Kinetics of blood free and milk casein-amino acid labelling in the dairy goat at two stages of lactation

B J Bequette, F R Backwell, M S Dhanoa, A. Walker, Alexander Graham Calder, D Wray-Cahen, J A Metcalf, J D Sutton, D E Beever, Gerald Lobley

Research output: Contribution to journalArticle

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Abstract

The kinetics of blood free amino acids (AA) transfer into milk casein were compared in goats (n 4) at 61 (SE 5) d (Expt 1; post-peak, 4.51 (SE 0.26) kg milk/d) and at 180 (SE 6) d (Expt 2; late, 2.36 (SE 0.16) kg milk/d) of lactation during non-primed, continuous (Expt 1, 12 h; Expt 2, 16 h) intravenous infusions of mixtures of L-[1-13C]leucine and L-[1-13C]phenylalanine with either L-[1-13C]valine (Expt 1) or L-[5-13C]methionine (Expt 2). The 13C enrichments of blood free and casein-bound AA were fitted to a single exponential model to estimate isotopic plateaux and the fractional rate constant for milk casein labelling. Milk protein output and its contribution to whole-body flux was higher in Expt 1 (post-peak) than in Expt 2 (late lactation), but the kinetics of 13C labelling of the casein-bound AA were similar for all AA tracers in both experiments. At both stages of lactation the delay (6-8 h) between the attainment of isotopic plateau for the blood free AA and the corresponding attainment of plateau for the casein-bound AA indicated that the blood free pool was not the immediate precursor pool for milk casein biosynthesis. Plateau enrichments of casein-bound AA were generally higher than those for the corresponding blood free AA in both experiments. These results indicate that the relative contributions of different AA sources to the immediate precursor pool for milk casein biosynthesis are similar at different stages of lactation despite major changes in the partitioning of whole-body flux towards milk protein output. Non-milk protein fluxes were also similar in post-peak and late lactation.
Original languageEnglish
Pages (from-to)211-20
Number of pages10
JournalBritish Journal of Nutrition
Volume72
Issue number2
Publication statusPublished - 1 Aug 1994

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Caseins
Lactation
Goats
Milk
Amino Acids
Milk Proteins
Valine
Phenylalanine
Intravenous Infusions
Leucine
Methionine

Keywords

  • Amino Acids
  • Animals
  • Caseins
  • Female
  • Gestational Age
  • Goats
  • Lactation
  • Leucine
  • Methionine
  • Milk
  • Milk Proteins
  • Phenylalanine
  • Pregnancy
  • Proteins
  • Valine

Cite this

Bequette, B. J., Backwell, F. R., Dhanoa, M. S., Walker, A., Calder, A. G., Wray-Cahen, D., ... Lobley, G. (1994). Kinetics of blood free and milk casein-amino acid labelling in the dairy goat at two stages of lactation. British Journal of Nutrition, 72(2), 211-20.

Kinetics of blood free and milk casein-amino acid labelling in the dairy goat at two stages of lactation. / Bequette, B J; Backwell, F R; Dhanoa, M S; Walker, A.; Calder, Alexander Graham; Wray-Cahen, D; Metcalf, J A; Sutton, J D; Beever, D E; Lobley, Gerald.

In: British Journal of Nutrition, Vol. 72, No. 2, 01.08.1994, p. 211-20.

Research output: Contribution to journalArticle

Bequette, BJ, Backwell, FR, Dhanoa, MS, Walker, A, Calder, AG, Wray-Cahen, D, Metcalf, JA, Sutton, JD, Beever, DE & Lobley, G 1994, 'Kinetics of blood free and milk casein-amino acid labelling in the dairy goat at two stages of lactation', British Journal of Nutrition, vol. 72, no. 2, pp. 211-20.
Bequette BJ, Backwell FR, Dhanoa MS, Walker A, Calder AG, Wray-Cahen D et al. Kinetics of blood free and milk casein-amino acid labelling in the dairy goat at two stages of lactation. British Journal of Nutrition. 1994 Aug 1;72(2):211-20.
Bequette, B J ; Backwell, F R ; Dhanoa, M S ; Walker, A. ; Calder, Alexander Graham ; Wray-Cahen, D ; Metcalf, J A ; Sutton, J D ; Beever, D E ; Lobley, Gerald. / Kinetics of blood free and milk casein-amino acid labelling in the dairy goat at two stages of lactation. In: British Journal of Nutrition. 1994 ; Vol. 72, No. 2. pp. 211-20.
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abstract = "The kinetics of blood free amino acids (AA) transfer into milk casein were compared in goats (n 4) at 61 (SE 5) d (Expt 1; post-peak, 4.51 (SE 0.26) kg milk/d) and at 180 (SE 6) d (Expt 2; late, 2.36 (SE 0.16) kg milk/d) of lactation during non-primed, continuous (Expt 1, 12 h; Expt 2, 16 h) intravenous infusions of mixtures of L-[1-13C]leucine and L-[1-13C]phenylalanine with either L-[1-13C]valine (Expt 1) or L-[5-13C]methionine (Expt 2). The 13C enrichments of blood free and casein-bound AA were fitted to a single exponential model to estimate isotopic plateaux and the fractional rate constant for milk casein labelling. Milk protein output and its contribution to whole-body flux was higher in Expt 1 (post-peak) than in Expt 2 (late lactation), but the kinetics of 13C labelling of the casein-bound AA were similar for all AA tracers in both experiments. At both stages of lactation the delay (6-8 h) between the attainment of isotopic plateau for the blood free AA and the corresponding attainment of plateau for the casein-bound AA indicated that the blood free pool was not the immediate precursor pool for milk casein biosynthesis. Plateau enrichments of casein-bound AA were generally higher than those for the corresponding blood free AA in both experiments. These results indicate that the relative contributions of different AA sources to the immediate precursor pool for milk casein biosynthesis are similar at different stages of lactation despite major changes in the partitioning of whole-body flux towards milk protein output. Non-milk protein fluxes were also similar in post-peak and late lactation.",
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T1 - Kinetics of blood free and milk casein-amino acid labelling in the dairy goat at two stages of lactation

