Sulfur and Methionine Metabolism in Sheep. V. Utilization of Methionine Isomers

Doyle, PT

doi:10.1071/bi9810047

Cited by 5 publications

(3 citation statements)

References 29 publications

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“…High bioavailability of d-Met has been reported in mouse, rat, chick, rabbit, dog, and pig (see Lewis and Baker, 1995), with these usually assessed by comparison of N retention or weight gain obtained with the various enantiomers. Similarly, in sheep, a mixture of dl-Met or d-Met was as effective as l-Met to support wool growth (Doyle, 1981;Reis et al, 1989), although Doyle (1981) reported a trend toward lower S and N retention with d-versus l-Met supplementation. In cattle, postruminal infusion of dl-Met tended to result in a lower N retention than observed with l-Met supplementation (Titgemeyer and Merchen, 1990) but, in a second study, d-Met was 96% as efficient as l-Met in supporting N retention (Campbell et al, 1996).…”

Section: Studymentioning

confidence: 92%

“…For ruminants, data are scarce and somewhat equivocal. For example, in sheep, lower utilization of d-Met than l-Met has been reported for both N and S retention (Doyle, 1981) although they appear equally effective for support of wool growth (Doyle, 1981;Reis et al, 1989). In growing cattle, d-and l-Met produced similar increases in N retention (Campbell et al, 1996) although this tended to be lower with dl-Met infusion compared with an equimolar dose of l-Met (Titgemeyer and Merchen, 1990).…”

Section: Introductionmentioning

confidence: 99%

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Is d-methionine bioavailable to the dairy cow?

Lapierre

Holtrop

Calder

et al. 2012

Journal of Dairy Science

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Rumen-protected forms of Met contain an equimolar mixture of the D- and L-isomers. Only L-Met can be directly used for protein synthesis, but it is unclear how much of the D-isomer can be transformed into L-Met in ruminants. Four lactating dairy cows, with an average milk yield of 32.4 kg/d, received a basal diet (12.5% crude protein, supplying 1,718 g/d of metabolizable protein) in 12 equal meals per day plus an abomasal infusion of amino acids (590 g/d, casein profile without Met). They were used in 3 consecutive studies to determine utilization of D-Met. First, the cows each received portal vein infusions for d of 5, 10, or 15 g/d of DL-Met in a Youden square. On the last day of each period, 6 arterial samples were collected at 45-min intervals. Concentrations of L- and D-Met were determined on a chiral column by gas chromatography-mass spectrometry. Portal infusion of 5, 10, and 15 g/d of DL-Met increased plasma total Met concentrations (19.7, 25.0, and 34.4±0.6 μM) and the proportion of Met as D (19.4, 30.5, and 37.3±0.7%). The fractional removal of D-Met was 6 to 7 times lower than the fractional removal of L-Met, with mean half-lives of 52 versus 8 min, respectively. Second, the same cows were infused for 8 h with L[methyl-(2)H(3)]Met at 1.3 mmol/h; at 2 h, cows received a bolus injection i.v. of D-[1-(13)C]Met (6.8 mmol), and arterial samples were collected after 10, 20, 30, 40, 60, 90, 120, 150, 180, 240, 300, 360, 420, and 480 min. Expressed relative to L-[(12)C]Met; that is, as tracer:tracee ratios, enrichments of plasma D-[1-(13)C]Met and L-[1-(13)C]Met averaged 1.77±0.14 and 0.144±0.026, respectively, 10 min after the bolus injection and declined exponentially thereafter. A minimum of 75±3% of the D-[1-(13)C]Met was transformed into L-[1-(13)C]Met. Third, the cows received, in a crossover design, an abomasal infusion for D of either DL-Met or L-Met (1g/d) and, on the last day of each experimental period, blood samples were collected simultaneously from arterial, portal, hepatic, and mammary vessels. Arterial total Met concentrations were higher with DL- versus L-Met infusions (37.4 vs. 25.4±0.5 μM), with 37.1±5.0% as D-Met. The mammary gland did not extract any D-Met. Hepatic removal of D-Met was observed, but was numerically lower than the fractional extraction of L-Met. In conclusion, much of the D-Met is transformed into L-Met by the dairy cow but at a slow rate. No uptake of D-Met occurs across the mammary gland but L-Met synthesized from the D-isomer elsewhere in the body can be utilized for milk protein synthesis.

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Section: Studymentioning

confidence: 92%

Section: Introductionmentioning

confidence: 99%

Is d-methionine bioavailable to the dairy cow?

Lapierre

Holtrop

Calder

et al. 2012

Journal of Dairy Science

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“…D-Methionine was as effective as Lmethionine for stimulating the synthesis of the ultrahigh-sulphur proteins in wool (Broad, Gillespie & Reis, 1970). More recently, Doyle (1981) has found that L-, D-and DL-methionine were equally effective for enhancing wool growth and increasing the sulphur content of wool. There would now seem to be sufficient evidence to conclude that D-and L-methionine are equally effective for enhancing wool growth.…”

Section: Discussionmentioning

confidence: 97%

Incorporation of abomasal and intravenous doses of [³⁵S]cystine and [³⁵S]methionine into wool

Reis¹,

Tunks²,

Sharry³

1989

J. Agric. Sci.

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SummaryThe fate of abomasal and intravenous doses of [35S]cystine and [35S]methionine was investigated in sheep to determine their relative efficacy as supplements for wool growth.Administration of L-[35S]cystine and L-, DL- and D-[35S]methionine via the abomasum produced similar patterns of 35S labelling in blood plasma. Only 10–16% of the administered 35S was excreted in urine over 7 days and 22–32% of the dose was incorporated into wool over 21 days. All isomers were utilized by the sheep with similar efficiency and it was concluded that D- and L-methionine and L-cystine are equally effective as supplements for wool growth at optimal dose rates. Abomasal supplementation with a large amount of methionine (10 g/day) resulted in the excretion of a high proportion of the 35S in urine (55% of the dose over 7 days) and low incorporation into wool.A comparison of the extent of incorporation of 35S into wool from intravenous doses of L-[35S]cystine and L-[35S]methionine in the same sheep, and in sheep from flocks selected for high and low wool production, showed that incorporation from methionine averaged 80% of that from cystine. It was concluded that, at moderate (2–3 g/day) methionine availability, methionine is utilized for synthesis of wool with about 80% of the efficiency of cystine, conversion of methionine to cysteine occurring via the transulphuration pathway.

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