Introduction
Understanding the biochemical and physiological mechanisms underlying growth is one of the major subjects of interest in the cattle industry. Several studies have investigated the growth factors and growth hormones that influence growth. However, it is still unclear which genes and how many genes are involved in the process of growth. Therefore, studies on a molecular level to identify genetic and environmental effects associated with growth traits are essential. Calpain, which is an endogenous protease (EC 3.4.22.17, Ca2+ dependent cysteine proteinase), has been studied (Goll et al., 1983; Goll et al., 1992), along with several growth factors, to investigate their effects on growth, and cell growth and differentiation (Murray et al., 1997; Temm-Grove et al., 1999). Cottin et al. (1994) studied the effects of the calpain system and IGF-I on cell growth at early embryonic stages, and found that the calpain system may influence cell growth. If the calpain system is highly heritable, and has moderate to high genetic correlations with economic traits of interest, its use in a selection program may increase the rate of genetic change. Therefore, this study was carried out to investigate the effects of calpain genotypes on weight and IGF-I traits to provide genetic information for improvement of these traits.