International Journal of Poultry Science 3 (12): 758-763, 2004 © Asian Network for Scientific Information, 2004 758 Satellite Cell Mitotic Activity of Broilers Fed Differing Levels of Lysine Simone Pophal , Paul E. Mozdziak and Sérgio L. Vieira 1 2 2 Departamento de Zootecnia, Universidade Federal do Rio Grande do Sul, Porto Alegre, RS, Brazil 1 Department of Poultry Science, North Carolina State University, Raleigh, North Carolina, USA 2 E-mail: pemozdzi@unity.ncsu.edu Abstract: Post-hatch myofiber growth is dependent upon the addition of new nuclei from the mitotically active satellite cell population. The objective of this study was to examine the relationship between different levels of dietary lysine and satellite cell mitotic activity during the early post-hatch period. Broiler chicks were split into five groups of 10 birds each immediately post-hatch. One group was not provided any feed or water for the first three days post-hatch, whereas the other groups were provided a standard starter diet with different levels of lysine (0.82, 0.99, 1.16, 1.33%) for the first three days post-hatch. All birds were injected with 5- Bromo-2’-deoxyuridine (BrdU) 2 hours before they were killed on the third day post-hatch. Mitotically active satellite cells were identified in the Pectoralis thoracicus and quantified using BrdU immunohistochemistry in combination with computer-based image analysis. Satellite cell mitotic activity was significantly (P < 0.05) lower in the starved compared to any of the fed groups. However, satellite cell mitotic activity was highest (P < 0.05) in the birds that were provided a lysine deficient diet (0.82%). The current study suggests that it is possible to nutritionally stimulate the satellite cell population in the early post-hatch chick, and that it is an important endeavour to re-examine the nutritional requirements of the early post-hatch chick to optimize meat yield. Key words: Chicken, nutrition, muscle, myofiber, growth Introduction Post-hatch muscle growth occurs exclusively through an increase in myofiber size without an increase in myofiber number (Remignon et al., 1995). Concurrent with the increase in myofiber size is an increase in myofiber DNA content. However, the increase in myofiber DNA does not occur through pre-existing myonuclei because they are post-mitotic (Stockdale and Holtzer, 1961). The increase in myofiber DNA content occurs through the action of the mitotically active satellite cell population that is located between the sarcolemma and the myofiber basal lamina (Mauro, 1961; Yablonka-Reuveni, 1995; McFarland, 1999; Goldring et al., 2002; Morgan and Partridge, 2003). The role of the satellite cell population during normal skeletal muscle growth is to proliferate then donate nuclei to the growing myofiber. Satellite cell fusion with the myofiber provides the genetic machinery for the age-related increases in myofiber size. Previous research has indicated that postnatal myofiber growth in avian species can be considered to occur in at least two phases (Mozdziak et al., 1994). The first phase of myofiber growth occurs early in life, and it is characterized by a high level of satellite cell mitotic activity. However, later in life, satellite cell mitotic activity falls to low levels, and myofiber growth occurs almost exclusively through an increase in the volume of cytoplasm surrounding each nucleus (DNA Unit Size; Mozdziak et al., 1994; Allen et al., 1999; Mozdziak et al., 2000). Therefore, satellite cell mitotic activity early in life governs the ability of the muscle to meet its full potential genetic size. Furthermore, it has been shown through hind-limb unloading of juvenile muscle followed by reloading that a temporary suspension in satellite cell mitotic activity results in a reduction in mature muscle size under normal growth conditions (Mozdziak et al., 2000). Similarly, it has been shown that temporarily reducing satellite cell activity through irradiation of the turkey Pectorailis thoracicus results in a decrease in mature muscle size (Mozdziak et al., 1997). Therefore, inhibition of myonuclear accretion/myonuclear number results in a reduction in mature muscle size. The interval between hatching to placement on feed for chicks and turkey poults may be as large as 72 hours. Delayed placement on feed results in a reduction in satellite cell activity (Halevy et al., 2000; Halevy et al., 2003; Mozdziak et al., 2002b), myonuclear apoptosis (Mozdziak et al., 2002a; Pophal et al., 2003), and most importantly a reduction in meat yield at market age (Vieira and Moran, 1999; Halvey et al., 2000). Therefore, the impact of nutrition on satellite cell mitotic activity during the early post-hatch period is very important in determining ultimate meat yield. Dietary lysine is also very important in poultry diets because it is an essential amino acid, it is associated with protein accretion, and growth has been correlated with the lysine content of poultry diets (Waldroup et al., 1976; Baker and Han, 1994). However, the relationship between dietary lysine levels and the mechanisms governing skeletal muscle growth have not been fully explored. The objective of this study was to examine the effect of dietary lysine level on