Emotional stimuli have been shown to suppress vasopressin and facilitate oxytocin release from the posterior pituitary in some mammalian species. However, it is not clear in horses. Here we examined effects of novel environmental stimuli on plasma concentrations of vasopressin, oxytocin, cortisol, adrenaline and noradrenaline in Thoroughbred horses. To impose novel environmental stimuli, horses were introduced to an experimental stall (4.5 × 5.0 m) with side walls of black rubber board, in which a yellow balloon (80 cm in diameter) was hung from the ceiling. Horses were exposed to the novel environmental stimuli for 3 min. Heart rates were significantly increased during the stimuli. Plasma concentrations of adrenaline and noradrenaline in the blood collected immediately after the stimuli were twice as high as those at rest and decreased to the basal levels within 10 min after the stimuli. Plasma cortisol concentration increased after the stimuli and reached the peak 20 min later. However, plasma concentrations of vasopressin and oxytocin did not significantly change throughout the experiments. These data suggest that the novel environmental stimuli do not significantly influence the hypothalamo-neurohypophysial system while the stimuli activate the sympatho-adrenal medulla and the hypothalamo-pituitary-adrenal cortical axes in horses.
The distribution of C cells in the thyroid gland was investigated histologically and immunohistochemically in 78 thoroughbred horses (37 males and 41 females) aged from 1 to 29 years and which were free of bone and endocrine diseases. C cells are scarce in both the cephalic and caudal ends of the thyroid gland, but large numbers are present in the central area. In annular sections of the thyroid gland with the maximum surface area, C cells are distributed throughout these sections, but an especially high frequency has been detected in the inner margin. C cells increase in number up until around 20-30 days after birth, but there is a tendency to a decrease in number thereafter with age. The thyroid gland of young animals is formed from a small round follicle, which becomes larger and undergoes flattening of the follicular cells with age. Compared to females in which the number of C cells starts to decrease at about 3 months of age, the rate of decrease is gentle in males and is consistently higher than in females.
Lancefield's group C streptococci often contaminate test samples taken from open lesions of the equine disease strangles, and it is difficult to distinguish the causal agent, Streptococcus equi (S. equi), from these other streptococci on the isolation plate. Here we have developed a microplate sugar-fermentation assay that distinguishes S. equi from other streptococci of Lancefield's group C. Within 18 hr of incubation, the assay distinguished between 19 strains of S. equi, 171 strains of Streptococcus zooepidemicus and 19 strains of Streptococcus equisimilis, which were isolated from clinical horse samples and identified by API 20 STREP and Western immunoblotting. Moreover, this microplate assay can simultaneously test up to 24 samples, and is therefore valuable for the diagnosis of strangles.
Four thoroughbred horses exhibiting abnormal respiratory sounds and coughing during exercise were examined clinically. Endoscopic examination revealed dorsolateral swelling of the pharyngolarynx and compression of the arytenoid cartilage corniculum, narrowing of the pharyngolarynx cavity, and guttural pouch empyema. These findings were consistent with those of retropharyngeal abscesses previously reported in Europe and North America. All horses were treated by topical and systemic antimicrobial therapy after flushing the guttural pouches with phosphate-buffered saline (PBS). Retropharyngeal abscesses and guttural pouch empyema completely disappeared after 7 to 10 days. This appearance suggests that topical and systemic antimicrobial therapy after guttural pouch flush with PBS coupled with systemically administered broad-spectrum antibiotics is an effective therapeutic regimen for this condition.