AU - Bequette, B J

AU - Backwell, F R

AU - Dhanoa, M S

AU - Walker, A.

AU - Calder, Alexander Graham

AU - Wray-Cahen, D

AU - Metcalf, J A

AU - Sutton, J D

AU - Beever, D E

AU - Lobley, Gerald

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N2 - The kinetics of blood free amino acids (AA) transfer into milk casein were compared in goats (n 4) at 61 (SE 5) d (Expt 1; post-peak, 4.51 (SE 0.26) kg milk/d) and at 180 (SE 6) d (Expt 2; late, 2.36 (SE 0.16) kg milk/d) of lactation during non-primed, continuous (Expt 1, 12 h; Expt 2, 16 h) intravenous infusions of mixtures of L-[1-13C]leucine and L-[1-13C]phenylalanine with either L-[1-13C]valine (Expt 1) or L-[5-13C]methionine (Expt 2). The 13C enrichments of blood free and casein-bound AA were fitted to a single exponential model to estimate isotopic plateaux and the fractional rate constant for milk casein labelling. Milk protein output and its contribution to whole-body flux was higher in Expt 1 (post-peak) than in Expt 2 (late lactation), but the kinetics of 13C labelling of the casein-bound AA were similar for all AA tracers in both experiments. At both stages of lactation the delay (6-8 h) between the attainment of isotopic plateau for the blood free AA and the corresponding attainment of plateau for the casein-bound AA indicated that the blood free pool was not the immediate precursor pool for milk casein biosynthesis. Plateau enrichments of casein-bound AA were generally higher than those for the corresponding blood free AA in both experiments. These results indicate that the relative contributions of different AA sources to the immediate precursor pool for milk casein biosynthesis are similar at different stages of lactation despite major changes in the partitioning of whole-body flux towards milk protein output. Non-milk protein fluxes were also similar in post-peak and late lactation.

AB - The kinetics of blood free amino acids (AA) transfer into milk casein were compared in goats (n 4) at 61 (SE 5) d (Expt 1; post-peak, 4.51 (SE 0.26) kg milk/d) and at 180 (SE 6) d (Expt 2; late, 2.36 (SE 0.16) kg milk/d) of lactation during non-primed, continuous (Expt 1, 12 h; Expt 2, 16 h) intravenous infusions of mixtures of L-[1-13C]leucine and L-[1-13C]phenylalanine with either L-[1-13C]valine (Expt 1) or L-[5-13C]methionine (Expt 2). The 13C enrichments of blood free and casein-bound AA were fitted to a single exponential model to estimate isotopic plateaux and the fractional rate constant for milk casein labelling. Milk protein output and its contribution to whole-body flux was higher in Expt 1 (post-peak) than in Expt 2 (late lactation), but the kinetics of 13C labelling of the casein-bound AA were similar for all AA tracers in both experiments. At both stages of lactation the delay (6-8 h) between the attainment of isotopic plateau for the blood free AA and the corresponding attainment of plateau for the casein-bound AA indicated that the blood free pool was not the immediate precursor pool for milk casein biosynthesis. Plateau enrichments of casein-bound AA were generally higher than those for the corresponding blood free AA in both experiments. These results indicate that the relative contributions of different AA sources to the immediate precursor pool for milk casein biosynthesis are similar at different stages of lactation despite major changes in the partitioning of whole-body flux towards milk protein output. Non-milk protein fluxes were also similar in post-peak and late lactation.

KW - Amino Acids

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KW - Caseins

KW - Female

KW - Gestational Age

KW - Goats

KW - Lactation

KW - Leucine

KW - Methionine

KW - Milk

KW - Milk Proteins

KW - Phenylalanine

KW - Pregnancy

KW - Proteins

KW - Valine

M3 - Article

VL - 72

SP - 211

EP - 220

JO - British Journal of Nutrition

JF - British Journal of Nutrition

SN - 0007-1145

IS - 2

ER -