Horses
Electrolyte Paste to Restore Fluid and Acid Base Balance in Horses
“Prolonged exercise in horses, particularly when performed in hot and humid conditions, brings about large fluid and electrolyte loses which, if not restored, may impair thermoregulatory responses and result in hyperthermia.” In horses, administration of oral rehydration solutions (ORS) is problematic, because many horses refuse to drink fluids containing electrolytes. Therefore, administration of ORS typically requires placement of a nasogastric tube with its inherent risks. An alternative is to give a concentrated electrolyte mixture as a paste. Leon et al. of Department of Veterinary Clinical Sciences, University of Sydney, NSW, Australia studied six Thoroughbred geldings to determine “whether oral administration of a concentrated electrolyte paste would promote the restoration of fluid, electrolyte, and acid base balance as well as fluid and electrolyte deficits induced by furosemide administration” (a standard model which induces significant contraction of plasma volume and consistent electrolyte deficit against which the effects of treatment could be measured). “As a general conclusion, horses that received concentrated electrolytes [and had free access] to water consumed more water, regained more weight, lost considerably less electrolytes in urine, and maintained plasma electrolyte concentrations and acid base balance closer to baseline values than did those that had ad libitum access to water only.” Administration of electrolyte paste provided a more practical source than supplementation using feed or salt blocks.
Am J Vet Res 1998 Jul;59(7):898-903
Progesterone for Estrus Induction in Mares
According to Robert R. Foss, DVM, progesterone in sesame oil, 150 mg per day, IM is equally as efficacious as altrenogest. The optimal formulation is the combination of progesterone and estradiol 17-beta; the addition of estradiol provides a greater feedback than progesterone alone, so cessation produces a more dramatic response. The estradiol is somewhat protective against exacerbation of endometritis. Dr. Foss commonly uses this combination at 150 mg progesterone and 10 mg estradiol 17-beta, IM, daily for 10 days. Estrus will usually begin in 6-8 days with ovulation around day 10-12. This combination has been effective in situations where altrenogest has failed.
114th IL VMA Proceedings, February, 1996
Prednisone (Oral) Ineffective in Horses
Jackson et al. compared the effects of prednisone with environmental management to environmental management alone for the treatment of heaves (recurrent airway obstruction), and reported that oral prednisone has no additional benefit.
To be effective, oral prednisone must be absorbed and metabolized to its active form prednisolone. Robinson et al. designed a study with two objectives:
- to compare oral prednisone with intravenous dexamethasone for the treatment of horses with heaves; and
- to measure serum prednisolone levels in horses after oral administration of prednisone and prednisolone.
Each of five horses received five drug formulations (prednisone and prednisolone in tablet and liquid form, as well as intravenous prednisolone sodium succinate as a positive control, all at a dose of 2.2 mg/kg) in a Latin square design study. Severity of airway obstruction was measured, and there were no significant differences between prednisone administration and no medication at any time. Prednisolone was detectable in serum immediately after intravenous administration, peaking at around 1000 ng/ml at 12 min. Oral administration of prednisolone tablets or liquid yielded peak serum prednisolone concentrations of 377-1032 ng/ml at 30-45 min. When horses received oral prednisone tablets or liquid, prednisolone never reached detectable levels in the serum. The authors concluded: “in order for the drug prednisone to be effective after oral administration it must be absorbed from the gastrointestinal tract and converted to the active drug prednisolone by the liver. Although trace serum levels of prednisone were detected, prednisolone never appeared in the serum. Our data do not allow us to determine if prednisone is poorly absorbed, rapidly excreted, or not converted to prednisolone by the liver. However, it is clear that prednisone is unlikely to have any anti-inflammatory effect when administered by mouth. Oral administration of prednisolone is likely to be beneficial because it is rapidly absorbed and achieves serum levels close to those that result from intravenous administration.”
