초록
An experiment was conducted to elucidate the effect of graded levels of vitamin $D_3$ in White Leghorn (WL) layer breeders on egg production, shell quality, hatchability of eggs and juvenile performance of offspring during their late laying period (72-88 wk). White Leghorn breeder females were randomly divided into 5 groups of 50 each and were housed in individual California cages in an open-side housing system. Considering birds in five cages as a replicate, 10 such replicates were randomly allotted to each treatment. A basal diet was formulated containing all the nutrients as recommended for WL layers except vitamin $D_3$, which served as control. Another, four diets were formulated by supplementing graded levels of feed grade crystalline cholecalciferol to the basal diet that contained 300, 600, 1,200 and 2,400 ICU of vitamin $D_3$ per kg. Each diet was offered ad libitum to one of the above five treatment groups. The egg production, egg weight, daily feed consumption and the feed intake per dozen eggs or kg egg mass of the birds fed diet without any supplemental vitamin $D_3$ was comparable with those of supplemental groups. Similarly, the level of vitamin in the diet did not have any effect on any of the above parameters. However, the specific gravity of eggs laid by the birds fed the diet without supplemental vitamin $D_3$ was comparable with either 600 or 2,400 ICU supplemental groups but significantly higher when compared to the 300 and 1,200 ICU groups. The egg -shell breaking strength was significantly lowered in the 600 ICU supplemental groups as compared to the strength of other dietary groups. The Haugh unit, egg shell weight, shell thickness, tibia breaking strength, bone ash and calcium content were not influenced by vitamin $D_3$ concentration in the diet. Serum Ca concentration was influenced by vitamin $D_3$ level in the diet. The serum Ca concentration of birds fed either control or the vitamin supplemented diet up to 1200 ICU/kg diet was comparable. However, increasing the concentration of vitamin $D_3$ to 2,400 ICU/kg diet significantly enhanced the concentration of Ca in the serum, which was significantly higher compared to other dietary groups. The serum concentration of P and protein, however, was not influenced by level of vitamin $D_3$ in the diet. Neither fertility nor hatchability was influenced by vitamin $D_3$ concentration in the diet. Feeding a vitamin $D_3$ deficient diet or supplementation of vitamin to hens did not have any influence on their progeny chicks. It can be concluded that dietary supplementation of vitamin $D_3$ may not be essential for optimum production, shell quality, hatchability, and juvenile performance of WL breeders during 72 to 88 weeks of age.