Main breakthroughs in pig nutrition // 11 Jan 2010

 

Pig production has advanced remarkably over the past 30 years. Although much of this progress has been mediated by small but incremental improvements in production, sporadic but significant breakthroughs have accelerated this progress. Some of the significant breakthroughs are discussed below.

 

 

The concept of formulating pig diets containing an ideal balance of essential amino acids to maximise the efficiency of protein utilisation was first reported in detail by the Agricultural Research Council (1981). This concept was refined by Fuller and Wang (1990), who showed that the amino acid requirement for maintenance differs from that for protein deposition and that the actual requirement is a combination of these components. Chung and Baker (1992) subsequently demonstrated that the level of cystine and threonine required for an ideal amino acid balance increases with body weight because the maintenance requirement increases with increasing body weight and these amino acids are predominant components of the maintenance amino acid profile. This research established that the optimal balance of essential amino acids is not fixed but varies according to body weight. This approach replaced previous methods of protein quality assessment such as the protein efficiency ratio, net protein utilisation, nitrogen retention and biological value as a more meaningful way of ascribing a relative value to a protein source based on its ability to complement other protein sources in a diet formulated using least-cost linear programming. This concept also superseded the limiting amino acid approach to protein assessment, which had little practical application. The ideal protein concept advanced feed formulation efficiency by enabling rapid identification of the optimum nutritional density of the diet (or least cost per balanced energy unit) using parametric analysis in which energy density is varied but the balance of the 114 total diet is maintained by linking lysine to energy and secondary essential amino acids to lysine in the ideal protein ratio and by ensuring that there is an adequate pool of non-essential amino acids.

 

 

Description of nutrients in feedstuffs on an available basis evolved over a long period involving much debate and many progressive refinements and, to some extent, still remains a little ambiguous. However, it was a major step forward from the simplistic digestible protein concept that preceded it. Key developments included:

 

• The development of ileal digestibility values to replace faecal digestibility values to avoid the confounding effects of hind gut fermentation.

 

• The progression from apparent to true digestibility values to correct for the confounding effects of endogenous secretions.

 

• In vitro assays (predominantly for lysine) for estimating available amino acid content using chemically reactive components such as flurodintrobenzine, dye binding, guanidination and homoarginine. Of these assays, the “reactive lysine” assay involving the homoarginine technique has emerged as the most reliable (Rutherfurd et al., 1997).

 

• Recognition that digestibility does not necessarily equate to utilisation and the development of techniques to assess true biological availability, e.g., the slope ratio and indirect oxidation techniques.

 

• Because of the expense and laborious nature of in vivo tests, the general consensus at present is to consider “standardised ileal digestibility” synonymous with “availability”.

 

• Expression of the amino acid content of feedstuffs on an “available” basis facilitates meaningful economic comparison and formulation of diets that result in consistent performance.