Ileal digestibility of phenylalanine and tyrosine in piglets

Phenylalanine (Phe) and tyrosine (tyr) are indispensible amino acids for growth. Tyrosine can be provided directly by the diet or indirectly by biosynthesis from dietary Phe. The standardised ileal digestible (SID) Phe:Lys and Tyr:Lys requirements have not been determined experimentally in piglets.

INRA has conducted three experiments to estimate the response of piglets (10-20 kg bodyweight) offered diets with different levels of SID Phe:Lys (33, 39, 46, 52, 58 and 65%; experiment 1), SID Tyr: Lys (21, 27, 33, 39, 45 and 52%; experiment 2) and the effect of equimolar substitution of Tyr by Phe (50, 43 and 36% SID Tyr: (Phe:Tyr); experiment 3).

The estimated SID Phe:Lys and SID Tyr:Lys for maximising daily gain were 54 and 40% respectively, using a curvilinear-plated model. A 10% deficiency in Phe and Tyr reduced daily body weight gain by 3.0 and 0.7% respectively. The equimolar substitution of Tyr by Phe resulted in a reduced growth rate of about 10%.

In conclusion, it is recommended not to express the Tyr requirement as the sum of Phe and Tyr, but rather to use the specific ratios for each of these amino acids to maximize growth, i.e. 54% SID Phe:Lys and 40% SID Tyr:Lys.

This study was presented at the 2014 Journées Reserche Porcine (Swine Research Days), held in Paris, France.