Methionine to cystine ratio in the total sulfur amino acid requirements and sulfur amino acid metabolism using labelled amino acid approach for broilers

Abstract

BackgroundAssuming that part of Methionine (Met) is converted into Cystine (Cys), but ignoring the rates with which such phenomenon occurs may lead to an excessive supply of Met in poultry diets. Such inconvenient could be easily avoided with the knowledge of the ideal Met:Cys/Total sulfur amino acids (TSAA) ratio and the rates of Met conversion into Cys.ResultsMet sources did not affect performance. Met:Cys/TSAA ideal ratio was determined using curvilinear-plateau regression model. Both optimum body weight gain and feed conversion ratio were estimated in 1007 g/day and 1.49, respectively, at 52% Met/TSAA ratio. Feed intake was not affected by Met:Cys/TSAA ratios. In the labelled amino acid assay, the rates with which Met was converted into Cys ranged from 27 to 43% in response to changes in Met:Cys/TSAA ratios, being higher at 56:44.ConclusionBased on performance outcomes, the minimum concentration of Met relative to Cys in diets for broilers from 14 to 28 d of age based on a TSAA basis, is 52% (52:48 Met:Cys/TSAA). The outcomes from labelled amino acid assay indicate that highest the Met supply in diets, the highest is its conversion into Cys.

Efficiency of methionine and cystine utilization by broiler chickens using stable isotopes

“…These data were then applied to the equation proposed by Nose (1992) which was first used to determine coefficients of apparent digestibility in fish. Although it was not possible to measure the amount of Met converted to Cys using this methodology, this value could be deduced from Met amount instead of the efficiency of Cys utilization (Pacheco et al, 2018). It is worth highlighting that unlike markers, biological tracers such as stable isotopes participate in biological reactions, which enables one to determine the efficiency of amino acid utilization in different compartments (e.g.…”

“…The amount of Met converted into Cys and intermediates was calculated based on labelled amino acid content in body and feathers, as described by Pacheco et al (2018). The 15 N efficiency (Equation 2) was calculated as follows (adapted from Nose, 1992):…”

“…Methionine is converted into cysteine, and the latter into cystine (Cys), and these conversion rates remain controversial. In a previous study, we determined the rate of Met to Cys conversion (Pacheco et al, 2018). Although universally used, this strategy should be reconsidered, since attempting to supply adequate amounts of Cys may result in excessive amounts of Met.…”

“…Although universally used, this strategy should be reconsidered, since attempting to supply adequate amounts of Cys may result in excessive amounts of Met. In a previous study, we determined the rate of Met to Cys conversion (Pacheco et al, 2018). Next, our goal was to determine Met and Cys efficiencies separately.…”

“…Moreover, we believe that Met conversion is taken into account in amino acid utilization thanks to the association of aminogram and stable isotope analysis. Although it was not possible to measure the amount of Met converted to Cys using this methodology, this value could be deduced from Met amount instead of the efficiency of Cys utilization(Pacheco et al, 2018).…”