Equine Laminitis

James K. Belknap, James K. Belknap

• Publisher: Wiley-Blackwell
• Year: 2016
• ISBN:
  9781119169222
• Edition: 1
• Topic: Médecine
• Subtopic: Sciences vétérinaires équines

The first book dedicated to this common, serious, and complex equine disease, Equine Laminitis is the gold-standard reference to the latest information on every aspect of the disease and its treatment.

• Provides the first book devoted specifically to equine laminitis
• Discusses the current state of knowledge on all aspects of the disease, including its history, relevant anatomical considerations, pathophysiology, the diagnostic workup, and clinical treatment
• Presents 50 chapters written by leading international experts, under the editorship of the foremost authority on equine laminitis
• Offers a thorough understanding of this common affliction, grounded in the scientific literature
• Describes effective prevention and treatment plans

PART 1
Overview: From Basic Research to Caring for the Laminitis Patient

CHAPTER 1
Historical Perspective on Equine Laminitis

Donald M. Walsh and Teresa A. Burns

Historical records reveal considerable well-documented evidence of Equine Laminitis as mankind has used horses throughout history. An excellent review of the entire history of laminitis was published by Wagner and Heymering in 1999 [1], and it is the purpose of this discussion to examine the history of Equine Laminitis as seen in the veterinary medical literature from 1800 to the present day.

Mention of laminitis associated with pasture exposure is conspicuously absent from the veterinary literature before approximately 1940. Absent also is reference to any particular breed predisposition to laminitis, or of obesity leading to the disease. Hormone-related endocrinopathic laminitis, the most common form of the disease today, is a relatively recently described veterinary diagnosis [2] and follows closely the first description of human metabolic syndrome in 1988 [3]. In industrialized countries during the 1900s, large numbers of horses were in daily use, and observations regarding the perceived primary causes of laminitis and response to treatments are recorded in detail [4]. In 1906, an observation was recorded that “…laminitis has been described as occurring when the animal is at grass, and when all causes – at any rate, active ones – have appeared to be absent.” H. Caulton Reeks was a Fellow of the Royal College of Veterinary Surgeons and, quoting a case history attributed to W. Stanley Carless (Veterinary Journal, vol. ix, p. 176) in his classic 1906 “Diseases of the Horse's Foot” [5], he describes an obese mare developing severe laminitis on pasture:

“On July 3 an interesting case of laminitis came under my notice. The subject was a mare, eight years old, which had been running on the common here for some months, and was taken up on the night of July 2 by a boy, who did not observe anything amiss with her. The following morning, on the owner going to the stable, he found the animal in great pain, and at once sent for me. I discovered her to be suffering from laminitis, and saw her again in the evening, when she was much worse. The attack proved to be a most severe one. The owner informed me that she had not been allowed any corn for two months, and that she had no distance to travel on the road from the common. Though on such a poor pasture, the mare was very fat she had never been unwell before this attack. This is the first case I have seen of laminitis occurring when the animal was on grass.”

This may be the first recorded reference to pasture-associated laminitis (and laminitis associated with obesity). Relatively rare 110 years ago, this classic association between clinical laminitis and horses and ponies grazing pasture was not generally made until recently. Many causes are listed pre-1940, but not pasture.

By 1800, the terms ‘founder’ and ‘laminitis’ were both used in the literature. While the exact mechanism(s) resulting in laminitis were not understood, the conditions associated with it were well documented [6]. One of the primary causes listed was excessive concussion to the feet of exhausted horses. What seemed perplexing was that an animal doing the same work and receiving the same care and feed as other horses could develop the disease while others did not. It was thought by some authors that an unknown ‘excitatory factor’ must have affected the animal's physiology, such as a core temperature change brought on by drinking cold water while very hot, or a cold draft that cooled a hot, standing horse too quickly [7].

The earliest reports of adverse effects from a particular feed are attributed to the Hittites in 1350 BC, where feeding barley was observed to result in ‘foot problems’ [8]. It was later established that feeding excessive barley, wheat, or corn could cause laminitis. Early authors also recognized that fever from infections could bring on the disease, and that laminitis was seen often seen after a horse had a severe illness resulting in diarrhea or pneumonia. This was commonly referred to as ‘metastatic laminitis.’ The use of cathartic medication was also reported to result in laminitis, as well as retained placental membranes in mares [9]. Additionally, it was well known that a horse with a severe injury to a limb could develop laminitis in the foot of the opposite limb if a sling was not used for support of the animal during recovery [4].

In 1915, the population of horses, ponies and mules in the United States peaked at 26.5 million [10]. This equated to one equid for every three people in the nation. With the advent of mechanized farming and the introduction of the automobile, the horse rapidly became functionally redundant. No longer needed for their role in war and as a ‘beast of burden’ in agriculture, the horse population declined dramatically and breeds of working horses virtually disappeared.

