Effect Of Birth Weight On Growth Performance?meat Quality And M Rna Expression Profle In 817 Broiler

The purpose of this study was to investigate the effects of birth weight(BW)on production performance,meat quality,and m RNA expression of growth axis related genes in 817 broilers.A total of 1200 0-day-old 817 broilers were wing banded,weighted individually,and assigned to one of three groups based on the BW: low BW(37.5±1.9g.BW?40g)and intermediate BW(42.8±0.5g,BW,42.0g-43.6g),and high BW(47.9±1.9g,BW? 46.0 g).Feed and water were provided ad libitum.The body weights were recorded individually every 7 days.At 49 days old,the growth curves of 817 broiler chickens were fitted according to their weekly weight.At 49 days of age,15 roosters with approximate average body weight were selected for carcass performance and meat quality analysis.Moreover,RNA was extracted from 3 hypothalamic samples of high BW and low BW to perform RNA-seq analysis.The results showed that the fitting degree of Logistic,Gompertz,and Bertallanffy growth models was higher than 0.996.Among them,the Logistic model had the best combination effect,and its fitting value was the most consistent with the actual measured value.The fitting degree,the weekly age at the inflection point,and the body weight at the inflection point were 0.998,4.85 weeks,and 951.54 g,respectively.At 49 days of age,roosters from high BW and intermediate BW group were heavier than that from the low BW group 101 g and 114 g,respectively(P < 0.05).There was no significant difference in body weight of roosters between high BW and intermediate BW group(P>0.05).The body weight of hens from Low BW group was lower than that of the other two groups only in the early stage(1-14 days old)(P<0.05).BW had no significant effect on carcass composition including the percentage of partially eviscerated carcass,percentage of full eviscerated weight,percentage of abdominal fat weight,leg muscle weight,and percentage of breast muscle weight.The proportion of spleen was significantly higher in the high BW group than in the intermediate BW group(P<0.05).The duodenal index of the low BW group was significantly higher than that of the high BW group(P<0.05).There was no significant difference in the index of heart,liver,muscle stomach,jejunum and ileum among the three groups(P>0.05).BW also had no significant effect on dripping loss,cooking loss,shear force,and meat color(P>0.05).By using a correction of Pvalue < 0.05 and log2 |foldchange| > 1 as the cutoff,a total of 424 differentially expressed genes(DEGs)were identified.These DEGs were significantly enriched in GO terms of "somatostatin signaling pathway" and "glucocorticoid secretion pathway".RNA-seq results revealed that the m RNA levels of SST and TRH genes in the hypothalamus of the low BW was significantly up-regulated when compared with the high BW groups.Further q PCR results showed that the expression of SSTR2 and SSTR5 genes were significantly up-regulated,TRHR and GH were down-regulated,while,GHRHR was no change in pituitary from the low BW group when compared with the high BW group.In summary,our results suggested that the BW had no significant effect on the slaughter performance,meat quality,and the final body weight of 817 hens.The growth rate of 817 roosters with lower BW is slow,which may be related to the high expression of SST gene that inhibition TRH-stimulated secretion of GH.