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.

PJ, Back, SR Davis, DDS MacKenzie, PM Harris, NC Roy, and J Lee

Proceedings of the New Zealand Society of Animal Production, Volume 61, Christchurch, 144-147, 2001
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