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Apparent metabolizable energy and performance of broilers fed selected grain sorghum varieties

      ABSTRACT

      Objective

      The objective of this study was to determine the nitrogen-corrected apparent ME (AMEn) content of tannin-free red/bronze, white/tan, and US No. 2 varieties of grain sorghum fed to commercial broilers and evaluate its effects on growth performance as an alternative to corn in poultry diets.

      Materials and Methods

      Nitrogen-corrected apparent ME content of red/bronze, white/tan, and US No. 2 grain sorghum varieties was determined using a dextrose control diet as the standard fed to 112 mixed-sex Cobb 500 female × Hubbard male broilers. Weekly measures of mean BW and feed consumption were used to calculate BW gain, feed intake, and feed conversion ratio. Analyses were based on a 2 × 4 factorial arrangement of treatments with age (grower and finisher phases) and grain types (corn-dextrose, red/bronze, white/tan, and US No. 2) defining the treatments. Cage was the experimental unit with data analyzed using JMP Pro version 15.2.0 (SAS Institute Inc.).

      Results and Discussion

      Mean AMEn values of modern grain sorghum varieties for broilers in the grower diet phase were determined as 3,336 (red/bronze), 4,000 (white/tan), and 3,341 (US No. 2) kcal/kg and, in the finisher-diet phase, as 3,001 (red/bronze), 3,599 (white/tan), and 3,599 (US No. 2) kcal/kg (P = 0.0155). No significant differences among treatments for growth performance (BW gain, feed intake, feed conversion ratio) in the grower- and finisher-diet phases were observed.

      Implications and Applications

      Responses indicate the potential for grain sorghum to replace corn without suboptimal effects on broilers. Growth performance trials with the full substitution of corn in feed formulation will be necessary to validate AMEn values and evaluate additional performance parameters.

      Key words

      INTRODUCTION

      Grain sorghum is an alternative feedstuff to corn due to its similar nutritional composition and its adaptations to drought and varying soil types, enabling it to be grown in locations coinciding with poultry production in the southeastern United States (US). Previous studies with commercial broiler diets indicated that low-tannin grain sorghum was an effective partial or complete replacement for corn, whereas high-tannin grain sorghum negatively affected feed intake, protein digestibility, and growth (
      • Gualtieri M.
      • Rapaccini S.
      Sorghum grain in poultry feeding..
      ). The combination of antinutritional factors, including tannin, phytate, and karafin compounds in grain sorghum, resulted in decreased nutritive value and palatability, affecting feed intake (FI) and, thus, reduced growth of broilers.

      Rodrigues, H., R. Perez-Maldonado, P. Trappett, K. Barram, and M. Kemsley. 2007. Broiler performance in Australian sorghum-based starter and finisher diets (2005 harvest). Pages 93–96 in Proc. 19th Australian Poult. Sci. Symp. The Poultry Research Foundation.

      evaluated broiler performance in Australian grain sorghum–based diets and concluded a negative relationship between grain sorghum tannins and apparent ME (AME) values. Correspondingly, nitrogen-corrected AME (AMEn) values have been lower in red grain sorghum varieties than in white grain sorghum varieties due to an increased tannin content in the red varieties (
      • Mandal A.B.
      • Tyagi P.K.
      • Elangovan A.V.
      • Tyagi P.K.
      • Kaur S.
      • Johri A.K.
      Comparative apparent metabolisable energy values of high, medium and low tannin varieties of sorghum in cockerel, guinea fowl and quail..
      ).
      • Dykes L.
      • Rooney L.W.
      Sorghum and millet phenols and antioxidants..
      indicated that, of the tannin-free grain sorghum varieties, red grain sorghum had a greater total of phenol compounds than white grain sorghum, resulting in adverse effects on performance. Low-tannin and tannin-free varieties may be potential replacements for corn as they are similar in nutritive value (
      • Gualtieri M.
      • Rapaccini S.
      Sorghum grain in poultry feeding..
      ). Overall, these inconsistencies have invoked a negative perception of using grain sorghum as an alternative; however, evaluation of low-tannin grain sorghum varieties proved to be effective relative to high-tannin grain sorghum varieties fed to broilers (
      • Hulan H.W.
      • Proudfoot F.G.
      Nutritive value of sorghum grain for broiler chickens..
      ).
      Today, modern varieties of grain sorghum in the US are tannin free for animal feed use; however, limited data are available to support modern varieties as an alternative feedstuff to corn in broiler diets. Validating the nutritional effects of modern grain sorghum varieties on the growth, health, and product quality of broilers is necessary to support the use of these varieties in poultry feed. In addition, validating the nutrient profile of tannin-free grain sorghum is important due to the variability of its nutrient content and previous data lacking comparable characterization of grain types, form, and processing methods (

      Taylor, J. R., and J. Kruger. 2019. Sorghum and millets: Food and beverage nutritional attributes. Pages 171–224 in Sorghum and Millets. AACC International Press. https://doi.org/10.1016/B978-0-12-811527-5.00007-1.

      ). Failure to accommodate for variations in energy values when formulating a diet can significantly affect the cost of feed and production. As a result, evaluating the nutritional composition of modern grain sorghum will provide commercial poultry nutritionists with up-to-date specifications for practical use in feed formulation, which is currently limited based on outdated or nonexistent nutritional profiles for tannin-free grain sorghum.
      Energy is arguably the most expensive and physiologically important component of a poultry diet. It is also the first parameter to consider in diet formulation due to its multifaceted functions for metabolism, maintenance, growth, and heat production in animals (
      • Wu S.B.
      • Choct M.
      • Pesti G.
      Historical flaws in bioassays used to generate metabolizable energy values for poultry feed formulation: A critical review..
      ). The energy provided from a feed and its availability to the bird can be measured by evaluating the ME of feedstuffs in a diet. Measures of FI and excretory output are the basis for quantitatively determining ME (

      Bedford, M. R., M. Choct, and H. M. O’Neill. 2016. Nutrition Experiments in Pigs and Poultry: A Practical Guide. CABI.

