Effects of protease and lipase supplementation in starter diet on growth performance, small intestine morphology, and immunity in young broilers

A 2 × 2 factorial study with 408 one-day-old male Ross 308 chicks evaluated the effects of dietary protease (0 & 0.1 g/kg) and lipase (0 & 0.2 g/kg) on performance, carcass traits, yolk sac absorption, intestinal morphology, and immune functions. Experimental diets were provided during the starter phase (days 1-10) of the 30-day trial. During days 1-10, protease decreased (P = 0.037) feed intake and lipase increased (P = 0.046) body weight (BW) gain. A significant (P = 0.029) interaction between protease and lipase supplementation was detected for feed conversion ratio (FCR), with lipase improving FCR only in diets without protease and protease improving FCR only in diets without lipase. The relative weight of residual yolk (RY) at 3 days of age was higher (P = 0.017) in chicks fed the protease-supplemented diet compared with those fed protease-free diets. At 5 days of age, RY relative weight was significantly (P = 0.043) influenced by the protease × lipase interaction, with higher value observed in chicks receiving protease-supplemented diet without lipase than in those fed protease-free diets. Protease supplementation positively affected ileal morphology, as evidenced by increased villus height (P = 0.002) and villus height-to-crypt depth ratio (P = 0.047). Supplementation with protease (P = 0.001) and lipase (P = 0.012) resulted in significant improvements in blood antioxidant status. However, the hepatic malondialdehyde concentration was influenced (P = 0.043) by the protease × lipase interaction, as lipase reduced its level only when protease was not supplemented. Additionally, protease upregulated hepatic nuclear factor erythroid 2-related factor 2 (Nrf2) gene expression (P = 0.020). The evaluations of cellular and humoral immune responses indicated no significant (P > 0.05) effects of protease or lipase supplementation. Overall, protease supplementation improved FCR, intestinal absorptive capacity, blood antioxidant status, and upregulated hepatic Nrf2 expression, whereas lipase supplementation improved BW gain, FCR, yolk sac absorption, and antioxidant capacity in both blood and liver. However, concurrent supplementation showed no additive effects, indicating that careful consideration is needed when formulating diets with combined enzyme supplements.