Azoturia or Paralytic myoglobinuria Paralytic myoglobinuria / Monday morning sickness/ Tying-Up in Horses/ set fast/ chronic exertional rhabdomyolysis (ER) in Horses

Synonym- AZOTURIA ,EXERTIONAL RHABDOMYOLYSIS, MONDAY-MORNING DISEASE, AZOTURIA, SET FAST, BLACK WATER, PARALYTIC MYOGLOBINURIA, EXERTIONAL MYOPATHY

There are many names for “it”: azoturia, set fast, paralytic myoglobinuria, and chronic exertional rhabdomyolysis (ER), but most of us know “it” as tying up. It is a common muscle problem in horses with multiple causes. The most common syndromes include Polysaccharide Storage Myopathy (PSSM), Recurrent Exercise Rhabdomyolysis (RER), vitamin/mineral deficiency, electrolyte imbalance, exhaustive exercise, especially on hot, humid days.  Some horses can have chronic episodes starting at a young age when exercised lightly. Depending on the cause of tying up, keeping your horse well hydrated and fit for exercise can help reduce tying up episodes.

Exertional rhabdomyolysis syndrome (ERS), also known as “tying up”, is a term used to describe a disease in which horses develop abnormal muscle pain and cramping during or immediately after exercise. ERS can develop as a one-time event, sporadic episodes, or chronic recurring events.
Chronic intermittent rhabdomyolysis (CIR) or exertional myopathy has long been recognized in horses performing various types of exercise. It once was referred to as Monday morning disease or hemaglobinemia paralytica14 because of its association with draft horses being rested but fed normal rations on Sunday and then resuming work on Monday. Although this is still the scenario for some horses with exertional rhabdomyolysis, many cases do not fit this pattern. Azoturia and paralytic myoglobinuria, and tying up were other terms for the condition. The term tying up or chronic intermittent (exertional) rhabdomyolysis is a broad clinical description. Although opinions and hypotheses abound, in many cases the cause and pathogenesis are unknown. Considering the varying causes for this clinical syndrome, it is not surprising that treatments and prophylactic measures are numerous, usually of undocumented efficacy, and frequently decided by trial and error. Exertional myopathy in endurance horses following prolonged exercise is probably different from rhabdomyolysis in the racehorse walking out to the track preceding any strenuous exercise. This article describes the clinical signs of CIR and presents current knowledge of conditions contributing to its manifestation, useful diagnostic tests, prophylaxis, and treatment of the acutely affected horse. Postanesthetic myopathy, exertional capture myopathy, and ear tick-associated muscle cramping42 are not included. Horses that are rested for a period of time after a regimen of work or exercise are more at risk of developing azoturia, especially if feed intake has not been reduced during periods of rest. Horses of any age can be affected, but it is more common in mares and fillies.

Azoturia in horses is known by several different names including Monday morning disease, tying-up, set-fast, and equine rhabdomyolysis syndrome or ERS. It is best described as severe muscle cramps affecting the hindquarters and back of your horse. This causes stiffness and extreme pain.

Symptoms of Azoturia in Horses

Be sure to thoroughly go over your horse after a period of rest and watch for any changes in behavior. Your horse will tell you if there is something wrong. If you notice any of these symptoms, contact your veterinarian for an assessment.

• Unwilling to walk
• Taking short steps
• Unsteady or stiff on hindquarters
• Muscles feel hard or hot to the touch in the hindquarters
• Cannot move, muscles seized up
• Unable to stand or collapses when trying to move
• Distressed behavior such as excessive head throwing or pawing the ground
• Raised pulse rate
• Reddish-brown or dark chocolate colored urine
• Frequent urination or frequent attempts to urinate
• Slight elevation in body temperature

Causes of Azoturia in Horses

The most common cause of azoturia is over-feeding an active horse during times of rest, such as feeding the same amount of food to a horse that is being stalled for a day or two instead of cutting rations to accommodate the lack of activity. Too many carbohydrates can cause the muscles to have an acid base imbalance and can cause muscle damage if severe enough.

Over-feeding is not the only cause of azoturia. Since fillies and mares are more at risk, a hormonal imbalance has been suggested as an underlying cause. A thyroid imbalance has also been determined as a cause of azoturia. Researchers have also found a link between azoturia and a deficiency of selenium, vitamin E and calcium.

Diagnosis of Azoturia in Horses

Your veterinarian will complete a full physical examination of your horse and may draw blood for a CBC to rule out other possible diseases. A complete medical history of your horse, as well as daily routines, will also be helpful when diagnosing azoturia. Since azoturia can closely mimic colic, it is important that you give detailed accounting of all recent activity, type of feed, and amounts of feed given.