      ). A more recent study in broilers by
      • Khalil M.M.
      • Abdollahi M.R.
      • Zaefarian F.
      • Chrystal P.V.
      • Ravindran V.
      Apparent metabolizable energy of cereal grains for broiler chickens is influenced by age..
      suggests that AMEn is affected by age, and in a study by
      • Bartov I.
      Differential effect of age on metabolisable energy content of high protein-low energy and low protein-high energy diets in young broiler chicks..
      , AMEn of corn and sorghum diets decreased with increasing age. Therefore, determining the AMEn value of each of these modern grain sorghum varieties is a critical factor in diet formulation for the full replacement of corn in poultry feed. The objective of this study was to determine the AMEn content of red/bronze, white/tan, and US No. 2 varieties of tannin-free, grain sorghum for feeding commercial broilers and evaluate its effect on growth performance.

      MATERIALS AND METHODS

      Animal Care and Use

      All experimental policies and procedures were reviewed and approved by the Clemson University Institutional Animal Care and Use Committee (AUP #2017-051).

      Birds and Husbandry

      A trial was conducted during a 1- to 47-d-of-age grow-out period to evaluate the AMEn response of 112 mixed-sex Cobb 500 female × Hubbard male commercial broilers from 22 to 24 d of age and 43 to 45 d of age. At 1 d of age, birds were housed in a solid-sided research house and randomly distributed (4 birds per cage) in heated battery brooder cages, 34 cm × 98 cm, and transferred at 21 d of age to grower battery cages, 61 cm × 71 cm (Petersime). Each grower battery cage was the experimental unit, with a metal trough feeder and water unit. The temperature of the cage was 35°C at placement and gradually decreased to reach 27°C, and a lighting program of 16 h of light to 8 h of dark (16L:8D) was followed throughout the study.

      Tannin Analysis

      Varieties of grain sorghum used in this experiment were analyzed for tannin content to ensure zero tannin content before use in experimental diets. An acid-butanol assay (

      Hagerman, A. E. 2002. Acid Butanol Assay for Proanthocyanidins Tannin Handbook. Miami University.

      ) for proanthocyanidins was conducted on red/bronze, white/tan, and the US No. 2 grain sorghum varieties. In this assay, acid was added to a sample of each grain to yield a colored product (known as cyanidin) or a colorless product (known as catechin) if tannins were present or absent, respectively (

      Hagerman, A. E. 2002. Acid Butanol Assay for Proanthocyanidins Tannin Handbook. Miami University.

      ). The colored product has an absorbance peak at 550 nm and is characteristic of a high-tannin grain (

      Hagerman, A. E. 2002. Acid Butanol Assay for Proanthocyanidins Tannin Handbook. Miami University.

      ).

      Experimental Diets

      Three modern varieties of grain sorghum commonly grown in the southeastern US, red/bronze, white/tan, and US No. 2, were obtained from the states of Florida and North Carolina and used for all diets. The red/bronze and white/tan grain sorghum varieties were identity preserved, whereas US No. 2 was a red/bronze-based variety that may have contained other mixed grain sorghum varieties. Nutrient and GE analyses of grain sorghum used in the experimental diets are shown in Table 1. All whole grain sorghum was ground through a hammer mill (Premier 1 Supplies) with a 4-mm sieve. The trial included 4 cages for the dextrose/control diet and 8 cages for each of the 3 treatments with a grain sorghum variety; therefore, cage was the experimental unit. Diets were fed as mash ad libitum and formulated based on an industry-standard supplied by a commercial nutritionist. All birds were fed a corn-based acclimation diet on d 1 to 3. On d 4, birds were randomly assigned 1 of 4 corn basal diets with 20% of the calories for the GE of corn replaced by the equivalent calories of the respective GE of grain sorghum (red/bronze, white/tan, or US No. 2; Table 1) or dextrose for the dextrose/control diet. Dextrose was used as a reference ingredient due to its known GE content. The classical basal substitution method (
      • Sibbald I.R.
      • Summers J.D.
      • Slinger S.J.
      Factors affecting the metabolizable energy content of poultry feeds..
      ) was modified in this study to target a more practical approach and for evaluation for future use by commercial nutritionists. The ingredient composition, nutrient analyses, and AMEn for the basal and complete test diets are shown in Tables 2, 3, 4, and 5.
      Table 1Nutrient and GE analyses of sources of corn and modern varieties of grain sorghum (red/bronze, white/tan, and US No. 2)
      ItemDextroseCornGrain sorghum variety
      Red/bronzeWhite/tanUS No. 2
      DM
      Proximate analysis and AA were determined using the AOAC International methods (Novus International Inc. Laboratory Services).
      (%)
      84.5887.4889.9384.44
      GE, as fed
      Determined by the University of Georgia Feed, Environmental and Water Laboratory.
      (kcal/kg)
      3,3763,9263,7523,6863,653
      Ash
      Proximate analysis and AA were determined using the AOAC International methods (Novus International Inc. Laboratory Services).
      (%)
      1.070.901.101.39
      Crude fat
      Proximate analysis and AA were determined using the AOAC International methods (Novus International Inc. Laboratory Services).
      (%)
      3.132.892.462.93
      Crude fiber
      Proximate analysis and AA were determined using the AOAC International methods (Novus International Inc. Laboratory Services).
      (%)
      1.501.801.702.20
      CP
      Proximate analysis and AA were determined using the AOAC International methods (Novus International Inc. Laboratory Services).
      (%)
      7.528.879.338.65
      Methionine (%)0.150.150.170.14
      Lysine (%)0.260.240.240.23
      Threonine (%)0.260.300.310.28
      1 Proximate analysis and AA were determined using the AOAC International methods (Novus International Inc. Laboratory Services).
      2 Determined by the University of Georgia Feed, Environmental and Water Laboratory.
      Table 2Ingredient composition of basal broiler diet (as fed) in phases of a 1- to 47-d grow-out for complete test diets (as fed)
      ItemBasal diet phase
      Starter

