Can dietary protease ameliorate performance and gut integrity in broilers fed on a diet low in digestible lysine?

This study investigated the effects of various levels of digestible lysine (dLys) and protease (PROT) on the performance, selected serum parameters, nutrient digestibility, and gut integrity of broiler chickens. In a completely randomized design, 1,024 male Ross 308 broilers were assigned to 8 treatments in a 4 × 2 factorial arrangement, with eight replicates per treatment and 16 birds per pen. The two factors tested were dLys levels set at 100 %, 98.5 %, 97.0 %, and 95.5 % of strain recommendations and PROT supplementation at 0 or 125 mg/kg feed. Significant dLys × PROT interactions were detected for performance during the grower (body weight gain (BWG), feed intake (FI), and FCR), the finisher (FI and FCR), and the overall period (BWG and FCR). Over the entire experimental period, chicks fed 95.5 % dLys without PROT exhibited decreased BWG and elevated FCR, whereas PROT supplementation restored both BWG and FCR to values similar to those of the control group. Significant dLys × PROT interactions were observed for serum parameters (uric acid, total protein, and bilirubin), short chain fatty acid (SCFA), jejunal histomorphology, total aerobic and lactic acid bacteria populations, and dry matter digestibility. PROT in diets comprising 95.5 % dLys increased branched-chain fatty acid (BCFA) and SCFA and by 8 % and 17.12 %, respectively, in comparison to diets lacking PROT (P < 0.05). The dLys × PROT interactions suggested that diets with reduced dLys tended to impair jejunal histomorphology, whereas the inclusion of PROT appeared to alleviate this effect, as reflected by numerical improvements in the measured parameters. Furthermore, feeding 95.5 % dLys without PROT led to a 16.00 % reduction in lactic acid bacteria counts compared to birds receiving 100 % dLys without PROT (P < 0.05). The results demonstrated that reducing dietary dLys below strain recommendations, particularly to 97 % and 95.5 %, impaired growth performance, intestinal morphology, and SCFA concentrations. However, PROT supplementation in reduced-dLys diets alleviated these adverse effects and supported improved intestinal integrity and performance.