Supplementing dietary Rosmarinus officinalis L. Powder in quails: The effect on growth performance, carcass traits, plasma constituents, gut microflora, and immunity

This study was conducted to investigate the effects of feed supplementation with rosemary (Rosmarinus officinalis L.) powder (RP) on the performance, carcass traits, blood variables, antibody responses, and gut microbiota of quails. 270 one-day-old male Japanese quails were allotted to 6 dietary treatments with 3 replications (15 birds per pen). The diets contained RP at levels of 0 g/kg of feed (CON), 5 g/kg of feed (T05), 10 g/kg of feed (T10), 15 g/kg of feed (T15), 20 g/kg of feed (T20) or 25 g/kg of feed (T25). The trial lasted 42 days. Body weight and feed intake were measured weekly by pen, and the feed conversion ratio (FCR) was calculated. Blood samples were collected for assessing the humoral immune response to Newcastle vaccination at the 29th and 42nd days of age. Analysis of caecal microflora was performed on one quail per replication on the 14th and 42nd days of age. At slaughter, the carcasses and the organs were weighed, and blood constituent analyses were performed. Quails fed with RP had higher weight gain (p<0.05) and FCR (p<0.05) than CON. T5 and T10 showed higher weight gain than T25 (p<0.05). The dietary inclusion of RP did not influence either the weight of organs (p>0.05) or the caecal microbiota of the quails (p>0.05). RP increased the antibody titre against vaccinations on the 29th day of age (p<0.05) and reduced the plasmatic LDL/ HDL ratio (p<0.05). The dietary supplementation of RP up to 25 g/kg of feed improved the performance and immunity of quails, without affecting their caecal microflora.