Epiphyseal Closure of the Paca's Humerus, Radius and Ulna (Agouti paca)
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2017-12-20
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Univ Fed Rio Grande Do Sul
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Background: After the capybara, the Agouti paca is the largest rodent in the neotropical region, with a body weight that usually varies from 5 to 10 kg, but may reach up to 14 kg. Pacas reach sexual maturity at around 10 months of age. Recently, this species has been increasingly being subject of studies on tissue morphology, placentation, and experimental surgery. The time at which epiphyseal plates close varies according to each bone; some can close during intrauterine life, while some can persist for many years. The aim of this research was to examine, through radiography, the long bones of the thoracic limbs (humerus, radius, and ulna) of the paca, and correlate their epiphyseal closure times with the animal's age. Materials, Methods & Results: Eight animals born in captivity were radiographically evaluated monthly from birth until 22 months of age. The animals were kept in stalls made of masonry, with an area of approximately 15 m(2). Each stall had one burrow with three internal interconnected sub-sections. Each stall housed one male and two or three females with microchip implants applied dorsally in the cervical region. The animals were fed rodent chow (1.0% of body weight per day) and fruits of the season (10% of body weight per day), which were offered daily in the afternoon. The animals were radiographed at the Division of Radiology of the Veterinary Hospital of the School of Veterinary Medicine, Sao Paulo State University, Jaboticabal, SP, Brazil. Craniocaudal and mediolateral views of the humerus, radius, and ulna were performed. Sedation was performed using meperidine (2.5 mg/kg) and diazepam (0.5 mg/kg) in a single intramuscular injection. For anesthesia, ketamine (20 mg/kg) and xylazine (1.5 mg/kg) were administered in leg muscles 10 minutes after sedation. The anesthesia used proved to be efficient for transportation, handling, and positioning of the animals for radiographic exams. In the humerus, epiphyseal plate activity ceased at 13 months of age in the head, 22 months in the greater tubercle, and 6 months in the distal epiphysis. Epiphyseal closure occurred at 13 months of age in the proximal radius, and at 15 months of age in the distal radius. In the ulna, the epiphyseal growth plate started to close in the central portion of the olecranon at 12 months of age, and closure was complete at 22 months of age. At 15 months of age, the animals no longer exhibited a radiolucent line in the distal epiphysis. Discussion: The age at which the proximal humeral epiphysis (in the humerus head) closes in Agouti paca (13 months) is similar to those reported for dogs (13 months or 10 to 15 months), but differs from that reported for cats (18 to 24 months). The age at which the distal humeral epiphysis closes in pacas (6 months) is similar to those reported for dogs (5 to 8 months or 6 to 8 months), but differs from that reported for cats (4 months). The age at which the proximal radial epiphysis closes in pacas (13 months) differs from that described for dogs (from 6 to 11 months). Whereas, the age at which the distal epiphysis closes in this species (15 months) is similar to that reported for dogs according to some authors (from 16 to 18 months), but different from those reported for dogs by other authors (from 6 to 12 months). In pacas, closure of the proximal ulnar epiphysis, in the olecranon, occurs later (22 months of age) than in dogs (from 5 to 15 months of age) or cats (9 to 13 months of age). The age at which distal ulnar closure occurs in pacas (15 months) was the same as that reported for dogs by some authors (15 months), and is within the range described by other authors for dogs (6 to 12 months) or cats (14 to 25 months).
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Acta Scientiae Veterinariae. Porto Alegre Rs: Univ Fed Rio Grande Do Sul, v. 45, 4 p., 2017.