ANIMALS AND ARID CONDITIONS 377 
Nitrogen Utilization on Low Grade Feed 
The rumen, however, serves another important function in the 
camel. Investigations on the physiology of renal function in the 
camel revealed an extremely low excretion of urea when the feed 
was low in protein. In one particular camel fed on dry dates and 
hay, the total urea excretion was less than 1 gram per day, cor- 
responding to the metabolism of about 2.5 grams protein per 
day. There is no reason to believe that the actual protein metabo- 
lism would be that low in such a large animal. If one remembers 
that urea (or ammonium compounds) when fed to cattle is syn- 
thesized into amino acids by the bacterial flora of the rumen, and 
that cattle can be fed a major part of their “protein” supply in 
the form of urea, one sees what may happen in the camel. Urea 
retained from secretion in the urine may be re-used as protein 
via bacterial synthesis in the rumen. 
When urea was injected in large amounts in a camel, less than 
one-tenth was recovered in the urine. Stomach samples showed 
an increased urea and ammonia content, and it is reasonable to 
conclude that protein was synthesized in the rumen as it 1s in 
cattle fed urea. 
The value of this ability to re-use the protein nitrogen is ob- 
vious to any animal husbandry man who works with low grade 
pastures. It is not unlikely that other ruminants would behave 
like the camel, and we are now in the process of investigating 
whether the sheep can utilize a similar “urea cycle” when fed an 
extremely low protein diet. 
Role of Physiology in Production Considerations 
If one summarizes the physiology of the camel the following 
features stand out: 
1. The camel can withstand an unusually high degree of water 
depletion, and it also has a very low rate of water loss; in com- 
bination, these two factors mean that the camel can go for ex- 
ceptionally long periods without drinking. 
2. The camel (as well as the donkey) has a very unusual drink- 
ing capacity, which means that, when water is available, it can 
fill up in a very short time. 
