Performance of broiler chickens fed South African sorghum-based diets with xylanase

M. Mabelebele, R.M. Gous, M. Siwela, H.V.M. O’Neil and P.A. Iji 1 University of South Africa, College of Agricultural and Environmental Science, Florida Campus, Rooderpoort, Johannesburg, South Africa 2 University of Kwa-Zulu Natal, School of Rural, Earth and Environmental Science, Scottsville, Pietermaritzburg, KwaZulu Natal, South Africa 3 AB Vista Feed Ingredients, Marlborough, Wiltshire, SN8 4AN, United Kingdom 4 University of New England, School of Environmental and Rural Science, Armidale, NSW 2351, Australia


Introduction
Sorghum-based diets are associated with inferior broiler performance in comparison to maize-and wheat-based diets (Selle et al., 2010).This inferiority has been observed in terms of breast meat yield and feed efficiency, which are crucial in broiler production.The purpose of adding enzymes to poultry feeds is mainly to improve the utilisation of nutrients.As described by Bedford and Schulze (1998), the mechanisms of xylanase include the degradation of the non-starch polysaccharides (NSP) in the cell wall matrix of the ingredients with the release of the encapsulated nutrients and lowered viscosity of digesta caused by soluble NSP and improved rate of diffusion between enzymes and digestion end products.Furthermore, xylanase increases accessibility of nutrients to endogenous digestive enzymes, stimulation of intestinal motility, improved feed passage rate, and supplementation of the enzyme capacity of young chicks.Xylanases, βglucanases, and phytases are enzymes commonly used in poultry feeds.Sorghum is an important cereal crop and plays a key role in animal feed (Kaufman et al., 2013).Although sorghum is similar to maize in chemical composition, it has been associated with sub-optimal and inconsistent poultry performance (Black et al., 2005;Bryden et al., 2009).Some sorghum varieties may contain condensed tannin, which has pronounced anti-nutritive properties.Grain sorghum contains high levels of phytate or phytic acid (Dorhorty et al., 1982).In addition to chelating minerals, phytate binds with protein through binary and ternary complexes and binds with starch directly or indirectly through starch granule-associated protein (Baldwin, 2001;Oatway et al., 2001).Due to this relationship, the enzymatic degradation of phytate increases availability of starch and protein in the sorghum.
The use of phytase in poultry feed has also increased in response to increasing concerns over phosphorus (P) pollution in the environment.The hydrolysis of the phytate increases the availability of phytate-bound P (phytate-P) and reduces its excretion (Simons et al., 1990).It also increases protein and starch utilisation (Selle et al., 2010).Combinations of xylanase and phytase have been of great interest in wheat-based diets.Xylanase reduces the digesta viscosity and releases the nutrients that are entrapped in the cell wall matrix.Enhanced apparent metabolisable energy (AME) and improved protein digestibility in wheat-based diets supplemented with xylanase and phytase have been reported (Ravindran et al., 1999).Despite the popularity of the use of phytase and carbohydrases or their combinations in wheat-and barleybased diets, published data on their use in sorghum is very limited.Consequently, two sub-experiments were conducted to evaluate the impact of exogenous enzymes added to South African sorghum-based diets on growth performance, internal organs, and nutrient utilisation of broiler chickens.

