Amino Acid Availability in Feedstuffs for the Growing Pig

Assessing amino acid (AA) availability in dietary ingredients is integral to the optimal formulation of diets both in terms of maximising nutrient utilization and profitability. Although the concept that nutrients in feedstuffs are not fully absorbed and metabolized by the animal is now widely accepted, a distinction needs to be made between the concepts of digestibility and availability. Digestibility is often referred to as the uptake of an AA from the gut, whereas availability is usually defmed as the degree of uptake and subsequent utilization of the AA for protein synthesis and other anabolic processes. Amino acid availability is a complex phenomenon affected by many interacting factors. For most AAs availability will digestibility, but there is likely to be some discrepancy between digestibility and availability, particularly for the amino acid lysine in heat-treated foods (Moughan 1989). Although the following discussion will place emphasis on aspects of AA digestibility, the availability of absorbed AA’s will also be considered with reference to heat-treated feed ingredients. The application of AA digestibility data, particularly in relation to diet formulation is stressed.