Low doses of exogenous xylanase improve the nutritive value of triticale-based diets for broilers

SUMMARY

Triticale, a hybrid of wheat and rye, is a cereal grain that displays a nutritive value similar to wheat and a resistance to hard agronomic conditions, which are more identical to rye. Because of its lower price in comparison with wheat or corn, triticale may be a potential alternative raw material for broiler diets. However, triticale is known to contain a significant proportion of soluble arabinoxylans, which are known to act as antinutritive factors in poultry. Nevertheless, levels of soluble polysaccharides in triticale are more similar to wheat and are not as high as in rye. In the present study, the capacity of xylanases, used at different levels, to improve the nutritive value of a triticale-based diet for broilers was investigated. On the basis of these data, triticale may be used effectively as the main feedstuff in broiler diets. However, supplementation with xylanase improved the nutritive value of the cereal-based diet when incorporated at 75% (wt/wt) of the recommended dose. Xylanases may modulate bird performance through the microflora route. As expected, incorporation of the exogenous enzymes reduced digesta viscosity. However, xylanase incorporation at 100 and 200% of the recommended levels did not have an effect on bird performance.

Primary Audience: Nutritionists, Researchers

DESCRIPTION OF PROBLEM

Several cereals grains are used in poultry nutrition around the globe. Triticale is a hybrid cereal that results from the crossbreeding of wheat and rye and could be used as an alternative grain for poultry. Triticale was developed with the intent of having a similar nutrient composition when compared with wheat and the resistance to hard agronomic conditions similar to rye [1–3]. However, early triticale varieties had poor feeding characteristics relative to wheat (although presenting a similar protein content), and triticale developed a reputation for being unsuitable for poultry diets [2]. Many cultivars were developed thereafter to improve its value for poultry diets. Thus, modern triticale varieties tend to have a lower proportion of the rye genome in comparison with the wheat genome, leading to increased grain plumpness and lower protein content than the early varieties [3].

On the basis of several studies performed with poultry, triticale may be incorporated in broiler diets with no major effect on the nutritive value of the diet or bird performance [4–7]. However, similar to what have been described for wheat, rye, and barley, triticale is rich in soluble nonstarch polysaccharides (NSP). The NSP increase digesta viscosity and, consequently, lead to a slower digesta passage rate, thus decreasing feed intake and nutrient digestion and absorption [8]. Wheat, rye, and triticale contain significant levels of xylans and arabinoxylans that limit their use in broiler diets [9]. However, triticale seems to have a soluble NSP content more similar to wheat than to rye [10]. It is well known that enzyme supplementation in diets containing significant levels of NSP improves the efficiency of feed utilization, contributing to a better incorporation of these low-cost feed ingredients in poultry feeds [4, 5, 11, 12]. Xylanase supplementation in diets based on wheat, rye, or triticale decreases the degree of polymerization of NSP, resulting in a decrease in digesta viscosity and improving the nutritive value of the diet [5, 7]. The digesta passage rate increases, leading to an improvement in feed intake and, consequently, in the productive performance of supplemented animals [13]. However, it has also been suggested that enzyme supplementation may promote the proliferation of beneficial microflora in the final compartments of the gastrointestinal tract by increasing the quantity or quality of the substrates available for fermentation [14, 15]. It is also possible that plant cell wall hydrolases mediate their effects by releasing endosperm plant cell wall-trapped nutrients that would otherwise be unavailable for digestion [16]. Thus, the addition of exogenous enzymes can enhance the digestive capacity of the young bird by complementing its repertoire of intestinal enzymes and by modulating the microbial population in the final part of the intestine. Several researchers have indicated that triticale can substitute partially, or totally, for corn, wheat, or barley without negative effects on the performance of the animal or bird [2, 17, 18]. However, the effectiveness of enzyme supplementation in triticale-based diets seems to be dependent on the triticale variety. For example, Jacobs et al. [19] found that exogenous enzyme supplementation was not required for the triticale variety Titan. It is also evident that the chemical composition of triticale varies between different cultivars, as a result of several hybrids with very different characteristics [17, 20].

