Laminitis

When the grass becomes lush and rich in the summer, many Icelandic owners try to restrict their horses’ grass intake to control weight gain.  The evolution of a horse breed from the extremes of Iceland seems to have developed a thrifty, easy keeper horse.  And recent research supports that some Icelandics can be easy keepers.  Using Icelandic and Standardbred horses, Ragnarsson and Jansson (2010) studied grass haylage digestibility from hay harvested at different stages of maturity and compared the resulting metabolic plasma profile.  Over the course of the study, the researchers found that the Standardbred horses lost weight and the Icelandic horses gained weight regardless of the type of haylage fed; the metabolic profiles also differed slightly.  Unfortunately, when you talk about easy keepers and weight gain, the dreaded word “laminitis” often comes up. 

“Laminitis is the most serious disease of the equine foot and causes pathological changes in anatomy that lead to long lasting, crippling changes in function (chronic laminitis or founder). It is the second biggest killer of horses after colic.  In the USA National Animal Health Monitoring System (NAHMS) report of the year 2000, 13% of all horse establishments (excluding racetracks) had a horse with laminitis in the previous year and 4.7% of these died or were euthanized” (Pollitt, n.d., para 4).   Horse owners can better help their horses lead long and comfortable lives by learning more about this debilitating disease. This article will focus on what is laminitis, how to recognize the symptoms, and some steps the average owner can take to help prevent its onset.

What is laminitis?

The Merck Veterinary Manual (Aiello, 1998) defines laminitis as “transient ischemia associated with coagulopathy that leads to breakdown and degeneration of the union between the horny and sensitive laminae.  In refractory cases, rotation of the pedal bone is a common sequel that may progress to perforation of the sole” (p. 216).  Ah, but what does this mean?
The Equine Information Library (Laminitis, n.d.) provides a definition of laminitis that is more understandable by the average reader.  Laminae are the leaf-like structures that secure the wedge-shaped coffin bone (or pedal bone) to the hoof wall.  Laminitis occurs when blood flow to the laminae is disrupted and the laminae are weakened.  In moderate cases, the coffin bone starts to rotate downwards. In severe cases the coffin bone and the hoof wall separate and the coffin bone starts to sink.  In extreme cases, the coffin bone may sink down and actually penetrate through the sole of the hoof.  See the figure below for the rotation of the coffin bone in the hoof in mild to severe cases of laminitis.




What causes laminitis?

In her excellent article “Laminitis,” Dr. Judith Mullholland (2005) states that “something has to happen within the body or to the body to trigger a laminitic episode” (para 1).  She goes on to discuss the multiple causes of and associations with laminitis such as overfeeding of grass or grain, injury, stress, genetics, interaction of certain drugs, bad shoeing, road founder, high doses of corticosteroids, retained placenta, exposure to certain fertilizers, any disease with a toxic basis such as pneumonia or colic, certain phenotypes (body type), starvation, and obesity.  High fever and bedding containing black walnut shavings can also cause laminitis (Laminitis, n.d., para 3).  Factors also associated with laminitis are Cushings’ disease or previous bouts of laminitis (Laminitis, n.d., para 4).

In a study of risk factors for laminitis among 160 ponies, Dr. Kronfeld. (2006) found that metabolic changes associated with pregnancy and obesity combined with changes in pasturage resulted in insulin resistance that led to laminitis.  This condition Pre-Laminitic Metabolic Syndrome (PLMS).has a genetic component so that individuals within a breed may have different levels of susceptibility for developing laminitis.

Dr. Harris (Kline, 2008) has found that certain horses are “thrifty;” they maintain weight easily and gain weight with just small amounts of excess food. This condition is related to the glucose transporter proteins, especially glut-4, that carry glucose to various parts of the body such as muscles, tissues, and hooves.  Certain horses have a gene that inhibits glut-4 and is associated with a propensity for laminitis. “It is conceivable that it may have been beneficial for ponies with the ‘thrifty gene’ in the wild, under harsh conditions of feed restriction. Blocking glut-4 would leave more available glucose for use in tissues like the endometrium (lining of the uterus) that do not require glut-4 to transport glucose in order to support pregnancy when times were tough. However, under modern conditions of feed abundance, these animals are more prone to high levels of visceral fat and elevated portal fatty acids which the liver converts to glucose” (Kline, 2008, para 3).

Recent research has found a strong link between insulin levels and laminitis. Sillence, Asplin, Pollitt, and McGowan (2007) examined the hormonal and metabolic causes of laminitis and its relationship to insulin and glucose transportation.  They discovered that in a healthy horse stress, exercise, or food in-take causes a short term increase in glucose followed by a short term increase in insulin which prevents the level of blood glucose from rising too high.  “However, when the glucose transport proteins are overworked (e.g. through chronically elevated cortisol concentrations or chronic overfeeding), they become less responsive to insulin, such that glucose intolerance/insulin resistance develops” (p.3).  The researchers found a direct link between excess insulin and laminitis. 

