Energy value of cereal grains for broiler chickens. I. Variation within and among grain species, and effect of exogenous enzymes

Context Cereal grains are the major source of energy for broiler chickens. Energy available to chickens varies widely within and among cereal species and must be measured to develop near-infrared (NIR) calibrations for predicting values when formulating diets. Aims To measure apparent metabolisable energy (AME) content of cereal grains sourced from a wide range of species, cultivars, growing conditions and regions, including outside Australia. Methods Cereal grains (wheat 136, barley 63, oats 3, triticale 42, sorghum 66, maize 11, rice 2) were selected with a range of chemical and physical characteristics from normal harvest, frosted, sprouted, screened (< >2–2.2 mm) and irrigated samples. Twenty-six experiments were linked, statistically, into one experiment, by incorporating in each experiment at least 30% of grains used previously. Single sex groups of five birds per cage reared under a controlled environment were fed ad libitum diets containing 80% grain from Day 22 to Day 28 of age. Feed intake was measured over 7 days and grain AME over the final 4 days. Diets in 10 experiments were fed with and without exogenous xylanase and phytase enzymes. Key results The mean and range in grain AME (MJ/kg as fed) were as follows: wheat 12.62, 2.81; barley 11.41, 3.08; triticale 12.93, 3.82; sorghum 14.50, 1.60; maize 15.37, 0.59; oats 11.85, 1.90; rice 15.93, 0.35. AME intake (MJ/bird.day) was positively related to grain AME content across all grains (R2 = 0.61). Grain AME and AME intake for overseas grains were not different from Australian grains. Female birds had significantly higher grain AME, but not AME intake, than did male birds. Response to endogenous enzymes for grain AME and AME intake were negatively related to grain AME content within grain species. Bird growth rate and feed:gain ratio were poorly related to grain AME content, but growth rate was positively and feed:gain negatively related to AME intake. Birds offered wheat, barley and triticale grew faster at the same AME intake than did those offered sorghum, maize and rice. Conclusions AME and AME intake of 323 cereal grains for broilers were measured. Implications The results are available to develop NIR calibrations for predicting values for unknown grains.