Counterirritation, one of my favorite therapeutic mechanisms which has been long ignored by the modern veterinary clinician. Less so by your old time racing practitioner, who has waged the war in the trenches at race tracks across the country and knows better. I recall racing a horse at Prairie Meadows Race Track a number of years ago. I had won a race and was back in the spit barn giving the required samples of saliva and urine. The track vet was taking my horse's saliva sample, and he had in tow, a young female 4th year Vet student out of Ames. She was commenting that counterirritation was useless, a myth, a superstition from the dark ages. I was a bit taken a back and ventured into her conversation saying that counterirritant was far more useful than she may realize. I am sure she looked down her young academic nose at me, probably resenting my intrusion into the conversation. Years later, I have often wished I had brought up to her a common experiment which demonstrates the value of counterirritation, wonderfully. What does one do naturally when one has an itch, an insect bite, or any abrupt injury to the body? Almost invariably, one scratches in the case of an itch or rubs briskly in the case of other injuries. What you have is instantaneous counter irritation applied with your scratches or rubbing actions. It feels better. Counterirritation simply works whether physically or chemically applied.

     Counterirritation is the application of a secondary man-made irritant to the site of the original injury, the primary irritant. Traditional Veterinary counterirritation applications were done with mineral/herbal irritants, massage, firing irons, setons, etc. All different degrees of irritation have been used and prescribed ranging from the mild stimulating properties of a body wash to the extreme burns perpetrated by mineral blisters or the firing iron. This degree of applied therapeutic irritation has always been a much debated controversy. How much is beneficial and how much is barbaric? No easy answers, just some basic guidelines.

     I have yet to see any scientific studies trying to demonstrate why counterirritation works. Many texts will honestly say up front that no one knows for sure how it works. I have only found possible theories thrown around. It is generally thought and rightfully so, that the therapeutic effects come from the secondary inflammation which is generated from the applied irritant. You will have vasodilation or increased blood flow as a primary reaction. Accordingly, you will have a cleansing of any toxic byproducts, blood vessel permeability/leaking, an increase in various leukocytes aiding in the healing process, a wide array of enzymes being released. It has long been known that an inadequate blood supply to the injured area will retard proper inflammation and, thus, healing. This theory does not satisfactorily explain why there is often a pain relieving benefit from counterirritation. As with most physiological processes, nothing is ever as simple as it seems.

     I have used counterirritation in my racing stable over the years as an indispensable adjunctant to keeping my horses sound. Leg paints, liniments, sweats, and hypodermic injections were my main routes of favored administrations. The leg paints would include what is commonly called working blisters. I have never resorted to firing or severe blistering, though they may have their place in certain isolated cases. I just have never found one. Barbarity can be found only in the practice of trying to apply far too much inflammation for the horse's well being. Too much inflammation is just as bad as too little. A close monitoring of the injury is always a must when applying your choice of counter-irritation for proper affect.

     Various leg paints, working blisters and severe blisters have been used for tendon and ligament problems for many years in the racehorse business.  These are mostly of the counterirritant variety that can contain varying amounts and combinations of  iodine, mercury, cedar oil, camphor, oil of wormwood, oil of organum, mustard seed oil, croton oil, etc.  These extracts are mostly carried in ethanol and/or DMSO bases and is designed to stimulate blood circulation when painted on the affected region. The only problem is, it doesn't stimulate a return mechanism.  Its a one-way street if you  only stimulate blood flow without pumping it out. Used by itself on a horse at rest is not particularly good.  You will get an accumulation of blood and fluid from this type of stimulation and stagnation could likely occur opening your horse up to adhesion formation.   What is known as a "working" leg paint  is useful as you use these types of light blisters while at the same time exercising your horse. The paint will stimulate blood lymph flow and the simultaneous daily exercise will stimulate the pumping away of the blood, lymph, toxins.   A combination that should be present when using a counterirritant!  I tend to like iodine in my counterirritant leg paints and there are all types of iodine formulas.  Rite's knee & hock paint is a pretty useful formula and I have used it for years.  For its formula, go to my leg paint web-page.  I would stay away from the severe blisters that particularly contain cedar oil and mercury.  I have seen and used my share of these while working for some old timers, but I have long felt that this degree of blistering does little therapeutic good.  This is one aspect of our racing history where our forefathers probably went wrong.  One should avoid tissue destruction that is seen in these types of blister applications.  If you have to use a neck cradle on your horse as is often the custom when using a severe blister, then something is inherently wrong with the treatment!  Same holds true for using a hot firing iron.  Even though our old time horsemen swore by the effectiveness of firing a horse, it is just another out-cropping of the human tendency to believe "more is better".   I never fired a horse in my life that I trained, nor used a severe blister.   I  feel I missed nothing in not using them.  I always  preferred a light blister that only would affect the skin by stimulating some scurf crusty formation after a few days of application---nothing more severe.  In most cases, I don't think you will need to apply a counterirritant paint to a bad suspensory but every case is different and at times, one may want to stimulate an increased blood supply to the injured ligament.  If so, then use a counterirritant.

