A study of parotid salivation in the horse.

This research article investigates the factors influencing salivation in horses, particularly focusing on the parotid gland. The researchers determined the effects of various stimulating and inhibiting substances on saliva flow and analyzed the effects of a dietary sodium bicarbonate supplement on the saliva’s electrolyte composition.

Research Methods

• The study focused on the parotid gland, one of the major salivary glands in horses. The researchers measured the saliva flow from the parotid duct during the horse’s mastication or chewing.
• The researchers administered a surface-active local anesthetic by mouth to observe its inhibitory effect on salivary secretion.
• They were also interested in the effects of stimulating and inhibiting substances on saliva production. For this, they used pilocarpine, a substance known to stimulate salivary secretion, and atropine, a substance known to inhibit it.
• To analyze the salivary composition, they measured the volume and identified the electrolyte levels (sodium, potassium, calcium, chloride, and bicarbonate) of the saliva secreted from one parotid duct in 24 hours.

Key Findings

• The results showed that saliva flowed from the horse’s parotid duct only during mastication. The surface-active local anesthetic administered by mouth inhibited salivary secretion.
• Consistent with expectations, salivary secretion was stimulated by pilocarpine and inhibited by atropine.
• The volume and composition of saliva varied, with the concentration of sodium, potassium, calcium, chloride, and bicarbonate depending on the rate of flow. The highest concentrations of these electrolytes were observed during periods of high flow rates.
• Interestingly, horse parotid saliva contained a high concentration of calcium, differentiating it from human saliva, which is typically high in sodium and potassium.
• The researchers also found that the sodium concentration in the saliva fell after about 21 days in the absence of a dietary supplement of sodium bicarbonate, with a concurrent increase in the potassium concentration. When a sodium supplement was added back into the diet, the sodium concentration of the saliva was restored within 24 hours.

Significance and Application

• This study provides valuable insights into the physiology of horse salivation and can improve our understanding of equine health and nutrition.
• The findings about electrolyte concentrations connected to saliva flow rates and diet composition could benefit the equine industry by informing dietary guidelines to promote horse health and performance.
• The ability to manipulate salivary production through administration of certain substances could have practical applications in veterinary medicine, such as treating horses with dry mouth conditions or other oral health issues.