Relationships between digestible energy and metabolizable energy in current feedlot diets

Authors: HALES PAXTON, KRISTIN

Submitted to: Translational Animal Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/8/2019
Publication Date: 6/1/2019
Publication URL: https://handle.nal.usda.gov/10113/6487975
Citation: Hales, K.E. 2019. Relationships between digestible energy and metabolizable energy in current feedlot diets. Translational Animal Science. 3(3):945-952. https://doi.org/10.1093/tas/txz073.
DOI: https://doi.org/10.1093/tas/txz073

Interpretive Summary: In beef cattle nutrition it is important to know how much energy is lost in various ways such as fecal energy, urine, energy, and methane energy. Energy lost in the feces is denoted as digestible energy; while total energy lost in feces, urine, and methane is denoted as metabolizable energy. It is commonplace that metabolizable energy is calculated from digestible energy using a factor of 0.82. However, recent published literature suggest that the relationship between digestible and metabolizable energy is variable depending on the type of diet used, and is typically greater than 0.90 when high-concentrate diets are fed. A previously published linear regression equation for predicting metabolizable energy from digestible energy was evaluated using a residual analysis. Unpublished data were used to develop a new equation for estimating metabolizable energy from digestible energy. A maximum biological threshold for the conversion of digestible to metabolizable energy was estimated at 3.78 megacalories per kilogram of digestible energy. In conclusion, these data suggests the relationship between digestible energy and metabolizable energy is not static, especially in high-concentrate diets. The equation developed is an alternative that can be used for the calculation of metabolizable energy from digestible energy in current feedlot diets, but it is not recommended for use in high-forage diets. The maximization of metabolizable energy capture in current feedlot diets, maximum biological threshold, occurs at 3.78 megacalories per kilogram of digestible energy consumption by beef cattle.

Technical Abstract: It is commonplace that metabolizable energy (ME) is calculated from digestible energy (DE) as DE × 0.82. However, recent published literature suggests that the relationship between DE and ME is variable depending on the type of diet used, and is typically > 0.90 when high-concentrate diets are fed. Literature means were compiled from 23 respiration calorimetry studies where total fecal and urine collections were conducted and gaseous energy was measured. The relationship between experimentally observed and predicted ME (DE × 0.82) was evaluated using these previously reported treatment means. Additionally, a previously published linear regression equation for predicting ME from DE was also evaluated using a residual analysis. Published (Hales, K. E., A. P. Foote, T. M. Brown-Brandl, and H. C. Freetly. 2017. The effects of feeding increasing concentrations of corn oil on energy metabolism and nutrient balance in finishing beef steers. J. Anim. Sci. 95:939–948. doi:10.2527/jas.2016.0902 and Hemphill, C. N., T. A. Wickersham, J. E. Sawyer, T. M. Brown-Brandl, H. C. Freetly, and K. E. Hales. 2018. Effects of feeding monensin to bred heifers fed in a drylot on nutrient and energy balance. J. Anim. Sci. 96:1171–1180. doi:10.1093/jas/skx030) and unpublished data (K. E. Hales, unpublished data) were used to develop a new equation for estimating ME from DE (megacalories/kilogram [Mcal/kg] of DM; ME = -0.057 ± 0.022 DE2 + 1.3764 ± 0.1197 DE – 0.9483 ± 0.1605; r2 = 0.9671, root mean square error = 0.12; P < 0.01 for intercept, P < 0.01 for linear term, and P < 0.01 for quadratic term). To establish a maximum biological threshold for the conversion of DE to ME, individual animal data were used (n = 234) to regress the ME:DE on DE concentration (1.53 to 3.79 Mcal DE/kg). When using experimentally derived data and solving for the first derivative, the maximum biological threshold for the conversion of DE to ME was 3.65 Mcal DE/kg. Additionally, the quadratic regression (equation 1) was used to predict ME from a wide range of DE (1.8 to 4.6 Mcal/kg). The ME:DE ratio was then calculated by dividing predicted ME by DE. The maximum biological threshold for the conversion of DE to ME was estimated by solving for the first derivative and was 3.96 Mcal DE/kg. In conclusion, this review suggests that the relationship between DE and ME is not static, especially in high-concentrate diets. The equation presented here is an alternative that can be used for the calculation of ME from DE in current feedlot diets, but it is not recommended for use in high-forage diets. The maximization of ME in current diets, maximum biological threshold, occurs between 3.65 and 3.96 Mcal DE/kg in the diet, which based on these data is approximately 3.43 to 3.65 Mcal/kg of ME consumption.