Abstract:
The thriving of the ostrich in an otherwise very
harsh environment has been an intriguing question to many
people. The objective of this study was to find out some
of the physiological explanations to this question.
Some aspects of nitrogen metabolism were studied in
the as trich : Major urinary nitrogen metabolites in
ostrich urine (uric acid nitrogen, urea nitrogen and
ammonia nitrogen) were partitioned. Plasma urea and
urinary ammonia levels were also determined using
commercial kits based on Berthelot's reaction while uric
acid was determined by the decrease in absorbance at 292nm
wavelenth before and after incubation with uricase.
Nitrogen requirement for maintenance in these birds was
determined by regressing apparently absorbed nitrogen on
the retained nitrogen. They-intercept of the regression
equation gave the Nitrogen maintanance requirement.
Nitrogen balance (the difference of nitrogen intake and
nitrogen output (in faeces and in urine) was determined
and used as a measure of efficiency of nitrogen
metabolism.
It was found that uric acid nitrogen was the most
abundant (76.60% ; as in other birds) followed by urea
nitrogen (10.20%). Ammonia nitrogen (2.3%) was the least,
unlike in chicken where the proportion of urea nitrogen
is least (3%). Nevertheless in absolute terms, ammonia
nitrogen in the ostrich urine (2.3%) was lower than in
chicken (7%). Efficiency of nitrogen retention and the
rate of nitrogen retention were found to be 50.0 and 32
% respective ly . An amount of 419 mg of nitrogen per
metabolic body weight was found to be required to
maintain zero nitrogen balance, a value that is lower than
for sheep(ruminant) and higher than that for the horse
(non-ruminants).
It is concluded that, like other birds, an ostrich
is uricotelic. The fact, that the amount of ammonia
excreted in the ostrich is less than in other birds may
be a unique feature of the former and has a physiological
backing as this may help to conserve water in the
otherwise arid environment where it inhabits. Again, the
apparently ,low nitrogen required for maintenance and the
high efficiency of nitrogen retention recorded may be part
of the explanation as to why the ostrich thrives in the
arid and semi-arid environments where quality of grass and
other herbage in terms of protein is very poor.
