Best growth performance seen in broiler starters fed diets with 28% barley

A recent study published in British Poultry Science evaluated the effect of barley inclusion on broiler performance on a wheat-based diet, with and without enzyme supplementation and concluded the optimal inclusion of barley was 28.3% with respect to growth performance.

Barley is sometimes thought of as an unfavourable ingredient for use in poultry diets due to its low energy but relatively high levels of fibre and non-starch polysaccharides (NSPs). The predominant NSP in barley (β-glucans), are anti-nutritive factors that limit the inclusion of barley in diets. High levels of barley in diets can have negative effects on digestion and absorption of nutrients and therefore growth performance of broilers.

Perera et al., (2019) evaluated barley inclusion at five levels in a wheat-based diet; 0, 14.1, 28.3, 42.4 and 56.5%, with the diet containing 56.5% barley fully replacing wheat in the ration. All diets were formulated to have equivalent nitrogen-corrected apparent metabolizable energy (AMEn) and digestible amino acid content.

Growth Performance

Growth performance parameters measured included weight gain, feed intake and gain to feed ratio. Weight gain increased when barley inclusion increased to 28.3% and then decreased with higher inclusions as shown in Figure 1. Other observations included an improvement in gain to feed ratio and a reduction in feed intake as barley inclusion increased. This reduction in feed intake and therefore nutrient intake could be due to a poorer quality pellet, a consequence of increased inclusion of barley, and because barley is less palatable than wheat. The addition of an NSP-degrading enzyme increased the weight gain and gain to feed ratio further.

Figure 1 The influence of barley inclusion on weight gain of broiler starters (0-21d) fed diets based on wheat and normal-starch hulled barley. Adapted from Perera et al. (2019)
Figure 1 The influence of barley inclusion on weight gain of broiler starters (0-21d) fed diets based on wheat and normal-starch hulled barley. Adapted from Perera et al. (2019)

 

Nutrient Digestibility

As barley inclusion increased, the coefficient of apparent ileal digestibility (CAID) of dry matter, starch, nitrogen and fat improved such that birds fed diets with 0% barley showed the lowest digestibility, and birds fed diets with 56.5% barley showed the highest digestibility for these nutrients. Digestibility of all these nutrients further improved with addition of an NSP-degrading enzyme.

The Gizzard

The gizzard is an important component of the digestive tract that helps regulate digesta passage rate, and can prevent starch overload further down the tract. Fibre, in particular the insoluble NSP fraction, has been shown to improve gizzard development. In this study, gizzard weights increased by almost 38% when wheat was completely replaced with barley, which has a greater concentration of insoluble NSP compared to wheat. These larger, well-developed gizzards are shown to improve digestion, by increasing retention and mixing time in the gizzard, allowing the feed particles to be exposed to digestive enzymes for longer.  

Digesta Viscosity

Jejunal digesta viscosity decreased with increasing barley inclusion, despite other studies contradicting this. Addition of an NSP-degrading enzyme further decreased digesta viscosity at each level of barley inclusion. Digesta viscosity also has an influence on passage rate with an increased digesta viscosity potentially having a negative effect on feed intake in young broilers. By reducing digesta viscosity, not only does passage rate increase, but it also allows better interaction of feed particles with digestive enzymes, thus improving nutrient digestibility, energy utilisation and improved feed efficiency. 

In summary, the optimum inclusion level of barley in wheat-based broiler starter diet is 28.3% with respect to growth performance. The improvement in nutrient and energy utilisation that was seen with increasing inclusions of barley could, in part, be explained by reduction in digesta viscosity and improved gizzard function.

Whilst you might not want to rush out and put 28% barley into your broiler diets, this trial suggests that we do not need to be quite as cautious with barley as perhaps we are currently.

Barley field