       One should look to a brilliant equine physiologist, Charles L. Strong to some insight into stimulating therapeutic vaso-dilation.  He writes:

"Some produce deep heat, others superficial heat, but none the less the effect is basically the same, i.e. dilates the blood-vessels and so brings more blood to the part but does little to stimulate the venous and lymphatic return.  So, in fact, the circumstances are similar to the tremendous in-flow traffic into a large city in the early mornings. So much traffic comes into the center of the town with so little going out that in a very short space of time the center of the town is so congested that there is hardly any circulation of traffic at all.  Too much heat, no mater how it is applied, does not increase circulation of the blood; as with the traffic, heat can cause such a congestion that it slows down the circulation, especially in denser structures such as tendons. It must be said, however, judicially applied heat is nearly always comforting; and it would be more comforting if the blood so brought to the part could be encouraged to return by the veins and lymphatics, but this cannot be achieved without muscular activity."

     
So take note,  it is all well and good to stimulate blood flow by counterirritation, but one must use muscular movement regime to avoid a congestion which will open many injuries up to adhesion formation--if blood and lymph are allowed to pool and stagnate.   This is why I almost only employ a working blister, that is, only apply a counterirritant when your patient can be worked at exercise.  One can stimulate blood flow with a counterirriant while also forcing a return of that blood flow via muscular movement!  This combination is vital for healing!

Below is an excerpt from Veterinary Materia Medica and Therapeutics by Kenelm Winslow, published in 1913:


Counter-Irritants

     A counter-irritant is an irritant which acts counter, or against an existing irritation, result of irritation, or pain. In applying a "twitch" to a horse, we are inflicting an irritation to relieve some other source of irritation elsewhere. It is taken for granted that the damage and pain caused by the artificial irritant are not as severe as those already existing. The amount of injury produced by an irritant depends upon the nature of the material, its strength, the duration of its action, the mode of application, and the part to which it is applied. We may consider the effects occasioned by a mild and increasing action following the continued use of a single agent, or representing the action of materials of different degrees of potency. There first appears redness of the skin, accompanied by some burning or pain (rubefacient action), and if the irritation progresses there is a serious exudates poured out into the mucous layer of the skin. This leads to swelling and edema. Greater irritation causes more exudation of serum and an elevation of the epidermis is a circumscribed area or areas, and the formation of blebs or blisters (vesication). If the irritation ceases at this point, the blisters break open and their contents dry on the surface, covering the parts with a thick scab. Synchronous with vesication we observe a similar process attacking the hair follicles. The hairs are loosened and fall, but as the papillae are usually unaffected, the growth of hair is soon renewed. The recovery of hair is facilitated by the application of grease to parts. Certain agents cause circumscribed inflammation of the gland orifices of the skin with the formation of pustules (postulants), as croton oil, and these create necrosis of the hair papillae, and, therefore permanent loss of hair. If the irritant is severe, suppuration follows vesication; or, if an ordinary irritant is applied with violent friction, is covered with a bandage, or placed over an already inflamed part, the same result happens. The terms referring to the degree of action inherent in agents are as follows:


1. A rubefacient, causing hyperemia.
2. A vesicant, or epispastic, inducing blistering.
3. A postulant, creating pustules.
4. An escharotic or caustic, occasioning death of the tissues.

      The same agent, as has already been pointed out, may produce one or more of these actions according to circumstances. The inner aspect of limbs and the flexures of joints are peculiarly sensitive owing to the thinness of the skin over these areas. If a counter-irritant is rubbed properly into the skin, it may penetrate into the mucous layer.

     Reference has been made to the local influence of irritants. We will now direct attention to their remote effect. It is certainly known that irritation of the surface decidedly affects distant organs. Brown-Sequard noted contraction of vessels in one arm when the other was immersed in cold water. Severe burns of the surface are followed by duodenal ulcers. The preceding and succeeding remarks enable us to partially account for the remote influence of counter-irritants, but although we know their practical value, it is not within our present knowledge to offer theories wholly explaining their effect.

