Application of a U-13C-labeled amino acid tracer in lactating dairy goats for simultaneous measurements of the flux of amino acids in plasma and the partition of amino acids to the mammary gland

B J Bequette, F R Backwell, Alexander Graham Calder, J A Metcalf, D E Beever, C MacRae, Gerald Lobley

Research output: Contribution to journalArticle

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Abstract

A preliminary study was conducted using lactating British Saanen goats (n = 5) at 109 to 213 d in milk that yielded 1.67 to 3.68 kg of milk/d to examine the application of a U-13C-labeled amino acid (AA) mixture obtained from hydrolyzed algal proteins as a tracer for measuring plasma flux (n = 5) and partition to the mammary gland (n = 3; arteriovenous difference) of 13 AA simultaneously. Except for Ile and Ser, there was incomplete (6 to 54%) equilibration of the tracer with AA from packed blood cells (> 90% erythrocytes) during the 6-h infusions. This result agreed with the large ratio of packed cells to gradients for plasma AA concentration that was also observed. However, net mass and isotope removals by the mammary gland were predominantly from plasma, indicating that the erythrocytes did not participate in kinetic exchanges. Plasma AA fluxes (millimoles per kilogram of metabolizable protein intake per kilogram of body weight 0.75) differed among goats that consumed different protein sources; however, overall rates were lowest for Met (5 to 14) and His (8 to 17) and highest for Leu (48 to 70) and Ala (53 to 88). On average, 25% of plasma flux was partitioned to the mammary gland. Less than 20% of His, Ser, Phe, and Ala were directed to the mammary gland; 20 to 30% of Arg, Thr, Tyr, and Leu were directed to the mammary gland; and 30 to 40% of Pro, Ile, Lys, and Val were directed to the mammary gland. The unidirectional AA flux in the mammary gland (AA apparently available for protein syntheses, oxidation, and metabolite formation) did not match the pattern that is required for casein synthesis, suggesting differences in the metabolic requirements of AA for nonmilk protein synthesis.
Original languageEnglish
Pages (from-to)2842-53
Number of pages12
JournalJournal of Dairy Science
Volume80
Issue number11
Publication statusPublished - 1 Nov 1997

Fingerprint

dairy goats
Human Mammary Glands
Goats
mammary glands
tracer techniques
Amino Acids
amino acids
algal proteins
erythrocytes
Algal Proteins
protein synthesis
goats
Milk
Proteins
Erythrocytes
milk
Saanen
amino acid requirements
protein hydrolysates
blood cells

Keywords

  • Amino Acids
  • Animals
  • Carbon Isotopes
  • Dietary Proteins
  • Erythrocytes
  • Female
  • Goats
  • Kinetics
  • Lactation
  • Mammary Glands, Animal
  • Milk Proteins
  • Protein Biosynthesis

Cite this

Application of a U-13C-labeled amino acid tracer in lactating dairy goats for simultaneous measurements of the flux of amino acids in plasma and the partition of amino acids to the mammary gland. / Bequette, B J; Backwell, F R; Calder, Alexander Graham; Metcalf, J A; Beever, D E; MacRae, C; Lobley, Gerald.

In: Journal of Dairy Science, Vol. 80, No. 11, 01.11.1997, p. 2842-53.

Research output: Contribution to journalArticle

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abstract = "A preliminary study was conducted using lactating British Saanen goats (n = 5) at 109 to 213 d in milk that yielded 1.67 to 3.68 kg of milk/d to examine the application of a U-13C-labeled amino acid (AA) mixture obtained from hydrolyzed algal proteins as a tracer for measuring plasma flux (n = 5) and partition to the mammary gland (n = 3; arteriovenous difference) of 13 AA simultaneously. Except for Ile and Ser, there was incomplete (6 to 54{\%}) equilibration of the tracer with AA from packed blood cells (> 90{\%} erythrocytes) during the 6-h infusions. This result agreed with the large ratio of packed cells to gradients for plasma AA concentration that was also observed. However, net mass and isotope removals by the mammary gland were predominantly from plasma, indicating that the erythrocytes did not participate in kinetic exchanges. Plasma AA fluxes (millimoles per kilogram of metabolizable protein intake per kilogram of body weight 0.75) differed among goats that consumed different protein sources; however, overall rates were lowest for Met (5 to 14) and His (8 to 17) and highest for Leu (48 to 70) and Ala (53 to 88). On average, 25{\%} of plasma flux was partitioned to the mammary gland. Less than 20{\%} of His, Ser, Phe, and Ala were directed to the mammary gland; 20 to 30{\%} of Arg, Thr, Tyr, and Leu were directed to the mammary gland; and 30 to 40{\%} of Pro, Ile, Lys, and Val were directed to the mammary gland. The unidirectional AA flux in the mammary gland (AA apparently available for protein syntheses, oxidation, and metabolite formation) did not match the pattern that is required for casein synthesis, suggesting differences in the metabolic requirements of AA for nonmilk protein synthesis.",
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T1 - Application of a U-13C-labeled amino acid tracer in lactating dairy goats for simultaneous measurements of the flux of amino acids in plasma and the partition of amino acids to the mammary gland