      (1–11 d)
      Grower

      (12–24 d)
      Finisher

      (25–47 d)
      Ingredient (%)
       Corn49.4558.6063.11
       Soybean meal, 47.5% CP42.0533.5528.81
       Fat, vegetable3.592.963.47
       Mono-dicalcium phosphate1.891.831.73
       Limestone1.571.561.50
       Sodium chloride0.550.590.60
      dl-Methionine0.330.280.24
      l-Threonine0.000.0050.01
       Biolys
      50.7% lysine, Biolys (Evonik).
      0.050.100.11
       Choline chloride, 60%0.180.190.12
       Vitamin and mineral premix
      Vitamin premix per kilogram of diet: vitamin A = 16,435.29 IU; vitamin D3 = 3,582,452; 25-hydroxyvitamin D3 = 0.08 mg; vitamin E = 156.53 IU; vitamin B12 = 0.05 mg; biotin = 0.47 mg; menadione = 7.04 mg; thiamine 4.23 mg; riboflavin = 14.09 mg; d-pantothenate = 23.48 mg; vitamin B6 = 7.44 mg; niacin = 93.92 mg; folic acid = 3.13 mg. Trace mineral premix per milligram per kilogram of diet: manganese = 113.59%; zinc = 107.90%; iron = 0.22%; copper = 5.68%; iodine = 3.41%; cobalt = 1.70%; selenium = 0.34%.
      0.220.230.20
       BMD 50
      Bacitracin methylene disalicylate (Zoetis).
      0.060.060.06
       Saccox 60
      Salinomycin sodium (Huvepharma).
      0.060.050.04
      Calculated composition
      Phase-fed basal diet formulation based on an industry standard supplied by a commercial nutritionist.
       ME (kcal/kg)2,9833,0393,125
       CP (%)23.6220.3818.51
       Crude fat (%)6.115.686.27
       Calcium (%)1.020.980.94
       Sodium (%)0.240.250.26
       Lysine (%)1.521.301.17
       Methionine (%)0.710.620.55
       Methionine + cysteine (SAA
      SAA = sulfur AA.
      ; %)
      1.110.970.88
       Total phosphorus (%)0.820.770.73
       Available phosphorus (%)0.470.450.43
      Analyzed composition
       CP
      Proximate analysis, AA, and minerals were determined using the AOAC International methods (Novus International Inc. Laboratory Services).
      (%)
      25.2820.9118.78
       Crude fat
      Proximate analysis, AA, and minerals were determined using the AOAC International methods (Novus International Inc. Laboratory Services).
      (%)
      5.884.755.74
       Calcium (%)1.042.711.17
       Sodium (%)0.200.130.13
       Lysine (%)1.761.151.19
       Methionine (%)1.320.380.47
       Methionine + cysteine (SAA; %)0.990.650.77
       Total phosphorus (%)0.820.920.98
      1 50.7% lysine, Biolys (Evonik).
      2 Vitamin premix per kilogram of diet: vitamin A = 16,435.29 IU; vitamin D3 = 3,582,452; 25-hydroxyvitamin D3 = 0.08 mg; vitamin E = 156.53 IU; vitamin B12 = 0.05 mg; biotin = 0.47 mg; menadione = 7.04 mg; thiamine 4.23 mg; riboflavin = 14.09 mg; d-pantothenate = 23.48 mg; vitamin B6 = 7.44 mg; niacin = 93.92 mg; folic acid = 3.13 mg. Trace mineral premix per milligram per kilogram of diet: manganese = 113.59%; zinc = 107.90%; iron = 0.22%; copper = 5.68%; iodine = 3.41%; cobalt = 1.70%; selenium = 0.34%.
      3 Bacitracin methylene disalicylate (Zoetis).
      4 Salinomycin sodium (Huvepharma).
      5 Phase-fed basal diet formulation based on an industry standard supplied by a commercial nutritionist.
      6 SAA = sulfur AA.
      7 Proximate analysis, AA, and minerals were determined using the AOAC International methods (Novus International Inc. Laboratory Services).
      Table 3Ingredient composition and nutrient analyses of complete starter-phase test diets (as fed) for 4 to 11 d of age (dextrose/control, red/bronze, white/tan, and US No. 2)
      ItemStarter treatment
      Dextrose

      control
      Red/bronzeWhite/tanUS No. 2
      Ingredient
      Phase-fed basal diet (Table 2) and complete diet formulation based on an industry standard supplied by a commercial nutritionist.
      (%)
       Basal starter diet
      Phase-fed basal diet (Table 2) and complete diet formulation based on an industry standard supplied by a commercial nutritionist.
      87.1288.4088.1689.35
       Grain sorghum0.0011.6011.8410.65
       Dextrose12.880.000.000.00
      Calculated composition
      Phase-fed basal diet (Table 2) and complete diet formulation based on an industry standard supplied by a commercial nutritionist.
       ME (kcal/kg)3,0663,0353,0003,000
       CP (%)20.4721.9921.8322.00
       Crude fat (%)5.115.505.455.52
       Calcium (%)1.161.181.171.19
       Sodium (%)0.190.190.190.20
       Lysine (%)1.201.241.241.23
       Methionine (%)0.590.620.620.63
       Methionine + cysteine (SAA
      SAA = sulfur AA.
      ; %)
      0.910.970.960.97
       Total phosphorus (%)0.710.760.760.76
       Available phosphorus (%)0.460.480.480.49
      Analyzed composition
       CP
      Proximate analysis, AA, and minerals were determined using the AOAC (Association of Official Analytical Chemists) methods (Novus International Inc. Laboratory Services).
      (%)
      22.0521.7325.4322.64
       Crude fat
      Proximate analysis, AA, and minerals were determined using the AOAC (Association of Official Analytical Chemists) methods (Novus International Inc. Laboratory Services).
      (%)
      5.556.365.355.76
       Calcium (%)1.131.141.120.94
       Sodium (%)0.180.170.140.13
       Lysine (%)1.191.221.401.33
       Methionine (%)0.690.680.660.62
       Methionine + cysteine (SAA; %)0.980.991.000.96
       Total phosphorus (%)0.760.820.820.76
      1 Phase-fed basal diet (Table 2) and complete diet formulation based on an industry standard supplied by a commercial nutritionist.
      2 SAA = sulfur AA.
      3 Proximate analysis, AA, and minerals were determined using the AOAC (Association of Official Analytical Chemists) methods (Novus International Inc. Laboratory Services).
      Table 4Ingredient composition, nutrient analyses, and calculated treatment nitrogen-corrected apparent ME (AMEn)
      Calculated AMEn of each complete test diet determined using the following equation: AMEn = {(GEI − GEE) − [8.73 × (NI − NE)]}/FI, where GEI = GE intake; GEE = GE output in excreta; NI = nitrogen intake from the diet; NE = nitrogen output from excreta; FI = feed intake; and 8.73 = nitrogen correction factor from previous research (Macleod et al., 2008).
      of complete grower-phase test diets (as fed) for 12 to 24 d of age (dextrose/control, red/bronze, white/tan, and US No. 2)
      ItemGrower treatment
      Dextrose

