Abstract
Energy feeding systems define energy as a whole, but progress made to define metabolizable energy (ME) as the sum of the metabolizable nutrients produced by digestion and available for tissue metabolism in a wide range of nutritional situations opens the way to quantitatively model and predict nutrient fluxes between and within tissues and organs and improve predictions of energy use. This review addresses the contribution of nutrient flux concepts and data to the evolution of the Institut de la Recherche Agronomique (INRA) energy feeding system for growing and fattening cattle and evaluates the outcomes on the net energy (NE) requirements. It summarizes recent progress made to quantitatively predict nutrient fluxes both at digestive and visceral levels. It reviews how nutrient flux concepts and results were introduced in the recently updated INRA feeding system, resulting in improvements in the accuracy of the revised digestible energy (DE) and ME value of diets. The use of an independent database showed that for diets fed to fattening cattle, DE and ME concentrations were downgraded for low-energy-dense diets and upgraded for high-energy-dense diets. We are also showing that compared with its previous version, the updated INRA system improves the quantitative relationship between ME supply and flows of metabolizable nutrients. Evidence is provided on how measured nutrient fluxes at portal level were used to evaluate the predicted flows of metabolizable nutrients. This review then revisits the NE values of diets for fattening cattle as defined by the INRA feeding system and not updated yet. Using an independent database and at similar ME intake, carcass composition was shown to be linearly related to the energy density of diets for fiber-rich diets but not for concentrate-rich diets, suggesting that the efficiency of energy utilization of ME into NE is not linearly related to differences in the composition of the gain. Accounting for the balance of metabolizable nutrients or their proxies in models used to predict carcass composition from ME intake can improve predictions. Overall partitioning aggregated energy fluxes into their subcomponent nutrient fluxes in a more physiological approach offers promising perspectives for the evolution of NE feeding systems.
Highlights
Feeding practices of livestock are facing new nutritional challenges besides optimizing performances, such as reduce losses to the environment, sustain animal health, and improve production and quality of products
This review addresses the contribution of nutrient flux concepts and data to the evolution of feeding systems, using the Institut de la Recherche Agronomique (INRA) energy feeding system for growing and fattening cattle as an example
All ingredients of experimental diets were characterized according to INRA (2018) for subsequent calculation of metabolizable nutrients, using the systool.fr application (Chapoutot et al, 2015). This concerned flows of acetate, propionate, butyrate, and minor volatile fatty acids (VFA) produced in rumen and the hindgut, absorbed glucose, and total amino acids truly absorbed in the small intestine (i.e., MP, expressed in protein digestible in the intestine [PDI])
Summary
Feeding practices of livestock are facing new nutritional challenges besides optimizing performances, such as reduce losses to the environment, sustain animal health, and improve production and quality of products. That is, models that predict nutritional supply to and requirements of the animals in similar units (e.g., fill unit, metabolizable protein [MP] and amino acids, digestible, metabolizable, or net energy [DE, ME, or NE], and absorbable minerals), are expected to address these current and new production challenges. To apply nutrient flux concepts to the NE feeding systems implies to partition the aggregated energy fluxes into their subcomponent fluxes in a top-tobottom approach and make sure that the sums add up. The perspective to define ME as the sum of the metabolizable nutrients produced by digestive processes and available for tissue metabolism in a wide range of nutritional situations opens the way to quantitatively model and predict nutrient fluxes between and within tissues and organs. It summarizes recent progress made to quantitatively evaluate nutrient fluxes both at digestive and metabolic levels It reviews how nutrient flux concepts and results were empirically introduced in the recently
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