A novel triticale variety was recently developed, the Alter variety. This variety has a grain production aptitude, a short vegetative cycle (spring variety), a CP content of 11%, and gross energy of 3,886 kcal/kg. The objective of the present study was to evaluate the effect of incorporating high levels of the triticale Alter variety on the productive performance of broilers. In addition, the capacity of exogenous xylanases, incorporated at different doses, to improve the nutritive value of the triticale-based diets for broilers was investigated.

MATERIALS AND METHODS

Birds, Diets, and Management

Bird experiments were conducted in accordance with the Ethics Committee of CIISA, Faculdade de Medicina Veterinária, and approved by the Animal Care Committee of the National Veterinary Authority (Direcção-Geral de Veterinária, Lisboa, Portugal), following the appropriate European Union guidelines (Council Directive 86/609/EEC) [21].

One hundred sixty 1-d-old Ross 308 [22] male broiler chicks were weighed and assigned to 40 pens of 4 birds each (n = 10 pens per treatment). Chicks were wing-banded for individual identification. The 40 pens were randomly assigned to 4 treatment groups consisting of a triticale-based diet supplemented with 0, 234, 312.5, or 625 g/ton of a commercially available xylanase (Avizyme 1310) [23] for the entire 28 d of the experiment. These levels of supplementation corresponded to 0%, 75% (X75), 100% (X100), and 200% (X200) of the enzyme manufacturer’s recommended dose, respectively (where X refers to xylanase). The basal diet (Table 1) contained 60% of the triticale Alter variety and was formulated to ensure nutrient availability as defined by the NRC [24]. Throughout the experiment, chicks were exposed to constant light for the duration of the trial and were given free access to water and feed, which were provided with automatic nipple drinkers and hanging feeders, respectively. Brooders were located in an environmentally controlled room adjusted to the recommended temperatures daily, according to standard brooding practices. Feed consumption and BW were determined weekly, and mortality was recorded daily throughout the experiment. At d 28, one bird per pen was slaughtered by an intravenous injection of an aqueous isotonic solution of 125 mg of thiopental [25]. The weights of the crop, gizzard, liver, duodenum, jejunum, ileum, and cecum and the lengths of the duodenum, jejunum, ileum, and cecum were measured. The jejunum was defined as the portion between the end of the duodenum and the region immediately before Meckel’s diverticulum, and the ileum was defined as the portion between Meckel’s diverticulum and the region immediately before the ileocecal junction. Digesta samples were collected at the terminal end of each gastrointestinal compartment to determine content viscosity. To measure the viscosity of small intestine contents, samples were collected from the duodenum plus jejunum and the ileum. Digesta samples were centrifuged for 10 min at 9,050 × g at 25°C, and the viscosity of the supernatant was measured at 6 rpm using a viscometer [26] with a cup maintained at 24°C.

Ingredient composition and calculated analysis of the cereal-based diet

Table 1

Ingredient composition and calculated analysis of the cereal-based diet

Item	Diet
Ingredient, %
Triticale	60.00
Soybean meal, 47% CP	31.25
Soybean oil	4.50
Dicalcium phosphate	1.80
Calcium carbonate	1.40
l-Lysine	0.18
dl-Methionine	0.20
Salt	0.47
Premix1	0.20
Calculated nutrient composition
ME, kcal/kg	3,066
CP, %	22.19
Lysine, %	1.23
Methionine, %	0.55
Calcium, %	1.01
Available phosphorus, %	0.45

1

The mineral-vitamin premix provided the following per kilogram of diet: retinol, 9,000 IU; cholecalciferol, 2,100 IU; α-tocopherol, 20 mg; nicotinic acid, 30 mg; cyanocobalamin, 0.12 mg; calcium pantothenate, 10 mg; phylloquinone, 2 mg; thiamine, 1 mg; riboflavin, 4.2 mg; pyridoxine, 1.7 mg; folic acid, 0.5 mg; biotin, 0.5 mg; iron, 80 mg; copper, 10 mg; manganese, 100 mg; zinc, 80 mg; cobalt, 0.2 mg; iodine, 1.0 mg; selenium, 0.3 mg; monensin, 100 ppm.