AU - Bequette, B J

AU - Backwell, F R

AU - Calder, Alexander Graham

AU - Metcalf, J A

AU - Beever, D E

AU - MacRae, C

AU - Lobley, Gerald

PY - 1997/11/1

Y1 - 1997/11/1

N2 - A preliminary study was conducted using lactating British Saanen goats (n = 5) at 109 to 213 d in milk that yielded 1.67 to 3.68 kg of milk/d to examine the application of a U-13C-labeled amino acid (AA) mixture obtained from hydrolyzed algal proteins as a tracer for measuring plasma flux (n = 5) and partition to the mammary gland (n = 3; arteriovenous difference) of 13 AA simultaneously. Except for Ile and Ser, there was incomplete (6 to 54%) equilibration of the tracer with AA from packed blood cells (> 90% erythrocytes) during the 6-h infusions. This result agreed with the large ratio of packed cells to gradients for plasma AA concentration that was also observed. However, net mass and isotope removals by the mammary gland were predominantly from plasma, indicating that the erythrocytes did not participate in kinetic exchanges. Plasma AA fluxes (millimoles per kilogram of metabolizable protein intake per kilogram of body weight 0.75) differed among goats that consumed different protein sources; however, overall rates were lowest for Met (5 to 14) and His (8 to 17) and highest for Leu (48 to 70) and Ala (53 to 88). On average, 25% of plasma flux was partitioned to the mammary gland. Less than 20% of His, Ser, Phe, and Ala were directed to the mammary gland; 20 to 30% of Arg, Thr, Tyr, and Leu were directed to the mammary gland; and 30 to 40% of Pro, Ile, Lys, and Val were directed to the mammary gland. The unidirectional AA flux in the mammary gland (AA apparently available for protein syntheses, oxidation, and metabolite formation) did not match the pattern that is required for casein synthesis, suggesting differences in the metabolic requirements of AA for nonmilk protein synthesis.

AB - A preliminary study was conducted using lactating British Saanen goats (n = 5) at 109 to 213 d in milk that yielded 1.67 to 3.68 kg of milk/d to examine the application of a U-13C-labeled amino acid (AA) mixture obtained from hydrolyzed algal proteins as a tracer for measuring plasma flux (n = 5) and partition to the mammary gland (n = 3; arteriovenous difference) of 13 AA simultaneously. Except for Ile and Ser, there was incomplete (6 to 54%) equilibration of the tracer with AA from packed blood cells (> 90% erythrocytes) during the 6-h infusions. This result agreed with the large ratio of packed cells to gradients for plasma AA concentration that was also observed. However, net mass and isotope removals by the mammary gland were predominantly from plasma, indicating that the erythrocytes did not participate in kinetic exchanges. Plasma AA fluxes (millimoles per kilogram of metabolizable protein intake per kilogram of body weight 0.75) differed among goats that consumed different protein sources; however, overall rates were lowest for Met (5 to 14) and His (8 to 17) and highest for Leu (48 to 70) and Ala (53 to 88). On average, 25% of plasma flux was partitioned to the mammary gland. Less than 20% of His, Ser, Phe, and Ala were directed to the mammary gland; 20 to 30% of Arg, Thr, Tyr, and Leu were directed to the mammary gland; and 30 to 40% of Pro, Ile, Lys, and Val were directed to the mammary gland. The unidirectional AA flux in the mammary gland (AA apparently available for protein syntheses, oxidation, and metabolite formation) did not match the pattern that is required for casein synthesis, suggesting differences in the metabolic requirements of AA for nonmilk protein synthesis.

KW - Amino Acids

KW - Animals

KW - Carbon Isotopes

KW - Dietary Proteins

KW - Erythrocytes

KW - Female

KW - Goats

KW - Kinetics

KW - Lactation

KW - Mammary Glands, Animal

KW - Milk Proteins

KW - Protein Biosynthesis

M3 - Article

VL - 80

SP - 2842

EP - 2853

JO - Journal of Dairy Science

JF - Journal of Dairy Science

SN - 0022-0302

IS - 11

ER -