Reference Values of Schirmer Tear Test I and II in Clinically Healthy Adult Donkeys (Equus asinus): Effect of Sex

The Schirmer tear test (STT) is essential for estimation of ocular tear production. The present study aimed to establish reference values of STT I and II and study the effect of gender on tear production in donkeys (Equus asinus). Twenty-four donkeys (12 males and 12 females) that had no ocular abnormalities were included in this study. In each animal, 4 STT readings were obtained from each eye, with 1 week interval (2 for STT I and 2 for STT II), with a total of 96 readings for each test. The readings were obtained at a fixed time of the day, while the animals were in the standing position, and without tranquilization. Donkeys were more tolerant to STT II than STT I. Values of STT II were significantly lower than those of STT I (P = .0007). There were nonsignificant differences between the right and left eyes in STT I and STT II (P = .517 and .222, respectively). Regarding sex, there were significant differences between the male and female donkeys in STT I and II (P = .028 and .008, respectively). However, in the males or females, there were nonsignificant differences between the right and left eyes for STT I (P = .204 and .621, respectively) and STT II (P = .640 and .640, respectively). The gender of the animal had a significant impact on STT values. The obtained reference values of this study may be of clinical relevance in the diagnosis and monitoring of keratoconjunctivitis sicca (KCS) in donkeys.