Bromelain as a feed additive to promote broiler performance, nutrient digestibility and health

Abstract

The broiler industry faces a growing pressure to reduce antibiotic growth promotors (AGP) from broiler feed due to public concern and the threat of antibiotic resistance. This has caused an upsurge in studies relating to natural alternatives to antibiotic growth promoters. Some such alternatives are exogenous proteases, which improves the digestibility of dietary protein. Bromelain, a natural protease found in pineapple, may be beneficial in livestock, however, there exists little literature on the effect of bromelain on broiler production specifically. This study aimed at determining the effects of supplementation of bromelain on broiler health and performance. Two trials were conducted: a performance trial and a digestibility trial. The performance trial was carried out to determine whether bromelain supplementation would improve broiler gut health and therefore broiler growth and performance. The aim of the digestibility trial was to determine whether bromelain supplementation would have any effect on the crude protein and dry matter digestibility of feed. Two-thousand four hundred male Ross 308 chicks were used in the performance trial and were reared in standard commercial conditions. All birds received a standard maize-soya based diet and were separated into 12 treatments of a combination of three levels of bromelain (0, 0.125, 0.75 g/kg), two levels of crude protein (standard or high) and either in the presence or absence of an AGP (zinc bacitracin) and there were 8 replicates per treatment. The trial lasted 34 days and birds were weighed weekly to determine body weight, body weight gain, feed intake and feed conversion ratio. On day 34, duodenum, jejunum and ileal samples of 16 birds from each treatment were analysed for villi height, crypt depth and villus height-to-crypt depth ratio. Bromelain had a significant effect on intestinal crypt depth, where a high level of bromelain lead to a lower crypt depth. Birds that received a standard crude protein diet without an AGP performed the best, and birds that received an AGP showed shorter villi and crypt depths. Bromelain did not have a significant effect on body weight, feed intake or FCR. For the digestibility trial, Ross 308 chicks were reared in floor pens receiving the same maize-soya based diet. On day 14, 180 birds with a body weight closest to the average were transferred to 30 metabolic cages with six birds per cage. From day 15 to 21, the birds received either a negative control diet, a diet supplemented with bromelain, or a diet supplemented with a commercially available protease that served as a positive control. On day 21, all birds were euthanised and ileal digesta was removed and analysed. Neither bromelain, nor the commercial protease product improved crude protein digestibility compared to the negative control. However, both bromelain and iii the commercial protease significantly increased dry matter digestibility, compared to the control. This study found that the performance and gut morphology of the birds that received supplemental bromelain was not significantly better than birds that did not receive supplemental bromelain, even though dry matter digestibility was improved. Thus, there might be room for bromelain in poultry production as it was seen to improve digestibility and gut health in this trial. Its benefits could perhaps be more attainable in different conditions, for example if a larger gut challenge was presented.