Effect of gelatin supplementation on growth performance and blood metabolites of broiler chickens fed diets varying in crude protein

•We investigated the effects of gelatin inclusion in the low and normal CP diets on the performance in broiler chickens.•Gelatin inclusion depressed growth performance, especially in the low CP diet.•Increasing gelatin level reduced N retention and the effects were most pronounced on the low CP diet.•Increasing dietary gelatin increased relative heart weight and elevated plasma uric acid level.

An experiment was conducted to investigate the effects of gelatin inclusion on growth performance, blood metabolites and carcass characteristics of broiler chickens fed diets varying in crude protein (CP) concentration in a 42-d study. Four concentrations of gelatin (0, 30, 60, and 90 g/kg) and 2 concentrations of CP in the starter (220 and 200 g/kg) and grower (195 and 182 g/kg) periods were evaluated in a 2×4 factorial arrangement of treatments. Each diet was fed to 5 replicate pens of 15 male broiler chickens (Ross 308) from d 0 to 42. Digestibility coefficients of amino acid (AA) of gelatin were in the range of 0.90-0.95. Gly, Pro, Ala, and Glu were the major AA in gelatin. There were interactions between dietary CP content and gelatin concentration for feed intake (FI; P=0.016), body weight gain (BWG; P<0.001) and feed conversion ratio (FCR; P<0.001) during the starter (d 0-21), grower (d 21-42), and the overall experiment period (d 0-42). In the low CP diets, gelatin inclusion had a greater negative effect on BWG and FCR compared with those fed the normal CP diets over the course of the experiment (gelatin×CP, P<0.001). The contrasts showed that the increase in dietary gelatin content decreased BWG and FI, whereas FCR increased with higher dietary gelatin content from d 0 to 42. The CP×gelatin interactions showed that gelatin addition to the low CP diets increased plasma concentrations of glucose (gelatin×CP, P<0.01) and uric acid (gelatin×CP, P<0.001), and decreased N retention (gelatin×CP, P<0.001) to a greater extent than was the case for the normal CP diets at d 42. The CP×gelatin interactions indicated that gelatin inclusion in the low CP diets decreased carcass yield (gelatin×CP, P<0.01) and abdominal fat (gelatin×CP, P<0.001), and increased heart weight (gelatin×CP, P<0.01) to a greater extent than was the case for the normal CP diets. The present findings showed that gelatin inclusion had a greater negative effect on growth performance and carcass yield in broiler chickens that received the low CP diets compared with those fed the normal CP diet over the course of the study. Also, increasing dietary gelatin content depressed growth rate and N retention.