     The influence of counter-irritants may be summed up in reflex action; i.e. the production and conduction of an impulse from the periphery to nerve centers, thereby modifying the nerve functions and blood supply in distant parts.

     The skin is commonly the point of application. It normally is an organ of protection, respiration, secretion and special sense, and, through its medium, a regulator of temperature, responding to such natural stimuli as heat, cold, moisture and dryness. Such an unnatural and considerable stimulation as is produced by counter-irritants consequently creates very sensible alterations in the bodily functions. Extensive counter-irritation causes the breathing to become slower and deeper by reflex stimulation of the respiratory center and also by making the respiratory movements more painful, if the application be made to the chest wall. The circulation is likewise affected by stimulation of the vagus and vasomotor centers, and both the force of the heart and blood pressure are increased, unless the irritation is very widespread and severe, when the reverse happens. The abdominal vessels are those constricted; the vessels of the skin and the limbs are unaffected. In accordance with the foregoing remarks the use of considerable heat, together with mustard or turpentine, is of great value in conditions of vital depression, surgical shock, collapse, and coma. Moreover, the effect on local blood supply is still greater and full of importance, since it may explain the beneficial action obtained in the ordinary use of counter-irritants. In experiments conducted upon animals, it has been observed that when sinapisms are placed over the head, the blood vessels in the pia mater are first dilated, but soon contract and remaining in that condition for some time. Likewise there was seen, following energetic counter-irritation of the chest, anemia of the underlying parts, including the muscles, pleura, and even the pulmonary tissue. It is essential to bear in mind, then, that while counterirritants induce local congestion in their immediate vicinity, they also cause reflex vascular contraction in more remote areas. In accordance with this demonstration, the important of these agents in remote inflammation lay not so much in their bringing blood to the surface, as in forcing it out of distant parts. This fact is not generally appreciated. The use of the word, "drawing" signifies the common idea of counter-irritant, and implies the first proposition.

     Temperature is not materially affected by therapeutic use of counter-irritants, and they are not necessarily contraindicated in fevers. Experiments, however, appear to show that mild counter-irritation may lead to a slight elevation of body-heat, owing to stimulation of the calorifacient centers, while extensive and prolonged action lowers temperature by depression of the heart and heat centers, and because more blood flows through the peripheral vessels owing to constriction of the vessels in the abdominal organs.

     Counter-irritants notably relieve pain. This result is not only due to overcoming congestion, but occurs when pain is purely neuralgic. The phenomenon is not altogether explicable. The subduing influence of the twitch in the case of pain inflicted upon a horse is an analogous example. Wechsberg, in some late experiments, notes, as a most striking effect of counter-irritants, edematous infiltration of the skin, subcutaneous tissue and muscle is sub-adjacent parts, with compression of blood vessels in the deeper-lying structures. He attributes the relief of pain afforded by counter-irritants to anemia and rapid compression brought to bear on the nerves in these underlying parts.

     Still this explanation does not interpret the relief of pain sometimes seen in parts remote from the point of application of counter-irritants.

I     n disease of internal organs, Head has constantly found certain corresponding areas of skin tenderness. This because both the internal organ and the skin area are innervated from the same segment of the brain or cord. Theoretically and practically counter-irritation of a skin area affects the internal organ corresponding (by nervous connection) to this area more than other parts. These areas of skin tenderness for diseased internal organs, and for application of skin irritants to relieve these conditions, have been mapped out in man. In the case of the chest and belly they are situated pretty nearly over the site of the internal organ. In the head the sensitive skin-sites are not over the diseased part.

     Pain is usually referable to the peripheral ends of an affected nerve. It is a good practice to apply counter-irritation directly over a deep seated inflammation or seat of pain (see above), but in assuaging superficial pain it is found, that where the treatment can be made over the root of the painful nerve, better results are obtained. In pain in the chest wall, a blister should be placed next the spine over the root of the spinal nerve involved; in pain in the head in man, counter-irritation is applied over the back of the neck. Counter-irritation should be done over the temple, in pain in the eye (iritis); behind the ear, for pain in that organ.

     In treatment of enlarged glands and in acute inflammations, as abscess, boils and carbuncles, by counter-irritants the application should be about the lesions rather than directly upon them.

