An in vitro alternative to the in sacco method to determine ruminal starch degradation
Abstract
Starch is a pivotal constituent of many ruminant feeds, serving as a key energy source. Determining its degradation
in the rumen is essential, as it enables to calculate the risk of acidosis and indirectly determines the
partitioning of energy digestion between the rumen and the intestine, thereby influencing nutrients intake. The
part of degradable starch in the rumen used to be determined on animals with the in sacco method. However,
societal demand on animal welfare led to the development of in vitro methods to determine ruminal degradation
of feeds, recognizing as well the significant cost and time savings offered by laboratory methods. An enzymatic
method was developed to estimate starch ruminal degradation and tested on 17 common concentrated feed used
in ruminant feeding (cereals, by-products, feed mixtures and legume seeds). Starch content of feed varied from
197 to 682 g/kg DM. The method consists of incubating dried and ground samples, at 60°C in buffer pH6 for
one hour with a Bacillus sp. alpha-amylase (10069, Sigma-Aldrich, France). Enzymatic starch degradation was
calculated as the ratio between the quantities of starch degraded (recovered from the residue after incubation) and
the initial starch content of feed. This enzymatic in vitro starch degradation was compared to the in sacco ruminal
degradation (assuming passage rate of 6%/h) of starch (ED6_St). ED6_St varied from 64% to 97% and enzymatic
degradation varied from 39 to 96%. The coefficient of determination between the enzymatic method and the
ED6_St was 69.9%, and the residual standard deviation was 6.3%. These first results are promising to obtain an
in vitro method to assess ruminal starch degradation. However, further tests are required to complete and validate
the method, including the incorporation of a broader array of feed types, such as forages.