Capping dietary starch:protein ratios in moderately reduced crude protein,wheat-based diets showed promise but further reductions generated inferior growth performance in broiler chickens

The hypothesis that capping dietary starch:protein ratios would enhance the performance of broiler chickens offered reduced-crude protein(CP)diets was tested in this experiment.A total of 432 off-sex,male Ross 308 chicks were allocated to 7 dietary treatments from 7 to 35 d post-hatch.The experimental design consisted of a 3×2 factorial array of treatments with the seventh treatment serving as a positive control.Three levels of dietary CP(197.5,180.0 and 162.5 g/kg)with either uncapped or capped dietary starch:protein ratios constituted the factorial array of treatments,whilst the positive control diet contained 215.0 g/kg CP.The positive control diet had an analysed dietary starch:protein ratio of 1.50 as opposed to a ratio of 1.68 in the uncapped 197.5 g/kg CP diet and 1.41 in the corresponding capped diet and the capped 197.5 g/kg CP diet displayed promise.The growth performance this diet matched the positive control but outperformed the uncapped 197.5 g/kg CP diet by 10.4%(2,161 vs.1,958 g/bird;P=0.009)in weight gain,by 3.10%(3,492 vs.3,387 g/bird;P=0.019)in feed intake on the basis of pairwise comparisons and numerically improved FCR by 4.04%(1.616 vs.12684).However,the growth performance of birds offered the 180.0 and 162.5 g/kg CP dietary treatments was remarkably inferior,irrespective of dietary starch:protein ratios.This inferior growth performance was associated with poor feathering and even feather-pecking and significant linear relationships between feather scores and parameters of growth performance were observed.The amino acid profile of feathers was determined where cysteine,glutamic acid,glycine,proline and serine were dominant in a crude protein content of 931 g/kg.Presumably,the feathering issues observed were manifestations of amino acid inadequacies or imbalances in the more reduced-CP diets and consideration is given to the implications of these outcomes.

Performance of broiler chickens offered nutritionally-equivalent diets based on two red grain sorghums with quantified kafirin concentrations as intact pellets or re-ground mash following steam-pelleting at65 or 97℃ conditioning temperatures

The Liverpool Plains is a fertile agricultural region in New South Wales, Australia. Two sorghums from the2009 Liverpool Plains harvest, sorghums #3 and #5, were extensively characterised which included concentrations of kafirin and phenolic compounds plus rapid visco-analysis(RVA) starch pasting profiles. Diets based on these two sorghums were formulated to be iso-nitrogenous and iso-energetic and were offered to male Ross 308 broiler chicks from 7 to 28 days post–hatch as either intact pellets or reground mash following steam-pelleting at conditioning temperatures of either 65 or 97°C. Thus the feeding study consisted of a 2×2×2 factorial array of dietary treatments: two sorghum varieties, two feed forms and two conditioning temperatures. Each of the eight treatments was replicated six times with six birds per replicate cage.Assessed parameters included growth performance, nutrient utilisation, apparent starch and protein(N) digestibility coefficients and disappearance rates from the distal jejunum and distal ileum. Intact pellets supported higher(P <0.001) feed intakes and weight gains by 9.83 and 9.08%, respectively, than reground mash diets. Feed conversion ratios of broilers offered diets steam-conditioned at 97°C were 2.46% inferior(P <0.001) in comparison to 65°C diets and both apparent metabolizable energy(AME) and N-corrected AME(AMEn) were compromised. Broilers offered sorghum #3-based diets significantly(P <0.001) outperformed their sorghum #5 counterparts in terms of weight gain by 3.75%(1,334 versus 1,223 g/bird), FCR by 4.81%(1.524 versus 1.601), AME by 1.06 MJ(13.61 versus 12.55 MJ/kg), ME:GE ratio(ME:GE) by 4.81%(0.806 versus0.769) and AMEn by 1.03 MJ(12.38 versus 11.35 MJ/kg). The inferiority of sorghum #5 appeared to be associated with higher concentrations of kafirin(61.5 versus 50.7 g/kg) and conjugated phenolic acids,including ferulic acid(31.1 versus 25.6 mg/g). There were no significant differences in jejunal and ileal starch and protein(N) digestibility coefficients between the two sorghums. However, starch to protein(N) disappearance rate ratios from the distal jejunum were significantly(P <0.001) correlated with ME:GE and AME. The multiple linear regression equations indicated that energy utilisation was enhanced by coupling rapidly digestible protein with slowly digestible starch, which suggests that bilateral bioavailability of starch and protein is pivotal to efficient energy utilisation.

Implications of excreta uric acid concentrations in broilers offered reduced crude protein diets and dietary glycine requirements for uric acid synthesis

In a previous experiment,male Ross 308 broiler chickens were offered dietary treatments with 3 levels of crude protein(222,193,165 g/kg)and 3 feed grains(ground maize,ground wheat,whole wheat)from 7 to 35 d post-hatch.Maize-based diets supported superior growth performance in comparison to wheatbased diets.Uric acid concentrations in excreta were retrospectively determined and related to total nitrogen(N)excreta concentrations.Uric acid concentrations ranged from 28.5 to 69.4 mg/g and proportions of uric acid-N to total excreta-N ranged from 27.4%to 42.6%in broiler chickens offered the 3×3 factorial array of dietary treatments.Proportions of uric acid-N to total N in excreta in birds offered the165 g/kg CP,maize-based diet were significantly lower by 10.6 percentage units(27.4%versus 38.0%;P=0.00057)than their wheat-based counterparts.Total excreta analysed had been collected from 35 to37 d post-hatch when feed intakes and excreta outputs were monitored.There were linear relationships between proportions of uric acid-N to total N in excreta in birds offered the three 165 g/kg CP diets with weight gain(r=-0.587;P=0.010),feed intake(r=-0.526;P=0.025)and feed conversion ratios(r=0.635;P=0.005).The possibility that increasing uric acid-N proportions in excreta is indicative of excessive ammonia accumulations compromising growth performance is discussed.The mean proportion of dietary glycine involved in uric acid excretion was 49.2%across all dietary treatments but ranged from 25.0%to 80.9%.Thus,the appropriate amount of dietary glycine is variable and largely dependent on the volume of uric acid synthesised and excreted.