THE STRUCTURE AND FUNCTION OF THE SHELL GLAND IN JAPANESE QUAIL UNDER DIFFERENT LEVELS OF DIETARY CALCIUM
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Date
1994
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College of Veterinary and animal Science,Mannuthy
Abstract
Literature available on the physiological aspects of
egg production in Japanese quail is scanty and many lacunae
exist in the knowledge of various mechanisms involved in the
formation of egg. Under the modern practice of intensive
quail husbandry it is often found that the egg shells of
Japanese quail are becoming thinner, more fragile and easily
broken. Consequently, safety in transportation and
marketability of these eggs are considerably reduced. Hence
it was thought worthwhile to investigate some of the factors
involved in egg production, more especially the egg shell
formation. In the present investigation attempts were made to
elucidate the mechanism of the egg shell formation with
respect to the structural and functional peculiarities of the
shell gland in Japanese quail (Coturnix coturnix "japonica)
under different dietary levels of pre-laying and layer
calcium. The study envisaged histological, histochemical
peculiarities of the shell gland; the mineral (calcium and
inorganic phosphorus) and enzyme (ALP and ACP) profile of the
plasma and shell gland. The influence of dietary calcium on
the body weight, development of the oviduct, egg production
and egg shell quality was also investigated.
Japanese quails attained sexual maturity early at the
sixth week of age, by which time they attained a body weight
of 131.8 + 0.600 g and started egg production. The birds grew
at a faster rate in the early weeks, came into peak production
at the 16th week of age, and the trend continued even at the
24th week of age, with a body weight of 198.033 +
0.220 g for good production. The length and weight of the
oviduct increased from the sixth to 24th week of age. The
variation in length and weight of the shell gland from the
16th and 24th week was marginal. Growth rate was almost
marginal from the 16th week onwards.
Histologically the quail shell gland showed similar
structure to that of the domestic fowl except for the tunica
muscularis. The inner circular muscle layer was thicker and
outer longitudinal layer was thinner. As age advanced, at the
16th and 24th week of age the mucosal foldings were numerous.
The inner circular muscle layer became thicker and even this
layer invaded the lamina propria and the vascularity in the
connective tissue core of the tunica muscularis increased.
The egg quality traits such as egg weight, shell
weight, shell thickness, shape index and specific gravity
markedly improved as age advanced from the sixth to 16th week.
From the 16th to 24th week the egg quality was lowered with an
increase in egg weight, lowering of shell weight, shell
thickness and specific gravity.
Dietary calcium significantly influenced the body
weight, egg production, shell quality, histology of the shell
gland and mineral and enzyme profile of plasma.
Birds exhibited optimum growth, and production at
higher pre-laying and layer dietary calcium levels. Pre
laying dietary calcium level of 0.7 to 0.9 per cent and layer
level of 3 per cent were found to be optimum in quail ration.
As far as the oviduct development is concerned, pre-laying
dietary calcium had negligible influence, whereas layer
dietary calcium level of 2.5 per cent was just sufficient for
optimum development of oviduct/shell gland. Histologically
the only difference noticed in highest (3.5%) layer dietary
#
calcium fed quails was the increased vascularity in their
connective tissue core of the lamina propria of the shell
gland.
There was a positive correlation between dietary
calcium (pre-laying and layer) level and plasma calcium
concentration at the sixth, and 16th week of age. But at the
24th week of age only layer dietary calcium induced such a
relationship. As age advanced, pre-laying dietary calcium
became insignificant.
In the case of plasma inorganic phosphate
concentration, there existed a negative correlation to that of
pre-laying and layer dietary calcium levels at all the age
groups of quails. It may be emphasized in this context that
the extent of the negative correlation existing between plasma
inorganic phosphate and pre-laying and layer dietary calcium
levels was considerably lower. The concentration of calcium
and inorganic phosphorus in the plasma and shell gland were
uninfluenced by the age. The shell gland concentration of
calcium and inorganic phosphorus was lower compared to their
plasma level. These minerals were not stored in the shell
gland for shell calcification. At the time of calcification
calcium was transferred from the plasma (blood) to the shell
gland and then to the shell. Dietary calcium significantly
influenced the plasma concentration.
Plasma enzyme concentration of ALP and ACP was
negatively correlated with dietary calcium (pre-laying and
layer) levels, whereas the shell gland ALP concentration was
uninfluenced by the dietary calcium and age and its
concentration was very low compared to those of plasma ALP and
shell gland ACP. Shell gland ALP was unimportant in shell
formation. Histochemical localisation of the shell gland ALP
was in confirmation with that of quantitative estimation.
Shell gland ACP content was comparatively higher than ALP,
which was also in agreement with histochemical localisation.
Shell gland ACP may be involved in the transfer of calcium
from the plasma to the shell through the shell gland mucosa#
since its level in the shell gland was higher and influenced
by dietary calcium. Variation in the plasma concentration of
ALP and ACP as influenced by dietary calcium levels were
related to the cyclic medullary bone formation and resorption
which is a normal feature in laying birds.
Variations in the dietary calcium induced changes in
the concentration of plasma minerals and enzymes supported the
view that dietary calcium is important for proper shell
formation. Higher level of dietary calcium improved the egg
shell quality, egg production and body weight. Pre-laying
dietary calcium level of 0.7 to 0.9 per cent and layer level
of of 3 per cent were found to be optimum in quail ration.
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