ORIGINAL ARTICLES
STUDIES ON PROTEIN METABOLISM
I. INVESTIGATIONS UPON THE ENDOGENOUS NITROGEN METABOLISM OF CATTLE
By NARAIN DAS KEHAR, R. MUKHERJEE and K. C. SEN, Animal Nutrition Section, Imperial
Veterinary Research Institute, Izatnagar
(Received for publication on 12 December 1942)
A KNOWLEDGE of the nutritive value of proteins
of different feeds is necessary for utilizing the avail-
able supplies to the best advantage. This is
specially desirable in this country where the ration
of cattle consists mainly of straws, with little or
no concentrates. The first step in the determina-
tion of the quality of dietary proteins according
to the Thomas-Mitchell method is the estimation
of the endogenous urinary nitrogen and metabolic
faecal nitrogen. The former is the minimum
constant level of urinary nitrogen output attained
by animals after prolonged subsistence on a nitro-
gen-free, but otherwise adequate, diet. For the
successful determination of its value for bovines,
one is confronted with the very difficult task of
devising a nitrogen-free ration, adequate in all
respects including the roughage content, and feed-
ing the animals required amounts of this ration for
a sufficiently long period. The observations of
some workers [Hart et al., 1912; Bull and Grind-
ley, 1919; Honcamp et al., 1923; and Hutchin-
son and Morris, 1936] who attempted such investi-
gations on bovines are not very satisfactory, as the
rations fed by them were not sufficiently low in
nitrogen; in some cases the experimental ration
was fed for an insufficient duration. In the present
investigation, attempts have been made to study
the endogenous nitrogen metabolism of Indian
bullocks fed on a very low nitrogen ration for a
prolonged period.
EXPERIMENTAL METHODS
For studying the endogenous nitrogen metabo-
lism, the ration should contain either all the diges-
tible nitrogen in an entirely utilizable state or no
nitrogen at all. It is, however, difficult at this
stage of our knowledge on the protein metabolism
of cattle to compute a ration, which will satisfy the
former condition. It seems essential, therefore,
to use a ration as free from nitrogen as possible
under practical feeding conditions.
(i) Roughage. In devising a nitrogen-free ration
for cattle, the chief difficulty was encountered in
the supply of a nitrogen-free roughage. The high
cost of regenerated cellulose and agar-agar and
the frequent impaction of rumen caused by paper
pulp [Hutchinson and Morris, 1936] precluded their
use. Bagasse, which is very poor in crude protein
(about 1 per cent on dry basis) and is occasionally
eaten by animals, was considered as a suitable
roughage, provided its protein content was further
reduced. Various processes, which included the
treatment of bagasse with sodium chloride, sodium
carbonate, sodium hydroxide, hydrochloric acid
and sulphuric acid at different temperatures and
in various concentrations, were tried. In a num-
ber of trials, the desired denitrification could not
be effected, while in others, though the nitrogen
content was reduced to a very low level, a pulpy
mass was obtained which formed into hard balls
on drying, thus rendering it unsuitable for feeding.
The best method, one which reduced the amount
of crude protein to 0.08 per cent and did not affect
the texture, proved to be the soaking of bagasse
in eight times its weight of 5 per cent sodium hy-
droxide solution for 24 hours, prior to its boiling
for three hours. The mass was thoroughly
washed several times with water, and then once
with a 0.1 per cent solution of hydrochloric acid.
The material was finally washed with water to free
it from the last traces of acid. This was then dried
and separated into shreds. In the low-N ration
untreated wheat bhusa or cold alkali-treated wheat
bhusa was used instead of hot alkali-treated bagasse.
The method of treatment in this case was similar
to that adopted by Beckmann et al. [1919] and
consisted in soaking the straw with eight times its
weight of 1.25 per cent caustic soda for 24 hours,
washing it free from alkali and drying in the sun.
(ii) Concentrates. It was considered that starch,
which has in recent years been used by Smuts
[1935] and Smuts and Marais [1938] for sheep, and
by Hutchinson and Morris [1936] for cows, would
form a suitable concentrate for animal require-
ments, but in an exploratory experiment on two
bullocks it was found that the animals developed
an apathy for starch after a few days of feeding.
Even dextrinized starch or a loaf made
of starch was little relished. Sago was then
tried in different forms and, after several
discouraging trials, it was found that a coarsely
ground pop-sago was preferred by the animals
to other preparations. The pops were made by
heating sago in an open iron pan.
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