     Among other actions accomplished by counter-irritants are: possible stimulation of trophic nerves and nutrition of a part; augmentation of tissue change, locally and generally, and dilation of vessels (when applied after the subsidence of acute inflammation or in chronically inflamed parts), with renewed activity of the circulation and consequent absorption of inflammatory exudations. The local action of skin irritants increases the leucocytes and opsinins in inflammatory area (acted upon) and leads to bacterial destruction. The toxins are also more rapidly removed by their influence. Furthermore, counter-irritants reflexly overcome spasm and pain occurring in colic, by stimulating and replacing normal peristaltic action in place of abnormal localized contractions. In like manner, they excite uterine contractions by stimulation of the involuntary muscular fibers of the womb.


Indications for Counter-irritants:


1. To overcome congetion and inflammation in remote parts.
2. To promote absorption of inflammatory products locally.
3. To relieve pain.
4. To stimulate the heart, respiration, and nervous functions.


Rubefacients. --- In this class are included the volatile oils: turpentine, oil of wintergreen, etc.; alcohol chloroform, balsams, resins, iodine, tincture of camphor, tincture of cantharides, mustard, and heat. These agents are used when it is desirable to stimulate the nervous system rapidly, and to relieve pain and congestion. To attain this end, we employ comparatively mild agents in order that we may apply them over an extensive surface without causing serious or permanent results. Mustard is rubbed with warm water into a thin paste (a sinapism), and rubbed over the chest of horses in congestion of the lungs, in acute bronchitis, or in the first stage of pleuritis, to obtund pain and lessen congestion. Sinapisms also relieve obstinate cough, revive failing respiration, and stimulate reflexly the vital functions in collapse, shock and narcotic coma. Applied over the cardiac region, they avert syncope. To assist the action of mustard, we often cover the application with hot blankets, and then with dry ones. Stimulating liniments are sometimes preferred. One volume of oil of mustard may be combined with fifteen volumes of oil of turpentine; or ammonia water, thirty parts, and oil of turpentine, fifteen parts, are added to spirit of camphor and soap liniment, each fifty parts.

     Turpentine is more valuable in abdominal disorders in horses. It is sprinkled on hot blankets, and applied as a stupe to stop pain, spasm, and stimulate normal peristalsis in colic; and to relieve pain and congestion in enteritis, peritonitis, diarrhea and other difficulties. The beneficial result accruing from the use of external counter-irritants in bowel troubles is often facilitated by the injection of hot (115 degrees F) rectal enemata.

     Stimulating liniments are serviceable in aiding resolution of swelling following the acute stage of cellulites, lymphangitis, neuritis, mammitis, rheumatism, strains and bruises. They are often employed in laryngitis. In chronic skin diseases, as eczema, mild counter-irritants (tar, oil of cade, Peruvian balsam, etc) substitute an active reparative process, tend to aid absorption of exudation and induration, and relieve pain and itching. The tincture of iodine may abort incipient inflammatory lesions as boils and abscess, by means of its counter-irritant and antiseptic properties.

Vesicants and the Actual Cautery.
Cantharides, red iodide of mercury, and croton oil are more commonly used in veterinary medicine to cause blistering. Reference will be had, hereafter, to cantharidal blisters. Blisters and the cautery are especially indicated to cause resolution of inflammatory products and modifications of inflammatory processes; to secure fixation and rest of parts, and to relieve pain. It is impossible to enumerate all the conditions in which they are useful. In the treatment of severe sprains, as curb and "breakdown"; and in exostoses, as ringbone and spavin, the actual cautery (firing) is used before and in conjunction with blistering to exaggerate the counter-irritant effect. Absorption is attained in the foregoing conditions by production of an acute inflammation, with increase of vascularity, tissue change and fatty degeneration. In "breakdown" the formation of scar tissue is thought (without reason) to assist in supporting the limb. Sometimes, on the other hand, osseous deposit is unabsorbed, but anchylosis and freedom from pain in a diseased joint is secured by the enforced maintenance of rest and fixation of the joint, together with the production of the new bone.

In exudative diseases of serous membranes, as pleuritis, percarditis, peritonitis, meningitis, arthritis, and synovitis, blisters facilitate absorption and recovery after the acute stage is over. The favorable result is not due to loss of serum, but to modification of the inflammatory process. In the first three diseases named above, blisters-flying blisters-may be applied in spots every few days in different places over the affected area.

Blisters reflexly stimulate the nerve centers in meningitis, in addition to their action on the inflammatory lesion. They should be applied over the poll or spine according to the location of the trouble. Absorption in chronically enlarged glands is assisted by blisters. They also hasten "ripening" of suppurating glands or abscess when this process is slow and hasten their resolution after evacuation of pus. The blister should be rubbed on about the inflamed area in these lesions.

