The THR requirement in early (35–53d),mid- (63-70d) and late (92–110d)
gestation was determined by indicator amino acid (IAAO) oxidation in six
second parity sows fed THR from 60 % to 150 % of NRC (1998) estimated
requirements. L[1-13C]phenylalanine was given orally at 30 min intervals for 8
meals and expired 13CO2 was quantified. The nonlinear Mixed model in SAS
was used to determine the THR requirement for each period by breakpoint
analysis. Plasma THR was also used to estimate requirement.
Sows responded differently to increasing levels of dietary THR in early and
late gestation. Preliminary breakpoint analysis resulted in a THR requirement
of 6.1 g/d in early gestation (R2=0.59), 7.0 g/d in mid gestation (R2=0.55) and
13.6 g/d in late gestation (R2=0.56). The THR requirement based on plasma
THR was 7.2 g/d (R2=0.90) in early gestation and 14.0 g/d (R2=0.76) in late
gestation. The current recommended THR intake during gestation is 10 g/d.