Endogenous Enzyme Activities and Energy Utilisation of Broiler Chickens Fed Maize-Based Diets Supplemented with Phytase and Carbohydrases

This study was aimed at assessing endogenous enzyme activities and utilisation of metabolisable energy by broiler chickens fed maize-based diets supplemented with phytase and carbohydrases. Birds were raised in cages in climate-controlled rooms. The jejunum and pancreas were collected at 10 and 24 d for analysis of endogenous digestive enzyme activities. Birds were also sampled at hatch and 24 d and analysed for gross energy, fat and crude protein contents. The data were used to calculate heat production, net energy of production and efficiency of energy utilisation. In the current study, the tested enzymes increased the activities of some of the endogenous enzymes and energy utilisation, and can be suggested for use in maize-based diets.

Maize is the main cereal grain used in poultry nutrition in many parts of the world. Maize quality has been found to be variable around the world and diets containing maize could be improved through supplementation with some microbial enzymes (Cowieson, 2005). The objective of this study was to assess the response of broiler chickens on diets containing maize and supplemented with some enzymes. The activities of endogenous enzymes and utilisation of dietary energy were assessed.

A total of 648 male and female Ross 308 broiler chickens were randomly assigned, in a 3 × 2 × 2 [Three doses of phytase none, standard (100 mg/kg) and superdose (300 mg/kg)] × two doses of and of β-glucanase [none and standard (100 mg/kg)] full factorial study in a completely randomised design. Each of the 12 treatments was replicated 6 times, with 9 birds per replicate. The diets were fed ad libitum from 0 to 35 days in 3 phases – starter as crumble (1-10 d), grower as pellet (11-24 d) and finisher as pellet (25-35 d). The test diets contained 60, 64 and 68 % of maize in starter, grower and finisher respectively and formulated to meet the specifications recommended in the Ross 308 broiler (Aviagen, 2014). A sub-sample of 10 day-old chicks was euthanised by cervical dislocation and minced to provide baseline data on body composition (gross energy, crude protein and fat contents). At 24 days, two birds per pen were randomly selected, slaughtered by cervical dislocation and processed (chopped, minced and freeze-dried) to determine carcass energy, protein and fat. On days 10 and 24, one bird was randomly selected from each cage, electrically stunned and euthanised by cervical dislocation to obtain the whole pancreas and anterior jejunum (4-5 cm long) and used to determine endogenous enzyme activities. Another 2 birds were similarly euthanised by cervical dislocation at 24 days and processed as described for the birds collected at d 0, to determine the energy, protein and fat contents of the intact carcass. The data from d 24 were related to the baseline data obtained from the d 0, to calculate the heat production (HP), net energy of production (NEp) and efficiency of utilisation of metabolisable energy. The remains birds were raised to 35d to measure meat yield. A general linear model procedure was used to analyse the collected data (Minitab Inc., 2013).

There was an interaction (P < 0.005) between the test enzymes and chymotrypsin activity in the pancreas at 10 d (Table 1). Pancreatic protein content was increased (P < 0.001) by supplemental phytase at standard and superdose level. At d 24, there was an increase (P < 0.01) in the activities of trypsin, general proteolytic activity and lipase due to phytase supplementation. Proteolytic activity was also improved (P < 0.01) through supplementation of β-glucanase. The activities of jejunal maltase, sucrase and alkaline phosphatase at 10 d were increased (P < 0.001) with phytase supplementation but there was no interaction between the microbial test enzymes. At 24 d, supplementation with phytase resulted in an increase (P < 0.001) in the activities of maltase, alkaline phosphatase and aminopeptidase. There was an interaction (P < 0.01) between xylanase and β-glucanase on the utilisation of apparent metabolisable energy (AME) retained as fat and protein, and efficiency of AME used for lipid retention. There was also interaction (P < 0.01) between phytase and β-glucanase on the efficiency of AME used for protein retention. Supplementation of phytase improved (P < 0.03) the AME content, AME intake, NEp, HP, energy retained as fat and as protein. Xylanase supplementation also increased (P < 0.01) AME contents, and AME intake, while the NEp and AME contents were improved (P < 0.05) by supplementation with β-glucanase (Table 2).

Supplementation with the test microbial enzymes increased the AME energy and NEp while interactions were observed between xylanase and β-glucanase. Dietary exogenous enzymes also increased the activities of some of the endogenous enzymes.

ACKNOWLEDGEMENT: We would like to thank AB Vista, UK and UNE for providing research funds.