The animal Article of the Month for October is entitled ‘Precursors for liver gluconeogenesis in periparturient dairy cows’

Balancing diets for transition dairy cows is a challenge due to limitations in our ability to delineate basic responses and interactions between energy and protein during the periparturient period. It has become dogma that amino acids are significant contributors to liver gluconeogenesis in early lactation presumably accounting for the observed lack of glucogenic precursors to balance estimated glucose need.

The review is based on a compiled data set from recent studies quantifying liver release of glucose concomitant with uptake of amino acids and other glucogenic precursors in periparturient dairy cows. The quantitative data on liver metabolism of amino acids do not support the hypothesis that the rapid post partum increase in liver release of glucose is supported by increased utilisation of amino acids for gluconeogenesis. Thus, the liver use of amino acids in the post partum transition period in general does not respond to decreased glucose status of the cows. Therefore, no amino acid sparing effect can be obtained by feeding more glucogenic diets to post partum transition dairy cows. Only alanine is likely to contribute to liver release of glucose through its role in the inter-organ transfer of nitrogen from catabolised amino acids.

Combining data from quantitative and qualitative experimental techniques on L-lactate metabolism, point to the conclusion that the quantitatively most important adaptation of metabolism to support the increased glucose demand in the immediate post partum period is endogenous recycling of glucogenic carbon through lactate. This is mediated by a dual site of adaptation of metabolism in the liver and in the peripheral tissues, where the liver affinity for L-lactate is increased and glucose metabolism in peripheral tissues is shifted towards L-lactate formation over complete oxidation.

In consequence of the limited glucogenic utilisation of amino acids, it seems that amino acids are prioritised for anabolic purposes, and hence, it is relevant to investigate effects of supplying additional protein to post partum dairy cows.

Until recently there has been paucity in quantitative data on liver nutrient metabolism in the periparturient period. Propionate is the quantitatively most important glucogenic precursor throughout the periparturient period. However, the immediate post partum increment in liver release of glucose is not followed by an equivalent increment in propionate uptake, due to the lower rate of increment in feed intake compared to the rate of increment in requirements for milk synthesis.

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Authors: M. Larsen and N. B. Kristensen

The animal Article of the Month is selected by the Editor-in-Chief and is freely available for one month.