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Clarification regarding in vitro digestion of whole crops
Dear foragers!
Based on some replies that I received, I guess I should have been more clear
stating the problem of using the Tilley and Terry method for digesting
herbage of whole crops.
We have problems repeating results when digesting fresh whole-maize and fresh
whole-wheat. The lack of repeatability occurs within samples, within growing
season and among growing seasons. In ring tests between three laboratories in
Denmark, there has been more variation in digestibility of fresh whole crops
compared with whole-crop silage and herbage and silage of conventional
forages (mainly ryegrass or ryegrass-white clover mixtures). The standard
deviation between duplicate samples was as high as 6% for whole-maize herbage
compared with 2 to 3% for conventional forage.
The in vitro method is standardized and cows receive one third concentrate
and two thirds hay. The feeding of hay, whole-wheat silage, or whole-maize
silage also has been compared when digesting fresh whole-crop samples
according to Tilley and Terry. We did not find any consistent improvement in
in vitro results by using whole-crops in the standard diet. It would have
been nice to use fresh whole-crops in the standard ration, but obviously this
is not manageable. In vitro results are calibrated with samples from in vivo
trials in which sheep are used. By using sheep, we reduce costs and we can
study more samples each year.
We do not necessarily think that the Tilley and Terry method is wrong to use,
because the variation in in vitro results for herbage of whole crops has not
worsened over the years. It is just that farmers demand better methods for
predicting energy concentration of forages before and after ensilage.
Sincerely,
Christer Ohlsson
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Christer Ohlsson, Senior scientist
Department of Forage Crops and Potatoes
Research Centre Foulum
P.O. Box 21
DK-8830 Tjele, Denmark
Phone: +45-89991833
Fax: +45-89991839
Present E-mail: CO%AFGK%Plante1@Foulum.min.dk
New E-mail (from 25 April, 1996): CMO@AFGK.SP.DK
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