Effects of insulin on amino acid uptake by the mammary gland of
the pasture-fed lactating ruminant
P.J. BACK, S.R. DAVIS, D.D.S. MACKENZIE, P.M. HARRIS, N.C. ROY
AND J. LEE
AgResearch Ltd., Grasslands, Palmerston North, New Zealand
E-Mail:
Proceedings of the New Zealand Society of Animal Production 2001. 61:
144-147
Twelve lactating ewes housed indoors were allocated to one of
two treatment groups (hyperinsulinaemic euglycaemic clamp (HEC) or
control) in a randomised block design experiment. Mammary amino acid
uptake from plasma and utilisation for milk protein synthesis was
measured during the fourth day of the HEC using the arterio-venous
concentration difference (A-V) technique. There was no change in milk
protein output during the HEC (P>0.05). The HEC induced a significant
decrease in arterial concentrations of all essential amino acids (EAA)
except for histidine and an increase in the extraction efficiency of
isoleucine (HEC, 61 ± 3% vs. control, 52 ± 3%, P<0.05)
and leucine (HEC, 64 ± 3% vs. control, 53 ± 3%,
P<0.05). There was no significant change in extraction efficiency of
other EAA or mammary blood flow. The ratio of amino acid uptake from
plasma to output in milk protein suggested deficits in uptake for some
EAA in both treatments, especially histidine. These results indicate
that the mammary gland can adapt to a changing arterial supply of amino
acids to maintain milk protein output by increasing extraction
efficiency and/or a greater reliance on amino acids supplied by
erythrocytes and/or plasma peptides.
Keywords: NZSAPAB;
insulin; amino acids; mammary; lactating; ruminant; pasture
Last Updated 7/08/01
