Laryngeal paralysis in Arabian foals associated with oral haloxon administration.

The research article discusses bilateral laryngeal paralysis in Arabian foals that have been administered oral haloxon. The study examines symptoms, treatment, and potential causes of this condition, concluding that the likely cause is the oral haloxon given to the foals at regular intervals starting from two days old.

Laryngeal Paralysis in Foals

• The study describes bilateral laryngeal paralysis in 5 Arabian and part-Arabian foals aged between 23 and 35 days. This condition severely disturbed their breathing processes, a problem that was however alleviated by performing tracheotomies.
• Treatment outcomes varied, with two foals seeing recovery of their right arytenoid cartilage’s abductor function after three weeks. One of them also regained left abductor function later on.

Post-Mortem Analysis

• Four of the foals were examined post-mortem between one week and 6 months after the start of respiratory obstruction. Histological analysis of their recurrent laryngeal nerves showed active Wallerian degeneration and loss of nerve fibres in many fascicles, especially for cases that had been affected for one to 2 weeks. In cases with a longer duration, there was a considerable deficiency of myelinated fibres.
• The dorsal and lateral cricoarytenoid muscles showed no abnormalities in cases affected from one to 5 weeks. However, in the foal affected for 6 months, there was a change in fibre diameter in the left dorsal cricoarytenoid muscle. Sections stained for myosin ATPase also showed signs of muscle fibre type grouping in both left and right dorsal cricoarytenoid muscles.

Potential Cause of the Paralysis

• The most likely cause of the paralysis is believed to be the administration of oral haloxon. This medication was administered to the foals starting at two days old, at a dose rate of 1 to 2 grams per fortnight. Further research is necessary to confirm this causality and to recommend future preventive measures.