INDU
BHUSAN
CHATTERJEE
221
second, and then by assuming that the digesti
bility of the first feed remains constant, the
value of the second is computed by difference,
i.e., by the method of elimination'. By a
similar process the values of the third or fourth
feed are obtained.
In the experiments conducted by Carbery,
Chatterjee and Hye [1934], it was pointed out
from actual tests that, when an incomplete
fodder like rice straw forms the sole feed, the
deficiency of nutrients in it is sometimes so
seriously reflected in the animal that the values
obtained cannot be valid for use in the calcula
tion, by difference, of the digestibility of asso
ciated feed or feeds. These difficulties prompt
ed those authors to design a comprehensive
experiment involving 18 individual tests in a
randomized cycle order and ultimately working
at the values directly by graphical method and
by regression equation.
While the theoretical background of the
method was beyond question, its main difficulty
lay in the large numbers of individual tests
involving a considerable outlay in men,
material, laboratory space and expense.
Moreover, the quantity of feed at disposal may
not always be sufficient for such an elaborate
test. This led to the approach to the problem
by a shorter method [Carbery and Chatterjee
1936] in which a simpler formula was worked
out on the basis of two individual tests, and
the data examined to arrive at a certain mini
mum standard of statistical accuracy. It was
found that, with feeds like rice straw and
linseed cake, a fair order of accuracy was en
sured with a replication of three to five in the
case of the majority of feed components.
It is not, however, possible by either of the
two methods to abtain the picture which an
individual animal may display, or which may
sometimes form the special feature in respect
to some particular animal or animals.
PRESENT METHOD
The method described here has originated
from these considerations. It aims at adjusting
the experimental procedure in such a way that
it may be possible to work out the values from
the data of a single animal. The fundamental
principal involved in calculation is the same,
viz. the application of multiple regression
equation in which, say,
R represents roughage,
C represents concentrate,
D represents amount digested,
while a and b are digestibility co-efficients of R
and C respectively.
Since R, C and D are numerical values, the
values of a and b can be worked out by simple
simultaneous equation [Carbery and Chatterjee
1936] or by multiple regression equation
[Carbery, Chatterjee and Hye, 1934] as is
given below:
a Σ R 2 + b Σ CR = Σ DR
a Σ CR + b Σ C 2 = Σ DC
Underlying principle
In the previous trials, the regression equation
was worked out, as already stated, with the
data of a number of animals. Each such datum
represented the mean of 10 days reduced to the
values of a single day. The modification now
suggested is based on the principle that, if
instead of taking the mean of ten or more days,
each day's performance of individual animals is
separately assembled, it will provide from the
source of a single animal as many single data as
the number of days used for their collection.
In other words if the number of experimental
days be regulated in due regard to statistical
requirement, the data obtained from each
animal can validly form the basic material for
the purpose of regression equation.
It is, however, necessary for facilitating the
numerical side of calculation that the individual
data from day to day should vary, otherwise
when the equation is worked out the values
of same or very nearly same magnitudes will
eliminate out.
In so far as the roughage is concerned, such
a probability is generally less so long as it is
fed ad lib. In the case of concentrates which,
the animal generally likes and eats whatever
is given, the best course is to fix the amount
(from day to day) on a random variation which
can be very conveniently worked out by a series
of varying factors applied on live weights.
This simplifies the calculation for individual
animals, as the same factors worked on differ
ent live weights would indicate the amounts to
be fed to individual animals.
The procedure used in the experiment under
report was drawn up in due regard to these
considerations. In order to enable the forma
tion of a clearer idea an instance of the data
used in the final calculation is given in the
following table.