The causes of laminitis are complex and varied.  Scientists are continually conducting research on this topic to improve our understanding of this disease.  Of course, the easiest way to deal with laminitis is to try and prevent its occurrence.

What are common symptoms of laminitis?

As Dr. Mullholland (2005) states, the classic symptoms of a full blown incidence of laminitis are: “A bloated horse with foul smelling manure with grain in it, a temperature of 39°C, a heart rate over 60, swollen legs, hot feet and strong digital pulses is a classic set of symptoms for carbohydrate overload laminitis” (para 5).  If symptoms progress to this point, the horse is in a lot of pain and you should contact the veterinarian immediately.  Dr. Mullholland goes on to suggest that the horse owner can greatly reduce the impact of a bout of laminitis by being extremely vigilant for any of the first signs of the disease.  Watch for constant foot shuffling, a stance with the forelegs out and the hindlegs underneath and an arched back, reluctance to move, standing in one place for long periods, or longer times than usual spent laying down.  Laminitis is more likely to occur in the front feet but can occur on any combination of feet.  If you even suspect laminitis, cool the feet by soaking them in cold water and call the veterinarian!

How to reduce chances of developing laminitis?

As previously noted there are many, many causes of laminitis but most of them are rarely encountered by the average horse owner.  As Dr. Vialls (2007) notes, “The vast majority of laminitis cases (especially if you include Low Grade Laminitis) appear to be caused or at the very least triggered by diet in some shape or form. So it makes sense if we're trying to either avoid laminitis or get an active attack under control to take a long hard look at the diet of the horse in question” (para 1).   Types of grass—orchard grass, legume hays, oat hays, alfalfa—can vary in their levels of protein, starches, sugars, and fructans.  For example, legume and Bermuda hays contain less carbohydrates than oat hay (Ask the, n.d.).  Factors such as location of harvest, harvest conditions, time of day harvested, recent rain, and drought also can impact levels of carbohydrates in the hay (Kline, 2008).  Further discussion of equine nutrition covers so many factors—such as protein, carbohydrates, minerals, roughage, etc. —that it is beyond the scope of this article.

Several authors (Kline, 2008; Ask the, n.d.) have made the following suggestions for feeding horses that may be prone to founder:

-       Use a type of hay that is lower in fructan.
-       Allow grazing at night when fructan concentrations are low and restrict grazing during the day.
-       Don’t allow horses to graze in frosted fields since sugars build up in the grass.
-       Feed hay that has been dried in the field for a longer time since it has lower carbohydrates.
-       Soak hay in water before feeding to reduce some of the sugar content.

If you think your horse is too “thrifty,” talk with your veterinarian about the proper diet to meet the nutritional needs of your horse and reduce the chance of laminitis.  You may also want to get your hay assayed to determine nutritional content.
Proper fit of the grass muzzle is important.  Note that this
grass muzzle is too small for this horse 

Another way to restrict feed is to use a grass muzzle.  Manufacturers make a variety of grass muzzles.  Which one you use will depend on your personal preferences, the grazing habits of your horse, and his or her puzzle solving abilities.  B. Benard (2010) reviewed several muzzles from several different manufacturers.   In general, she suggests that the muzzle “should be lightweight, but durable enough to withstand at least one full season of use. It should be airy and comfortable for the horse. It needs to come in many sizes and/or have multiple adjustments to fit every equine head and, once fitted, it should stay on that head. It must be safe. In the rare event of entrapment, its safety mechanism should release long before the muzzle sustains damage” (para 3).  She also suggests looking for reinforced bottoms on basket style muzzles to help combat repeated scrapping and safety snaps that can release if the muzzle becomes entangled on something.  You may need to pad the muzzle straps with sheepskin to prevent rubbing away hair.  Be prepared to experiment with different styles of grass muzzles since Bernard found out that at least one horse could eventually remove each of the models tested.

If all else fails, you can put your horse in a dry lot so that you can precisely control what they are fed.  Try to prevent boredom by supplying frequent small feedings and providing more attention.  And increased exercise is also a good way to control weight for any species.  There is always a discussion as to whether grazing muzzles or dry lots are better for equine weight control.  Nobody wants ro risk laminitis!  Dry lots versus grass muzzles have different advantages and disadvantages so the owner needs to find the best compromise that meets her horse’s needs.

How do you tell if your horse is too fat?

Most of us don’t want to admit that our horses are too fat.  And with the amount of hair that Icelandics sport, it may be difficult sometimes to differentiate between excess weight as opposed to fluffiness.  Harrison (n.d.) lays out a precise method to measure and calculate body weight. You assign a numeric rating to six areas on the horse—neck, withers, tack crease, tailhead, ribs, behind the shoulder—to calculate your horse’s basic body condition.  This may be a useful tool if you need more precision because your horse is prone to laminitis.
One should be able to easily feel the horse's ribs.

