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Protein in


broiler nutrition: a conundrum


Defi ning protein Before entering any discussion on the protein content of poultry diets, an examination of what is meant by protein needs to be entered into. Crude protein is widely used as a measure of protein quality of both feed and ingredients. It is a calculated value in which the nitrogen content of a material is multiplied by a factor of 6.25. Whilst this may be so for milk and eggs, nutritionists have known for decades that this is not accurate for feed ingredients (Jones, 1931). It is an inadequate measure for use in feed formulation, and true protein is the measure that we are interested in. True protein is composed only of amino acids, 22 of which are known to be used for the structure of all tissues by means of large, complex combinations. Essential amino acids are those in which the carbon skeleton cannot be synthesised by the birds themselves and must be supplied through the diet while non-essential amino acids can by synthesised from amino nitrogen precursors. All amino acids found in tissue are biologically mandatory, so this classification pertains to their dietary necessity. The difference between crude protein and true protein are a group of compounds known as non-protein-nitrogen, which comprises material of little use to the bird, urea for example, and other such as nucleic acids and nucleotides, which are important for the bird. Amino acids are deposited in fixed ratios into tissue thus the


By Rick Kleyn, Poultry Nutrition Consultant, SPESFEED (Pty) Ltd


Modern broiler genotypes continue to improve, growing faster, leaner and with a capacity to develop large, protein- rich breast muscles. This is the high-value component of the broiler in many countries. It is known that high dietary protein levels stimulate its formation. Conversely, the broiler industry is being forced to consider its operations in terms of sustainability. High-protein diets negatively impact upon sustainability. They increase demand on scarce resources such as arable land and water and are responsible for pollution. High-protein diets cause elevated nitrogen levels in manure, which indirectly leads to gut health issues, wet litter and ultimately, ammonia production in broiler sheds. This has a negative impact on bird welfare. Nitrogen is a general pollutant leading to greenhouse gas production, eutrophication and soil acidification. Nitrogen levels in poultry manure are regulated in some countries. Nutritionists and producers are faced with a dilemma. They are required to feed high protein levels to ensure financial viability yet they risk being unsustainable with regards to the environment and welfare. This short article will examine these aspects.


nutritional requirement is for the constituent amino acids rather than protein per se. Nutritionists strive to feed broilers diets that contain a perfect amino acid balance, known as balanced proteins. A balanced protein meets the requirement for essential amino acids and provides sufficient amino nitrogen for the synthesis of non-essential amino acids. Should the true protein content of a diet be low, there is a possibility that some precursors of non-essential amino acids may be limiting, or that they can’t be synthesised fast enough to meet requirements for rapid growth (Alhotan and Pesti, 2016).


Reducing dietary protein levels The determination of essential amino acid requirements of broilers has been well researched and reasonable consensus has been reached. Our understanding of the requirements for non-essential amino acids, and for that matter for true protein, is limited. In our effort to reduce the crude protein levels of our diets, to both reduce costs


Figure 1: The performance 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)


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Bringing Different Perspectives to Nutrition


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PAGE 26 SEPTEMBER/OCTOBER 2018 FEED COMPOUNDER


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