Effects Of Early And Later Feed Restriction On The Pectoralis Major Growth And Its Underlying Mechanisms In Broiler Chickens

By subjecting broiler chickens of different growth stage to intermittent feed restriction, we compared the impacts on muscle growth and the expression patterns of genes which are involved in myocyte apoptoisis, growth, and metabolism to investigate the effects of feed restriction on the growth of pectoral muscle and the underlying mediate pathway, and to find whether devoid of nutrition had long-term effects on broiler chicken growth.1. Effects of early and later feed restriction on the pectoralis major growth of broiler chickens1-day-old (1d) broiler chickens were allocated randomly into control (CON), early feed restriction (EFR) and late feed restriction groups (LFR). Chickens of CON group were fed ad libitum throughout the experiment for 9 weeks, while chickens of EFR and LFR groups were subjected to intermittent feed restriction with feed provided on alternate days for the first and the last 2 weeks of their posthatch life respectively. 10 chickens from each group were sacrificed on 14d and 63d, and the pectoralis major was sampled. The results showed: 1) the body weight of EFR group was significantly lower during the whole experiment, and the body weight of LFR group was significantly lower after feed restricting for 1 week whereas no difference on 63 d compare with the control group; 2) in EFR group the pectoralis major weight and myofiber cross-sectional areas were significantly lower on 14d and 63d, and the same lower trend was found on 63d in the LFR; 3) DNA and RNA concentration in EFR group was higher significantly on 14d, while DNA, RNA and protein content were significantly lower. On 63 d, RNA concentration in EFR group still higher than CON group, while DNA concentration and content were markly decreased, and RNA/DNA increased in LFR group; 4) About AMPK activity, we observed a drop trend along with increased age, and no significantly changes was found between groups at the same age. The results indicated feed restriction could markedly delay pectoralis major growth of broiler chickens at different growth stage, and early feed restriction had long lasting effect.2. Effects of early and later feed restriction on the genes expression related to myocyte apoptosis of pectoralis major in broiler chickensRT-PCR was used to detect the apoptotic genes expression patterns in pectoralis major of 14d and 63 d broiler chicken. The results showed that the expression of Bax and Bcl-2 mRNA significantly increased on 14d in EFR group, but no difference of Bax mRNA/Bcl-2 mRNA could be found between groups. Compared with CON group on 63d, there was no marked difference of Bax mRNA, Bcl-2 mRNA, or Bax mRNA/Bcl-2 mRNA in EFR and LFR groups, in despite of a obvious increase ratio in EFR group from 14d (7.23%) to 63d (41.17%) and in LFR group (41.17%). These results indicated early and later feed restriction could not promote myocyte apoptosis.3. Effects of early and later feed restriction on the pectoralis major genes expression which relate to growth and metabolism of broiler chickensRT-PCR was used to detect the expression patterns of genes which were involved in growth axis and metabolism on 14d and 63 d broiler chickens. The results showed that the expression of IGF-IR mRNA significantly increased on 14d and GHR mRNA significantly decreased on 63d in EFR group. However, both of IGF-I and IGF-IR mRNA expression decreased significantly in LFR group. Early feed restriction also caused the decrease expression of Calpain3 mRNA on 63d. These results indicated EFR and LFR blocked the growth of pectoralis major through different mechanisms respectively, and EFR had' long-term effects. EFR group decreased GHR mRNA expression on 63d while LFR group depressed the expression of IGF-I/IGF-IR to inhibit the synthesis of muscle protein. Moreover, EFR group reduced metabolic ratios of protein by decreasing the expression of Calpain3 on 63d.