Pigs fed diets deficient in tryptophan show reduced performance, especially due to reduced feed intake. L-Tryptophan, in general, became economical in swine diets due to the increased availability and reduced costs of feed-grade amino acids as replacement of intact proteins (i.e., soybean meal).

Recent studies suggest requirement estimates that range from 16.5 to 23.5% Standardized Ileal Digestible (SID) Trp to Lysine (Lys) ratio(1-4). A recent series of nine experiments, conducted with PIC 337 × 1050 in commercial research facilities, demonstrated that the optimum Trp to Lys ratio was greater than previously thought(5,6). For nursery and finishing pigs, Trp requirement is greater for average daily gain (ADG) compared to feed efficiency (F/G).

Figure 1. SID Trp:Lys ratio at different target performance levels as a percentage of optimum performance of nursery pigs.

In nursery pigs, diets formulated at 22% SID Trp:Lys are able to achieve 100% of optimum ADG and F/G (Figure 1). However, diets formulated at 19% are able to reach 98% of optimum ADG.

In turn, for finishing pigs, diets formulated at 18% SID Trp:Lys are able to reach 100% of optimum F/G and 96% of optimum ADG (Figure 2).

Figure 2. SID Trp:Lys ratio at different target performance levels as a percentage of optimum performance of finishing pigs.

The specific Trp:Lys level to be used will depend on the market scenario. However, economic models in multiple market scenarios suggest that there is a great reduction in the economic risk when formulating diets above 19% SID Trp:Lys for nursery and 18% SID Trp:Lys for finishing pigs. Therefore, the current recommendation is that diets should be formulated at least 19% SID Trp:Lys for nursery pigs and 18% SID Trp:Lys for finishing pigs.