Nigerian Veterinary Journal 37(1). 2016 Igado et al NIGERIAN VETERINARY JOURNAL ISSN 0331-3026 Nig. Vet. J., March 2016 Vol. 37 (1): 54-63. ORIGINAL ARTICLE Cranio-facial and Ocular Morphometrics of the Male Greater Cane Rat (Thryonomys swinderianus) 1 2 1 1 Igado, O. O. *; Adebayo, A. O. ; Oriji, C. C. and Oke, B. O. 1Department of Veterinary Anatomy, Faculty of Veterinary Medicine, University of Ibadan, Nigeria.. 2Department of Veterinary Anatomy, College of Veterinary Medicine, Federal University of Abeokuta, Ogun State, Nigeria. *Corresponding Authors: Email: [email protected]; Tel No:+2348035790102. SUMMARY Cranio-facial indices still remain a useful means of early detection of the characteristic facial appearance of some syndromes. The cranio-facial and gross ocular morphometry of the male Greater cane rat (Thryonomys swinderianus) was studied using 9 adults. A total of twenty seven parameters were determined for each head. Linear measurements were determined on each eyeball using digital vernier calliper, measuring rule and a piece of twine. Cranio-facial parameters assessed included distance between medial canthi, height of the incisor, extent of oral commissures, width and length of the pinnae. All measured parameters were correlated with the body weight. The highest positive correlation was observed between the body weight and the width of the head, while the heights of the two upper incisors showed the lowest negative correlation with the body weight. The weights of the animals, heads and both eyeballs were 1.97 ± 0.37 kg, 252.00 ± 36.89 g, and 1.00 ± 0.12 g respectively. With increase in the use of wildlife as experimental animals, results from this study may find application in the field of comparative anatomy and pathological studies as well as in wildlife clinical applications. Key words: Greater cane rat, craniofacial index, anthropometric indices, ocular measurements. INTRODUCTION The greater cane rat - GCR (Thryonomys domesticated and captive-reared in parts of swinderianus), which is also known as West Africa where they are sometimes grasscutter, is a wild, herbivorous, referred to as micro livestock (Karikari and hystricomorphic rodent, reputed for its tasty Nyameasem, 2009). and high quality meat. In the West African The GCR lives by reed-beds and riverbanks sub-region, it is a potential food source in Sub-Saharan Africa and can grow to providing high quality protein for both urban nearly 2 ft (0.61 m) in length weighing as and rural populations (Addo et al., 2007). much as 8.6 kg (van der Merwe, 2000; Consequently, grasscutters are now being Adebayo et al., 2009). It has rounded ears, a 54 Nigerian Veterinary Journal 37(1). 2016 Igado et al short nose, and coarse bristle hair. The MATERIALS AND METHODS forefeet are smaller than the hind feet. Cane Ethical approval for this research was rats have a tendency to adopt plantations as obtained from the Faculty of Veterinary habitat, feeding on agricultural crops such as Medicine, University of Ibadan, Nigeria, maize, wheat, sugarcane and cassava, ethical code no: ethics 03/14/04. All thereby earning the label ‘agricultural pest’. procedures and handling of the rats followed The cane rat is said to be sexually matured the guide for the care and use of at 7 months of age and at the weights of 1.6 experimental animals (National Institute of kg and 2.1kg for male and female Health (NIH), USA and the Faculty of respectively (Adu and Yeboah, 2003; Veterinary Medicine, University of Ibadan, Adebayo et al., 2009) Nigeria. A total of nine adult male greater Regional anatomy of the head is an cane rats were obtained from the rat colony important aspect of gross anatomy showing housed in the Experimental Giant Rat Unit, the spatial relationship of the organs in this College of Veterinary Medicine, Federal region and is a tool that has been extensively University of Agriculture, Abeokuta, used in forensic archaeology. Craniofacial Nigeria. The rats were raised from birth in indices in humans have been useful in the the University and their ages ranged from 18 early detection, diagnosis and study of the to 24 months. development of the characteristic facial Each animal was weighed with a weighing appearance of some syndromes like the scale (Electronic Kitchen Scale, Camry® Williams syndrome (Hovis and Butler, EK5350) and euthanized with chloroform, 1997). Craniofacial indices have been using a chloroform chamber (0.1 ppm, reported in several animals such as the Sahel Analar®). The heads were severed with goat (Shawulu and Kwari, 2010), dog quick cervical decapitation at the atlanto- (Igado, 2014), pig (Olopade et al., 2011) and occipital joint, the eyeballs removed by fruit bat (Igado et al., 2012). enucleation according to the method Previous research on the