      control
      Red/bronzeWhite/tanUS No. 2
      Ingredient
      Phase-fed basal diet (Table 2) and complete diet formulation based on an industry standard supplied by a commercial nutritionist.
      (%)
       Basal grower diet
      Phase-fed basal diet (Table 2) and complete diet formulation based on an industry standard supplied by a commercial nutritionist.
      85.0486.5486.3086.18
       Grain sorghum0.0013.4613.7013.82
       Dextrose14.960.000.000.00
      Calculated composition
      Phase-fed basal diet (Table 2) and complete diet formulation based on an industry standard supplied by a commercial nutritionist.
       ME (kcal/kg)3,1263,0903,0503,052
       CP (%)17.1018.8018.6318.62
       Crude fat (%)4.645.075.035.06
       Calcium (%)1.051.061.061.06
       Sodium (%)0.200.200.200.20
       Lysine (%)1.011.051.051.05
       Methionine (%)0.500.540.530.53
       Methionine + cysteine (SAA
      SAA = sulfur AA.
      ; %)
      0.780.850.840.84
       Total phosphorus (%)0.660.710.710.71
       Available phosphorus (%)0.430.450.450.45
      Analyzed composition
       CP
      Proximate analysis, AA, and minerals were determined using the AOAC International methods (Novus International Inc. Laboratory Services).
      (%)
      20.4719.5220.5320.17
       Crude fat
      Proximate analysis, AA, and minerals were determined using the AOAC International methods (Novus International Inc. Laboratory Services).
      (%)
      4.504.634.924.91
       Calcium (%)0.921.041.020.97
       Sodium (%)0.160.180.160.17
       Lysine (%)1.001.091.101.14
       Methionine (%)0.550.530.590.54
       Methionine + cysteine (SAA; %)0.800.820.870.31
       Total phosphorus (%)0.700.760.760.73
       GE
      Determined by the University of Georgia Feed, Environmental and Water Laboratory.
      (kcal/kg)
      4,0254,2664,3034,340
      1 Calculated AMEn of each complete test diet determined using the following equation: AMEn = {(GEI − GEE) − [8.73 × (NI − NE)]}/FI, where GEI = GE intake; GEE = GE output in excreta; NI = nitrogen intake from the diet; NE = nitrogen output from excreta; FI = feed intake; and 8.73 = nitrogen correction factor from previous research (
      • MacLeod M.G.
      • Valentine J.
      • Cowan A.
      • Wade A.
      • McNeill L.
      • Bernard K.
      Naked oats: metabolizable energy yield from a range of varieties in broilers, cockerels, and turkeys..
      ).
      2 Phase-fed basal diet (Table 2) and complete diet formulation based on an industry standard supplied by a commercial nutritionist.
      3 SAA = sulfur AA.
      4 Proximate analysis, AA, and minerals were determined using the AOAC International methods (Novus International Inc. Laboratory Services).
      5 Determined by the University of Georgia Feed, Environmental and Water Laboratory.
      Table 5Ingredient composition, nutrient analyses, and calculated treatment nitrogen-corrected apparent ME (AMEn)
      Calculated AMEn of each complete test diet determined using the following equation: AMEn = {(GEI − GEE) − [8.73 × (NI − NE)]}/FI, where GEI = GE intake; GEE = GE output in excreta; NI = nitrogen intake from the diet; NE = nitrogen output from excreta; FI = feed intake; and 8.73 = nitrogen correction factor from previous research (Macleod et al., 2008).
      of complete finisher-phase test diets (as fed) for 25 to 47 d of age (dextrose/control, red/bronze, white/tan, and US No. 2)
      ItemFinisher treatment
      Dextrose

      control
      Red/bronzeWhite/tanUS No. 2
      Ingredient
      Phase-fed basal diet (Table 2) and complete diet formulation based on an industry standard supplied by a commercial nutritionist.
      (%)
       Basal finisher diet
      Phase-fed basal diet (Table 2) and complete diet formulation based on an industry standard supplied by a commercial nutritionist.
      84.0685.6685.4085.27
       Grain sorghum0.0014.3514.6114.74
       Dextrose15.950.000.000.00
      Calculated composition
      Phase-fed basal diet (Table 2) and complete diet formulation based on an industry standard supplied by a commercial nutritionist.
       ME (kcal/kg)3,2073,1713,1273,130
       CP (%)15.2617.0516.8816.87
       Crude fat (%)5.095.565.515.54
       Calcium (%)0.960.980.980.98
       Sodium (%)0.200.200.200.20
       Lysine (%)0.890.940.940.94
       Methionine (%)0.450.480.480.48
       Methionine + cysteine (SAA
      SAA = sulfur AA.
      ; %)
      0.700.770.760.76
       Total phosphorus (%)0.620.670.670.67
       Available phosphorus (%)0.400.430.420.42
      Analyzed composition
       CP
      Proximate analysis, AA, and minerals were determined using the AOAC International methods (Novus International Inc. Laboratory Services).
      (%)
      18.4917.6318.4418.10
       Crude fat
      Proximate analysis, AA, and minerals were determined using the AOAC International methods (Novus International Inc. Laboratory Services).
      (%)
      4.955.685.825.80
       Calcium (%)0.900.951.041.07
       Sodium (%)0.130.170.150.21
       Lysine (%)0.950.991.020.91
       Methionine (%)0.350.500.480.44
       Methionine + cysteine (SAA; %)0.620.770.750.70
       Total phosphorus (%)0.670.640.700.70
       GE
      Determined by the University of Georgia Feed, Environmental and Water Laboratory.
      (kcal/kg)
      4,2494,3424,3484,423
      1 Calculated AMEn of each complete test diet determined using the following equation: AMEn = {(GEI − GEE) − [8.73 × (NI − NE)]}/FI, where GEI = GE intake; GEE = GE output in excreta; NI = nitrogen intake from the diet; NE = nitrogen output from excreta; FI = feed intake; and 8.73 = nitrogen correction factor from previous research (
      • MacLeod M.G.
      • Valentine J.
      • Cowan A.
      • Wade A.
      • McNeill L.
      • Bernard K.
      Naked oats: metabolizable energy yield from a range of varieties in broilers, cockerels, and turkeys..
      ).
      2 Phase-fed basal diet (Table 2) and complete diet formulation based on an industry standard supplied by a commercial nutritionist.
      3 SAA = sulfur AA.
      4 Proximate analysis, AA, and minerals were determined using the AOAC International methods (Novus International Inc. Laboratory Services).
      5 Determined by the University of Georgia Feed, Environmental and Water Laboratory.

