Endogenous enzyme activities and energy utilization of broilers fed sorghum-based diets supplemented with phytase and carbohydrases

M. Al-Qahtani 1 , K.I. Al-Qahtani 1 , E.U. Ahiwe¹, H.J. Gausi¹, M.E. Abdallh¹, E.P. Chang’a¹, M.M. Ari 1 , M.R. Bedford² and P.A. Iji ¹,3 ¹School of Environmental and Rural Science, University of New England, Armidale, Australia ²AB Vista, Woodstock Court, Marlborough, UK ³ College of Agriculture, Fisheries and Forestry, Fiji National University, Koronivia, Fiji

This study was conducted to evaluate the endogenous enzyme activities and energy utilization of broiler chickens fed sorghum-based diets supplemented with phytase and carbohydrases.

The birds were housed 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 utilization. There were improvements in digestive enzyme activities and utilization of energy, in terms of metabolisable energy and net energy of production (NEp), suggesting the suitability of the exogenous test enzymes for use in sorghum-based diets.

A recent study on Australian sorghum by Selle et al. (2017) reported that sorghum produced in Australia is used almost exclusively for feed, especially cattle, pigs and poultry. The objective of the present research is to assess the response of broiler chickens to diets based on sorghum, when supplemented with a combination of enzymes, targeting different substrates.

A total of 648 male and female Ross 308 broiler chickens was randomly assigned in a 3 × 2 × 2 factorial arrangement of treatments [3 doses of phytase none, standard (100 mg/kg) and superdose (300 mg/kg)] × 2 doses of xylanase and of β-glucanase [none and standard (100 mg/kg)] 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 sorghum in the starter, grower and finisher respectively and were formulated to meet the specifications recommended for the Ross 308 broiler chickens. A sub-sample of 10-day-old chicks was euthanised by cervical dislocation, minced and analysed to provide baseline data on body composition: gross energy, crude protein and fat contents. At d 24 two birds per pen were randomly selected, euthanised by cervical dislocation and processed (chopped, minced and freeze-dried) and used to determine carcass energy, protein and fat. On d 10 and d 24 one bird was randomly selected from each cage, electrically stunned and euthanised by cervical dislocation.

These were dissected to obtain the whole pancreas and anterior jejunum (4-5 cm long) and used to determine the endogenous enzyme activities. Another 2 birds were similarly slaughtered at d 24 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 day-old chicks, to calculate the heat production (HP), NEp and efficiency of utilization of metabolisable energy. Between d 25 and d 35 birds were fed finisher diets to measure meat parts yield. A general linear model procedure was used to analyse the collected data (Minitab Inc., 2013).

There was an interaction (P<0.003) between phytase, xylanase and β-glucanase on chymotrypsin activity at d 10. Addition of phytase increased (P<0.02) pancreatic protein content, trypsin activity and general proteolytic activity. At d 24 pancreatic protein content and enzyme activities (chymotrypsin, trypsin and general proteolytic activity) also responded (P<0.02) to interactions between phytase and