anatomy of the previously described by Igado (2011); and GCR includes neuro-morphometry (Byanet weighed immediately with a digital et al., 2009), reproductive studies (Adebayo weighing scale having a sensitivity of 1 x et al., 2009; Olukole et al., 2010; Adebayo 10-3 grams (Microwa swiss balance®, et al., 2014), tooth eruption and dentition Mettler-Toledo, Switzerland). (van der Merwe, 2000) and the alimentary Measurements on the eyeballs were obtained canal (van Zyl et al., 2005). with the aid of digital Vernier callipers In spite of the availability of some literature (Neiko®, sensitivity of 0.01mm), a length of on the craniofacial and ocular indices of string and a centimetre rule. All weights domestic animals and wildlife in literature, obtained were recorded in grams (g), while electronic search did not reveal any all linear measurements were recorded in documentation on the craniofacial indices in centimetres (cm). All specimens were the greater cane rat. This study therefore photographed with a digital camera (Sony® aims to document the craniofacial indices Cyber-shot, 7.2 megapixels) and named and gross ocular morphometry that can serve according to Nomina Anatomica Veterinaria as baseline data for comparative, (NAV), 2005. A total of twenty seven (27) pathological and forensic/archaeological parameters were measured on each studies as well as in wildlife clinical specimen. manipulations. 55 Nigerian Veterinary Journal 37(1). 2016 Igado et al Weight of animal (WOA) Lengths of pinnae, left and right (LPil & This was determined using a standard digital LPir respectively) scale (Electronic Kitchen Scale, Camry® This was measured from the base of the EK5350). Measurements were recorded in pinna to its tip. kilograms and converted to grams. Palpebral Fissure Lengths, Left and Weight of head (WOH) Right (PFLl & PFLr) Also determined using a standard digital Measured as the distance between the scale. Measurements were recorded in medial and lateral canthi of each eye. kilograms and converted to grams. Philtrum Height (PH) Weights of left and right eyeballs (WOE/l Measured from the most dorsal aspect of the & WOE/r respectively) philtrum to the lowest aspect of the Determined with a digital weighing scale philtrum. (Microwa® Swiss balance, Mettler-Toledo, Switzerland) and recorded in grams. Height of the External Nares, Left and Right (HeENl & HeENr respectively) Width of head (WiOH) Maximum vertical distance between the This was the maximum width of the head, dorsal and ventral borders of each of the measured as the distance between the right nares. lateral and the left lateral sides, across the zygomatic bones, with the aid of Vernier Height of Upper and Lower Incisor Both calipers. Left and Right (HeUIl, HeUIr, HeLIl and HeLIr Widths of the pinnae, left and right Height of the externally visible incisors, (WiPil & WiPir respectively) measured from the gumline to the tip of the This was measured as the widest distance teeth; recorded in centimetres. between the lateral edges of each pinna. Antero-posterior circumference of the Distance between Medial Canthi (DMC) eyeball Left and Right (AP/l & AP/r Distance between the two medial canthi of respectively) the left and right eyes. The circumference of the eyeball, around the median plane from the anterior to the Length of the head (LOH) posterior pole, determined with the aid of a Distance from the most rostral part of nasal string, which was then measured with region to the caudal portion of the occipital Vernier calliper. bone. Medio-lateral circumference of the Extent of oral commissures (ROL) eyeball Left and right (ML/l & ML/r This was determined using a string, as the respectively) distance between the two lateral The circumference of the eyeball along the commissures of the closed lips. The length mediolateral plane (equator), determined of the string was thereafter determined with with the aid of a string, which was then a meter rule. measured with Vernier calliper. 56 Nigerian Veterinary Journal 37(1). 2016 Igado et al Peri-orbital circumference of the eyeball The relative weights of the head and Left and Right (PO/l & PO/r respectively) eyeballs were obtained by using this The circumference of the eyeball, measured formula ( ) immediately caudal to the cornea, along the mediolateral and antero-posterior planes. This was determined with the aid of a string, Statistical Analysis: All data obtained were which was then measured with Vernier analysed with Student’s ‘t’ test (Graph pad calliper. prism version 4), and level of significance The craniofacial and ocular parameters was calculated at P<0.05. measured are illustrated in Plates 1-4. Table I: Values for craniofacial indices and ocular parameters in the male adult greater cane rat (Thryonomys swinderianus)