Vesicants are also valuable in pharyngitis and laryngitis for severe cases, when stimulating liniments are ineffectual; and, in lessening pain, exudation and swelling of the throat, may avert the necessity of tracheotomy. A blister applied about the coronet in diseases of the feet is serviceable in stimulating the growth of the hoof and promotes repair in navicular disease, laminitis, and cartilaginous quittor, after the acute stage is passed. In arthritis and synovitis, the whole disease area, with the exception of the flexure of the joint, is covered with a blister. Since it is often impossible to immobilize a part, in veterinary practice, by splints, blisters are sometimes employed for this end after reduction of dislocations.

The hair should be clipped from an area to be blistered, the skin washed with soap and water, and the animal tied up or restrained in some way from biting the part. It is the custom to cover immediately the surrounding parts with grease, but protection from the acrid discharge can be secured more effectively by frequent sponging with soap suds and water; or painting the skin, under the blistered surface, with a solution of rosin in alcohol. Grease is not so good a protective, since it is a solvent for cantharides. Vaseline should be applied following the active stage. (pages: 626-631)

McKay's Maxlin Injection (internal blister) as sold in the 1980s packaged in a sterile serum vial.
     McKay's was produced to be used for strains & sprains of muscles, tendons, and ligaments in horses. It was formulated with 2% iodine USP in an almond oil NF base or sometimes peanut oil in earlier versions. It was very useful stuff and seemed to help in the healing of very hard to treat anatomical injuries often characterized by limited blood circulation. McKay's was a must for rear-end lameness of all types and I would often use two 50cc bottles on a horse in one setting, injecting 2-3cc per site throughout the major gluteal muscles. This was sometimes known as injecting the "whirlbone",  particularly in Standardred racing circles.   I have also used this injectable to treat bad stifles by injecting the three patellar ligaments. I would put about 1-2cc on each side of each ligament.

     I have seen a number of miracle recoveries using such a protocol. You would inject a horse and immediately take him to the track for a work which would help distribute the injected solution. A good sign the next day would be how sore your horse was. The sorer he was, the better the results!

     I know it says on the bottle's instructions to only inject under the skin, but one can and often did,  deep muscle injections.  However, one should try to avoid hitting a vein or nerve when going deeper.   This is done by withdrawing the plunger before injecting the oil.  If you get flow of blood, find a new site.   I have injected cases of this stuff over the 15 years while I trained racehorses and this was how I did it:  My horses suffered no side-effects, only good.

1)    Fill a bucket with very hot-to-the-touch water and place the vials of McKays you plan to inject in it to allow the almond oil base to warm up, reducing oil viscosity. Much easier to inject warm oil that way. I also throw in a bottle of isopropyl alcohol to warm that up, too.

2)    When you get ready to inject, I would advise injecting your horse before a morning work. After injection, take animal out and work normally.

3)    Take the isopropyl alcohol and rub down all of the regions you plan to inject. I only inject 1-2cc per site so one 50cc vial should give you about 25 separate injection sites if you are injecting the rear-end musculature. I give intramuscular injections from the bottle for the heavy rear-end muscles, not the recommended Subq. You can also hit the traditional acupuncture points of this region. I fill a 12cc syringe full of the warm fluid and take a 19 or 20 gauge needle in my right hand and pound my target site with my bare hand (needle protected from insertion) a few times and then the third time down, I move the needle in place and stick the horse rather than inserting the needle first time off the bat into a new site. This seems to trick the horse in not knowing when an actual injection will occur. Once the needle is in the muscle (1-1.5" deep), I take the filled syringe (usually being held in my mouth) and aspirate it slightly to see if blood is drawn into the neck. If no signs of blood, I continue the injection of 1-2cc per site of the iodine solution. I do this all along the injection pattern on the rear-end. I mostly use one bottle per side. You want to stay away from injecting to close to the spinal cord on the top mid-line or other major nerves and veins.
 
4)    With stifles, I usually place 1cc on each side of the ligaments, subcutaneously injected.

5)    After, injection, I gave a very deep muscle massage to try to work the iodine/oil into the muscles. You can use rubbing alcohol or a liniment of some type to facilitate this post-injection massage.

6)    Once injected, take the animal out for a normal work. This tends to work the iodine into and around the muscle even more.

7)    I have found that the sorer the animal is the next day the BETTER! Some of my most successful cases were with horses that could hardly walk out of the stall the next morning as compared to those that walked out normally.





