In vitro addition of antibiotic resistant bacteria (Lactococcus lactis) modulates ruminal nutrient disappearance kinetics of diets varying in lactose/starch ratios

In vitro ruminal culture was carried out to assess the effect of the concentration of an antibiotic resistant transgenic bacterium (Lactococcus lactis, L. lactis) along with different dietary lactose/starch ratios on first order kinetic disappearance of nutrients using an exponential model. Dietary treatments were designed to include lactose (L), using whey powder which was substituted of corn grain, as zero (L0.0), 36 (L36) and 72 (L72) g/kg dry matter (DM), with different L. lactis count (CFU/mL) as 0.0 (Bact0.0), 1.25×108 (Bact1.25) and 2.5×108 (Bact2.50) in a 3×3 factorial arrangement. The DM and CP disappearance was significantly influenced by the dietary inclusion of L. lactis. Constant rate of crude protein (CP) disappearance significantly decreased in both L36 and L72 using bacteria as Bact2.50. Bact2.50 enhanced the constant rate of neutral detergent fiber (NDF) disappearance of the diets. DM disappearance was significantly increased in lactose containing diets, while crude protein disappearance was significantly enhanced in L36 only. NDF disappearance decreased significantly in L36 and L72 treatments, and the indigestible fraction of NDF was significantly higher for L72 compared with L0.0 or L36. NFC digestible fraction was significantly improved in L36 and L72.There was significant diet× bacteria interaction in most of the studied parameters. Ruminal L. lactis abundance measured using RT-PCR altered in all diets, and the highest values were recorded in L72 diet. Regarding the dietary inclusion of lactose, some alterations were detected, while the effect of the bacteria on nutrient disappearance was consider and related to the dietary lactose/starch ratios.