Taken together, our findings provide evidence that the effects of 25(OH)D₃ on male broiler breast muscle are likely mediated through the mTOR-S6K pathway.

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A study was conducted to evaluate the effect of white striping ( ) of broiler breast muscle ( Pectoralis major ) on protein turnover and gene expression of genes related to protein degradation and fatty acid synthesis. A total of 560 day-old male broiler chicks Cobb 500 were allocated in a total of 16 pens, 35 chicks per pen. A completely randomized design was conducted with a 2 × 3 factorial arrangement (2 scores: severe and normal, and 3 breast meat samples sites). At d 60, 20 birds were randomly selected, euthanized, and scored for white striping. Scoring was either normal ( , no WS) or severe ( ). Also, the same day, 17 birds (16 infused, one control) were randomly selected and infused with a solution of 15 N Phen 40% ( ). Breast muscle tissue was taken for gene expression analysis of the following genes: MuRF1, atrogin-1, IGF-1, insulin receptor ( ), fatty acid synthetase, and acetyl CoA carboxylase ( ). Each bird was humanely euthanized after 10 minutes of infusion and scored for WS (NORM or SEV). Samples of the breast muscle ( Pectoralis major ) were taken at different layers (3 samples per bird: ventral, medial, dorsal), along with a sample of excreta for 3-methylhistidine analysis. Out of the 16 breast samples taken, only 10 were selected for analysis based on the WS score (5 NORM and 5 SEV). No significant differences ( P > 0.05) were found in fractional synthesis rate ( ) between SEV WS, NORM and sample sites for breast meat. However, fractional breakdown rate ( ) was significantly higher in birds with SEV WS compared to NORM (8.2 and 4.28, respectively, P < 0.0001). Birds with SEV WS showed significantly higher ( P < 0.05) relative expression of MuRF1 and slightly higher ( P = 0.07) relative expression of atrogin-1 than the NORM birds. These birds also showed lower ( P < 0.05) relative expression of IGF-1 than NORM birds. Further studies are needed to better understand why birds with severe white striping are degrading more muscular protein and mobilizing more fat.

A study was conducted to evaluate the effect of four different feeding regimens on breast muscle protein turnover in broiler breeder Cobb-500 parent stock (PS) pullets and breeder hens. The four feeding regimens based on BW curves utilized for the study were as follows: Everyday feeding (STD-ED) (Cobb Standard BW curve), skip-a-day feeding (STD-SKIP) (Cobb Standard BW curve), lighter BW (LBW-SKIP) (BW curve 20% under), and heavier BW (HBW-SKIP) (BW curve 20% over). Each feeding regimen was provided to pullets from 4 wk to 21 wk of age. Protein turnover was determined in PS pullets/breeders at 6, 10, 12, 16, 21, 25, 31, 37, 46, and 66 wk of age. A completely randomized design was used with a 4 × 10 factorial arrangement (four feeding regimens, 10 ages), each pullet represented a replicate. Five pullets/breeders at each age were given an intravenous flooding-dose of 15N-Phe (15N phenylalanine 150 mM, 40 APE (atom percent excess)) at a dose of 10 mL/kg BW for the determination of fractional synthesis rate (FSR). After 10 min, birds were euthanized and the breast muscle (pectoralis major) excised for protein turnover and gene expression analysis. Excreta was collected from each pullet or breeder for 3-methylhistidine (3-MH) analysis. No feeding regimen affected protein turnover. There was an age effect for breast muscle FSR. The FSR in breast muscle of pullets significantly increased from 6 wk to 12 wk and then decreased significantly for 31 wk-old breeders. FSR in breeder breast muscle increased significantly from 31 wk to 66 wk. There was an age effect for breast muscle fractional breakdown rate (FBR). FBR in breast muscle significantly increased from 21 wk to 25 wk and 31 wk (peak egg production), then significantly decreased at 66 wk. The expression of the genes related to protein degradation (Atrogin-1, MURF-1) in breast muscle was significantly higher at peak egg production. Protein turnover in skeletal muscle tissue is believed to be a source of nutrients for egg production.

The present study was conducted to determine whether the addition of β-mannanase in broiler feed changes hormonal profiles in the blood and broiler performance and nutrient availability. Five hundred and four Cobb male chickens were studied during d 7 to 21. Three corn-soybean meal (SBM) based diets 1) Low SBM (18% SBM); 2) High SBM (31% SBM); and 3) High SBM+GG (31% SBM + Guar Gum (GG) 0.5%) with 3 levels of β-mannanase (0, 200, and 400 ppm) were mixed to produce 9 diets. A factorial design 3 × 3 was performed with JMP pro 13 (SAS, 2017). Analysis of variance and contrast analysis were used to test significance level at P < 0.05. Glucose (190 and 188 mg/dL) was increased with 200 and 400 ppm of β-mannanase, respectively, compared to control (182 mg/dL) in the fasted state (P < 0.037). Glucose was higher in chicks fed with the High SBM and High SBM + GG diets but lower in the fasted re-fed state (P < 0.01). Insulin was higher with 200 and 400 ppm added β-mannanase in the fed state (P < 0.021). Insulin-like growth factor-1 was higher with 400 ppm added to High SBM+GG. β-mannanase improved feed conversion ratio (FCR) 9 points with 400 ppm in High SBM diet (P < 0.01) and 16 and 18 points with 200 and 400 ppm, respectively, added to the High SBM+GG diet (P < 0.01). Viscosity decreased from 19.2 to 7 cps with both enzyme doses in the High SBM + GG diet (P < 0.01). Digestible energy was +152 kcal/kg with 400 ppm β-mannanase in the High SBM diet and +200 kcal/kg with both levels of enzyme in High SBM+GG diet. Digestibility of amino acids was improved from 0.8 to 3.6% with β-mannanase in High SBM+GG diet (P < 0.05). In conclusion, chicks fed with High SBM and High SBM+GG diets with added β-mannanase significantly improved blood glucose and anabolic hormone homeostasis, FCR, digestible energy, and digestible amino acids compared to chicks fed with same diets without β-mannanase.