The crude protein ( CP ) content of 4 iso-energetic, maize-based diets containing 11.00 g/kg digestible lysine was reduced in gradations from 200 to 156 g/kg with increasing inclusions of synthetic, or unbound, essential amino acids. A constant dietary electrolyte balance ( DEB ) of 230 mEq/kg was maintained, but a second 156 g/kg CP diet had a DEB of 120 mEq/kg, and energy densities of the 156 g/kg CP diet were reduced in the sixth and seventh treatments. Each of the 7 dietary treatments were offered to 7 replicate cages (6 birds/cage) or a total of 294 Ross 308 off-sex male broilers from 14 to 35 D posthatch. Reductions in CP from 200 to 156 g/kg did not influence weight gain but quadratically increased feed conversion ratio ( FCR ) and linearly increased relative abdominal fat-pad weights and feed intakes. The reduction in DEB did not influence growth performance but did adversely influence some amino acid digestibilities. Reducing energy density by 100 kcal/kg did not influence growth performance of birds offered the 156 g/kg CP diet but numerically reduced fat-pad weights. The transition from 200 to 156 g/kg CP diets generally enhanced jejunal and ileal amino acid digestibility coefficients but had diverse effects on free amino acid concentrations in systemic plasma with a remarkable 116% increase in threonine. Starch:protein disappearance rate ratios linearly increased in the jejunum and the ileum following the same transition, and these expanding ratios were related to heavier fat-pads and compromised FCR. This study indicates that reductions in dietary CP from 200 to 172 g/kg supported by inclusions of unbound essential amino acids do not compromise growth performance, but a further reduction to 156 g/kg CP significantly increased FCR. Both heavier relative fat-pad weights and inferior FCR were related to expanding starch:protein disappearance rate ratios, which suggests condensed dietary starch:protein ratios may advantage birds offered reduced CP diets.
A total of 294 male, off-sex Ross 308 chickens were offered 7 dietary treatments with crude protein (CP) contents of 210, 195, 180, and 165 g/kg. One of the four 165 g/kg diet was consistent with the higher protein diets and 3 were modified to investigate the effects of increased methionine levels, pre-pellet inclusion of whole maize, and whey protein concentrate in reduced-CP broiler diets. There were 7 replicate cages, 6 birds per cage, from 14 to 35 D post-hatch. The average feed conversion ratio (FCR) of birds offered 210, 195, 180 g/kg CP diets was 1.555 which was superior ( P < 0.05) to the 1.608 FCR of their 165 g/kg counterparts. The transition from 210 to 165 g/kg (diet 4) CP diets linearly increased ( P < 0.001) relative fat-pad weights from 8.64 to 14.62 g/kg. The same transition linearly increased jejunal and ileal starch digestibility coefficients ( P < 0.001), metabolizable to gross energy ratios (ME:GE) ratios ( P < 0.001) and nitrogen (N)-corrected apparent metabolizable energy (AMEn) ( P = 0.001) but did not influence N retention. Starch:protein disappearance rate ratios increased linearly ( P < 0.001) from 2.68 to 3.82 in the jejunum and from 1.76 to 2.94 in the ileum following dietary CP reductions. Ileal disappearance rate ratios were quadratically related to FCR (r = 0.486; P < 0.005) and linearly related to relative fat-pad weights (r = 0.663; P < 0.001) where both parameters were disadvantaged by widening ratios. The transition from 210 to 165 g/kg crude protein diets linearly increased the average digestibility coefficient of 17 amino acids from 0.459 to 0.594 in jejunum and from 0.744 to 0.790 in the ileum. The present study demonstrates that dietary CP can be reduced from 210 to 180 g/kg without negatively influencing broiler performance but the further reduction to 165 g/kg compromised FCR. However, the three modifications to the 165 g/kg CP diet failed to enhance broiler performance.
Background The minimum to which dietary crude protein (CP) level for broiler chickens can be reduced without decreasing growth and the glycine equivalent (Glyequi) concentration required are not known. The plasma metabolome might reflect dietary influences on physiological processes. Objective The aim of this study was to investigate the effect of 3 low CP levels with 4 Glyequi concentrations on growth and characteristics of nitrogen excretion, and to identify plasma metabolome variations. Methods Male Ross308 broiler chickens were provided 1 of 12 dietary treatments in 84 metabolism cages (10/cage) from days 7 to 21. Three diets with 163 (CP163), 147 (CP147), and 132 (CP132) g CP/kg were formulated, each containing 12, 15, 18, and 21 g Glyequi/kg. Essential amino acid concentrations were the same in all diets. Animals and feed were weighed on days 7 and 21 to determine average daily gain (ADG) and gain:feed ratio (G:F). Excreta were collected from days 18 to 21 to analyze nitrogenous components, and blood was obtained on day 21 to conduct a metabolome analysis. Results Two-factor ANOVA showed significant interaction effects for ADG, G:F, and nitrogen efficiency (P < 0.001). Reduction of CP decreased ADG and G:F, and increased nitrogen efficiency. Glyequi supplementation increased ADG (by 7.9 g/d) and G:F (by 0.07 g/g) at CP132. The ADG (by 2.4 g/d) at CP147 and G:F (by 0.02 g/g) at CP147 and CP163 increased up to 15 g Glyequi/kg. Multivariate statistical analysis showed an influence of Glyequi on plasma acylcarnitine and lysophosphatidylcholine concentrations, and a decrease of plasma phosphatidylcholine and sphingomyelin concentrations with reduced CP. Conclusions These results suggest that a nutrient other than Glyequi limited growth when CP was reduced from CP163 to CP147, and that the response of broiler chickens to Glyequi is dependent on the dietary CP level. Plasma metabolites indicate dietary influences on the physiological state of the animals.
Two broiler lines A and B were fed experimental diets from 21 to 42 days with an objective to determine Pectoralis major protein turnover (PT) as affected by the dietary amino acid (AA) levels and ambient temperature. Experimental diets (n = 9 replicate pens per diet) were formulated to 3,150 kcal/kg with five levels of digestible lysine (dLys) −80, 90, 100, 110 and 120% of recommended AA level giving g dlys/Mcal values of 2.53, 2.85, 3.17, 3.48 and 3.80 respectively. All other AA was formulated to a fixed ratio to dLys. Fractional synthesis or degradation rates (FSR or FDR) of P. major were measured on day 36 and day 42 for all dietary treatment levels for both broiler lines using stable isotope of AA (15N‐phenylalanine) as metabolic tracer. Experimental feeding studies were conducted once in hot season (24‐hr mean ~ 85.3°F; 80.9% RH) and repeated in cool season (24‐hr mean ~ 71.6°F; 61.7% RH) of the year. The FSR values increased (p < .05) as digestible AA in diet increased for both broiler lines in hot season until break point FSR occurring at 106.2% AA level. The average FSR values measured were higher for Line B at day 36 (20.98%/D for Line B vs. 20.69%/D for Line A) and at day 42 (16.07%/D for Line B vs. 12.47% D for Line A). FDR values observed at day 36 and day 42 were not different between lines (p > .05). Similar trends but elevated values of FSR and FDR in cool season than in hot season were recorded for both the lines. Line B showed the higher mixed muscle protein accretion (%/D) than Line A by actually increasing the FSR which was correlated by higher lean mass deposition and higher feed intake (p < .05). The overall findings indicated that PT response in P. major due to effects of digestible AA levels and ambient temperature was different and line‐specific.
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