Statistical Analysis

Data related to bird performance were subjected to ANOVA according to the GLM procedure of SAS [27]. The experimental unit was a cage of 4 birds. Duncan’s procedure was used to detect significant differences among treatment groups. Differences were considered significant when P < 0.05, and they tended toward significance when P < 0.1.

RESULTS AND DISCUSSION

Growth performance data, expressed weekly in terms of BW, BW gain, feed intake, and FCR, are summarized in Table 2. Final BW of broilers was at the level expected for the genotype Ross 308 (1,505 g of BW at d 28, per the Ross 308 management manual) in diets containing or not containing exogenous enzymes. Thus, the triticale variety used in this study at high incorporation rates displays an appropriate nutritive value for broilers; therefore, levels of antinutritive soluble arabinoxylans in this cereal were low. However, diet supplementation with microbial enzymes led to a positive effect on broiler performance by increasing the BW of birds from d 14 onward. At 14, 21, and 28 d of age, birds receiving the X75 treatment had a higher BW when compared with nonsupplemented birds. Final BW of birds from treatments X100 and X200, which received a higher dose of exogenous enzyme than birds in treatment X75, was not significantly different in comparison with the BW of unsupplemented birds. There is considerable evidence suggesting that enzyme supplementation improves the BW of birds fed triticale-based diets [5, 28], although in numerous experiments there was a lack of response to enzyme supplementation [19, 29]. On the basis of these observations, the effect of xylanase addition to triticale-based diets may depend on several unaccounted for factors, such as the triticale variety, environmental growth and storage conditions, the composition of the enzyme mixture, or, as discussed below, exogenous enzyme levels [29, 30]. No differences were observed in feed intake and FCR of birds between the 4 treatments. Similar findings were reported previously [28, 31]. However, overall, based on these data, feed enzymes in the X75 treatment increased the final BW of birds through an improvement in nutrient digestion and availability, rather than an improvement in feed intake.

Growth performance of broilers fed the different dietary treatments¹

Table 2

Growth performance of broilers fed the different dietary treatments¹

Item	NC	X75	X100	X200	SEM	Probability (F)
BW, g
0 d	45	45	45	45	0.20	NS
7 d	154	158	158	157	1.15	NS
14 d	415b	438a	438a	432ab	3.01	0.023
21 d	865b	908a	913a	894ab	6.87	0.059
28 d	1,459b	1,542a	1,508ab	1,489ab	11.9	0.093
Feed intake, g
0 to 7 d	123	124	126	124	1.43	NS
7 to 14 d	359	373	363	367	4.03	NS
14 to 21 d	658	705	682	678	6.94	NS
21 to 28 d	909	957	891	892	12.4	NS
0 to 28 d	2,049	2,158	2,062	2,060	20.9	NS
BW gain
0 to 7 d	109	113	113	112	2.19	NS
7 to 14 d	262b	281a	279a	274ab	4.29	0.007
14 to 21 d	449	470	475	462	9.31	NS
21 to 28 d	594	624	598	586	15.2	NS
0 to 28 d	1,414b	1,497a	1,462ab	1,444b	23.8	0.091
FCR
0 to 7 d	1.14	1.11	1.13	1.12	0.010	NS
7 to 14 d	1.38	1.34	1.34	1.35	0.010	NS
14 to 21 d	1.51	1.57	1.48	1.51	0.026	NS
21 to 28 d	1.58	1.65	1.56	1.65	0.032	NS
0 to 28 d	1.48	1.47	1.52	1.46	0.013	NS

^a–cMeans within a row with different superscript letters differ, P < 0.05.

