Epiphyseal Closure of Femur, Tibia and Fibula of the Paca (Cuniculus Paca, Linnaeus, 1766)

After capybara, paca (Cuniculus paca) is the largest rodent in the neotropical region and the body weight varies from 5 to 10 kg, and may reach up to 14 kg. They are animals that reach sexual maturity at around 10 months of age. The aim of this research is to examine, through radiography, the femur, tibia and fibula of the paca. The animals were anaesthetized for radiographic exams. At 6 months of age, the growth line of the femoral proximal epiphysis ceases to perform its functions. At 12 months of age, there is the closure of the line growth of distal femoral epiphysis. At the paca’s tibia, at 12 months old, there was the closure of the growth of the proximal epiphysis. In the distal epiphysis, the closure of the line growth also occurred at 12 months old. At the paca’s fibula, the bone activity of proximal epiphysis ceases with only 23 months old. The distal fibular epiphysis ends its development with 15 months. There are similarities and differences relative to the closure of the pacas’ epiphysis femur, tibia and fibula comparing with dogs and cats.

Keywords: Bones; Rodent; Wild animal; Morphology; Anatomy

After capybara, paca (Cuniculus paca) is the largest rodent in the neotropical region [1-3]; the adult males measure from 60 to 80 centimeters, from nose to tip of tail, and the females from 55 to 70 centimeters [1,4]. The body weight varies from 5 to 10 kg, and may reach up to 14 kg [2], but it does not exceed 10 kg [5]. They are animals that reach sexual maturity at around 10 months of age [6].

The moment of the epiphyseal cartilage closing varies according to the bone, some closing already in the uterine life and others remain present for several years [7]. Still, the whole axial correction deviations processes of limbs also depend on the age at which the closing of the growth plate closing occurs. Not only the non-surgical techniques but also the surgical ones for correction of conformations depend on the physiological activity of the growth plate of long bones [8].

Regarding paca, anatomic-radiographic details have already been described. Paca’s femur has long axis, round head, and apparent neck; the greater trochanter is well developed, unlike the lesser trochanter and the third trochanter. The tibia and fibula are equal in length and are partially melted by a fibrocartilage at their edges. The tibia cranial border extends to the middle third of the diaphysis and is almost parallel to the largest bone shaft [9].

There are several recent researches on pacas and they involve teeth radiographic anatomy [10] and the axial [9] and appendicular [11] skeletons, heart topographic anatomy [12], dental eruption for age determination [13] and lumbo-sacral epidural anesthesia [14]. Other studies on this species are about the description of the structure, ultrastructure and morphometry of the superior vena cava [15] and morphology and topography of the male genital organs [16]. Still, recent study on miology demonstrates similarities between pacas and dogs [17]. The objective of this work is to determine the age of the epiphyseal closure of femur, tíbia and fibula in pacas, an animal that has shown great scientific recent interest.

For this research, were used, 10 male or female pacas, kept in captivity in the Sector of wild animals of the Department of Animal Science of the Faculty of Agrarian and Veterinary Sciences, São Paulo State University, Jaboticabal Campus, after aproval of the University Ethical Committee (process 011553/13).

The animals were kept in stalls of approximately 15m2 of masonry, one burrow per stall, subdivided into three connecting internal sub-sections, remaining in each stall, one male and two or three females with individual marking of microchips, applied dorsally in the cervical region.

In feeding, rodents ration was used (1.0% of body weight per day) and seasonal fruits (10% of body weight per day), offered daily in the afternoon.

The animals were X-rayed (Siemens Tridoros^™ 812- E; 50 kVp and 10 mAs) in the sector of Radiology Veterinary at the Governador Laudo Natel Hospital, from UNESP Jaboticabal, monthly from birth up to 24 months old. Radiographic projections of cranio-caudal and lateral side of the femur were performed.

Tranquilization was used with meperidine (2.5mg/kg) and diazepam (0.5 mg/kg) via intra-muscular, in the same syringe. For the anesthesia, 10 minutes after sedation, ketamine hydrochlorides (20 mg/kg) and xylazine (1.5 mg/kg), similarly to the technique already described in the literature for chemical restraint in this species (OLIVEIRA et al., 2003).

The anesthesia used proved to be efficient for transport and the animals radiographic positioning until the Radiology Sector of the Governador Laudo Natel Veterinary Hospital of UNESP - Jaboticabal and there was not any kind of inconvenience caused by the use of the selected drugs, similarly to that described in the literature for these animals through the use of xylazine, meperidine and ketamine [14].

It was observed that radiographically, at 6 months old, the line of femoral proximal epiphysis growth ceases its functions, unlike described for this boneous region in dogs, which perform their functions until 9 months [18,19] or 18 months [20-22]. Unlike also for cats [23], who reported that the proximal femoral epiphysis ends its development between 7 and 10 months.

At 12 months old, the growth line closure of distal femoral epiphysis takes place, unlike described in dogs [20-22], who describe that this region exhibits osseous activity until 18 months, and similarly to that described for this species, which reported line growth closure of distal epiphysis until 12 months [18,19]. Unlike, however for cats, which report that the proximal femoral epiphysis finalizes its development up to 10 months, while the distal, up to 19 months old [23].

At the paca’s tibia, at 12 months old, there was the growth line closure of the proximal epiphysis, which is different than the one depicted in dogs [20,21], animal whose physical closure occurs around 18 months, and as reported for cats, in which the closure happens between 12 and 18 months [23]. However, our results are similar to 12 months old [22] and from 6 to 15 months old described for dogs [18,19] and from 12 to 18 months described for cats [23].

In the distal tibial epiphysis, the line growth closure also occurred at 12 months old, unlike from 14 to 15 months old [20,21] and from 5 to 11 months described for dogs [18,19]. Our results were similar to those from 12 to 13 months old reported for dogs [22] and from 10 to 13 months old for cats [23] regarding the distal tibial epiphysis.

In the paca’s fibula, the proximal epiphysis osseous activity ends with only 23 months old, which is different from 15 to 16 months [20,21] and from 6 to 12 months described for dogs [18] or from 13 to 18 months reported for cats [23]. The fibular distal epiphysis ends its development at 15 months, similarly to what has been described by some authors [20] for dogs, being different from 5 to 13 months described by other authors also in dogs [18,19] and from 5 to 13 months reported in cats [24] (Figure 1). There was no distinction between male and female epiphysial close time.

There are similarities and differences relative to the closure of the pacas’ epiphysis femur, tibia and fibula comparing with dogs and cats.

The authors are grateful for the financial support of Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP; 2013/25937-5).