      Internal blisters (2% iodine in almond oil) are rather hard to come by in these modern times.   In the past, anyone could buy McKay's over-the-counter at many tack shops.   No more.   About the only way you can procure some now is via a vet's prescription to a specialized compounding pharmacy.   In my book, A Racehorse Herbal ,  I will show you how you can make a  simplified version of your own in your kitchen.  For now, If you are a vet, I can show you how to make it in your clinic with common lab equipment.



McKay's Maxlin Injection Bulletin #4    (1980s)


Description:          McKay's  injection is a 2.14% (+ or - 0.2%) by weight of total iodine in sweet almond oil.

Action:                   McKay's injection is prepared expressly for the treatment of strains and sprains to muscles, tendons and ligaments which often occur in the training and racing of horses. It is to be used in those cases where a counterirritant would normally be an aid to nature.

Uses:                     It is recommended that McKay Injection be administered b by a registered veterinarian. Best results ware obtained by the use of a # 20 gauge hypodermic needle, 1/2" long.  During cold weather it is advisable to warm McKay Injection by partly submerging the bottle in warm water for a few minutes before using.   All injections are made just underneath the skin.  The exact area to be injected should be fully determined before injections are made. The injections should be made at the focal point of the strain or sprain and within the area involved.  It is essential to cover all points  of the extreme soreness.  Be sure to make  the first injection at  the extreme upper edge of the area involved as the injection tends to work down.

Shoulder & Hips:     Where the strain or sprain has occurred to a muscle or muscles of the shoulders or hips, inject along the area involved, spacing injections from 3 to 4 inches apart  using approximately 3-5cc at each injection  site. After injections have been made, rub the surface gently with the hands  the right way of the hair, for 5 minutes to distribute  McKay  injection underneath the skin as much as possible.  Then apply McKay liniment sparingly, rubbed out between the palms of the hands over the entire area injected.   Apply McKay liniment twice daily thereafter as it aids in keeping up the external stimulation.

Tendons & ligaments:     Where the strain or sprain has occurred in a tendon or ligament, make 2 or more injections according to the length of the area involved, spacing the injections from 2 to 3 inches  apart, using approximately 3-5cc at each injection site.   If soreness is present on both inside and outside of the leg, inject both sides.   After injections have been made, massage the area injected gently with the hands, the right way of the hair for 5 minutes, to distribute McKays injection underneath the skin as much as possible.  Then apply McKay liniment the right way of the hair to entire area injected.  Cover with at least 3 sheets of cotton and then bandage.  Redo the leg twice daily thereafter, using Mckay Liniment each time to aid in keeping up external stimulation.  It is recommend that the horse be given mild exercise each day thereafter, increasing exercise from day to day.  When the horse recovers, training exercises may be started.  Judgement should be used in carefully bringing the horse along in his work.  Special care and attention thereafter should be given the parts that have been injected.  Avoid muddy and slippery tracks as much as possible in training.

Leading Veterinarian  and trainers Testimonies (pre-1970s):

R.P. Wilson DVM:  "After using McKays injection, I am glad to recommend it for the treatment of various kinds of lameness in horses.   In using Mckay injection it has been my pleasure to observe and study physiological changes that take place in diseased tissue.  First,  it dilates the tissues in and around the seat of trouble, allowing the capillaries a free circulation of blood.  The white corpuscles are thereby increased by the thousands which is the only factor that plays any part in repair and because of its proper blending, does not cause an abscess which would tear down tissues,  hereby retarding the building up process which you have started.   In using McKay injection there are several outstanding features.  First,  the injections are made just underneath the skin and not in the diseased tissues.  Secondly, it does not form a hard swelling at the seat of the injection.  With a little hand massage it is diffused in and around the diseased tissues and does not cause any soreness at the point of injection.   The practice of firing has its advantages,  but also its disadvantages when the operator may cut the tissues instead of cauterizing them.  This causes a sluff and again we are tearing down tissues instead of building them up.  Then too, the animal is laid up indefinitely wafting for repair of the broken down tissues,  but when an animal has received treatment of McKay injection,  he is exercised daily and in doing so,  resolution is hastened by increased blood supply to the affected parts.  I have in mind,  one horse that pulled up lame after every work.  After various treatments,  the owner consented to use McKay injection.  After the required amount of time for adjustment and absorption of diseased tissue,  this horse,  to my knowledge has started eight times and won six races."

Vic Fleming:    "I used Mckay injection in my stable with such remarkable success that I do not hesitate to recommend it to everyone!"

Harry Short:     "The  mare I treated for muscular lameness is perfectly sound.  I also used McKay injection on three other horses, one for whirlbone lameness, one for knee lameness, the other had two very bad splints which had been fired twice and blistered several times.  All are now perfectly sound."