Your veterinarian will also do a muscle biopsy from the muscles just to the side of the tail, the semimembranosus or semitendinosus muscles. The biopsy will determine if there are excessive proteins within the muscles, indicating that your horse is suffering from azoturia.

Clinical Findings: 

1-  Signs can be mild and resolve spontaneously within 24 h or be severe

and progressive.

2-  Horse that does not perform to expectation and displays a stiff or short

stepping gait that may be mistaken for lower leg lameness.

3-  Reluctant to move when placed in its stall.
4-  Apprehensive and anorexia, paw, and frequently shift its weight.
5-  More severely affected have hard and painful muscles (usually gluteal

muscles).

6-  Sweat excessively.
7-  Tremble or have widespread muscle fasciculations.
8-  Elevated heart and respiratory rates.
9-  Deep red urine (myoglobinuria) occurs but is not a consistent finding.
10- Severely affected horses may be recumbent.

Differential diagnosis: 

1-  Polysaccharide storage myopathy of Quarter horses
2-  lonophore intoxication (monensin, salinomycin).
3-  Equine lower motor neurone disease.
4-  Hyperkalemic periodic paralysis.
5-  Laminitis.
6-  Colic.
7-  Pleuritis.
8-  Aorto-iliac thrombosis.

 Clinical Pathology: 

1-  Mildly  or  inapparently  affected  horses  have  moderate  increases  in serum  creatine  kinase  (CK)  (20  000-5  0  000  IU/L),  aspartate aminotransferase (AST), and lactate dehydrogenase (LDH) activity.

2-  Severely affected horses have large increases in CK (>100 000 IU/L) and other muscle-derived enzymes.

3-  Serum myoglobin concentrations increase markedly during exercise in affected horses, and decline within 24-48 h.

4-  Severely  affected  horses  are  often  hyponatremic,  hyperkalemic, hypochloremic and azotemic.

5-  Myoglobinuria is detectable either grossly or on chemical analysis.
6-  Muscle biopsy.

 Pathogenesis: 

1. during exercise or inadequate antioxidant activity.
   2.  Increased oxidant formation lead to oxidant injury to cells.
   3.  Accumulation of calcium in intracellular fluids secondary to deranged energy and/or membrane function.

4. Dysfunction and death of myocytes.
   5.  Subsequent  release  of  cellular  constituents,  including  the  enzymes creatine  kinase,  aspartate  aminotransferase  and  carbonic  anhydrase, and myoglobin.

6. Necrosis  of  myocytes  caused  pain  and  inflammation  in  the  muscle, with infiltration of inflammatory cells.

7. Release  of  cellular  constituents  results  in  electrolyte  abnormalities,primarily  a  hypochloremic    metabolic  alkalosis,  a  systemic inflammatory response, and pigmenturia.

8. acute renal failure can develop as a result of myoglobinuric nephrosis.

 Treatment of Azoturia in Horses

Once it has been determined that your horse is suffering from azoturia, your veterinarian will give you detailed instructions on caring for your horse.

Rest

Keep your horse calm and allow them to rest, preferably in their own stall. Keep the hindquarters warm by putting a coat or blanket over them. Put some hay out for your horse. Eating can calm a horse, just do not give any feed that is carbohydrate based.

Hydration

Encourage re-hydration by offering clean, fresh water often. Keep an eye on how often your horse urinates and if the color is not normal. If you notice extremely dark urine, contact your veterinarian for another assessment as there could be an underlying cause that was not diagnosed.

Supplements

In cases of azoturia where nutrient deficiencies are present, your veterinarian may prescribe a special nutrient rich food for your horse. In some cases, vitamin injections may be necessary.

How do you treat Azoturia in horses?

The treatment protocol of Azoturia in horses is as follows.

• Treatment of the severely affected horse involves preventing further muscle damage, correcting metabolic abnormalities and dehydration, and analgesia in animals that are in extreme pain and reluctant to move.
• In severe cases, even walking back to the barn is contraindicated. In those cases, transport to a stall should be arranged. In mild cases, with minimal muscle damage, hand-walking has proven to be beneficial. Experienced clinical judgment is necessary to ascertain which cases benefit from additional exercise.
• In cases of severe dehydration and electrolyte imbalance, a balanced polyionic electrolyte solution should be administered IV or through a nasogastric tube.
• Many endurance horses suffering from this disease will be alkalotic, and therefore bicarbonate therapy should be avoided.
• Myoglobin can be nephrotic, especially in the dehydrated animal. Myoglobin possesses vasoactive properties that in the dehydrated horse may encourage the development of renal ischemia and tubule damage. Serial monitoring of the PCV, TP serum electrolytes, and creatinine should be performed.
• NSAIDs, such as phenylbutazone, help relieve muscle pain and spasm. Acetylpromazine reduces anxiety and improves peripheral blood flow through the alpha-adrenergic blockade. In extremely anxious horses, small doses of xylazine butorphanol or detomidine may be indicated.

