Variability of cranial morphometrical traits in Suffolk Down Sheep

Abstract

The widespread use of measures and indices associated with the head for racial analysis suggests that such measures have a strong relationship with the underlying bone structure. Few studies analyse the variability of the bones of the head and the relationship with their external expression. The objective of this work was to identify and measure the magnitudes of the main skull parameters in Suffolk Down adult sheep. This study was carried out on sixteen adult Suffolk Down sheep skulls at INIA Butalcura. Their skeletons were obtained and digital morphometry was performed. Each skull was photographed from dorsal, ventral, lateral and nuchal views with a total of 28 parameters evaluated (10 dorsal, 5 ventral, 6 lateral and 6 nape). The results indicate that the externally observable variability in the cranial zone of a sheep cannot be extrapolated to the rest of the bony components of the cranial zone, either in length, width or height. It was observed that the variability of a cephalic dimension can be contrasted with the variability of individual bones that participate in a certain dimension as part of a plasticity adjustment mechanism independent of the genetic variability of each bone separately. The cranial dimensions are still useful in defining the productive potential of a sheep population; however, they should be taken cautiously for racial definitions, where the individual variability of the bones could be a better reflection of the genetic structure of the population and the dimensionality could be biased by adaptive plasticity.