uk)

Offering a vitamin A, D, and E in the winter months will help.  Horses in Canada are not exposed to enough sunshine during the winter. (People need to supplement Vitamin D in winter as well).  Find out what minerals are deficient in your area.  (Crabbe, 2013, Crandell, 2013, Larson, 2015)

References

Best, C, DVM, in conversation with, November, 2016

Capen, C.C. and Rosol, T.J. (1986). Calcium-regulating hormones and disease of abnormal mineral metabolism.  In Kaneko, J.J. (ed.): Clinical Biochemistry of Domestic Animals, ed. 4. San Diego, CA:  Academic Press, pp. 678-752.

Crabbe, B. DVM, (2013)  Horse Health:  Vitamins and Minerals, http://www.equisearch.com/article/horse-health-vitamins-and-minerals-13326?ctid=2

Crandell, K. November, 2016, in conversation with

Crandell, K, (April 11, 2013) Vitamin D in Equine Diets, http://www.equinews.com/article/vitamin-d-equine-diets

David, J.B., Cohen, N.D. and Nachreiner, R (1997). Equine Nutritional Secondary Parathyroidism. The Comendium, 19(2), 1380-1388.

Norton, J. VMD. (2013). Your Horse’s Endocrine System, http://equimed.com/health-centers/general-care/articles/your-horses-endocrine-system

Equisearch Staff.  (2005), Feeding Brans. http://www.equisearch.com/article/feeding-brans?ctid=2

Forageplus Staff.  Should I feed bran to my horse.  https://forageplus.co.uk/feeding-wheat-bran-to-my-horse/

Kentucky Research Staff. (2013). Prevent nutritional secondary parathyroidism in horses.  www.equinews.com/article/prevent-nutritional-secondary-hyperparathyroidism-horses.

Larson, E, June 18, 2015, Do blanketed horses get enough vitamin D?http://www.thehorse.com/articles/35953/do-blanketed-horses-get-enough-vitamin-d

Lenz, T.R. Horse Health, www.aaep.org/info/horse-health?publication=2313

Little, D., Redding, W.R., Spaulding, K.A., Dupree, S.H., and Jones, S.L. (2000). Case report: unusual presentation of nutritional secondary parathyroidism in a paint colt. Equine Veterinary Education, 12, 6, 297-302

Petalia, (2009) Big Head (Nutritional Secondary Parathyroidism). www.petalia.com.au

Sojka, J., van der Kolk, H. and Toribio, R. (2014) Endocrine:  hyperparathyroidism. Vetstream Equis.

________Veterinary Treatments and Medications for Horsemen, Grapevine, Texas: Equine Research, 1977