INFLUENCE OF DIETARY SUPPLEMENTATION OF PROTEIN AND IODINE ON TAPIOCA TOXICITY
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Date
1994
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COLLEGE OF VETERINARY AND ANIMAL SCIENCE,MANNUTHY
Abstract
A three phase experiment was carried out to assess the
level of cyanogenic glycoside (CNG) content in seven varieties
of tapioca, its removal by various processing methods and its
effect on metabolism in rats and kids. The role of dietary
protein and iodine in modifying the deleterious effects of
cyanide was investigated. Histopathological studies on the
liver, pancreas and heart were also carried out in rats.
The first phase of the study revealed that CNG content
in terms of cyanide varied from 40.86 + 2.79 to 186.31 +
5.30 ng/g of fresh tuber v/ith the lowest concentration in
'fl-4' and higher concentrations in 'H-165' and ' Karkidakkan' .
Processings like boiling and sun drying lowered the CNG
content by about 50 per cent of the original.
In the second phase 60 male albino Wistar rats,
divided into six groups were given the following diet.
Group I - Protein = 15%; Tapioca = Nil; Iodine = Nil
Group II - Protein = 15%; Tapioca = 30%; Iodine = Nil
Group III - Protein = 7.5%; Tapioca = 30%; Iodine = Nil
Group IV - Protein = 7.5%; Tapioca v/ithout HCN = 30%;
Iodine = Nil
Group V - Protein = 15%; Tapioca = 30%; Iodine = 0.17 mg/kg
Group VI - Protein = 22.5%; Tapioca = 30%; Iodine = 0.17 mg/kg
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Performance of rats was evaluated by recording grov/th
rate, feed consumption and feed efficiency for a period of 12
weeks. Dry matter digestibility v/as also determined over a
period of 24 h. At the end of 10th, 11th and 12th week of the
study the rats were sacrificed and endocrinological,
biochemical and histopathological evaluation of blood/serum
and tissues v/ere made.
Performance of rats was poor on tapioca-based diet not
supplemented v/ith iodine (Groups II and III). Rats fed on
protein deficient diet in the presence of cyanide containing
tapioca were the most affected (Group III) . Hov/ever, there
\7as no significant variation in the performance in Groups V
and VI compared to Group I when tapioca-based diet were
supplemented v/ith iodine. The digestibility of dry matter in
six groups of rats was almost inversely related to the
quantity of feed consumed.
There was significant increase in DNA and decrease in
protein content of thyroid thereby increasing the DNA: protein
ratio, follov/ed by extremely lov/ levels of thyroxine and
hyperplasia of the thyroid in Group III. In Group II also
there occurred a significant reduction in the levels of
thyroxine and a resultant hypertrophy of the thyroid.
Higher levels of dietary protein and iodine
supplementation v/ere found to play a decisive role in
Ill
counteracting the inhibitory effects of cyanide and
thiocyanate of tapioca origin especially on thyroid functions.
The DHA: protein ratio per unit weight of pancreatic
tissue v/as increased in groups fed on low levels of dietary
protein (Groups III and IV).
Insulin levels in different groups of rats were found
to be primarily related to the levels of blood glucose. There
v/as no significant difference in insulin-to-glucose ratio
between the groups. The synthesis and release of insulin from
the pancreas was not affected by cyanide present in the diet
of tapioca fed groups.
Rats showed no definite pattern of response in their
blood glucose levels to cyanide contained in the diet of
tapioca fed groups.
There was elevation in the levels of serum total
protein, cholesterol and lipid concentrations in rats fed
tapioca v/ithout supplementation of iodine (Groups II and III).
This may be the result of the development of hypothyroidism.
However, the increase in serum total protein and lipid in
Group II v;as not significant. The results indicated that the
above parameters could be used as reliable biochemical
indicators of thyroid activity.
A significant reduction in haemoglobin concentration
IV
in rats of Groups II and III compared to Groups I and IV
reflected the deleterious effects of cyanogens on thyroid
functions as v/ell as the importance of availability of dietary
protein for haemoglobin synthesis.
The hepatic cells in Group II appeared slightly
swollen with occasional cells showing vacuolar changes.
Pancreas showed slight oedema and occasional mild degenerative
changes of exocrine cells. Also there was slight interstitial
oedema in the myocardium. Intensity of pathological changes
in the liver, pancreas and heart v^ere more severe in rats fed
on protein deficient, tapioca diet (Group III) compared to
that of Group IV in the diet of v;hich tapioca was made cyanide
free. The hepatic cells in Group III shov/ed marked diffused
vacuolar changes with condensed or vesicular nuclei and
occasional cell necrosis. Many pancreatic exocrine cells
shov/ed vacuolar and degenerative changes. Interstitial oedema
v/as prominent. Inspite of these pancreatic exocrine changes,
it is important to note that the islets remained almost intact
in all the groups studied. Myocardium showed interstitial
oedema v/ith swollen sarcoplasm and fragmented sarcolerama. At
the same time only moderate vacuolar changes in the liver,
distention of interlobular space and interstitial oedema in
myocardium were observed in Group IV. Since the diet of
Groups V and VI were supplemented v/ith iodine, no significant
cytological alterations could be seen in their organs.
V
In the third phase of the study thirty 2^5-3 months old
Alpine-Malabari kids of both sexes were divided into 3 groups.
They were given the following diet.
Groups I Protein = 15%; Tapioca = Nil; Iodine = Nil
Groups II Protein = 15%; Tapioca = 30%; Iodine = 2 mg/kg
Groups III Protein = 25%; Tapioca = 30%; Iodine = 2 mg/kg
The study included evaluation of the performance of
kids and determination of certain endocrinological and
biochemical parameters in their blood at fortnightly intervals
for 3 months.
There was no significant effect on the performance
(body weight gain, dry matter intake and feed efficiency) of
kids fed on tapioca-based diet supplemented with iodine,
compared to Group I. However, the significant difference in
body weight gain between tapioca fed groups (Groups II and
III) was probably due to the difference in the relative
availability of protein in their diet.
The results of the study in kids indicated that there
\/as no significant influence of cyanogenic principles present
in tapioca on the thyroxin and insulin levels v/hen iodine was
supplemented in the diet. Similarly the blood glucose, serum
total protein, cholesterol, lipid and haemoglobin levels v/ere
also not influenced throughout the study.
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