Advances in body size measurement and conformation appraisal for sheep

Abstract: Body size parameters and conformation appraisal for sheep can reflect its growth development, production performance and genetic characteristics. Therefore, it is very important to study the way of body size measurement and conformation appraisal in improving the breeding efficiency of sheep. A review on the body size measurement and conformation appraisal for sheep was presented in this paper, focused on the body size measuring parameters, the conformation appraisal method, and the relationship between body size and growth development, body size and production performance, body size and genetic characteristics of sheep. Five core conclusions were summarized: parameters in body size measurement, methods of conformation appraisal, relationship between body size and growth, development, relationship between body size and production performance, and relationship between body size and genetic characteristics . Generally, the parameters of body size consist of four type indicators: body length, body width, body height and circumference. While, in some places, such as the region from west Asia into Tunisia in North Africa, the fat-tailed breeds represent the dominant sheep breeds, and the studies confirmed that the role of the tail fat was an adaptive character of the fat-tailed sheep breeds. So, several linear traits of the fat tail were individually measured to research the sheep's trails. All collected data of body size were analyzed to design efficient selection and breeding strategies for genetic improvement and appropriate genetic evaluation. The genetic and non-genetic effects for each of the growth traits were analyzed and evaluated using the animal model and statistical methods such as containing regression analysis, principal component analysis, factor analysis, cluster analysis, discriminant, and correlation analysis, etc. . During the last decade or so, there has been extensive development in statistical procedures for estimation of variance components, and the BLUP (best linear unbiased prediction) has been used extensively for analyzing the data. The results showed that some body sizes from each individual were correlated each other, and the genetic change depends not only on the heritability of traits, but also on the observed phenotypic variation. In view of the problems or limitations of the present manual measurement, including the tools of measuring stick, tape measure, etc., the sheep having to stand on a flat place with correcting posture, a non-contact measuring method for sheep's body dimensions based on machine vision has been proposed and discussed. The new method would ease the livestock measuring workload greatly and overcome the limitations of manual measurement, which is specially suitable for the current situations of sheep feeding in intensive and large-scale way, the development and application of information and sensor technologies. Furthermore, with the attraction of application of machine vision technique in non-contact measurement, and the development of image processing technique , it pointed out that these would must be the trend in future body size measurement for livestock since it prevents from the animal's stress actions and anthropozoonosis. This will provide a basis on the rational management and production efficiency improvement in sheep breeding.