Effect Of Dietary Protein Level Of Langshan Breeder Laying Hens On Offsprings Early Development And Expression Of Muscle Growth-Related Genes

Langshan breeder hens, a famous local breed, were employed in the present study to investigate the mechanism of the effect of maternal nutrition changes on offspring development. Different levels of protein were supplemented to laying hens and offspring early growth performance was observed. Yolk deposition of maternal hormones and growth-related and myogenic genes expression were further studied.1 The Effect of Dietary protein on offspring early growth performace160 Langshan breeder hens were randomly divided into 3 groups, fed with 10% (LP), 15% (Con) and 20% (HP) crude protein diet. Contents of Lysine, Methionine, Methionine+Cysteine were adjusted synchronously. Energy, vitamins and trace elements were kept the same in all the three groups. Dietary protein level showed no significant effects on body weight of hens, yet the egg laying rate decreased markedly in LP diet group (P＜0.05). Results showed weights of eggs in HP diet group were significantly higher than the control (P＜0.05), while weights of eggs in LP diet groups were significantly lower (P＜0.05).Fertile eggs were collected and incubated after the dietary treatment. Offspring were raised under the same conditions until Day 28. The birth body weights in HP diet group were significantly higher than the control (P＜0.05), while the birth body weights in LP diet groups were significantly lower (P＜0.05). A strong positive relationship was found between hatching weight and fertile egg weight (R² = 0.9275, P＜0.05). However, both LP and HP diet groups showed higher growth rate after hatching compared with the controls. 7 days later, the average body weights of chicks in LP diet groups were even higher and the advantage was kept until Day 28. Relative liver weights didn't show significant difference among groups neither on Day 1 nor Day 28. Relative weight of breast muscle didn't differ among groups until Day 28. On Day 28 relative weight of breast muscle in LP diet group was markedly higher than that in the controls and HP diet group (P＜0.05). It indicates different levels of dietary protein can remarkably affect the growth performance of offspring.10 eggs from each group were used to determine the yolk deposition of maternal thyroid hormones and glucagon with radioimmunoassay. Also 10 chicks from each group were sacrificed on day 1 and day 28, respectively for sampling. Results: Yolk contents of T₃ and glucagon didn't show differences among groups, while that of T4 in HP diet group was significantly higher than the other two groups (P＜0.05). At hatching, serum levels of T₃ in LP group and T4 in HP diet group were significantly higher than the controls (P＜0.05). It indicated after hatching chicks in LP diet group had higher metabolic activities.2 The Effect of Dietary protein on growth-related genes expressionGene expression IGF-L IGF-â…¡,IGF-IR and TRa in both the breast muscle and the thigh muscle were determine by relative quantity RT-PCR on E14 and Day 1. On E14, the breast muscle in LP diet group had higher expression of IGF-â… ,IGF-â…¡and IGF-IR than the other two group (P＜0.05), while no differences were found between HP diet group and the controls. It indicated embryonic breast muscle in LP diet groups had higher growth potential. TRαgene expression didn't differ among groups either. However, on Day 1 after hatching, TRαexpression in breast muscle from LP diet group was significant higher than the controls (P＜0.05), which is synchronous with serum T₃ level. It may relative with the surpassing of body weight and relative breast muscle weight.Compared with results on the breast muscle, gene expression IGF-â… ,IGF-â…¡and IGF-IR in the thigh muscle didn't show significant differences among groups. On Day 1 after hatching, IGF-â… mRNA expression was lower than the controls in both LP and HP diet groups (P＜0.05) and no difference was found between them. IGF-â…¡and IGF-IR didn't differ among the groups at this point. TRa expression was found to be the same as it showed in the breast mucle. No difference was observed among groups on E14 and expression in LP diet group was significant higher than the controls on Day 1 after hatching (P＜0.05). 3 The Effect of Dietary protein on MyoD and Pax 7 genes expressionIn the breast muscle, MyoD mRNA expression in both LP and HP diet groups was markedly higher than that in controls (P＜0.05) on E14, while no difference was observed on Day 1 after hatching. Pax 7 expression didn't differ among groups on either time points.Compared with the results form the breast muscle, the thigh muscle expression of MyoD didn't differ among groups neither on E14 nor on Day 1 after hatching. On E14, Pax7 gene expression in LP diet groups was significant lower than the controls (P＜0.05). Gene expression of Pax7 didn't show any significant difference on Day 1 after hatching. All the results proved that the changes of maternal nutrition can affect the expression of myogenic genes in offspring. However, the effects differ in the breast muscle and thigh muscle due to the various composition of myofiber.These results indicated that: different dietary protein levels could affect the breeders' performance and the offsprings' early growth, significantly increased the relative breast muscle weight and upregulated muscle growth-related genes in the LP diet group.