¹Treatments consisted of a triticale-based nonsupplemented diet (NC) or a diet supplemented with 234 (X75), 312.5 (X100), or 625 g/ton (X200), which corresponds to supplementation with, respectively, 75, 100, or 200% of the manufacturer’s recommendation of a commercially available xylanase [23].

Given our results, the effectiveness of enzyme supplementation in triticale-based diets may depend on the xylanase dose. Apparently, the optimal levels of enzyme incorporation are lower than the levels recommended by the manufacturer. Rather than further improving the final BW of birds, an increase in the levels of xylanase incorporation led to a decrease in bird performance. Although this was an unexpected observation, it is possible that products of arabinoxylan hydrolysis were severely changed at higher xylanase doses, resulting in different substrates being available for fermentation by the microflora colonizing the lower parts of the gastrointestinal tract.

The effects of the different levels of exogenous enzymes used in a triticale-based diet in the absolute weight and length of gastrointestinal compartments and the viscosity of intestinal contents were assessed (Table 3). Absolute weights and lengths of the different digestive compartments were not different between birds fed the different dietary treatments. The general lack of effect of the different diets in the length and weight of the gastrointestinal tract compartments of the birds may be due to the low viscosity of the diets. Ileal viscosity was shown to be similar between birds fed the 4 different treatment diets. However, duodenal and jejunal viscosities were significantly higher (P = 0.007) when birds were fed a nonsupplemented triticale based-diet in comparison with broilers receiving supplemented diets. Therefore, the exogenous enzymes had the capacity to reduce the degree of polymerization of the soluble NSP present in triticale, contributing to a reduction in digesta viscosity. However, the actual difference in viscosity between the supplemented and nonsupplemented treatments was slight and the overall viscosity of the digesta might be considered low [32]. Therefore, the triticale variety used in this study was a low-viscosity variety.

Absolute weight (g) and length (cm) of the gastrointestinal tract and viscosity of the intestinal contents of broilers fed the different treatments¹

Table 3

Absolute weight (g) and length (cm) of the gastrointestinal tract and viscosity of the intestinal contents of broilers fed the different treatments¹

Item	NC	X75	X100	X200	SEM	Probability (F)
Weight
Crop	6.97	6.66	7.22	6.87	0.431	NS
Gizzard	15.4	16.0	16.0	16.3	0.78	NS
Liver	53.2	56.2	58.4	58.5	2.59	NS
Pancreas	4.05	4.00	3.97	3.87	0.185	NS
Duodenum	12.3	12.7	11.8	11.6	0.67	NS
Jejunum	22.4	23.1	23.4	22.4	1.11	NS
Ileum	17.1	16.9	16.5	16.4	1.04	NS
Cecum	7.32	6.96	6.81	7.07	0.402	NS
Length
Duodenum	31.7	30.6	30.6	31.4	0.78	NS
Jejunum	74.3	72.7	75.9	75.0	2.31	NS
Ileum	76.8	76.0	74.7	77.0	1.89	NS
Cecum	17.8	18.0	17.7	17.7	0.63	NS
Viscosity, cP
Duodenum + jejunum	4.17a	3.35b	3.37b	3.31b	0.109	0.007
Ileum	7.39	6.47	7.18	6.15	0.268	NS

^a–cMeans within a row with different superscript letters differ, P < 0.05.

¹Treatments consisted of a triticale-based nonsupplemented diet (NC) or a diet supplemented with 234 (X75), 312.5 (X100), or 625 g/ton (X200), which corresponds to supplementation with, respectively, 75, 100, or 200% of the manufacturer’s recommendation of a commercially available xylanase [23].

It is well established that enzyme supplementation in high-viscosity diets containing high levels of soluble NSP can significantly reduce the viscosity of digesta, leading to more efficient nutrient digestion and absorption [8]. In addition, a reduction in digesta viscosity contributes to accelerating feed passage [33], which, in turn, improves feed intake. Moreover, as suggested by Choct [34], the hydrolysis of dietary insoluble arabinoxylans leads to a release of cellular constituents that will be available for digestion in the small intestine. Overall, the positive effects of enzyme supplementation of high-viscosity diets on bird performance are usually observed in the first weeks of bird growth.