Materials and methods
A total of 480 day-old sexed Ross 308 broiler chicks (40.10 g weight), obtained from National Chicks (Pietermaritzburg, Kwa-Zulu Natal, South Africa), and were used in Experiments 1A and 1B.Chicks according to their experiments were assigned to cages (42 × 75 × 25 cm) in four-tier battery brooders housed in an environmentally controlled room.Initial brooding temperature was 33 °C, but was gradually reduced to 24 ± 1 °C at 19 days of age.The first day, 24 hours of light was provided, after 18 hours of lighting and 6 hours darkness was maintained each day.Access to feed and water was ad libitum.The Animal Ethics Committee of the University of KwaZulu-Natal, UKZN, Pietermaritzburg, KwaZulu-Natal, South Africa approved the experiment, with approval number 016/14/Animal.
Three commercial hybrid sorghum varieties were selected for their outstanding yield performance, agronomic characteristics, preference by farmers and tannin contents.The sorghum varieties, Pan8816 (non-tannin variety, 0.1 mg of catechin equivalent /100 mg), Pan8906 (non-tannin variety, 0.2 mg of catechin equivalent /100 mg) and Pan8625 (tannin variety, 2.0 mg of catechin equivalent/100mg) were grown in a controlled field trial at Pannar Research Services (Pty) Ltd, Klerksdorp, South Africa of November 2013 to February 2014.The mean temperature was 27.3 °C and rainfall of 527 mm (South African Weather Services, http:/www.weathers.co.za).The grains were field-dried and harvested at less than 14 % moisture content.The chemical and nutritional properties of the selected varieties were considered and reported by Mabelebele et al. (2015).
The basal starter diet was formulated to meet the requirements as recommended in the Ross broiler specifications (Aviagen, 2014).The diets were supplemented with 500 FTU microbial phytase (Quantum Blue, AB Vista Feed Ingredients Marlborough, UK) and with or without 1600 BXU of xylanase (Econase XT, AB Vista Feed Ingredients Marlborough, UK) for a total of six experimental diets (Table 1).PAN8816 plus phytase with or without 1600 BXU/kg xylanase, PAN8625 with 500 FTU/kg phytase with or without 1600 BXU/kg xylanase and PAN8906 with 500 FTU/kg phytase with or without 1600 BXU/kg xylanase).The diets were fed as mash to male and female broiler chickens from one to 21 days of age.For experiment 1A each treatment was randomly assigned to 24 pens in a 2 (sex) × 3 (sorghum variety) × 2 (with or without 1600 BXU xylanase/kg diet) factorial arrangement in a completely randomized design with 10 chickens per pen.Feed intake and body weight measurements were taken weekly and used to calculate growth performance.The mortality was recorded as it occurred.At 21 days of age, two chickens per pen with an average mean pen weight was taken, weighed and slaughtered.The carcass traits and visceral organs were weighed and dressed weight determined.The carcass was subsequently weighed, followed by removal and weighing of breast, thighs and drumsticks, all bone-in with skin.
For experiment 1B a total of 108 female broiler chickens were randomly assigned to 18 pens to a 3 (sorghum variety) x 2 (with or without xylanase) factorial arrangement in a completely randomised design with 6 chickens per replicate.The diets were formulated similar to that of experiment 1A.Celite, a major component of acid-insoluble ash, was included in the diet as an inert marker.Initial and final feed intake and body weight for an experimental period of four days was measured.On day 25, all birds were euthanazed by intravenous injection of sodium pentobarbitone, digesta contents from the distal half of the ileum were collected and processed as described previously (Ravindran et al., 1999a).
The nitrogen (N) contents of diet and ileal digesta samples were analysed using a FP-428 nitrogen determinator (LECO® Corporation, St. Joseph, Michigan, USA) as described by Sweeney (1989).Nitrogen freed by combustion at high temperature in pure oxygen was measured with a thermal conductivity detector using helium as a reference and converted to crude protein using a numerical factor of 5.70.The furnace temperature was maintained at 950 °C for hydrolysis of samples in ultra-high purity oxygen.To interpret detector response as percentage nitrogen (w/w), calibration was carried out using a pure primary standard of ethylenediaminetetraacetic acid (EDTA).Diet and ileal digesta samples were also analysed for phosphorus by the inductively coupled plasma (ICP) method (Vista MPX-radial) as described by Anderson and Henderson (1986).Acid insoluble ash was determined using the method described by Vogtmann et al. (1975).A 5 g (feed) or 4 g sample (excreta) was placed in a previously weighed glass beaker to which 50 ml of 4-N HCl added.The beaker was covered with a watch glass and boiled gently for 45 min.The slurry was then filtered through ashless filter paper and washed twice with double-distilled water.The filter paper containing the washed residue was placed in a dried, pre-weighed crucible and dried for 24 h at 70 °C.The dried residue was then ashed at 600 °C for at least 4 h, allowed to cool in a desiccator, and weighed to determine the weight of the cooled ash (acid insoluble ash).The crude protein content was calculated by multiplying it with a factor of 6.25.Starch and fat was measured following the standard method of AOAC (2005).The apparent ileal protein digestibility coefficients were calculated using the below formula: Where: (NT/AIA) d = ratio of nutrient and acid insoluble ash in diet, and (NT/AIA) i = ratio of nutrient and acid insoluble ash in ileal digesta.

