The
branched-chain amino acids (BCAA)
valine (Val) and
isoleucine (Ile) are considered to be among the next-limiting
amino acids for growth in piglets. In earlier studies, we estimated the standardized ileal digestible (
SID)
Val : Lys (
lysine) requirement to be at least 70%, whereas the Ile : Lys requirement may be as low as 50%. Because the BCAA partially share a common route of catabolism, the supply of one BCAA may affect the availability of the other BCAA. Four experiments were conducted to determine the response of 6-week-old piglets to the Val supply in relation to the other BCAA. A deficient supply of Val or Ile typically results in a reduction in average daily feed intake (ADFI). Experiment 1 was designed to determine the effect of a limiting Val supply, independent of the effect on feed intake. In a dose-response study using restrictively fed piglets,
nitrogen retention did not increase for an
SID Val : Lys supply greater than 64%. In the remaining experiments, piglets were offered feed ad libitum using ADFI, average daily gain (ADG) and gain-to-feed ratio as response criteria. The interaction between the Val and
leucine (Leu) was studied in Experiment 2 in a 2 × 2 factorial design (60% and 70%
SID Val : Lys, and 111% and 165%
SID Leu : Lys). Performance was considerably lower in piglets receiving 60%
Val : Lys compared with those receiving 70%
Val : Lys and was lowest in piglets receiving the diet with low Val and high Leu content. To further evaluate the interaction between Val and Leu, a dose-response study was carried out in which the response to Val supply was studied in combination with high Leu supply (165%
Leu : Lys). Using a curvilinear-plateau model, the average
SID Val : Lys requirement was 72%. However, low Val supply (60%
SID Val : Lys) reduced performance by 13% to 38%, which was much greater than what we observed in earlier studies. Experiment 4 was carried out to test the hypothesis that the Val requirement is not affected by low Ile supply (50%
SID Ile : Lys). Performance was not improved for
Val : Lys supplies greater than 65%, which may indicate that Ile (and not Lys) was second-limiting in this study. In conclusion, the first response of piglets to deficient Val supply appears to be a reduction in ADFI, rather than a reduction in ADG or
nitrogen retention. A large supply of Leu may not affect the Val requirement per se, but may aggravate the consequences of Val deficiency.