WHEN cows chew the cud, they get unexpected help from the grass they鈥檝e just
eaten. It kickstarts the digestion鈥攖he plant equivalent of committing
suicide. The finding may lead to ways of making cattle convert food more
efficiently.
Mike Theodorou and Alison Kingston-Smith of the Institute of Grassland and
Environmental Research, part of the University of Wales in Aberystwyth, have
shown that within dying plant cells, powerful enzymes called proteases break
down proteins in grass, liberating amino acids.
The process occurs in the rumen, part of the cow鈥檚 stomach that softens up
and ferments grass. Only when the mush passes into the true stomach鈥攖he
abomasum鈥攄oes the cow begin to digest the amino acids, converting them
into milk and meat.
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Theodorou and Kingston-Smith made models of the rumen, one containing the
usual microorganisms and one sterilised. Yet the grass was equally well digested
at the end of the experiment, showing that the microorganisms weren鈥檛
needed.
Theodorou says that farmers may be able to use the finding to control the
speed of digestion. If the process goes too fast, the amino acids are turned
into useless urea and ammonia. Breeding grass with low levels of proteases will
slow it up, says Kingston-Smith, turning more of the amino acids into meat and
milk. The results will appear in the Journal of Dairy Science.