Following World War II, horses became ‘leisure animals,’ relegated principally to sport and recreational purposes. In the USDA Yearbook of Agriculture (1942), mention is made of laminitis being caused by over-feeding, chiefly on grains but also green plants or any palatable feed consumed to excess [11]. A lifestyle lacking routine strenuous exercise along with ready access to abundant feed was imposed on a population of horses and ponies genetically predisposed to be ‘easy keepers,’ ones that required less food than others to maintain and exceed their optimum weight. No longer ‘working horses,’ these animals were now susceptible to a new form of laminitis linked to obesity and insulin resistance [12].

Equine Laminitis Treatments from the 1800s to the Present Day

Treatments for laminitis described throughout the nineteenth century cited bleeding via jugular, toe, or coronary band phlebotomy in volumes of up to 6–8 quarts (ca. 7–9 liters) as absolutely essential [13]. Some practitioners monitored the digital pulse in the foot and bled the animal until the pulse was no longer palpable over the palmar digital artery. It was believed that if bleeding was performed sooner rather than later, less damage would occur within the foot. Even after 1900, when the practice of bleeding was for the most part abandoned by veterinarians, some still insisted it was indicated for acute laminitis [14]. The stated purpose was to lower blood pressure in the extremity, which then reduced the pressure inside the hoof capsule.

Other early practices to treat acute laminitis were to dose orally with diuretics such as potassium nitrate in the water three times a day [15]. Saltpeter was also used as a diuretic aimed at lowering blood pressure. Removing all cereal grain from the diet and feeding only forage was a recommended treatment [16]. If the case involved over-consumption of grain, a cathartic such as tartar emetic was given or a bran mash fed to evacuate the bowel. Caution was recommended, however, as excessive use of cathartics was suggested to actually cause laminitis in horses [4].

Treatment of the feet during a bout of laminitis usually included the removal of shoes when possible. Most early authors advocated using cold water on the feet [11]. It was suggested that this could be accomplished by standing the horse in a tub with ice, if available. Some described using warm water for 20 minutes, then switching to cold. Early in the twentieth century, the US Calvary used ice if available up to the knees and hocks [16]. When the affected horse was not standing in cold water, it was encouraged to lie down by providing it with a well-bedded stall. Bran or linseed oil poultices and ointments such as arnica were applied to the feet to soften them and reduce inflammation [4,14].

Pain control was of great interest to early health providers working with laminitic horses. Many authors stated that the pain of laminitis was greatly relieved by the horse lying down [15]. To help control pain, Dadd recommended using hops or poppy heads (opium) [17]. Youatt recommended using digitalis as a sedative and nitre (potassium nitrite) to cool the feet in acute laminitis [13]. The 1918 U.S. Manual for Stable Sergeants recommends administering an oral tincture of Cannabis indica for the control of excessive pain. Interestingly, it was also the drug of choice for the control of colic pain in cavalry horses [16].

Exercise was then, as it is today, a controversial issue. By the early 1900s exercise was encouraged after recovery had started and the horse was willing to move on its own. It was then recommended that the exercise be gradually increased until soundness returned [4,16].

From 1800 to 1920, the main cause of laminitis cited in the literature was that due to excessive concussion to the feet. Horses worked long hours pounding their feet on very hard surfaces, unlike our sport horses today, which perform on very controlled surfaces to protect their limbs. It is interesting to note that horsemen believed it to be important to condition horses' feet before working them intensely to prevent this form of the disease. They knew that exercise made the foot stronger and the lamellae less likely to be injured by concussive impact. Perhaps coincidentally, the only reference to obesity found in this 1800–1920 literature was advice to “…not work a plethoric horse hard before the feet are in condition” [18]. Plethoric means ‘large or excessive,’ so this statement is assumed to refer to a horse that was heavy and out of condition and therefore without feet in good condition for work [4]. Authors also cautioned against over-working a green horse until its feet were conditioned to hard work. This concept that exercise strengthens the foot seems to have been lost on many horsemen today, who often allow animals to largely stand idle in stalls. From 1920–1940, little new information about laminitis is found in the literature. The sections on acute laminitis and its treatment in the USDA Diseases of the Horse are virtually identical in the 1911, 1928, and 1942 editions.

Changes in Pasture from 1920 to the Present Day

The first reference to pasture as a suspected cause of laminitis was published in the Yearbook of Agriculture 1942. In fact, pasture was cited in that reference as the most frequent cause of the disease: “Overeating and consumption of green plants…is the most common cause…” [11]. This seems to signal the start of an era in which the most common form of laminitis is what we now call the ‘pasture-associated laminitis’ form of endocrinopathic laminitis.

The factors that increased either the incidence and/or the reporting of cases of pasture-associated laminitis after 1942 are unclear, but the following factors may have played a role. Widespread pasture improvement in the United States through advances in agronomy practices may have increased exposure of horses to pastures that were primarily meant to provide forage for production animals (especially cattl...