      Excreta Collection and Measurements

      Excreta collection and other measurements for AMEn determination of grain sorghum were determined in the grower- and finisher-diet phases for broilers from 22 to 24 d of age and 43 to 45 d of age during a 72-h total excreta collection period. At the end of each collection period, feed disappearance and total excreta weight were measured. A 30-g sample of feed and excreta was analyzed, on a DM basis, for GE with a bomb calorimeter and nitrogen content with a combustion N analyzer at the University of Georgia Feed, Environmental and Water Laboratory. Feed intake, excreta weight, GE, and nitrogen content results were used to calculate the AMEn of grain sorghum using the difference method by
      • MacLeod M.G.
      • Valentine J.
      • Cowan A.
      • Wade A.
      • McNeill L.
      • Bernard K.
      Naked oats: metabolizable energy yield from a range of varieties in broilers, cockerels, and turkeys..
      :
      DietAME:AMEn=GEIGEE8.73×NINE/FI.
      [1]


      SorghumAMEn:AMEngrain sorghum=AMEnbasal+AMEndietAMEnbasal/proportion of grain sorghum in diet
      [2]


      where GEI = GE intake; GEE = GE output in excreta; NI = nitrogen intake from the diet; NE = nitrogen output from excreta; and 8.73 = nitrogen correction factor from previous research (
      • Titus H.W.
      • Mehring Jr., A.L.
      • Johnson Jr., D.
      • Nesbitt L.L.
      • Tomas T.
      An Evaluation of MCF (Micro-Cel-Fat), a new type of fat product..
      ).
      Birds were group weighed (kg/cage), and feed disappearance was measured weekly on d 1, 8, 15, 22, 29, 36, 43, and 47. Mortality was recorded daily for birds that died over the grow-out period. Weekly measures of group BW and feed disappearance were used to calculate BW gain (BWG), FI, and feed conversion ratio (FCR) per treatment (15 to 22 d of age and 36 to 43 d of age):
      GrowerphaseFCR1522dofagenot adjusted for mortality=meanFI1522dofage÷meanBWG1522dofage,
      [3]


      FinisherphaseFCR3643dofagenot adjusted for mortality=meanFI3643dofage÷meanBWG3643dofage,
      [4]


      Statistical Analysis

      The analyses were based on a completely randomized design with a 2 × 4 factorial arrangement of treatments with age (grower phase and finisher phase) and grain types (dextrose/control, red/bronze, white/tan, and US No. 2) defining the treatments. Cage represented the experimental unit, and ANOVA followed by Fisher’s LSD procedure was used to determine specific differences among the grain type means. P-values ≤0.05 were considered evidence of statistical significance. All statistical calculations were performed using JMP Pro version 15.2.0 (SAS Institute Inc.).

      RESULTS AND DISCUSSION

      Tannin Analysis

      The absorbance measured for each grain sorghum variety for this experiment yielded no product at 550 nm compared with the pure sorghum with spectra at 550 nm; thus, no tannins were present in the varieties used for this experiment. Additional confirmation for the presence of tannins in the red/bronze variety, which is more commonly known to contain greater tannin content, was tested at a high and low concentration of tannin to ensure that there were no traces of tannins in larger sample sizes. Results showed similar spectra for both concentrations with no peak at 550nm, indicating no tannin traces in any of the samples.

      AMEn Determination

      Determined AMEn for grain sorghum in the grower phase (22 to 24 d of age) presented in Table 6 were 3,336 (red/bronze), 4,000 (white/tan), and 3,341 (US No. 2) kcal/kg. White/tan had the greatest AMEn, and US No. 2 was intermediate (P = 0.0387). In the finisher phase (43 to 45 d of age), shown in Table 6, the determined AMEn was 3,001 (red/bronze), 3,599 (white/tan), and 3,705 (US No. 2) kcal/kg, respectively. The US No. 2 had the greatest AMEn, and white/tan was intermediate (P = 0.0387). Relative to AMEn determination, FI was greatest in the finisher phase (P = 0.0123).
      Table 6Mean nitrogen-corrected apparent ME (AMEn) of dextrose/control and grain sorghum varieties (red/bronze, white/tan, and US No. 2), and 72-h feed intake during the grower- and finisher-diet phases of the excreta collection period, 22 to 24 d of age and 43 to 45 d of age, in commercial broilers
      TreatmentAMEn grain
      Least-squares means ± SEM; each mean represents 4 cages with 4 birds per cage for dextrose/control and 8 cages with 4 birds per cage per treatment of red/bronze, white/tan, and US No. 2.
      The AMEn of dextrose and grain-sorghum varieties was calculated by difference using the following equation: AMEn grain sorghum = [AMEn basal + (AMEn diet − AMEn basal)]/proportion of grain sorghum in diet (Macleod et al., 2008).
      (kcal/kg)
      72-h Feed intakediet
      Least-squares means ± SEM; each mean represents 4 cages with 4 birds per cage for dextrose/control and 8 cages with 4 birds per cage per treatment of red/bronze, white/tan, and US No. 2.
      (kg)
      Grain typeDiet phase
      Dextrose/controlGrower3,883 ± 262ab1.55 ± 0.13d
      Red/bronzeGrower3,336 ± 185bc1.77 ± 0.09d
      White/tanGrower4,000 ± 185a2.04 ± 0.09c
      US No. 2Grower3,341 ± 198bc1.70 ± 0.09d
      Dextrose/controlFinisher2,904 ± 262c2.17 ± 0.13bc
      Red/bronzeFinisher3,001 ± 185b2.33 ± 0.09b
      White/tanFinisher3,599 ± 185ab2.81 ± 0.09a
      US No. 2Finisher3,705 ± 198ab2.68 ± 0.09a
      Main effects means
       Dextrose/control3,394 ± 185ab1.86 ± 0.11c
       Red/bronze3,168 ± 131b2.05 ± 0.08bc
       White/tan3,800 ± 140a2.43 ± 0.08a
       US No. 23,523 ± 140ab2.19 ± 0.08b
      Grower3,640 ± 105a1.77 ± 0.05b
      Finisher3,302 ± 105b2.49 ± 0.05a
      P-value
       Grain type0.01340.0012
       Diet phase0.0277<0.001
       Grain type × diet phase0.03870.0123
      a–dMeans within a column with the same superscript are not significantly different.
      1 Least-squares means ± SEM; each mean represents 4 cages with 4 birds per cage for dextrose/control and 8 cages with 4 birds per cage per treatment of red/bronze, white/tan, and US No. 2.
      2 The AMEn of dextrose and grain-sorghum varieties was calculated by difference using the following equation: AMEn grain sorghum = [AMEn basal + (AMEn diet − AMEn basal)]/proportion of grain sorghum in diet (
      • MacLeod M.G.
      • Valentine J.
      • Cowan A.
      • Wade A.
      • McNeill L.
      • Bernard K.
      Naked oats: metabolizable energy yield from a range of varieties in broilers, cockerels, and turkeys..
      ).
      The nutritional composition of grain sorghum in the present study (Table 1) was similar to published reports for low-tannin grain sorghum containing 8 to 10% CP (
      • Douglas J.H.
      • Sullivan T.W.
      • Bond P.L.
      • Struwe F.J.
      Nutrient composition and metabolizable energy values of selected grain sorghum varieties and yellow corn..
      ). Grain sorghum has comparable DM, protein, and limiting AA (lysine, methionine, and threonine) content to that of corn despite the major difference in composition reported as grain sorghum having slightly greater protein and less fat (

