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To obtain the correct estimation of
a protein, the amino acid compositions must be known along with their availability
when the feed reaches the mouth of the animal, after the necessary
manipulations have been carried out (drying, grinding, cubing, extrusion,
etc…) For this, it seems necessary to carry out a correct analysis of the
proteinic amino acid composition (a) Tryptophan is destroyed by the hydrolyse
acid of proteins, this is why a specific hydrolyse is carried out in an
alkalin environment.
To estimate the food value of lipides in the diet, certain factors
must be taken into consideration :
digestibility.
The great proteinic requirement can be justified very synthetically, by
the three following factors:
- slow proteinic speed at muscle level (which make up 60% of the
whole body ) when compared with other animal species.
From a
nutritional point of view, the characteristics resistance of these inhibitors to
thermic treatment and to the trypsine effects is interesting; these
properties probably depends on the remarkable capacity of the proteinic
molecule stabilized by the numerous dissulphuric bridges.
Amylasic inhibitors
In wheat, barley and rye, are found great quantities of proteinic
molecules, capable of inhibiting the amylasis (enzymes responsible for the
destruction of the polysaccharides of the food diet).
The insaturable fatty acids are more easily digested than saturated ones (NOSE, 1966) (1)
Experiments carried out with salmonidae, fed diet containing
saturated fats showed clearly, how these are the cause of what is known as the ciroid degeneration of the liver, which was pointed out by GHITTINO (32).
Therefore fish have a great proteinic requirements when
compared with other monogastric animals (chickens, pigs).
A vitamin A deficiency diet
brings about the delay in growth and in bone development; disorders at
epithelial cell level are remarked also.
This evident bad use of proteins could be caused by a bad proteinic
balance, but also by the fact that a great part of the proteins are used
for energetic reasons.
Recent experiments carried out by GHITTINO, CORBARI and AMERIO
(14) demonstrate clearly that after a relatively short period (20 to 30 days)
of feeding a rancid fats diet, sea-bass fry have ciroid fluid in the liver,
showing anemia symptoms and high death rates.
Fish species are capable of digesting high quantities in the diets
(20 to30 % of the food) as long as there are adequate quantities of choline,
methionine and vitamin E.
Normally, the fact that the whole rate of amino acids contained in feed is
only employed partially is not taken into account; the concept of amino acid
availability is identified with the concept of digestibility, in the sense
that this is normally an integrant part of the proteinic structure, it becomes
available at absorption level only when the proteins have been digested.
This metabolic system seems to be modulated by the concentration of some unessential fatty acids in the diet
(oleic acid for example as given by HALVER, 1975) (9).
Without trout fry, fed diets which have a 0,5% phytic acid level, a
reduction of 66% in the digestion of proteins was remarked, together with
decreases of around 10% in growth and the inconsumption ratio of the feed.
VITAMINS
The research work carried out so to define the requirements,
activity mechanisms and consequence due to dificiency or excess of vitamins in the diet, dealt especially with salmonidae (15).
In practice,
this deficiency can be found when fish are fed fish: In the fish viscera, there is an antivitamin-thiaminase which destroys the greater part of vitamin B1 present in diet.
Research carried out on chickens, fed diets enriched in antiamylasic
factors of wheat proved in the decrease of growth and the hypertrophy
of the pancreas.
The knowledge of the amino acid composition
permits the application of certain calculation methods: the chemical rate,
the index of essential amino acids by OSER; the index of the proteinic
balance by ARNOLD, which give the global estimate of the protein, without
carrying out biological research, which is very difficult and costly when
concerning fish.
When formulating a food diet, so to cover the vitamin requirements correctly, without taking into account the specific needs, the real avaibility
of the vitamin factors in foodstuff, the presence of anti-vitamin factors must be taken into consideration.
It is widely
known that carnivorous fish make better use of proteins of animal rather than
of vegetables origin, and as this has been remarked as far as trout are
concerned, who are unable to one non proteinic nitrogen, urea, ammonium
citrate, this last product can even be toxic.
- the high rate of amino-acids which are directly utilized by the
oxidation processes for the energy supply and which can consequently become
the limiting factors at proteinic synthesis level.
Technics used for intensive rearing and alimentation of fish and shellfish
It was found present in variable
resorchinols play a possible antinutritional role, and have been stated as
responsible for the loss in appetite and the decrease in growth, remarked in numerous animal species when given diets which have a high rye content.
Consumption of food rich in tannin causes the reduction of the body
growth and the use of proteinic nitrogen.
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