Robert N. Oglesby, DVM (The Horseman’s Advisor, www.horseadvice.com) reports his reaction to hearing the above presentation at the November, 2000 meeting of the American Association of Equine Practitioners: “I was shocked and looking around me hundreds of other vets were also: oral prednisone doses are in every equine medicine text with many descriptions of its indications. Why has no one noticed the lack of effect before now? The reason is simple: no one believed it was possible that [prednisone] was not effective [in horses]. Its usefulness in other species was too well established… we did not even question its use. Looking back on it, it was the management changes that were responsible for the clinical improvement…”
We can compound prednisolone into the most appropriate dosage form, including oral pastes or “chewies” that horses will love!
Equine Vet J 2000 Sep;32(5):432-8
AAEP Proceedings, Vol. 46, 2000, pp. 266-267
Equine Vet J. 2002 May;34(3):283-7
Pentoxifylline
In horses, a dose of 8.5 mg/kg orally two times daily is recommended for reducing the cytokine effects in endotoxemia. For the treatment of navicular disease, 6 g/day orally for 6 weeks should be used.
Compendium 23(7), July 2001, 603-4
Anti-Diarrheals for Foals & Horses
Treatment of diarrhea should always be based on establishing a diagnosis and correcting the basic cause. Anti-diarrheal products are not a substitute for adequate fluid and electrolyte therapy when dehydration or shock threatens. When the veterinarian deems anti-diarrheal therapy is appropriate, the following options may be considered.
According to James L. Becht, D.V.M., M.S., Diplomat ACVIM, preparations containing bismuth subsalicylate seem superior to those containing kaolin, pectin, or activated charcoal for treating the foal with diarrhea. Bismuth subsalicylate neutralizes bacterial toxins, has some antibacterial activity, and may exert an antisecretory effect. It can be administered at a dosage of 4 oz q 6h; darkened feces will result. If no effect is seen within 48 hours, continued administration is probably not indicated. (105th Ohio VMA).
Wendy E. Vaala, V.M.D., Diplomate ACVIM reports (ACVIM 16th Veterinary Medical Forum) that delayed gastric emptying and gastroduodenal dysmotility can be improved in some foals with metoclopramide (0.25-0.6 mg/kg, PO q4-6h), erythromycin (1.0-2.0 mg/kg PO q6h), or cisapride (10 mg/kg PO q6h). If colic, ileus, and gastric reflux are present, Dr. Vaala recommends an abdominal sonogram to rule out the presence of an intussusception prior to initiating prokinetic therapy. Diarrhea may be treated symptomatically with bismuth subsalicylate (1-2 ml/kg, PO, q4-6h) and may also respond to psyllium administration. Intestinal probiotics containing Lactobacillus bacteria … may be given to foals receiving antibiotics to help reestablish intestinal flora.
Adult horses may be treated with bismuth subsalicylate 1 oz per 8 kg of body weight PO TID-QID (Clark and Becht 1987).
Headshaking in Horses
Headshaking may include additional signs such as nose rubbing, striking at the nose with the forelegs, or active avoidance of light, warmth, or wind on the face. Newton et al studied 20 mature horses with typical headshaking of 2 week to 7 year duration, and concluded that the etiopathology may be a trigeminal neuritis or neuralgia. In 12 of 20 horses, drug therapy was initiated. Cyproheptadine (CP) alone was ineffective but the addition of carbamazepine (CM) resulted in 80-100% improvement in 80% of cases within 3 to 4 days of beginning drug therapy. Seven cases were treated with a combination of CM (4 mg/kg, three to four times daily) and CP (0.2-0.5 mg/kg every 12 to 24 hours).
Carbamazepine alone has been effective in 88% of cases. Some headshaking horses have responded well to CM doses of 1.6 – 2.4 grams every six hours without apparent side effects. Horses are treated for 10 to 20 days and if they respond, the treatment is discontinued. If clinical signs of headshaking recur, treatment is restarted. In practice, there is a realistic possibility of controlling but not curing headshaking with carbamazepine therapy at the present time. Other studies have reported that cyproheptadine alone was beneficial in more than two thirds of treated horses.
Equine Vet J 2000 May;32(3):208-16
Equine Vet J Suppl 1998 Nov;(27):28-9
J Am Vet Med Assoc 2001 Aug 1;219(3):334-7
ISU Vet Med Sept 2000
The Pennsylvania State University Veterinary News, Dec 2000, pp 9-10