In Vitro Digestibility and Models of Cumulative Gas Production of Forage-Free Diet

SIMPLE SUMMARY: Diets for confined cattle are generally high in concentrated ingredients, which need attention to avoid ruminal disorders. Adding an adequate fiber quantity can help in this scenario, and by-products derived from the agroindustry can be used as a fiber source. Thus, in this research, we performed an in vitro evaluation to understand if cottonseed cake would be able to replace corn silage in a forage-free diet. In addition, the in vitro trials for feed digestion needed equations to describe the results, and it is of major importance to know if the chosen equation can adequately describe the digestion process. In the present study, it was shown that the forage-free diet containing cottonseed cake as a fiber source stimulated higher gas production and that Brody and Ørskov models presented higher precision and accuracy in explaining in vitro digestion in both diets. ABSTRACT: Our objectives were to evaluate the use of cottonseed cake in replacing corn silage in a diet without forage and to identify the model with higher precision and accuracy of adjustment of parameters of ruminal degradation kinetics. A diet containing corn silage and another with cottonseed cake as a fiber source were formulated. Gompertz, Dual-pool Logistic, Brody, and Ørskov models were evaluated for goodness of fit to gas production. There were significant differences in dry matter (DM), organic matter (OM), and neutral detergent fiber (NDF) in the in vitro digestibility for diets and fiber sources. The estimated values of the Gompertz (6.77), Brody (6.72), and Ørskov (6.73) models were similar to the observed mean of gas production in the corn silage diet (6.73 mL/100 mg DM). Similarly, the estimated values of the Brody (5.87) and Ørskov (5.89) models were similar to the observed mean of gas production in the cottonseed cake diet (5.87 mL/100 mg DM). The roughage-free diet containing cottonseed cake as a fiber source stimulated higher gas production. Brody and Ørskov models presented higher precision and accuracy in the fitting of kinetics of degradation independent of the fiber source in the diet.