VARIABILITY OF THE EXTERNAL EAR OF THE WEST AFRICAN DWARF SHEEP OF NIGERIA

Abstract

491 individuals comprising rams and ewes belonging to the West African Dwarf
sheep population sampled within the South-West Nigeria were investigated. These
were stratified into six age groups determined by dentition. Five variables of
the external ear including two zoometrical characters (ear length and ear width)
and three visible traits (ear size, ear length and ear width) were investigated as
appropriate for phenotypic and genetic variability. The ear was also classified.
The ear of the breed was between 8.82cm and 10.17cm in length the width was
between 5.19 and 6.10cm. Phenotypic variability indicated by associated
coefficient of variation was small for both measurements. There was no significant
difference (P>0.05) between sexes within all age groups. Based on the linear
function, regression of ear length and width on age were not significant (P>0.05),
as was that of ear length on width (P>0.05). The discontinuous variation tested
on three phenotypes: 'normal' 'shortened' and 'vestigeal' showed that the ear
may be classified 'normal' overlapping the 'shortened' variation in size. In
attitude, it is horizontal rather than erect or drooping. It is also pendant in
consistency. The phenotypic profile indicated great uniformity for each visible
trait in the breed. Allelic profile suggested that the breed is homozygous for
the 'standard' allele in size and attitude with allelic constitution of EL* t and
EC*+ respectively. These suggested the absence of mutants EL* R and EC* P
respectively at the locus controlling the traits, thus, both loci are monomorphic
in the sheep. Using the scale of length and attitude, based on the idea that the
oldest were closest to the wild ancestor, the breed is considered archaic.
Because of the small variability observed in the length (size) of the appendage,
cross breeding with longer eared sheep (indigenous or exotic) rather than selection
within the indigenous population is suggested to be tho best option for improving
the structure. The presence of mutants which increase the length of the ear is
desirable in sheep productivity because of the positive association which has
been established between the ear length and skin texture. Very few published
works in sheep genetics deal with qualitative and quantitative examination of
the ear. Further investigation is needed to exploit the genetic significance of
the structure as regards increased productivity in the species