Given our data, the triticale-based diet under study had low levels of soluble arabinoxylans and thus had a minor effect on digesta viscosity. In addition, in contrast to what is described for high-viscosity diets, the major effects of enzyme supplementation on bird performance were observed during the last weeks of the experimental period and did not reflect an improvement in feed intake, but rather a possible improvement in nutrient digestibility. Thus, a different mechanism operates to improve bird performance in low-viscosity diets, such as those under study here, which is not mediated by a major reduction in digesta viscosity. Previously, researchers have indicated that in low-viscosity diets, improvements in animal and poultry performance are potentially mediated mainly by the microbial route [15, 35, 36]. Microbial populations that colonize the gastrointestinal tract of the bird seem to be quite active only after the first 2 to 3 wk of age [37]. The addition of carbohydrate-active enzymes to low-viscosity diets leads to a significant hydrolysis of the soluble NSP, also contributing to a change in the nutrient profile available for microbial fermentation. Thus, in these circumstances, feed enzymes influence bird performance primarily through manipulation of the microbial population [38], which means that the improvement in bird performance is fundamentally observed at later stages of bird growth. In this study, the differences in BW between treatments were apparent only in the later stages of the experiment, which could meant that a modification of microflora had occurred.

We suggest that supplementing a triticale-based diet with xylanase at 75% of the recommended dose released xylooligosaccharides that may promote the proliferation of beneficial microflora [30, 39]. Although not confirmed with microflora analysis in this trial, it has been suggested that selected xylanases convert water-insoluble arabinoxylans into substances with prebiotic potential and will prevent the generation of xylose monomers [39]. Oligosaccharides are already used as prebiotics [40]. Two of the most studied prebiotic oligosaccharides are fructooligosaccharides, which act as a means of increasing the substrates for beneficial gut microflora [33–36, 41, 42], and mannanoligosaccharides, which attach to pathogenic bacteria through the mannose residues [43, 44]. The use of xylooligosaccharides has not been as widely studied, but there is an indication of their beneficial role in the intestinal health status of poultry [37, 45]. In the present study, a higher dose of xylanase incorporation, such as 100 and 200% of the recommended dose, may have led to an extensive depolymerization of arabinoxylans into monomers such as xylose and xylobiose, which the monogastric bird is unable to utilize. Previously, researchers have found that xylose in broiler diets may, in fact, inhibit the growth and digestibility of proteins and fat [46].

CONCLUSIONS AND APPLICATIONS

1. The Alter variety of triticale can be used at high levels in diets for broilers. Birds fed a triticale-based diet (60%) reached the expected BW recommended by Ross 308 guidelines.

2. Exogenous xylanases are effective from d 14 onward. Enzyme efficacy was reflected in an improved BW and a lower viscosity of duodenal and ileal contents at the end of the experiment.

3. The optimal level of enzyme supplementation was found to be 234 g/ton of diet for broilers, which represents 75% of the manufacturer’s recommended dose. Bird performance in birds receiving 75% of the enzyme level was significantly improved when compared with that of nonsupplemented birds.

4. It is proposed that enzyme supplementation of triticale-based diets at 75% of the recommended dose potentiates the release of xylooligosaccharides, which act as health promoters for broilers and thus improve the nutritive value of the triticale-based diet. Nevertheless, future evaluation of intestinal microflora should be an important approach to support the productive parameters obtained in this study.

1

These authors contributed equally to the paper.

Acknowledgments

We thank Sociedade Agrícola da Quinta da Freiria SA (Bombarral, Portugal) for supplying the 1-d-old broilers used in these experiments. This work was supported by Fundação para a Ciência e a Tecnologia (Lisboa, Portugal; grants PTDC/CVT/69329/2006 and PTDC/CVT/103942/2008). Teresa Ribeiro was supported by Fundação para a Ciência e a Tecnologia through an individual fellowship (SFRH/BD/32321/2006).