Yogurt acid whey powder dietary inclusion level modulates broiler cecal microbiota composition and metabolic activity

• YAWP inclusion up to 100 g kg -1 is possible without negative effects on performance. • YAWP decreased cecal total bacteria, and counts of E. coli and C cluster I subgroup. • YAWP fortified the cecal microbiota with beneficial Lactobacillus spp. • YAWP positively altered cecal VFA pattern. All over the world, the increasing demand for Greek yogurt generates vast quantities of acid whey as a by-product. The large volume and nutrient composition of yogurt acid whey makes it worthwhile to investigate potential uses in animal nutrition. This study aimed to investigate the inclusion of yogurt acid whey powder (YAWP) in four dietary levels on broiler performance, cecal microbiota composition and metabolic activity. A total of 300 male one-day-old male Ross broiler chickens were randomly assigned into 4 treatments of 5 replicates each. Broilers were fed maize-soybean meal basal diets following a 2-phase feeding program. Depending on the YAWP inclusion level (g kg -1 diet), treatments were no YAWP addition (W0), YAWP at 25 g kg -1 (W25), YAWP at 50 g kg -1 (W50) and YAWP at 100 g kg -1 (W100). Overall body weight gain, feed intake and feed conversion ratio were not affected by YAWP addition. In the ceca, a linear decrease in total bacteria counts and a linear increase in Lactobacillus spp . was noted with increasing YAWP dietary level. A linear reduction of Clostridium cluster I and E. coli species was noted with increasing YAWP dietary level. A linear increase in total volatile fatty acids concentration, acetic acid and butyric acid molar ratios was shown with increasing YAWP level. In conclusion, the addition of YAWP did not affect overall performance but positively modulated the cecal microbiota and metabolic activity of 42-day-old broiler chickens.