Comparison of equations to predict the metabolisable energy content as applied to the vertical strata and plant parts of forage sorghum (Sorghum bicolor)

Abstract

Context: Nutritive values, particularly energy content of tropical forages, need to be accurately assessed so that rations can be more precisely formulated. Aims: The research aimed to collate and compare equations used to predict metabolisable energy content in forage sorghum (Sorghum bicolor (L.) Moench) to ascertain the effect of vertical strata on metabolisable energy content to assist in producing silage of defined quality. Methods: Twenty-four predictive metabolisable energy equations derived from international feeding standards were compared using forage sorghum samples grown under fertiliser and growth stage treatments. Samples were separated into leaf, stem and seed heads (where present) over four vertical strata. Key results: Equations based on digestibility with crude protein were robust in the prediction of metabolisable energy and had application to routine laboratory use. Conclusions: The current study suggests that predictions based on digestibility and crude protein content are best placed for metabolisable energy application. Such equations should be originally based on measured metabolisable energy content to establish a regression so as to be used for predictive purposes, and satisfy the biological requirement of in vivo and the laboratory measurement relationship with acceptable statistical error. Chemical composition relationships predicted different metabolisable energy contents. Implications: Improved accuracy of the prediction of metabolisable energy content in tropical forages will provide better application of production models and more accurate decisions in ration formulation.