Investigation of the postruminal methionine requirement of growing lambs by using the indicator amino acid oxidation technique

Abstract

Methionine was demonstrated to be the most limiting amino acid for growing sheep when microbial protein is the predominant source of absorbable AA, but its specific requirement was not well quantified. The indicator amino acid oxidation (IAAO) method is based on the concept that when the most limiting amino acid (LAA) is deficient for protein synthesis, then all other AAs will be oxidized. With increasing intakes of the LAA, IAAO will decrease until the requirement for the LAA is met, and there is no further change in the indicator oxidation afterwards. Therefore, the catabolism of 13 C-Phe was used to indicate the effects of varying duodenal infusing levels of Met on the oxidation rate by 4-month-old Kazakh lambs (30.8 ± 0.4 kg BW). After a 6-d adaptation period, the IAAO test was conducted on d 7. Each lamb received a priming dose of 0.67 mg/kg BW of 13 C-Phe injected via the jugular vein, together with 0.18 mg/kg BW of NaH 13 CO 3 at time 0. Then, constant infusions [1.33 mg 13 C-Phe/(kg h) −1 ] were started. Breath samples were collected prior to and half-hourly between 90 and 210 min after the start of the 13 C-Phe infusions. An estimate of the mean Met requirement was determined by a breakpoint analysis of the rate of 13 CO 2 released by 13 C-Phe oxidation, with a 2-phase linear regression model. The oxidation rate of 13 C-Phe decreased (P < 0.001) with increasing amounts of methionine infused in a dose-dependent fashion up to 1.65 g/day, and it was not different from 1.65 to 2.15 g/day (P > 0.05). The mean Met requirement was estimated to be 1.28 ± 0.11 g/day of supplementation. The total postruminal minimum requirement of Met would be 2.02 g/day when the basal passage of Met (0.74 g/day) was summed.

Effects of Rumen-Protected Methionine Supplementation on Growth Performance, Nutrient Digestion, Nitrogen Utilisation and Plasma Amino Acid Profiles of Liaoning Cashmere Goats

“…When adequate energy is available, protein deposition shows a linear relationship with the supply of the most limiting AA, until another AA becomes more limiting [43]. Inconsistent results have been reported regarding the ability of RPM supplementation to render Met available for absorption in the small intestine [44,45]. However, the present study showed that Met was absorbed, which affected the utilisation of other AAs.…”

Determination of a steady-state isotope dilution protocol for carbon oxidation studies in the domestic cat

“…This less invasive approach was further supported in a following study (9) in which identical lysine requirement estimates were found in humans repeatedly fed 13 C-Phe or intravenously supplied 13 C-Phe. Since then, the IAAO technique has been broadly used under different states of health (10)(11)(12) and in different species (13)(14)(15)(16)(17) due to its noninvasive and highly sensitive nature.…”