Results and discussion
The influence of xylanase on sorghum-based broiler diets on gross performance at 1 -21 days is presented in Table 2.The broiler chickens offered sorghum variety Pan8816 and Pan8906 had similar (P >0.05) feed intake, body weight and FCR from 1 to 21 days of age.The tannin-containing sorghum variety evaluated in the current study Pan8625 resulted in poor feed intake, weight gain and FCR in the period 1-7 days.These results contradict those reported by Nyachoti et al. (1996) who found that broiler chickens on high-tannin sorghum-based diets had higher feed intake and feed efficiency.These researchers went further to suggest that the effects of tannins are related to their astringency, an effect resulting from binding of salivary proteins to cause dryness in the mouth.However, as taste acuity in the chicken is not well developed, it seems unlikely that taste plays a role in decreasing feed intake.Enzyme inclusion did not improve (P >0.05) the feed intake, body weight and FCR at all ages.It was apparent that enzyme supplementation had a more pronounced effect during the early phase of the feeding trial.A study by Selle et al. (2010) reported an increase in feed intake and weight gain but depressed feed efficiency when xylanase was added to sorghum-based broiler diets.This may be due to the fact that sorghum is a 'non-viscous' grain with only 4% soluble NSP (Choct, 2006;Selle et al., 2010).Furthermore, the disruption of insoluble NSP in sorghum endosperm cell walls by NSP-degrading enzymes is considered to be limited, which is attributed to the extent of arabinose substitution and high levels of glucuronic acid in sorghum arabinoxylan (Taylor, 2005).Ibrahim et al. (2012) indicated that inclusion of the β-glucanase enzyme in sorghum-based diets significantly decreased total feed intake and significantly improved weight gain and the FCR of broiler chickens.No treatment interaction was observed in all production parameters throughout the experimental period.Male broiler chickens had higher weight gain (7.46%), feed intake (11.13%), and feed efficiency (9.64%) than females over 1 -21 days of age.Several authors have also stated that male chickens, irrespective of the strain, are superior in live and carcass weights compared to females (Gous et al., 1999;Scheuermann et al., 2003;Abudulla et al., 2010).The differences observed between male and female chickens may be the result of sexual dimorphism, which tends to favour males over females in poultry (Ilori et al., 2010;Peters et al., 2010).
Similar (P >0.05) carcass weights, breast, thighs and drumsticks were observed in chickens on all sorghum varieties at 21 days of age (Table 3).The addition of Xylanase into diet did not improve (P >0.05) meat parts yield of broiler chickens aged 21 days.These results are in agreement with the report by Elnagar and Abdel-Wareth (2014) who indicated that there was no sorghum and enzyme interaction on carcass weights and meat cut-up parts of broiler chickens aged 21 days.The effect of microbial enzyme and sorghum variety on relative organ weights is presented in Table 4.The small intestine was heavier (P <0.05) in broiler chickens fed a tannin-containing variety, Pan8625, the variables others did not chance.The addition of xylanase were not affected (P >0.05).Sex had no effect (P >0.05) on relative weights of organs measured except for the bursa where females had heavier (P <0.05) weights than males.No treatment interaction was observed.Similar to the results of the current study Elgnagar and Abdel-Wareth (2014) reported that enzyme supplementation had no influence on organ weights.Nyachotti et al. (1996) indicated an influence of sorghum tannin on small intestinal development, resulting in low intestinal weights at 21 days and suggested that this could be due to the coarse nature of the diet.   5. Crude protein digestibility was no affected (P>0.05) by neither variety nor xylanase addition.Similar (P >0.05) crude protein digestibility were observed in all diets regardless of sorghum varieties or xylanase supplementation.It was expected that a tannin-containing variety without xylanase would be poorly digested, although it is not clear how xylanase acted in the presence of tannin in this variety to improve its digestibility.Dicko et al. (2006)   It is uncertain why xylanase did not improve fat digestibility in the current study.Significant (P <0.05) interactions between the treatments were observed.Xylanase supplemented to Pan8906 showed better (P<0.05)starch digestibility than Pan8816 without xylanase additions.However, when xylanase was included in all sorghum varieties, numerically, starch digestibility tended to improve.There was no significant (P >0.05) treatment interaction observed.Similar phosphorus (P >0.05) digestibility values in all three sorghum varieties with or without xylanase supplementations were observed.Taylor (2005) went further to say that when the protein matrix and bodies are poorly digested, starch digestibility could be affected and digestibility of the two nutrients appear to be highly correlated.The current study is similar to that of Perez-Maldonado and Rodrigues (2009) in that different sorghum cultivars were used, and starch and protein digestibility were found to be highly correlated.

