Selecting chicken for improved meat production has altered the relative growth of organs in modern broiler lines compared with heritage lines. In this study, we compared the growth and feed efficiency of a heritage line, UIUC, with a modern production line, Ross 708, for 5 wk posthatch. During this period, the BW and feed efficiency of the modern strain was higher than that of the heritage line, indicating that the Ross 708 birds were more efficient than the UIUC birds at converting feed to body mass. The relative growth of the breast, heart, liver, and intestine were also compared during these 5 wk. The breast muscle of the heritage line constituted 9% of the total body mass at 5 wk, whereas in the modern line, the breast muscle was 18% of the total mass of the bird. In contrast, the relative size of the heart decreased after d 14 in the modern line, suggesting that selection for increased breast muscle has translated into relatively less weight of the heart muscle. The liver matured earlier in modern lines, possibly improving nutrient utilization as the birds shift from lipid- to carbohydrate-rich feed. Finally, jejunal and ileal sections of the intestine were 20% longer in the modern line, perhaps allowing for increased nutrient absorption.

A study was conducted with an exogenous monocomponent protease added to corn-soybean meal diets fed to straight-run Ross 708 broilers from 7 to 22 d of age. Broilers were randomly placed into 42 battery pens (5 birds/pen) and allocated to 6 treatments with 7 replicates. A positive control diet (PC; 22.5% CP) and a low protein basal diet (20.5% CP) were formulated. Low protein diets (LP) comprised 98.67% of low protein basal diet and 1.33% Celite (indigestible marker and filler; Celite Corp., Lompoc, CA). Protease [75,000 PROT units/g; 1 PROT unit is defined as the amount of enzyme that releases 1 µmol of p-nitroaniline from 1 µM of substrate (Suc-Ala-Ala-Pro-Phe-p-nitroaniline per minute at pH 9.0 and 37°C] was added at the expense of Celite (0 mg/kg, LP0; 100 mg/kg, LP100; 200 mg/kg, LP200; 400 mg/kg, LP400; and 800 mg/kg, LP800) to create the LP diets (20.25% CP). At 22 d of age, ileal contents were collected from all birds for apparent CP and amino acid (AA) digestibility determinations. Broilers fed the PC diet were 7.5% heavier (P < 0.05) compared with those fed the LP0 diet. Birds fed the LP diets containing protease regardless of concentration grew as well as the birds fed the PC diet. Feed conversion was impaired (P < 0.05) in birds fed the LP0 and the LP100 diets compared with those fed the PC diet, but no difference was found between birds fed the PC diet and those fed diets containing more protease (LP200, LP400, and LP800). Digestibility of CP was increased (P < 0.05) in broilers fed the LP-supplemented diets compared with those fed either the PC or LP0 diets, but it was similar between those fed LP diets with any protease concentration. Digestibility of AA was not different between the PC and LP0 diets. The protease used in this study restored live performance and digestibility of CP (6.1%). When benefits in AA digestibility occurred, they were similar at all protease inclusions and averaged as follows: Arg, 3.5%; Ile, 3.2%; Lys, 5.4%; Thr, 7.8%; Asp, 6.5%; His, 3.3%; Cys, 4.6%; and Ser, 5.5%. Methionine was increased only at 400 and 800 mg/kg (6.5%) and Val was increased only at 200 and 800 mg/kg (5%).

Diet modification to decrease phosphorus (P) concentration in animal feeds and manures can reduce surpluses of manure P in areas of intensive animal production. We generated turkey and broiler litters from two and three flock trials, respectively, using diets that ranged from "high" to "low" in non-phytate phosphorus (NPP) and some of which contained feed additives such as phytase. Phosphorus forms in selected litters were analyzed by sequential chemical fractionation and solution (31)P nuclear magnetic resonance (NMR) spectroscopy. Selected litters were also incubated with four contrasting soils. Reducing dietary NPP and using phytase decreased total P in litters by up to 38%. Water-soluble phosphorus (WSP) in litters was decreased 21 to 44% by feeding NPP closer to animal requirement, but was not affected by phytase addition. Solution (31)P NMR spectroscopy showed that feeding NPP closer to requirement decreased orthophosphate in litters by an average of 38% and that adding phytase to feed did not increase the concentration of orthophosphate in litters. Phytase also decreased phytate P in litters by 25 to 38%, demonstrating that it increases phytate P hydrolysis. Incorporation of litters with soils at the same total P rate increased WSP in soils relative to the control; this increase was correlated to soluble P added with litters at 5 d, but not by 29 d. Changes in soil Mehlich-3 phosphorus (M3-P) were related to total P added in litter, rather than soluble P. We conclude that feeding NPP closer to requirement and using feed additives such as phytase decrease total P concentrations in litters, while having little effect on P solubility in litters and amended soils.

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Three floor pen experiments (Exp) were conducted to evaluate low nonphytin P (NPP) concentrations and the NPP sparing effect of phytase (PHY) and 25-hydroxycholecalciferol (25D) on bone mineralization, bone breaking during commercial processing, litter P, and water-soluble P (WSP) concentrations. Tested treatments (TRT) were control, National Research Council NPP; University of Maryland (UMD) NPP; UMD + PHY, UMD NPP reduced by 0.064% NPP + 600 U of PHY/kg; UMD + PHY + 25D, UMD NPP reduced by 0.090% NPP + 600 U of PHY and 70 microg of 25D/kg; control + PHY mimicked the industry practice of diets by 0.1% when PHY is added; and negative control with 90% UMD NPP concentrations. UMD + PHY and control + PHY diets contained 600 U of PHY/kg, and UMD + PHY + 25D contained 600 U of PHY + 70 microg of 25D/kg. Performance results were presented separately. After each Exp, litter P and WSP were determined, and bone measurements were obtained on 8 or 10 broilers per pen. Tested TRT did not affect broiler BW. Femur ash weight of broilers fed the UMD and UMD + PHY + 25D was lower in all Exp compared with that of broilers fed the control diet. Femur ash was similar for control and UMD + PHY broilers, yet averaged over all Exp, UMD + PHY broilers consumed 39% less NPP and required less NPP per gram of femur ash than those on the control (4.87 and 7.77 g of NPP/g of ash, Exp 3). At the end of Exp 3, broilers were processed in a commercial facility. Despite reductions in NPP intake and bone mineralization, no differences were observed in measurements of economic importance (parts lost, carcass yield, and incidence of broken bones). The P excretion per bird was lowest for birds fed the UMD + PHY + 25D diet followed by those fed the UMD + PHY and negative control diets (10.44, 12.00, and 13.78 g of P/bird, respectively) and were highest for those fed the control diet (19.55 g of P/bird). These results suggest that feeding diets low in P together with PHY and 25D will not affect performance or increase losses at processing while resulting in improved P retention and reductions in P and WSP excreted.