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ThesisItem Open Access THE STRUCTURE AND FUNCTION OF THE SHELL GLAND IN JAPANESE QUAIL UNDER DIFFERENT LEVELS OF DIETARY CALCIUM(College of Veterinary and animal Science,Mannuthy, 1994) P. T. PHILOMINA; M.G. Ramakrishna PillaiLiterature 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.