STUDIES ON THE DETERMINATION OF
DIGESTIBILITY
COEFFICIENTS:
95
The divergencies are naturally indicative of both high and low rates of diges-
tion, the higher values sometimes working out above cent per cent and the lower
ones receding into negative values.
If we compare the standard deviations in relation to the procedure of cal-
culations by the three different groupings, viz., 1 lb. and 2 lb., 1 lb. and 3 lb. and
2 lb. and 3 lb., we note that in the midst of all the divergencies, the standard
deviations with respect to the calculations under 1 lb. and 3 lb. grouping, have
been uniformly low, except in one solitary instance of crude fibre under cake.
It might be noted here that the difference in the amount of cake consumed is
largest in the case of 1 and 3 lb. as compared to 1 and 2 lb. or 2 and 3 lb. This
might partially account for the low error, as in the estimate of digested amount
(the equation being on a linear basis) a given error in the slope representing diges-
tibility will necessarily be reduced when such difference is greater.
It need hardly be stated here that the figures have been worked out from
the data of an experiment where every attempt was made to obtain reasonable
uniformity in the selection of the animals, regarding age, live weights, feeding
and other treatments. Yet it is very difficult from the very nature of the animals
to maintain a strict order of uniformity. In other words there is bound to be some
difference due to variation amongst the animals. The standard deviations in
columns 5 and 8 in Table III, thus represent the total variability arising out of
(1) experimental errors and (2) variations amongst the animals. As already
stated, the standard deviations of some particular components such as crude
protein of paddy straw and crude fibre of linseed cake are enormously high. As
the experimental order of procedure was identical in all, the experimental errors
are also expected to be of an identical order. It is unlikely that in these cases
alone the experimental errors were particularly high. Assuming, therefore, a more
or less similar order of experimental error, it may be tentatively suggested that
the digestibility coefficients with regard to these components are more susceptible
to variation than those of others. But unless the extent of this susceptibility is
brought within the range of measurable estimation, it is bound to affect the
accuracy in proportion to the degree of such susceptibility. To that extent the
values obtained will necessarily be affected. Yet, until we have some means to
eliminate such variability, we have to proceed on an assumption that the
behavior of the animals is uniform. This assumption is as much implicit in the
already prevailing method of computation as it is in the one now suggested.
It is obvious that if there is a mathematical uniformity in the process of
digestion, the application of the equation (formulae 3 and 4) is fully justifiable and
the results obtained even from a single animal would be fully dependable. Since
however, strict uniformity in animals is out of the question in actual practice,
the only alternative, as has been stated before is to replicate the experiment
adequately in order that the mean values so obtained are dependable.
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