Effects of carriers for oils in compound feeds on performance, nutrient digestibility, and gut microbiota in broiler chickens
Carrier materials for oils in compound feeds may be used in animal nutrition to supply liquid feed additives, but consequences of such carriers for digestibility of the contained oil are unknown. This study investigated the potential of oil carriers in compound feed and their effect on performance, metabolizable energy, fatty acid (FA) retention, amino acid (AA) digestibility, and gut microbiota in broiler chickens. Six experimental diets were formulated in a 2 × 3 factorial design with 20 g/kg or 40 g/kg of rapeseed oil supplied with no carrier or bound in a silica-based (SC) or lignocellulose-based (LC) carrier in a mass ratio of 1:1. The six diets were assigned to 48 metabolism units with 15 animals each in a randomized complete block design and fed from day 18 to 28 of the trial. Total excreta were collected from day 24 to 27 and used to determine total tract retention (TTR) of FA and metabolizable energy corrected to zero nitrogen retention (MEN). On day 28, AA digestibility by the distal half of the jejunum and the distal half of the ileum was determined and microbiota of ileal and cecal digesta was analyzed using 16S rRNA sequencing. Addition of SC decreased average daily gain, average daily feed intake, and gain:feed ratio (P<0.001), while LC at 40 g/kg oil/carrier inclusion increased gain:feed ratio and MEN (P<0.001). The TTR of crude fat and the FA C18:1, C18:2, C18:3, and C22:0 was increased by the addition of SC (P=0.016), while LC increased the TTR of the FA C18:1 and C18:2 as well as the TTR of C18:3 at 20 g/kg oil/carrier inclusion (P=0.016). Adding SC and LC increased the digestibility of seven and two AA by the distal half of the jejunum, respectively, and the digestibility of eight and 13 AA by the distal half of the ileum, respectively (P=0.039). The cecal microbiota was affected by addition of LC and SC while no treatment effect on the ileal microbiota was found. The results indicate a complete release of the oil supplied bound to SC and LC because the TTR of most FA was increased. LC may be used to supply liposoluble feed additives without drawbacks for nutrient digestibility and growth while SC requires further examination.