Figure 2: The N-utilisation characteristics (relative to 19%CP) of Ross PM3 male broilers fed with diets differing in CP between 21 and 35 days of age (after Belloir et al., 2017)
and to improve sustainability, we run the risk of underfeeding amino nitrogen, negatively impacting on performance. Belloir et al., (2017) investigated the impact of a reduction in dietary crude protein, but not the levels of essential amino acids, in growing-finishing broilers (from 21 days of age). From Figure 1 it can be seen that this had little impact on weight gain but low crude protein diets negatively impacted on feed conversion ratio. Nitrogen retention efficiency increased with reduced crude protein as did nitrogen excretion and litter moisture (Figure 2). Surplus dietary protein may be used as a nitrogen source by the proteolytic and other bacteria in the caecum and these have the potential to cause dysbacteriosis and inhibit nutrient uptake (Leeson, 2018).
Requirements of the modern broiler. Simply reducing crude protein from a standard at the expense of performance is likely not the whole story. Evonik (2017) demonstrated that modern broilers are responsive to dietary balanced protein (as measured by dietary Lys level), with regards body weight, FCR and breast meat yield. Different levels of balanced protein were fed to male Ross 308 broilers from 21 to 37 days of age. Figure 3 shows that increasing balanced protein impacted on the amount of saleable
(as determined by lysine content) on performance and carcass traits of male Ross 308 broilers from 21 to 37 days (after Evonik, 2017)
Figure 3. The effect of increasing levels of balanced protein
breast meat and feed efficiency. Hirai et al., (2017) and Johnson et al., (2018) had similar findings using Cobb 500 X MV and Cobb 700 broilers respectively. Modern genotypes respond to balanced protein in a manner not reported by the primary breeding companies. High balanced protein levels result in improved field performance and greater proportions of high-value breast meat.
The conundrum Sustainability is measured using a number of parameters, which include financial, welfare and environmental aspects. Clearly, increasing profitability can be achieved by using higher balanced protein levels in the diet, at the expense of reduced sustainability in other areas. How then can we expect to achieve sustainable production in all of its facets? The use of exogenous enzymes is known to improve protein utilisation by 4 to 5 percentage points, so their use is a consideration. Crystalline forms of many of the essential amino acids are now available, enabling nutritionists to reduce crude protein while maintaining adequate balanced protein levels. Our understanding of exactly how to meet the provision of the non-essential amino acids is still unclear, resulting in performance issues when we get it wrong. Alternative broiler production systems, such as slow growing or
organic broilers, use more protein to achieve the same saleable weight because of higher demands of protein for maintenance purposes. It is true that they may be more sustainable from a welfare perspective, but their high land usage, high carbon footprints and higher demand for protein (resources) makes them an environmental liability. In future, decisions about protein usage in broiler diets will need to be made against the background of all aspects of sustainability and some form a sensible balance will need to be found.
FEED COMPOUNDER SEPTEMBER/OCTOBER 2018 PAGE 27
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