      NASEM (National Academies of Sciences, Engineering, and Medicine). 1994. Nutrient Requirements of Poultry. 9th rev. ed. National Academy Press.

      ). Variations in nutrient composition of an ingredient can be attributed to the region, environment, and season in which it is grown (
      • Scott T.A.
      • Silversides F.G.
      • Classen H.L.
      • Swift M.L.
      • Bedford M.R.
      • Hall J.W.
      A broiler chick bioassay for measuring the feeding value of wheat and barley in complete diets..
      ). Therefore, due to these existing variations, it is necessary to determine the energy content of feedstuffs to adequately formulate a diet, especially when considering alternative feed ingredients (
      • Sibbald I.R.
      Metabolizable energy in poultry nutrition..
      ).
      Researchers, nutritionists, and grain producers are most familiar with tannin-containing or “bird-proof” grain sorghum and its suboptimal effects on digestibility and growth performance in broilers (
      • Selle P.H.
      • Liu S.Y.
      • Cai J.
      • Cowieson A.J.
      Steam-pelleting temperatures, grain variety, feed form and protease supplementation of mediumly ground, sorghum-based broiler diets: Influences on growth performance, relative gizzard weights, nutrient utilisation, starch and nitrogen digestibility..
      ). In this present study, grain sorghum varieties were acquired in the US and analyzed as tannin free. Although more red grain sorghum, known as a high-tannin variety, is grown and used in broiler feed worldwide due to its bird-resistant and high-yield attributes, white sorghum–based diets have been shown to outperform red grain sorghum–based diets because of lower tannin content (
      • Mandal A.B.
      • Tyagi P.K.
      • Elangovan A.V.
      • Tyagi P.K.
      • Kaur S.
      • Johri A.K.
      Comparative apparent metabolisable energy values of high, medium and low tannin varieties of sorghum in cockerel, guinea fowl and quail..
      ;
      • Liu S.Y.
      • Truong H.H.
      • Khoddami A.
      • Moss A.F.
      • Thomson P.C.
      • Roberts T.H.
      • Selle P.H.
      Comparative performance of broiler chickens offered ten equivalent diets based on three grain sorghum varieties as determined by response surface mixture design..
      ).
      The AMEn values for grain sorghum in this study were greater than those reported for tannin-free white and red sorghum varieties (
      • Truong H.H.
      • Neilson K.A.
      • McInerney B.V.
      • Khoddami A.
      • Roberts T.H.
      • Cadogan D.J.
      • Liu S.Y.
      • Selle P.H.
      Comparative performance of broiler chickens offered nutritionally equivalent diets based on six diverse, ‘tannin-free’ sorghum varieties with quantified concentrations of phenolic compounds, kafirin, and phytate..
      ).
      • Truong H.H.
      • Neilson K.A.
      • McInerney B.V.
      • Khoddami A.
      • Roberts T.H.
      • Cadogan D.J.
      • Liu S.Y.
      • Selle P.H.
      Comparative performance of broiler chickens offered nutritionally equivalent diets based on six diverse, ‘tannin-free’ sorghum varieties with quantified concentrations of phenolic compounds, kafirin, and phytate..
      determined AMEn values of 2,790 and 2,651 kcal/kg of DM for white and red sorghum varieties, respectively, in broiler chickens from 7 to 28 d of age.
      • Khalil M.M.
      • Abdollahi M.R.
      • Zaefarian F.
      • Chrystal P.V.
      • Ravindran V.
      Apparent metabolizable energy of cereal grains for broiler chickens is influenced by age..
      reported AMEn values of 3,762 kcal/kg at wk 1 and 3,556 kcal/kg at wk 6 for grain sorghum sourced from Australia. Results in the current study show decreased AMEn values for all treatments in the finisher phase. This observation may be similar to previously reported data suggesting that as age increases, FI increases, which can influence the rate of feed passage and digestion, resulting in lower AMEn (
      • Khalil M.M.
      • Abdollahi M.R.
      • Zaefarian F.
      • Chrystal P.V.
      • Ravindran V.
      Apparent metabolizable energy of cereal grains for broiler chickens is influenced by age..
      ). In fact, a study by
      • Svihus B.
      Limitations to wheat starch digestion in growing broiler chickens: a brief review..
      observed the effect of starch digestibility in wheat and found that it is negatively correlated with increasing FI, which results in reduced AMEn. Therefore, AMEn determination can be extremely variable due to variations in FI and excreta measurements (
      • Dozier III, W.A.
      • Kerr B.J.
      • Corzo A.
      • Kidd M.T.
      • Weber T.E.
      • Bregendahl K.
      Apparent metabolizable energy of glycerin for broiler chickens..
      ).
      • Sibbald I.R.
      • Summers J.D.
      • Slinger S.J.
      Factors affecting the metabolizable energy content of poultry feeds..
      has suggested that lower inclusion rates of a test ingredient may increase AMEn variability, whereas greater inclusion levels may reduce the variability of AMEn values. However, high inclusion levels could be detrimental to performance. As a result, it is practical to choose an inclusion rate that is applicable to the poultry industry in formulation and has a well-characterized nutritional profile. For these reasons, the typical range of inclusion level for a test ingredient in AMEn studies is between 20 and 40% (
      • Alvarenga R.
      • Zangeronimo M.
      • Pereira L.
      • Wolp R.
      • Almeida E.
      Formulation of diets for poultry: The importance of prediction equations to estimate the energy values..
      ). In this study, replications for grain sorghum treatments were increased using a lower inclusion range to account for any variation specifically associated with the inclusion level of grain sorghum. Differences in nutrient composition of ingredients and inclusion levels in diets between this present study and previously reported studies using sorghum to replace corn might explain the variation and inconsistencies of determined AMEn values.
      Energy is one of the first parameters to consider in feed formulation, but it has been recently reported that there are widely inconsistent values depending on what bioassay is used for the determination of ME (
      • Wu S.B.
      • Choct M.
      • Pesti G.
      Historical flaws in bioassays used to generate metabolizable energy values for poultry feed formulation: A critical review..
      ). Dextrose was used for the control diet as a reference ingredient to reduce variability associated with corn for AMEn determination. Typically, glucose represents a baseline for comparison with a known energy content compared with the potential variability of the energy content of other ingredients (e.g., corn) in a basal diet (

