In Vivo Digestibility and In Vitro Fermentation of High Dietary Fiber Forages in Growing Pigs' Diets

The pig farming industry is constantly challenged to seek low-cost ingredients that fulfill animal requirements. In this study, two summer forage brassica meals were assessed as sources of dietary fiber in growing pigs by in vivo digestibility and in vitro fermentation experiments. The control diet included corn, soybean meal, and wheat middlings. The experimental diets replaced wheat middlings (15%) with turnip (Brassica rapa) roots or fodder rape (Brassica napus) whole plant meal, respectively. All diets were elaborated to be iso-nitrogenous and iso-energetic. The turnip diet had a greater digestibility rate for gross energy (p = 0.020). The ash digestibility was greater for the rape diet and intermediate for the turnip diet, with the lowest value for the control diet (p = 0.003). When incubating pure brassica forages, only gas production at 72 h was greater for the turnip than rape diet (p = 0.04). No differences (p > 0.05) in the in vitro gas production parameters were observed among the diets. The pure fermentation of turnip increased the VFA concentration and propionate molar proportion, whereas acetate was reduced (p < 0.05), which resulted in a trend towards a greater propionate molar proportion with the inclusion of turnip in the diet (p = 0.067). The inclusion of 15% of turnip meal increased the in vivo energy digestibility and tended to modify the fermentation parameters, increasing the molar proportion of propionate, whereas the inclusion of whole plant fodder rape did not affect the in vivo digestibility or in vitro fermentation compared with the control diet.