Care of Azoturia in Horses

Care and Management of Monday Morning Disease

-Horses that have a history of tying-up need to be trained and exercised on a regular basis. Each individual horse is different, the best training schedule will probably be determined by trial and error. Nervous patients need to be calmed down by educating them or with drugs if necessary. In our practice we have used hormone therapy in racing females, however, their behavior will become somewhat aggressive and we do not recommend this treatment where children or inexperienced horsemen are involved. Nutritional supplements help some of these horses.

• Good nursing care is essential. A warm, comfortably bedded stall in an environment that encourages the horse to rest is essential.
• The horse should not be encouraged to stand if it wishes to remain recumbent.
• However, prolonged recumbency in one position can be detrimental, and frequent repositioning may be necessary.
• If the patient remains recumbent for an extended period, a padded helmet helps protect the head and eyes, and ocular lubricant and antibiotic ointments help prevent corneal ulcers.
• The distal limb should be bandaged to prevent self-trauma.
• Massage and warm blankets may also encourage muscle relaxation and blood flow.
• A variety of od hand-held electric, pulsating massagers is commercially available.
• By using light pressure, the massager is directed ina circular motion over the large muscle groups for 10-15 min two to four times daily.
• Severely affected horses with painful muscles may object to this technique.

 

Tying Up in Horses

Tying up in horses is commonly used to describe horses that are stiff and reluctant to move due to pain originating from the muscle groups within the back, pelvis and hind limbs, it may also be accompanied by excessive sweating, increased heart rate and respiratory rate. Tying up in horses may also be known as; Monday morning disease, Azoturia and Paralytic myoglobinuria.

Tying up can be classed as;

1. RER- Recurrent Exertional Rhabdomyolysis
   • RER is often seen in Thoroughbreds, Standardbreds and Arabians
   • It is most likely due to the inability to regulate electrolyte levels in skeletal muscle, affecting muscle contraction
   • Is more prevalent in fillies with alert temperaments (>20%)
   • RER has been found to affect approximately 4.9% (USA), 5.4% (AUS) & 6.7% (UK) of racing Thoroughbreds.
   • A survey 69 farms within KSA concluded the prevalence of tying up as being 4.5% (Al-Ghamdi, 2008)
   • High-performance exercise in hot, humid climates may elicit sporadic ER due to the degree of fluid and electrolyte loss
2. PSSM- Polysaccharide Storage Myopathy (PSSM)
   • Most commonly found in Quarter horse-related breeds, draft horses and Warmbloods
   • PSSM is a heritable trait which results in insulin sensitivity and the abnormal accumulation of glycogen within skeletal muscle
   • May be identified by muscle biopsy and the presence of abnormally high glycogen concentrations – 1.5 – 4 times higher than a normal horse
   • The accumulation of sugars within the muscle tissue may occur gradually over a period of up to 18 months
     • Genetic carrier may not present signs of PSSM due to prolonged glycogen accumulation

Indicators of tying up in horses

• Episodic tying up is associated with poor performance, reluctance to move and a significant elevation in muscle enzyme levels
• Blood enzyme indicators:

Creatine Kinase (CK) and Aspartate Transaminase (AST)

• CK is a short term muscle enzyme used as an indicator of recent (peaks at 6-12 hours) muscle tissue damage. >400IU
• AST is a muscle enzyme which may remain elevated for days-weeks following CK elevation. >1,000IU

• High myoglobin levels may be found in the urine as a result of muscle fibre breakdown, giving a coffee coloured appearance
• Clinical signs usually arise shortly after the onset or commencement of exercise, during times of stress and/or excitement

What horses are at risk of tying up in horses?

Risk factors associated with tying up include;

• Dietary excess of soluble carbohydrates (e.g. starch and sugars)
• Frequency of exercise or changes in exercise routine
• Heritability
• Vitamin E and selenium deficiencies
• Degree of fluid and electrolyte loss
  • General electrolyte deficiency
  • Calcium regulation

TYING-UP IN HORSES

Monday morning disease

 

Compiled  & Shared by- Team, LITD (Livestock Institute of Training & Development)

Image-Courtesy-Google

Reference-On Request.