ADVANCE THOUGHTS ON POULTRY NUTRITION
DEFINING NUTRIENT COMPOSITION AND INGREDIENT QUALITY
Poultry producers are continually looking for opportunities that allow more flexibility in both the types and the levels of feed in-gredients for use in feed formulations. Such opportunities are becoming increasingly frequent because of advances in nutrient analysis and feed evaluation techniques.
The principal role of feed ingredients is to provide the nutrients that the bird digests and utilizes for productive functions. Currently, considerable data are available on the ability of raw materials to supply these nutrients. However, a degree of variability is inherent to each raw material, and this places pressure on precise feed formulations.
Data on variation (or matrices) are available for the main feed ingredients and are applied in feed formulation programmes to achieve better precision. A related development is the availability of rapid tests, such as near-infrared reflectance analysis, to predict gross nutrient composition and assess the variability in ingredient supplies on an ongoing basis. It is recognized that not all the nutrients in ingredients are available for production purposes, and a portion of nutrients is excreted undigested or not utilized. As feed evaluation techniques develop, data have been accumulating on the availability of nutrients for poultry, especially of amino acids and phosphorus. For example, a recent development has been the wider use of digestible amino acid concentrations, rather than total amino acid concentrations, in feed formulations.
The use of digestible amino acid content is particularly relevant in developing countries, where highly digestible conventional ingredients are not available and diet formulations may include ingredients of low digestibility. Formulating diets based on digestible amino acids makes it possible to increase the range of ingredients that can be used and the inclusion levels of alternative ingredients in poultry diets. This improves the precision of formulation, may lower feed costs, and ensures more predictable bird performance.
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BETTER FEED FORMULATION
Once the nutritional needs are defined, the next step is to match these needs with combinations of ingredients and supplements. The object of formulation is to derive a balanced diet that provides appropriate quantities of biologically available nutrients. For commercial producers, a further object is to formulate a balanced diet at least cost. Given the range of possible feedstuffs and nu-trients needed, a large number of arithmetical calculations are required to produce a least-cost diet. Over the years, feed formu-lation has evolved from a simple balancing of a few feedstuffs for a limited number of nutrients to a linear programming system that operates with the aid of computers. Systems using stochastic non-linear programming are now becoming popular, with commercially available formulation software. Variability in ingredient composition is non-linear, so stochastic programmes address this issue in the most cost-effective manner possible.
A related development is the use of growth models to simulate feed intake and production parameters under given husbandry conditions. Such models are effective tools for: i) comparing actual versus potential performance, which can indicate the extent of management or health problems in a flock; and ii) providing economic analysis of alternative feeding regimens.
Several commercial growth models are available for predicting the production performance of both meat chickens and laying hens. However, because of the extreme complexity of biological responses, the models are only as good as the data used to establish them. There is a need for accurate and detailed information and data from a variety of production systems to enable the development of ro-bust models that can provide accurate prediction of performance
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