      NASEM (National Academies of Sciences, Engineering, and Medicine). 1994. Nutrient Requirements of Poultry. 9th rev. ed. National Academy Press.

      ). As a result, it was also more appropriate to use a modified substitution method in this current study because it reflects how a nutritionist would formulate if only given the GE specification for a test ingredient to determine AMEn in broilers. As a result, it is appropriate to formulate based on the GE of corn and grain sorghum and then equate the calories needed to replace either ingredient rather than a specific inclusion level as the classical substitution method reported in literature. This modified method is much more practical in formulation, allowing for any synergistic or antagonistic interactions in production to happen in commercial formulation (Concept 5, CFC Tech Service Inc.) when other ingredients and their nutrients are contributing alongside the inclusion of grain sorghum.
      Kafirin, a common nontannin phenolic compound in grain sorghum, has been shown to negatively affect starch and energy utilization in grain sorghum diets fed to broilers (
      • Truong H.H.
      • Neilson K.A.
      • McInerney B.V.
      • Khoddami A.
      • Roberts T.H.
      • Cadogan D.J.
      • Liu S.Y.
      • Selle P.H.
      Comparative performance of broiler chickens offered nutritionally equivalent diets based on six diverse, ‘tannin-free’ sorghum varieties with quantified concentrations of phenolic compounds, kafirin, and phytate..
      ). White sorghum varieties contain lower polyphenol concentrations, which are associated with lower kafirin concentrations.
      • Truong H.H.
      • Neilson K.A.
      • McInerney B.V.
      • Khoddami A.
      • Roberts T.H.
      • Cadogan D.J.
      • Liu S.Y.
      • Selle P.H.
      Comparative performance of broiler chickens offered nutritionally equivalent diets based on six diverse, ‘tannin-free’ sorghum varieties with quantified concentrations of phenolic compounds, kafirin, and phytate..
      found that white grain sorghum was a better option than red sorghum when feeding poultry, which has been correlated with yielding greater AMEn values and better starch and energy utilization compared with those with high kafirin content typically found in red grain sorghum. Results in the present study showed white/tan grain sorghum having the greatest AMEn value compared with previously reported results.
      Overall, slight variations in specific parameters including total excreta weight and FI during the excreta collection period have been reported to attribute highly variable AMEn values (
      • Dozier III, W.A.
      • Kerr B.J.
      • Corzo A.
      • Kidd M.T.
      • Weber T.E.
      • Bregendahl K.
      Apparent metabolizable energy of glycerin for broiler chickens..
      ). In this present study, AMEn values were determined for 2 diet phases (grower and finisher) over a 72-h period compared with previous AMEn studies, which typically determined AMEn during the grower phase.
      • Scott T.A.
      • Silversides F.G.
      • Classen H.L.
      • Swift M.L.
      • Bedford M.R.
      • Hall J.W.
      A broiler chick bioassay for measuring the feeding value of wheat and barley in complete diets..
      have described the advantage of allowing the broiler chick to adjust its gut capacity and microflora to the diet by providing a 13-d feeding period on a diet before AMEn determination.
      In the current study, the modified method also considered AMEn at different ages and diet phases; there was evidence of an age effect on AMEn and 72-h FI. Few published AMEn studies have actually done this, neglecting the fact that diets are formulated with varying energy levels according to the age of the bird (

      NASEM (National Academies of Sciences, Engineering, and Medicine). 1994. Nutrient Requirements of Poultry. 9th rev. ed. National Academy Press.

      ;
      • Barzegar S.
      • Wu S.B.
      • Choct M.
      • Swick R.A.
      Factors affecting energy metabolism and evaluating net energy of poultry feed..
      ). The AMEn determination in 2 different diet phases can explain energy utilization and efficiency in the growing bird. Meat-type birds increase BW with age; thus, greater energy at an older age is necessary to meet demands for maintenance and production as broilers consume feed until their energy requirement for maintenance is met (
      • Sibbald I.R.
      Metabolizable energy in poultry nutrition..
      ;
      • Leeson S.
      • Caston L.
      • Summers J.D.
      Broiler response to diet energy..
      ;
      • Gous R.M.
      • Faulkner A.S.
      • Swatson H.K.
      The effect of dietary energy: Protein ratio, protein quality and food allocation on the efficiency of utilisation of protein by broiler chickens..
      ). Therefore, a feed with greater AMEn may satisfy this energy requirement (
      • Zelenka J.
      Effects of sex, age and food intake upon metabolisable energy values in broiler chickens..
      ). Feed intake is closely related to growth performance and influenced by several factors including energy density of feed, environment, housing, feed form, age, breed, sex, and health status of the bird (
      • Ferket P.R.
      • Gernat A.G.
      Factors that affect feed intake of meat birds: A review..
      ;
      • Dozier III, W.A.
      • Kerr B.J.
      • Corzo A.
      • Kidd M.T.
      • Weber T.E.
      • Bregendahl K.
      Apparent metabolizable energy of glycerin for broiler chickens..
      ;

      Bedford, M. R., M. Choct, and H. M. O’Neill. 2016. Nutrition Experiments in Pigs and Poultry: A Practical Guide. CABI.

