In situ evaluation of dried distillers grains (DDG) and of diets containing different levels of DDG inclusion replacing soybean meal, urea and corn, and development of alternative methods to estimate in vivo digestibility of diets

Abstract

This study aimed to evaluate ruminal in situ degradation of diets containing different levels of dried distillers grains (DDG) replacing soybean meal, urea and corn and the effect of these diets on in situ ruminal degradation of DDG, and to propose alternative methods to estimate in vivo digestibility of diets. Four rumen-cannulated Nellore bulls were used in a 4 × 4 Latin square design, for both in situ incubation and in vivo digestibility. We evaluated the following treatments: diet without DDG (D0) or containing 150 (D150), 300 (D300), or 450 g/kg (D450) of inclusion. For in situ evaluation, DDG was incubated in all animals, and diets only in those fed with the same diet that would be incubated. To estimate in vivo digestibility, three days of total feces collection were performed in each period. Data was analysed in PROC MIXED, PROC NLIN and PROC REG of SAS (version 9.4, SAS Institute Inc., Cary, NC, USA). There was no effect of diet on the in situ degradation parameters of the DDG (P > 0.05). However, for the diets, the readily soluble fraction (parameter "a") (P < 0.01), and the rate constant for degradation (parameter kd) of the potentially degradable fraction in the rumen (parameter “b”) (P = 0.05) of dry matter (DM), decreased linearly. On the other hand, the parameter "b" (P < 0.01) and kd rate (P = 0.03) of the neutral detergent fiber (NDF) of the diets increased linearly. The in situ incubation time to estimate the in vivo DM digestibility ranged from 27.2 h to 37.7 h. For the NDF, the time was 60-h for all diets. In addition, to estimate the in vivo digestibility of DM (DMD), and the residual NDF (RNDF) of diets, two equations were suggested for each one: DMD = 804.8 - 0.092 × level, and DMD = 658 + 0.468 × a; RNDF = 393.9 - 0.138 × level, and RNDF = 874.3 - (0.602 × b) - (0.805 × I) + (1,662 × kd), where I = indigestible NDF. We conclude that the DDG can be incubated in animals fed diets without DDG or inclusion level up to 450 g/kg (DM basis), and that the inclusion of DDG in finishing diets reduced DM degradability, and it is possible to estimate in vivo digestibility using alternative methods .