Roll out the Barrel (and stave)!

October 18, 2021 Issue

At the recent NASEM 2021, Dr. Mark Hanigan discussed the efficiency of milk protein production. For years we have considered the barrel and staves analogy for limiting nutrients in diet formulation. In this single limiting nutrient theory, the lowest stave determines the water level in the barrel or the limiting nutrient for milk production or milk component production. If supply exceeds the lowest stave, water flows out and nutrients will be wasted. In the case of amino acids, the barrel and stave analogy not only establishes the most limiting amino acid, but also the order of limitation.

Hanigan says, “milk responses to individual EAA (Essential Amino Acids) requires a new approach”. He suggests that there is no exact dietary requirement and no such thing as an order of limitation. The efficiency of milk protein production is variable. From field experience and research studies, milk protein production responds to individual EAA supplies, energy supply and hormonal signals. Regressions in trials based on feeding multiple amino acids are much superior to single amino acid responses. Calculations from these regressions increase the accuracy of milk protein yield predictions.

Hanigan proposes a new analogy. The barrel is not spilling over and there is plenty of substrates available. There is no such thing as a first limiting nutrient. Instead, as we add nutrients, we reduce the size of the holes in the barrel and enhance the efficiency of milk protein production.

To help you understand this analogy we have prepared a calculator. This tool calculates the total EAA supply, limiting EAA (lys + met + his) and mTor EAA (arg + thr + leu + ile + met). Stimulation of mTor signalling is a driver of milk production.

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Barrel and Stave Analogy