Comparison of chicken genotypes: myofiber number in pectoralis muscle and myostatin ontogeny

Abstract

This study was performed to evaluate breast muscle development in chicken genotypes divergently selected for muscularity. In the first experiment, 2 commercial broiler lines (a high breast yield, HBY, and a normal breast yield broiler strain-cross, NBY) and a Leghorn line were grown up to 35 d to evaluate BW, breast weight, and breast yield. At 7 and 21 d of age, pectoralis muscle was used to estimate myofiber density (MFD, number of myofibers per mm2) and total apparent myofiber number (MFN). In the second experiment, the ontogeny of myostatin was determined from broiler- and Leghorn-type chick embryos, at embryonic days 1 to 20 (E1 to E20), using reverse transcription (RT)-PCR. As expected, the Leghorn line had lower BW, breast weight, and breast yield than broiler lines. The HBY line showed higher breast yield at all ages evaluated, but lower BW at 21 and 35 d than the NBY line. The Leghorn line had 45% higher MFD than broilers, which indicates an increased cross-sectional area of the myofibers in broiler lines. No MFD difference was observed between the broiler strains (P > 0.05). The myofiber number of broilers was more than twice that of Leghorns and HBY had 10% higher MFN than the NBY line. Myofiber number was correlated to BW (r = 0.58), breast weight (r = 0.58), and breast yield (r = 0.69). Conversely, MFD showed negative correlation with BW, breast weight, and breast yield (r = -0.85, -0.83, and -0.88, respectively). No effect of genotype or interaction between genotype and embryonic age was observed for myostatin expression. This study showed that broilers have higher MFN in the breast muscles than Leghorn-type chickens, and that high breast yield of broiler strains may be due to increased MFN. Higher muscularity of broilers, as compared with Leghorns, was not attributed to lower expression of myostatin during embryonic development.

Increasing the incubation temperature between embryonic day 7 and 10 has no influence on the growth and slaughter characteristics as well as meat quality of broilers

“…For the analysis of the total fibre number and the muscle fibre diameters the MPS was cross-sectioned perpendicularly to the direction of the myofibres, and the cross-sectional area was traced on transparent paper (Scheuermann et al, 2004). After that a tissue block (1 3 1 3 1 cm) was removed from the centre of the cross-sectional area, frozen in liquid nitrogen and stored at 2708C until analysis.…”

“…The cryopreserved muscle samples were transferred to a cryo-microtome (Cryocut CM 1900, Leica GmbH, Nussloch, Germany) and allowed to equilibrate to 2208C before being cut into slices of 12 mm thickness. The slices were stained with eosin (Scheuermann et al, 2004) and investigated with a stereo microscope (Nikon GmbH, Duesseldorf, Germany) at a low magnification (34), and several sections were transferred through a digital camera to a personal computer. For the determination of the crosssectional areas at least 200 muscle fibres were circumscribed and semi-automatically analyzed using LUCIA software (Nikon GmbH, Duesseldorf, Germany).…”

Breast meat quality of chickens with divergent growth rates and its relation to growth curve parameters

“…Indeed, at day 18 of in ovo development, broiler embryos revealed a 2-fold higher number of myofibers in the cross section of breast muscles than layer chicks (Al-Musawi et al, 2011). Post hatch, at days 7 and 21 of age, both myofiber number and diameter increased for two commercial broiler lines compared with a slow-growing Leghorn-type layer (Scheuermann et al, 2004). By implication, comparing muscles at a given mass, slow-growing chickens must compensate for the reduced number of prenatally formed myofibers by increased hypertrophy.…”

Muscle fiber characteristics of pectoralis major muscle as related to muscle mass in different Japanese quail lines

“…However, genetic selection for muscle growth and muscling in poultry has altered many characteristics of the modern commercial bird, especially the breast muscle (Chiang et al, 2008). Generally, broiler-type chickens that have a greater muscle mass tend to exhibit a greater number and size of muscle fibers in the pectoralis muscle than layertype chickens (Scheuermann et al, 2004).…”