Maize-based diets are more conducive to crude protein reductions than wheat-based diets for broiler chickens

Implications of elevated threonine plasma concentrations in the development of reduced-crude protein diets for broiler chickens

“…When the highest-and lowest-CP diets in each experiment were compared, analysed CP concentrations decreased by an average of 42 g/kg from 212 to 170 g/kg and, in response, free threonine plasma concentrations increased by an average of 64.8% (867 versus 526 mmol/L). Across the individual experiments, elevations in threonine plasma concentrations ranged from 39.6% (863 versus 396 mmol/L) in Chrystal et al (2021) to 116.4% (1027 versus 619 mmol/L) in Chrystal et al (2020c). Clearly, the elevations in threonine plasma concentrations are variable; however, they are related to both FCR and relative fat-pad weights.…”

“…In a series of five feeding studies, off-sex, male Ross 308 chickens were offered maize-based diets from 7 to 35 days post-hatch, with dietary CP concentrations ranging from 222 to 156 g/kg (Moss et al 2018;Chrystal et al 2020b;2020c, 2020d, 2021. The relevant data are presented in Table 1 where the dietary mean molar concentration of threonine was 68.3 mmolar, with a standard deviation of AE4.87.…”

“…In Studies 1-4, molar proportions of plasma threonine increased in an essentially linear fashion in response to declining dietary CP from an average of 8.48% to 14.16%, which is an increase of 67.0%, when the highest-and lowest-CP diets in each experiment were considered. In Study 5 (Chrystal et al 2021), both maize and wheat-based diets were investigated where the 66.1% (19.91 versus 11.99%) increase in threonine molar proportions with wheat was more pronounced than the 24.1% (14.18 versus 11.43%) increase with maize-based diets. This difference between wheat and maize is discussed later.…”

“…This substitution achieves reductions in CP and then targeted amino acid requirements are met by increasing inclusions of an expanding array of non-bound amino acids. For example, soybean meal inclusions were decreased by 52.7% (157 versus 331 g/kg) and maize inclusions increased by 31.6% (732 versus 556 g/kg) collectively, with the transition from the highest-to lowest-CP diets in Chrystal et al (2020bChrystal et al ( , 2020cChrystal et al ( , 2020dChrystal et al ( , 2021. Also, inclusions of non-bound amino acids increased from 5.8 to 26.7 g/kg to meet requirements.…”

“…Given these increases in maize or wheat inclusions, the starch and protein concentrations of the feed grain assume more importance. Moreover, it does appear that the birds are better able to accommodate CP reductions of maize-based diets than of wheat-based diets (Chrystal et al 2021). In this study, birds offered 165 g/kg CP maize-based diets significantly outperformed birds offered wheat based by 53.0% (2370 versus 1549 g/bird) in weight gain, 22.4% (3481 versus 2843 g/bird) in feed intake and by 19.9% (1.473 versus 1.840) in FCR.…”