N surpluses

It is generally accepted that the ways to reduce N excretion in animals by ways of nutrition include :

  • The amount of nitrogen that is consumed by the animal;
  • The digestibility of N that is consumed. This also includes the endogenous losses in the gastrointestinal (GI) tract;
  • The amino acid pattern of absorbed or available N.

Together these determine the efficiency by which dietary N is converted into animal products.

Reduction in amount of N consumed

The most obvious way is to reduce surplus of N-intake; this entails removal of the safety margin. It means that there can only be minor errors in feed preparation and in estimation of actual N content in the batch from which the feed is chosen. It also means that reliable and accurate data on AA composition or preferably AA availability should be known. The knowledge of and the use of data on ileal digestible or rather available amino acid in the diet is a possibility to increase the accuracy of diet composition. De Lange and Fuller (2000) argued that by using standardized true digestible amino acid of each feedstuff one can add these to obtain the total amount in the diet. A portion of the nitrogen excreted by the pig is a direct result of feeding excessive levels of nitrogen, the greater the excess, the greater the portion of N excreted. Results of surveys of the nutrient composition of diets indicate that diets commonly include excess amounts of certain AAs. If these are essential AAs these excesses are called a 'safety factor', which are included in the diet to allow for the variability of nutrient composition of feed ingredients, or to compensate for uncertainty about the availability and requirements of the nutrients. The typical range of university recommendations was 110-120% of the National Research Council (1998) recommendations, whereas the typical range of industry recommendations was 120-130% of these recommendations (Kornegay and Verstegen, 2001). The excess for the sows was a little lower than for finishing pigs. Other surveys have reported similar findings and that some safety is also included for poultry.

Use of highly digestible feedstuffs in diets

This is an effective means of reducing excretion of nitrogen and other nutrients. As cited by Van Heugten and Van Kempen (1999) and FEFANA (1992) it is estimated that nutrient excretion in waste could be reduced by about 5% (Kerr, 1996).

Enhancing biological value of dietary protein

This is a common practice in feed formulation. It is done by accounting for differences in available AA contents in different feedstuffs and also by adding crystalline AAs (Table 24.2). This means lowering the dietary protein level and supplementing with certain crystalline amino acids. This is a well-established method of formulating diets to achieve a more ideal amino acid pattern. In addition a diet with a well-balanced AA pattern is also very-effective in reducing nitrogen excretion. This can also be obtained by using a protein source with superior amino acid balance. If diets are formulated in this way one obtains a dietary protein closer to ideal protein. These diets will generally have a lower protein content and they form a basis to reduce the excretion of nitrogen and other nutrients. Both procedures (highly digestible protein and an AA acid pattern close to ideal) reduces excesses of not needed amino acids. These will otherwise be degraded and excreted as urea nitrogen.

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