Comparison of tear pH in dogs, horses, and cattle.

The research study compares the pH level of tears in three different animal species: dogs, horses, and cattle. The results reveal significant differences in tear pH and total solid concentration among these species, which could potentially influence their susceptibility to ocular disease and the effectiveness of eye treatments.

Experiment Procedure

• The study involved 28 dogs, 24 horses, and 29 cattle. Under manual restraint, tears were collected from each subject’s left eye using cotton spears.
• The tear volume was measured, and the pH was determined using a microelectrode.
• A Schirmer tear test, which measures the rate of tear production, was conducted in the right eye of each subject.
• The total solids (TS) concentration of the tears was measured using refractometry, a method that measures pressure as light travels through a liquid.

Results

• The mean pH of cattle tears was found to be higher (8.32 ± 0.14) compared to dogs (8.05 ± 0.26) and horses (7.84 ± 0.30).
• The total solids concentration was significantly higher in horses (2.04 ± 1.29 g/dL) compared to cattle (1.07 ± 0.60 g/dL) and dogs (0.33 ± 0.18 g/dL).
• Results from the Schirmer tear test in all three species were within the appropriate reference range for each species.

Conclusions

• The pH of tears in dogs, horses, and cattle differed from the pH values of blood and from commonly administered ophthalmic medications.
• These differences may influence variations in ocular flora (microorganisms in the eye) and defense mechanisms, an animal’s susceptibility to ocular diseases, and the effectiveness and comfort of topical treatments.