A meta-analysis of whole grain feeding and the possible mechanisms driving responses other than heavier gizzard weights

Abstract

Whole grain feeding (WGF) is widely adopted in countries where wheat is the dominant feed grain to reduce feed manufacturing costs, improve gut integrity, feed conversion ratio (FCR), apparent metabolisable energy (AME) and litter quality. However, responses of broilers to WGF is variable due to the range of methodologies adopted in WGF studies. Therefore, a meta-analysis was conducted to determine the effect of pre- and post-pellet WGF on relative gizzard weights and contents, FCR and AME of broiler chickens. The database consisted of 42 papers after applying selection criteria. Data were analysed by General Linear Model procedures using JMP Pro I3 and experiment identifiers included in models as a co-variate. Post-pellet WGF increased gizzard weights by 32% {16.78 versus 12.67 g/bird; P < 0.001) and gizzard contents by 31 % (7.17 versus 5.48 g/bird; P < 0.001) compared to the control. Overall, relative gizzard weights were not related to FCR. However, FCR was linearly related to gizzard contents, and was more indicative of performance than gizzard weights. Pre- and post-pellet WGF tended to generate more efficient FCR (1.671 and 1.672, respectively) compared to the control (1.695). Additionally, the highest AME was achieved by birds offered pre-pellet WGF, significantly increasing AME by 0.41 MJ (13.63 versus 13.22 MJ/kg DM) compared to the control. Thus, pre-pellet WGF increased energy utilisation and tended to improve FCR without a robust gizzard response. These performance responses may be driven by increases in slowly digestible starch (Moss et al., 2017). Therefore, generating performance responses under WGF regimes is more complex than simply heavier gizzard weights, and is likely influenced by starch and protein digestive dynamics.