Del Cameron:  "Words cannot express the faith I have in your fine product McKay's injection, having used it for at least 34 years in shoulders, stifles, and whirlbones with remarkable success.  I always keep a supply on hand for our veterinarians to use on the horses as I've never had any success  using other internal blisters."

T.A. Hilt:    "I never saw anything work like your McKay injection did on Theo Volo and Lindale.  As you know, they were both lame and we tried everything on them with no results.  Lindale was injected for a splint and six days after the injection,  she was sound and never bothered afterwards.  Theo Volo was lame in he shoulder  and it took only a few days until he was sound,  he never had a reoccurrence of his trouble."

A. F.  Simonson:    "Thanks for your letter concerning Calumet Fieber.  He seems absolutely sound.  Should even be a better horse than last  year.  If it wasn't for McKay injection and good advice last winter;   he wouldn't have been worth a nickle to me.  Injected several good horses on the circuit with good results."

Michael Schneider:    "Raider bowed a tendon so badly he couldn't be cooled out.  We injected with McKay injection and in one week's time returned to the track sound and won.   Finished the season winning."

Fred H. Post:  "We have used quite a number of McKay injections in connection with our polo ponies considering the satisfactory results we have received, we do not hesitate to recommend it  for deep seated lameness."

R.B. Plaxico:      "We  used McKay injection on a two year old filly's hip that looked like I was going to have to quit with and I am very glad to say that I am now training her again."

Harry Fitzpartrick:    "My pacing mare became seriously lame from a curb.  After injection with McKay's, she was sound in ten days  and had no reoccurrence of this trouble.  I cannot speak too  highly for this treatment."

Dale Baker:      "I have injected several horses with McKay injection and have hand 100% success.  Every horse treated got sound."

A. T. Morrison:     " I have found McKay injection to be a great aid to my stable and past year and it  proved successful in all instances where used."

Carl Scott:    "One of my outstanding horses was injected for suspensory trouble. Came home in the fall with his legs looking like a colt's and raced sounder than at any time in his life."




Dr. Borthwick writes about using a similar injection for a bad stifle:

"First, I palpate the three patellar ligaments: the medial, the middle and the lateral patellar ligaments. I inject 5cc at the site where these ligaments meet over the tibeal tuberosity. I then inject 5cc at each of the three sites where the ligaments originate from the patella. The 15cc (from each of the three injections sites) over the patella are concentrated at the site of origin but some is infiltrated over the surfaces of the patella. I then infiltrate 5cc at the site of the lateral femoro-tibial ligament over the lateral femoral condyle. The remaining 20cc I use to infiltrate the muscle mass around the stifle. I use 4cc per site in five sites starting a few inches above the point of the stifle and make an arc over the lateral side and above the stifle joint. I then take another 50cc vial and repeat this procedure on the other leg. Following the injection, the horse should then be worked. This would be a four or five mile jog for a standard-bred or even a training mile. A riding horse should be saddled and ridden for 25-30 minutes with intermittent walk and trot, depending on the horse's condition."

Accupuncture points that are good sites for internal blister injections.
     Lugol's solution can be used as an injectable counterirritant. Here is an excerpt from the Merck Manual on exactly that:

Trochanteric bursitis is an inflammation of the tendon of the middle gluteal muscle, of the bursa between this tendon and the trochanter major, or of the cartilage of the trochanter major. It is most common in Standardbreds, in which bursitis and gluteal myositis are secondary to hock problems.

The weight is placed on the medial wall of the foot so that it is worn more than the lateral wall. The stride of the affected leg is shorter, and the leg is rotated inward. The horse tends to carry the hindquarters toward the sound side. In chronic cases, the muscles between the external and internal angles of the ilium are atrophied, giving the croup a flat appearance. Pressure over the greater trochanter results in evidence of pain.

If the inflammation is acute, the horse should be rested and hot packs applied over the affected area. Injection of corticosteroid into the bursa temporarily relieves the inflammation. In chronic cases, the injection of 1 mL of 5% Lugol
's solution diluted with equal parts of distilled water into or around the bursa as a counterirritant has been recommended.


