Application of multifactorial discriminant analysis in the morphometric structural differentiation of West African Dwarf (WAD) and Yankasa Sheep in South West Nigeria
A total of 264 adult sheep comprising WAD and Yankasa rams and ewes traditionally managed in flocks within the south West Nigeria were investigated. Ten zoometrical variables were monitored in order to contrast their validity as racial markers and breed discriminants and identify metric characters which can be valuable for population classification within the species. Descriptive statistic showed that the Yankasa generally appear superior to the WAD in all variables measured except for shoulder width where WAD appeared superior giving the breed a blockier look than Yankasa which is relatively narrower. Neck circumference exhibited the highest variability in both sheep studied, c. v. being 18.34 and 20.12% respectively. These were followed by shoulder width in WAD and body length in Yankasa. The cephalic characters (head width and face length) exhibited the lowest variability in both breeds (c.v. being between 3.62 and 5.67%). High environmental sensitivity of neck circumference and shoulder width in WAD population explains the observed variability although measurement of neck circumference were affected by the neck ruff of the rams. The low variability exhibited by the cephalic characters in both breeds is a reflection of their relative insensitivity to environmental elements resulting from their close association with cranial bone growth. Stepwise discriminant analysis showed that tail length (the most discriminant variable between the breeds) was followed by shoulder width, the cephalic characters, body length and wither height in that order. Other variables did not qualify to enter the model. The small number of variables exhibiting high discriminant power (i.e. tail length, shoulder width, and head width) are explained by the genetic exchange that has existed between the breeds.
Keywords: Discriminant analysis, morphometry, structure, differentiation, sheep, breeds