Effects of dietary calcium and phosphorus levels of dehydrated kitchen waste on laying performance and eggshell quality in hens

An experiment was conducted to study the effects of various levels of dietary calcium (Ca) and phosphorus (P) in dehydrated kitchen waste (DKW) on the laying performance and eggshell quality in egg-laying hens. A total of 96 (Rhode Island Red, YR line) 28-week-old egg-laying hens were assigned to 8 treatment groups. The experiment period lasted 11 weeks. In the first 7 weeks, the control birds were fed a 100% commercial diet (diet 1) or a 50% DKW and 50% commercial diet (diet 2) by weight. Diet 2 was used as a basal diet. In the next 4 weeks, diet 1 or one of the 7 diets, namely, diet 2 to 8, were fed. Diets 3-5 comprised basal diet ; 3.33% Ca ; and 0.75, 1.00, and 1.25% P, respectively, and diets 6-8 comprised basal diet ; 0.75% P ; and 2.90, 3.20, and 4.00% Ca, respectively. Each treatment was tested in duplicate with 6 birds each. The egg-laying performance was recorded throughout the experiment, and the contents of crude ash, Ca and P in the tibia, and serum Ca and P contents were determined at the end of experiment. The Ca and P contents in the eggshell and excreta were determined in the last week of the experiment. In the first 7 weeks, feed intake, feed conversion, hen weight, egg mass, and egg weight were significantly low in the case of hens fed with diet 2. In the next 4 weeks, there were no differences in the egg mass, egg production, and feed conversion with increased dietary Ca or P levels. However, shell strength and shell thickness remarkably increased with dietary Ca levels. The serum Ca level significantly increased compared to that observed in the case of diet 2 (P0.05). The serum P level significantly increased with dietary P levels and tended to decrease with increased dietary Ca levels. Ca and P retentions in the case of diet 1 and 2 were equivalent. Ca and P retentions were significantly higher in the case of birds fed with diets 3 to 8 than diets 1 and 2 (P0.05). From these results, we concluded that raising the Ca and P levels in 50% DKW increased the serum Ca and P concentrations and effectively improved shell strength and shell thickness. However, the effects of increased Ca and P on egg production, lightness of eggshell, and redness of eggshell were not clear from our results.