Biometric and Morphologic characetistics of the Skull of the Gwembe Valley Dwarf Goat(Capra hircus)breeds of Zambia

Abstract

This study gives the first morphometric description of the skull of the Gwembe Valley Dwarf (GVD) goat, the applied regional anatomy of the head region as well as the gross morphology of this indigenous goat breed of Zambia. The dearth of information on the cranial morphometry, applied anatomy of the head region and general morphology on domestic animals and the indigenous goats in particular was the motivation behind this study. Thirty heads (15 male and 15 female heads) were collected from purposively and randomly sampled GVD goat aged 18 months and above from a slaughter slab and processed for cranio-morphometry investigation. Forty three morphometrical measurements were recorded from each of the 30 skulls. From these, simple descriptive statistics, multivariate statistics, craniofacial indices, and the coefficient of variation analyses performed and obtained. Further, the variance of the skull structure was determined using a Principal Component Analysis (PCA). The comparative craniometry analysis of the male and female skulls was also carried out. Additionally, twelve measurements of some clinically important landmarks around the skull useful for regional anesthesia in the mandibular regions of head were taken on all 30 skulls and summarized using descriptive statistics. The gross morphology or the macro-anatomy of the general skull of this breed was equally noted. The skull length and skull breadth were 15.02 ± 1.09 cm and 8.14 ± 0.39 cm, respectively. According to the results, the GVD goat breed can be classified as mesocephalic (cephalic index 54.4 ± 3.37), and mesoprosopic (facial index 58.5 ± 3.46); and orbits were rounded (orbital index 99.10 ± 0.08).The skull length and the skull breadth of the GVD goat were positively correlated to the facial index (p < 0.025) at 95% significance level (two-tailed). On the other hand the skull length was negatively correlated to the cephalic index. The results from Principal Component Analysis indicated that skull variance was concentrated on the first two principal components. The first principal component explained only 34.2 % of the generalized variance in skull parameters while the first three principal components explained 56% of the variance. The analysis (PCA) did not give any special emphasis to a particular variable. Broadly speaking, the skull variation in GVD goat was centred on total variation in shape of the skull. A Non-Parametric One-way Analysis of Variance (NPMANOVA) test with Mahalanobis distance reflected no differences between male and female skulls from the general skull parameters (F=1.104, p=0.317), and significant difference (p<0.05) between male and female goat skulls based on the horn parameters (F=4.752, p=0.006) was observed. The distance between the lateral ends of the alveolus of the incisor tooth to the mental foramen was 1.58 ± 0.19 cm. The length and maximum height of the mandibles were 11.24 ± 0.52 cm and 6.64. ± 0.44 cm, respectively. The distance from mandibular angle to below of mandibular foramen was 1.21 ± 0.08 cm, while the distance from the mandibular foramen to the base of the mandible and mandibular angle to below mandibular foramen were 2.35 ± 0.26 cm and 1.10 ± 0.07 cm, respectively. These results are of clinical importance and aid in regional nerve blocks of the infraorbital, mental and mandibular nerves. From the gross morphological examinations of all the 30 skulls of the GVD goat, it was observed that morphologically, sexual dimorphism was evident in the frontal bone with the frontal eminence being more prominent in males than females. Accessory supraorbital foramina were observed in some skulls irrespective of the sex. This study has described the biometric and the morphologic characteristics of the GVD goat and concludes that a contribution for comparative model for other African local caprine breeds in general and Zambian caprine breeds in particular has being made. Being the first study of its kind in Zambia, it makes a significant contribution to a better understanding of the GVD skull typology. It is envisaged that the results obtained in this study will be useful as baseline research data in comparative goat neuroanatomy and neuropathology. The result further provides a valuable reference data for regional anaesthesia of the head region in Gwembe Valley Dwarf goat breed.