The genetics of morphological traits in the grasscutter

Abstract

The objectives of this study were to estimate phenotypic and genetic parameters of morphological traits of the grasscutter, and to find the best morphological trait predictor of body weight. The study was carried out at the grasscutter section of the Department of Animal Science Education, University of Education, Winneba, Mampong-Ashanti campus, Ghana from 2009 to 2010. Data were recorded on morphological characteristics and body weights of 116 animals (66 females and 50 males) selected at random. Body weights and linear body measurements were recorded for the animals at birth, at weaning (2 months) and at 6 months. Mean body, tail and head lengths, heart girth and height-at-withers were 35.6, 10.2, 8.2, 18.0 and 11.6 cm, respectively. At birth, males and females had similar (P > 0.05) body measurements for all the morphological traits. However, at 2 and 6 months, males had significantly (P < 0.05) longer body, head and tail lengths, larger heart girth and taller height-at-withers than females. The best predictor of body weight was heart girth. Direct genetic diversity (variability) of body length, head length and heart girth were low whilst those of tail length and height-at-withers were moderate. Proportion of phenotypic variance due to permanent environmental effects of dam (c 2) was low to moderate (3-23%). Covariances between direct and maternal effects were negative (-2.3 to -29.2). Direct heritability for all traits was high (0.52-0.60) and maternal heritability was medium to high (0.39-0.75). Correlations between direct and maternal genetic effects were high negative (-0.61 to -0.78). Genetic correlations among morphological traits were medium (0.45) to high (0.85), whilst their phenotypic correlations were high (0.71 to 0.90). Genetic correlations between body weight and all morphological traits were low (0.04 to 0.23), whilst their phenotypic correlations were high (0.75 to 0.90). It was concluded that genetic selection will be effective in improving all the morphological traits. However, little to no correlated response in body weight would be expected. It was also concluded that heart girth can be used by farmers to predict body weight of grasscutters. It was recommended that farmers should not use head shape for sex determination at birth.