Experimental diets
The formulation and chemical composition of the experimental diets (%) are presented in Table 1. The live baker’s yeast was obtained as a commercial preparation Actisaf® (Lesaffre, France). Heat-inactivated yeast was prepared by incubating live yeast at 80 °C for 30 min. The inactiveness was confirmed by culturing on YPD agar, and there were no yeast colony growing on the plates. The basal diet was supplemented with live yeast or its heat-inactivated counterpart. The procedures of feed preparation have been described by Huang et al. [19]. Briefly, the dietary ingredients were blended with water (100 ml water per 1 kg diet) to form a paste which was then passed through a meat grinder equipped with a 3-mm die to obtain uniform pellets. The pelleted diets were air-dried till the moisture was lower than 10%. The levels of S. cerevisiae in diets supplemented with live yeast were verified by pellet homogenization, serial dilution and spreading of the dilutions on YPD plates. All the diets were stored in plastic bags at 4 °C until use. The viability of the supplemented live yeast during storage was confirmed by spread plate method described above.