However, for most of us it may be easier to answer the following questions based on S. Raston’s (2004) criteria:
·         Is it true that you can’t feel your horse’s ribs?
·         Is your horse’s neck “cresty “or bulgy and floppy along the line of the mane?
·         Is the top of the withers covered with fat?
·         When you girth your horse, does fat bulge on either side?
·         Is the loin area directly behind the saddle creased?
·         Is there is a pad of fat at both sides of the root of the tail?
·         Does your horse’s inner thighs rub together when the horse stands square?

If you answered “Yes” to more than one or two of these questions, your horse is probably fat not fluffy and you may want to look at restricting food intake and increasing exercise. Sometimes strict rationing and a gradual exercise program are the only way to save a horse’s life.  In extreme cases of obesity, consult your own veterinarian to develop a nutritional and weight loss program tailored for your horse.

How to treat laminitis?

As mentioned earlier, you should call the veterinarian if you even suspect laminitis.  As Dr. Mullholland (2005) cautions, “In all cases of laminitis, if the acute phase can be kept to 12 hours or less, damage within the foot will be greatly reduced.  Never wait until the next day to ring the veterinarian, do it at the very first signs, even if you are unsure whether it is laminitis” (para 4).  Soak the horse’s feet in cold water while you are waiting for the veterinarian. She will prescribe the proper treatment.  If the horse has already foundered, consult with your veterinarian and farrier to develop an appropriate maintenance plan.  Once foundered, the horse will be even more susceptible to further outbreaks.   With proper treatment and care, a horse with laminitis can often live a comfortable and even productive life. 

Conclusion

“The best way to deal with laminitis is preventing the causes under your control” (Laminitis, n.d., para 10).  However, even if you think you are doing everything to control those causes you may be unpleasantly surprised.  Ultimately the responsible horse owner needs to be ever vigilant.  By educating ourselves on equine nutrition, hoof care, and signs of illness, we can better help our horses from developing this painful disease.

References:
Aiello, S.(Ed.)  (1998).  The Merck Veterinary Manual, Merck & Co., Inc., Whitehouse Station, NJ.
Ask the expert. (n.d.).  What kind of hay is good for a laminitis-prone horse?  Rutgers New Jersey Agricultural Experimental Station.  Retrieved March 4, 2011, from http://www.esc.rutgers.edu/ask_expert/ate_nuth.htm

Benard, B.  (2010).  Muzzle your horse to prevent obesity and laminitis.  The Horse Journal.  Retrieved March 10, 2011, from http://www.equisearch.com/horses_care/health/anatomy/muzzle-your-horse-to-prevent-obesity-and-laminitis

Harrison, A.  (n.d.).  How to tell if your horse is fat.  Equiresearch.  Retrieved March 10, 2011, from http://www.equisearch.com/horses_care/health/anatomy/fathorse_102907
Hutchinson, J. , & Hutchinson, K.  (n.d.)   Dieting the obese Icelandic.  Retrieved March 26, 2011, from http://www.icelandichorses.co.uk/Dieting%20an%20obese%20horse.htm
Kline, K.  (2008).  Understanding and Avoiding Laminitis and Founder in Horses.  Illini Horsenet Papers.  Retrieved March 14, 2011, from http://www.livestocktrail.uiuc.edu/horsenet/paperDisplay.cfm?ContentID=9964
Kronfeld. D.  (April, 2006).  Pasture laminitis breakthrough, Equus,  342, pp. 47 - 63.
Laminitis: Prevention and treatment.  (n.d.).  Conejo Valley Veterinarian Hospital Equine Information Library.  Retrieved March 15, 2011, from http://www.conejovet.com/EquineLibrary/laminitis.html
Mullholland, J.  (2005).  Laminitis.  BVMS Farrier, Retrieved March 16, 2011, from http://www.farriervet.com/laminitis.html
Pollitt, C.  (n.d.).  What is laminitis: learn more about laminitis.  School of Veterinary Science, The University of Queensland, Retrieved March 11, 2011, from http://www.laminitisresearch.org/chrispollitt_whatislaminitis.htm
Ragnarsson, S., & Jansson, A.  (2010).   Comparison of grass haylage digestibility and metabolic plasma profile in Icelandic and Standardbred horses.  Journal of Animal Physiology and Animal Nutrition, no. doi: 10.1111/j.1439-0396.2010.01049.x
Ralston, S.  (2004) Maintenance of the “easy keeper” horse, Rutgers New Jersey Agricultural Experimental Station, Retrieved March 10, 2011, from http://www.esc.rutgers.edu/publications/factsheets_nutrition/FS799.htm
Sillence, M.,  Asplin,K.,  Pollitt, C., & McGowan, C.  (2007).  What causes equine laminitis? The role of impaired glucose uptake.  RIRDC Publication No 07/158 RIRDC Project No UCS-35A

Vialls, R.  (2007).  Diet for laminitics.  Retrived March 17, 2011, from http://www.bodrwyn.org/articles/dietforlaminitis.php.

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