The experiments were carried out on four groups of Hy-Line var. Brown hens (n = 350 each) monitored from 20 to 68 weeks of age. The hens were fed on diets which provided the following calcium intakes (%): 2.56 and 3.12 in groups I and II, respectively, 3.86 in control and 4.22 in group III. The shell weight increased during the laying period proportionally to the ingested calcium. The thickness of the eggshell decreased: the decrease was higher in the groups which ingested less calcium. The eggshell strength increased from 20 to 36 weeks of age in all the hen groups. Further, the eggshell strength decreased from 36 to 68 weeks of age. These decreases were higher as the amount of calcium intake increased. In conclusion, calcium diet influences on eggshell properties are agedependent and more pronounced at the peak of laying period. The increase in diet calcium content from 3.86 to 4.22% has less and negative influences on the physical properties of the eggshell.
The experiment was carried out on four groups of Hy-Line var. Brown hens (n = 350 each) fed on diets which provided 2.49, 3.07, 3.78 and, respectively, 4.15 g% calcium (Ca) during the laying period. Consequently, mean daily Ca intake was 2.74, 3.38, 4.16 and 4.60 g/cap., respectively. Ca metabolism was assayed at 20 weeks of age (start of the laying), 36 weeks of age (the peak of the laying) and 68 weeks (the end of the laying period). A significant part of the ingested Ca was not absorbed. The percentage of Ca exonerated by feces was higher at the start of the laying and lowers in the peak of laying and at the end of the laying period. The amount of Ca exonerated as unabsorbed Ca increases as the amount of ingested Ca increases inside of each age level. It was found also an increase of the Ca content of the egg shell according the Ca intake statistically significant (P<0.05) in 36- and 68-wk.-old hens, but not in 20-wk.-old hens. Blood plasma Ca showed significantly higher values in 3.38-, 4.16- and 4.60-g/day-Ca-intake groups when compared by 2.74-g/day-Ca-intake group (P < 0.05) but the level of increasing showed lowest values in hen groups with highest intake of Ca. The daily eggshell Ca export strongly correlates with the amount of daily Ca intake in 36-wk.-old hens and 68-wk.-old hens: r = +0.72 and +0.84, respectively, but no correlation was found in 20-wk.-old hens (r = -0.74, negative correlation). The results showed a limited physiologic capacity of the Ca absorption in hen, the Ca surplus being lost. Dietary Ca level should be closely correlated with the laying level of hens.
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