Even though Merck suggests using 5% diluted in half, I would be more inclined to injecting a 2% iodine solution more on the lines of McKay's etc. Because Lugol's is an aqueous solution, it may be a bit easier to formulate than a McKay's substitute that uses an oil base. I would make an injectable 2% Lugol"s solution like this and inject without the need for diluting:


USP or ACS Iodine......................................2g

USP or ACS Potassium Iodide.........................4g

USP sterile injectable water.......................amount added with above to make 100 ml

Preparation:

Combine the iodine and potassium iodide, then add 5 mL of the water. The iodine should dissolve in a few seconds. When it has, add the remaining water and filter with around a .4 micron sterile filter. The use of a ultrasonic bath may aid in more easily and effectively dispersing the iodine in water before filtering, if you own such a unit. Use sterile technique throughout.
This  is how McKays was packaged pre-1970s.  Notice it was simply packaged in a capped bottle open to the air when ready to fill  a syringe.
Journal of Equine Veterinary Science - J EQUINE VET SCI 01/1983; 3(5):149-153:



The effects of injection of an iodine counterirritant into the patellar ligaments of ponies: Application to stifle lameness



ABSTRACT

Patellar fixation is a common cause of lameness in horses and has been successfully treated by infection of the patellar ligaments with counterirritants. To investigate the effects of this treatment, the medial and middle patellar ligaments of 10 ponies were injected with an oil-based iodine counterirritant solution and then examined morphologically. Vacuoles of counterirritant were present in the paratenon and endotenon of the ligaments and caused severe necrosis and inflammation. At 1 day after injection, there was a marked neutrophilic infiltration which progressed to a lymphocytic infiltrate by 3 days. By 7 days, fibroplasia was present and became more organized with time. Disrupted collagen fibers and numerous, large, pale fibroblasts were present in the fasciculi, but neutrophilic infiltration was absent. The fibrous response in the fasciculi was similar to that present in the paratenon and endotenon. At 28 days, the drug was still present as lipid vacuoles in the paratenon and endotenon, and the damaged fasciculi had not regained their normal appearance. The clinical effect of this treatment was attributed to the change in size and shape of the patellar ligaments resulting from the inflammatory response.
Approximately 90-95% of stifle lamenesses have been attributed to problems involving the patellar ligaments,2 which are essentially continuations of the tendons of insertion of the quadriceps femoris and biceps femoris muscles.3 Upward fixation of the patella has long been recognized in horses in which the stifle joint becomes locked in extension, thus preventing flexion and normal advancement of the limb.6 If forced to advance the limb, the horse may drag its toe on the ground. A more common and subtle form of this condition also occurs. A momentary fixation of the patella may occur which results in a painful, inflamed joint, but obvious locking of the stifle is not seen.8 This problem is common in performance horses.


Diagnosis of the mild form of patellar fixation can be made by standing the horse squarely with the affected stifle in extension and the patella in its most proximal position. According to Habel,4 this is the resting position of the patella as described by Preuss and Henschel.10 With the palm of the hand placed on the patella (left hand for left patella, right hand for right patella), the examiner forces it caudally and slightly proximolaterally (Figure 1). While pressure is maintained on the patella in this manner, the person handling the horse is instructed to move the horse ahead one step. Normally, the medial parapatellar fibrocartilage, which is considered part of the medial patellar ligament,3 will readily disengage from the medial femoral trochlea,4 in our clinical experience, this is not the case in conditioned horses.


Medial patellar desmotomy is commonly performed on horses with patellar fixation.  This procedure has the disadvantage of interrupting the horse's training program. An infrequent but disastrous sequel is rupture of the middle patellar ligament and the resulting inability to extend the stifle joint.  
As an alternative, application of external blisters to the stifle was recommended many years ago.   Injection of counterirritants into the medial and middle patellar ligaments has been described.   This latter treatment, in conjunction with a continued exercise program, has been used successfully by one of the authors (MPB) to treat clinical cases of patellar fixation.

The purpose of this study was to evaluate the histological effects of injection of an iodine counterirritant solution into the patellar ligaments of ponies and relate these changes to the apparent clinical effectiveness of this treatment in horses with patellar fixation.
     Below  is a YouTube video of a thought-to-be promising race prospect Thoroughbred in Argentina that was purchased very sore in late  2014.  He  could hardly walk out of his stall being so lame in his shoulder, nor could he be mounted. The vet thought the old fashion technique of  injecting his shoulder with a 2% iodine in almond oil was the answer, but this formulation is very hard to come by in these post-1980's times.  Only a few compounding pharmacies specialize in formulating this  injectable. Owner  came to me and I  sent two vials of the above 2% to Argentina  for his treatment.  Vet injected horse twice  in January with a successful outcome.   He raced his first start back since a 2 year lay-off on April 19, 2015  in a 1000 meter  Handicap as seen below.  The treated horse went a very spectacular come-from-behind performance goiing way wide on the last turn.  He is the # 3  horse coming in second.