      ). As a result, when feed is not consumed to meet the full nutritional requirements of meat-type birds, they will not grow adequately to their genetic potential (
      • Ferket P.R.
      • Gernat A.G.
      Factors that affect feed intake of meat birds: A review..
      ).

      Performance

      Growth performance responses including BWG, FI, and FCR are shown in Table 7 for the grower- and finisher-phase diets corresponding to each period for AMEn determination on 22 and 43 d of age. Responses were not negatively affected by grain sorghum treatments compared with dextrose/control, as shown, with no significant differences for both diet phases (P > 0.05). The characteristic physiological behavior of a broiler chicken is that they will eat to meet their energy needs (
      • Dozier III, W.A.
      • Kerr B.J.
      • Corzo A.
      • Kidd M.T.
      • Weber T.E.
      • Bregendahl K.
      Apparent metabolizable energy of glycerin for broiler chickens..
      ). Results from this study showed this physiological behavior in birds fed the red/bronze sorghum treatment during the grower phase; birds consumed more feed to meet their energy requirement because red/bronze had the lowest energy. Thus, birds were less efficient as seen in the poorer FCR of 1.53; however, birds in this treatment group were able to compensate for their BW by eating more feed of lower energy compared with the other treatments. No differences in BWG, FI, and FCR among treatments demonstrated similar performance of broilers when not optimally fed diets of equal energy.
      Table 7Effect of dextrose/control, red/bronze, white/tan, and US No. 2 grain sorghum on growth performance responses (BWG, FI, and FCR)
      BWG = BW gain; FI = feed intake; FCR = feed conversion ratio.
      of broilers during the grower- and finisher-diet phases at 15 to 22 d of age and 36 to 43 d of age, respectively
      Treatment
      Least-squares means ± SEM; each mean represents 4 cages with 4 birds per cage (kg/bird) for dextrose/control and 8 cages with 4 birds per cage (kg/bird) per treatment for red/bronze, white/tan, and US No. 2.
      Diet phase
      Grower (15–22 d)Finisher (36–43 d)
      BWG

      (kg/bird)
      FI

      (kg/bird)
      FCR

      (kg/kg)
      BWG

      (kg/bird)
      FI

      (kg/bird)
      FCR

      (kg/kg)
      Dextrose/control0.49 ± 0.030.66 ± 0.051.35 ± 0.120.78 ± 0.141.34 ± 0.121.72 ± 0.42
      Red/bronze0.48 ± 0.020.72 ± 0.041.50 ± 0.080.90 ± 0.101.36 ± 0.081.51 ± 0.30
      White/tan0.48 ± 0.020.69 ± 0.041.44 ± 0.080.67 ± 0.101.29 ± 0.081.92 ± 0.30
      US No. 20.49 ± 0.020.70 ± 0.041.43 ± 0.080.66 ± 0.101.30 ± 0.081.97 ± 0.30
      P-value0.96290.83420.69820.32720.91060.4158
      1 BWG = BW gain; FI = feed intake; FCR = feed conversion ratio.
      2 Least-squares means ± SEM; each mean represents 4 cages with 4 birds per cage (kg/bird) for dextrose/control and 8 cages with 4 birds per cage (kg/bird) per treatment for red/bronze, white/tan, and US No. 2.
      • Liu S.
      • Selle P.H.
      • Cowieson A.
      Influence of white-and red-sorghum varieties and hydrothermal component of steam-pelleting on digestibility coefficients of amino acids and kinetics of amino acids, nitrogen and starch digestion in diets for broiler chickens..
      reported that broilers fed white grain sorghum–based diets performed better than broilers fed red grain sorghum–based diets, supporting the data in this study showing no negative effects on growth performance.
      • Dykes L.
      • Rooney L.W.
      Sorghum and millet phenols and antioxidants..
      also indicated that, of the tannin-free grain sorghum varieties, red grain sorghum had a greater content of phenol compounds than white grain sorghum, resulting in adverse effects on performance. Overall, other studies have shown that using high-tannin grain sorghum varieties would not be feasible. Still, low-tannin and tannin-free varieties may be potential replacements for corn as they are similar in nutritive value (
      • Gualtieri M.
      • Rapaccini S.
      Sorghum grain in poultry feeding..
      ). In fact, Hulan and others observed that a lower-tannin grain sorghum variety with an inclusion up to 45% in broiler starter diets and 58% in broiler finisher diets can replace corn without any detrimental effects on BW, FI, and FCR, whereas greater-tannin grain sorghum varieties resulted in decreased BW and FI and poorer FCR (
      • Hulan H.W.
      • Proudfoot F.G.
      Nutritive value of sorghum grain for broiler chickens..
      ;
      • Scott T.A.
      • Silversides F.G.
      • Classen H.L.
      • Swift M.L.
      • Bedford M.R.
      • Hall J.W.
      A broiler chick bioassay for measuring the feeding value of wheat and barley in complete diets..
      ).
      Therefore, current results of AMEn determination for broilers demonstrated that tannin-free modern grain sorghum varieties show potential for replacing corn in diet formulation without sacrificing important performance factors, including BWG, FI, and FCR. Findings from this study further suggest that existing nutrient composition and performance data for grain sorghum fed to broilers is inconsistent and focused on high-tannin varieties associated with their negative influence when fed to poultry. Growth performance trials will be necessary to validate these AMEn values and evaluate additional performance parameters of grain sorghum varieties at the full substitution of corn in feed formulation.

      APPLICATIONS

      Current nutrient composition of grain sorghums and performance results when fed to commercial broilers are inconsistent with previous studies that focused on high-tannin varieties and their negative influence on performance. Results from this study can provide nutritionists with an updated nutrient composition of tannin-free grain sorghum and redefine negative perceptions to give producers confidence in using commercial, tannin-free varieties in broiler production. The AMEn values determined in this study should be used as a reference and not as absolute values due to nutritional variations of grain quality and the region or environment where feedstuffs are grown and sourced.

      ACKNOWLEDGMENTS

      The authors acknowledge funding and support for this research from the United Sorghum Checkoff Program, Fieldale Farms Corporation, Novus International Inc., Oakway Farm and Garden, and the University of Georgia Feed and Environmental Water Laboratory. Author R. M. Kaminski was supported by Clemson University’s James C. Kennedy Waterfowl and Wetlands Conservation Center.

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