The effect of the calcium source, level and the particle size on calcium retention, eggshell quality and the overall calcium requirement in laying hens
Résumé
Four different sources of calcium in isonitrogenous and isoenergeric diets were fed to laying hens for two-week digestion trial when they were 56 and 57 weeks old. The mineral percentages in the feed were as follows: 29% fine limestone (LF) and 71% large limestone (LG), 32% fine limestone (LF) and 68% eggshell, 32% fine limestone (LF) and 68% oyster shell, 50% fine limestone and 50% large limestone (LG). The contents of these sources of calcium in the diets were as follows: 10.33%, 9.33%, 9.33% and 9.33% respectively. 2. The coefficients of calcium retention were significantly higher (P=0.0271) in 50:50 LF:LG (0.578) and 32:68 LF:Eggshell (0.576). The midnight feeding significantly improved the coefficient of calcium retention (P<0.01)in all mixtures except 50:50 LF:LG. 3. In the mixture 29:71 LF:LG and 32:68 LF:Oystershell, there was significantly higher eggshell quality; eggshell weight (P=0.0035), eggshell thickness (P=0.0000) and eggshell strength (P=0.0012). The midnight feeding had no significant effect on eggshell quality. 4. In the ration with oyster shells, 96.5% of the retained Ca was deposited into the eggshell, but in ration 32:68 LF:Eggshells and 50:50 LF:LG the utilization was only 73.9% and 78.6% respectively. 5. To ensure good quality eggshells in the last third of production, the recommendation for calcium is 4.1 g/kg (90 percent dry matter, feed intake 110 g/d). As a source of calcium in this stage of production, a feed mixture containing two-thirds large particles should be used (limestone grit or oyster shell).
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