Conclusion
Sorghum variety affected the growth performance of broiler chickens.Moreover, nutrient digestibility was affected by the differences in variety.However, there were some observed treatment effects in the early life of broilers chickens offered sorghum-based diets.Xylanase supplementation did not improve the performance and nutrient digestibility of broiler chickens.In the current study, the sorghum was fed as mash and, therefore, there might be a need to investigate and explore nutritive value of sorghum fed in different forms.

2
Small intestines with digesta a,b,c Mean values in a column not sharing the same superscript are significantly different (P <0.05).SEM: Standard error of the meanThe nutrient digestibility of broiler chickens offered sorghum-based diets with added xylanase is shown in Table

Table 1
Composition and calculated analysis of the starter diet

Table 2
Influence of xylanase inclusions in sorghum broiler-based diets on feed intake (FI, g/bird), body weight gain (gain, g/bird), and feed conversion ratio (FCR, g: g, FI: BWG)

Table 3
Effect of sorghum variety and xylanase supplementation carcass weight and parts yield of chickens (21d)

Table 4
Effect of sorghum variety and xylanase supplementation on broiler organ weights (g/100gBW) at 21 days 1 Proventriculus and gizzard weight with digesta; Cowieson et al. (2006)t have shown that protein, proteincarbohydrate, protein-polyphenol, and carbohydrate-polyphenol interactions are the main factors affecting According toCowieson et al. (2006), it is well documented that xylanase-based enzymes act on NSP through two main modes of action.

Table 5
Nutrient digestibility (%) of broiler chickens offered sorghum-based diets added with microbial enzymes a,b,c Mean values in a column not sharing the same superscript are significantly different (P <0.05).SEM: Standard error of the mean Enzyme inclusion significantly increased (P <0.05) the crude protein digestibility.A treatment interaction was observed (P <0.0001) because numerically crude protein digestibility tended to increase when xylanase was added.Sorghum variety Pan8906 with xylanase supplementation had lower fat digestibility (P>0.05)than the same variety without enzyme inclusion.Sorghum varieties with xylanase had lower (P>0.05)fat digestibilities compared to those without xylanase supplementation.Sorghum Pan8816 and Pan8625 offered to broiler chickens significantly improved (P <0.05) fat digestibility (75.93 and 76.60%, respectively) compared to when Pan8906 (65.94%) was offered to broiler chickens.Xylanase inclusions significantly yielded low (P>0.05)fat digestibility.