Inclusion of barley in broiler diet: Impact on digesta properties and growth performance

Barley hasn’t been routinely used in broiler diets in the Asia-Pacific region for several reasons: (1) Inferior performance and its association with intestinal dysbacteriosis due to the presence of soluble 1,3-1,4-mixed-β-glucan, (2) no economic merit over using corn and wheat, and (3) limited quantities available for the feed industry. However, a recent increase in corn and wheat prices and increased availability of barley in the ASPAC region due to trade disputes involving the major barley trading countries has attracted industry attention to consider the use of more barley in monogastric animal feeds. However, one of the most common questions nutritionists would ask is whether barley will increase intestinal viscosity and whether β-glucanase should be used to alleviate the inferior performance commonly seen in the barley-based diet. In a recent study completed in Australia, we tested whether supplementation of either traditional xylanase + β-glucanase or alternatively a stimbiotic, a product designed to stimulate microbial fibre fermentation in the gastrointestinal tract, can ameliorate the negative impact of barley inclusion for broilers.          

The study used 240 mixed-sex Cobb 500 chicks and allocated them to 24 pens of 10 birds per pen. There were three dietary treatments: Control, Control with supplementation of 100 g/MT stimbiotic (Signis, AB Vista), and Control with 100g/MT xylanase + β-glucanase (X+G; used recommended dose of a commercial X+G product). Diets were fed in three phases (Starter d0-14, Grower d15-21, Finisher d22-35). The experimental diets included 30% barley and 28-36% wheat, 32-26% soybean meal with 3.8-4.2% canola oils. The three-phase diets contained 3,000, 3,050, and 3,100 kcal AME and 1.3, 1.2, and 1.12% SID lysine for the Starter, Grower and Finisher diets, respectively. All diets included 500 FTU phytase (Quantum Blue, AB Vista) and Salinomycin as a coccidiostat.
Considering that the typical 35d FCR in the research facility is around 1.40-1.45 range, including 30% barley in the broiler diet increased FCR at least by 5 points. Supplementation of stimbiotic or xylanase + β-glucanase brought the FCR back to the best performance level in the facility (1.40, and 1.39 respectively, Figure 1 Left graph). Although statistically not significant, the 35d mortality was high in the control diet (12.4%), while supplementation of stimbiotic (4.8%) and X+G (7.3%) reduced the mortality (Figure 1 centre graph). Overall, considering all performance parameters in the European production efficiency factor (EPEF), it was significantly higher in the birds supplemented with the stimbiotic (460) compared with the Control diet-fed birds (373), while supplementation of X+G intermediately improved EPEF (448, Figure 1 Right graph).

Figure 1. Effect of supplementing Signis or xylanase + beta-glucanase on performance, liveability and EPEF measured over 35 days of broilers fed wheat, 30% barley and soybean meal-based three-phase diets.

The digesta samples from the ileum were collected on day 21 and 35 by euthanising one bird per cage (n=8). The β-glucan content in the 21-day ileal digesta was 25 g/100 g DM basis in the birds fed the control diet, while supplementation of stimbiotic or X+G reduced it to 18.8 and 17.9 g/100g DM, respectively (Figure 2 Left graph). Consequently, the viscosity of the ileal digesta was high in the birds fed the control diet, while supplementation of stimbiotic or X+G significantly decreased the viscosity (Figure 2, Right graph). Although not shown in the graph, the β-glucan content and the viscosity of the ileal digesta at 35-day old birds were similar to the levels found at 21-day old birds. The β-glucan contents in the 35-day ileal digesta were 21.8, 19.0, 21.1 g/100g DM, and the ileal digesta viscosities were 4.21, 2.63, and 2.80 cP in birds fed a control, Signis or X+G, respectively. These findings suggest that (1) a diet containing 30% barley showed a higher digesta viscosity in the small intestine compared with the other treatments, which is the potential reason for the impaired growth performance and higher mortality in the birds fed a control diet; and (2) supplementation of Signis and xylanase + β-glucanase reduced β-glucan content and hence the digesta viscosity in the ileum.

Figure 2. Effect of supplementing Signis or xylanase + b-glucanase on ileal β-glucan content and digesta viscosity measured on 21 days of age.

The volatile fatty acid (VFA) production in the caeca was measured on day 21 and 35 and presented in Figure 3. It is generally well accepted that birds at an early age have an immature intestinal microbiome and hence have less ability to ferment soluble fibre fractions entering into the caeca. As presented in Figure 3 Left-hand-side graph, the birds fed a control diet or with supplementation of xylanase + β-glucanase produced the least amount of VFA, indicating that the intestinal microbiome was not mature enough to effectively utilise the soluble fibre fractions entering into the caeca. In contrast, the birds fed Signis (stimbiotic) supplemented diet showed significantly increased VFA production in the caeca compared with the birds fed either a control diet or the diet with xylanase + β-glucanase. This finding indicates that Signis effectively stimulated the intestinal microbiome at an earlier age and enhanced the birds’ ability to ferment the soluble fibre fractions entering the caeca. A similar effect was seen in birds fed a diet with Signis supplementation on day 35, while the birds fed a diet with xylanase + β-glucanase also increased VFA production at the older age.

Figure 3. Effect of supplementing Signis or xylanase + β-glucanase on caecal VFA contents measured on 21 and 35 days of age.

In conclusion, the results provide clear pieces of evidence that:
• Supplementation of xylanase + β-glucanase effectively reduced intestinal viscosity maybe by hydrolysing soluble NSP and β -glucan. However, the birds fed a xylanase + β-glucanase supplemented diet were not able to effectively ferment the hydrolysed soluble fibre entering into the caeca on day 21. The fermentation of soluble fibre in the caeca was improved at day 35 but less effectively than the birds fed a diet supplemented with Signis.

• Signis supplementation reduced ileal β-glucan content, reduced ileal viscosity and increased VFA production in the caeca already at an early age compared with supplementation of xylanase + β-glucanase.

• This finding indicates that rather than supplementing xylanase + β-glucanase, supplementation with Signis  stimulates the intestinal microbiome to hydrolyse NSP and ferment the soluble NSP in the wheat/barley-based diet. Even though the Signis product does not contain a β-glucanase itself, it clearly has stimulated production of this enzyme in the ileum (and hence reduced betaglucan concentration as well as viscosity) and a suite of fibre degrading enzymes in the caeca which is a much more efficient strategy to alleviate the negative effect of barley in broiler diets.