‌‌‌‌بررسی تأثیر افزودن منابع مختلف فیبر نامحلول و اندازه ذرات کربنات کلسیم بر عملکرد تولیدی و کیفیت تخم مرغ مرغان تخمگذار

Introduction: The eggshell is composed of approximately 95% calcium carbonate, and optimal calcium supply for laying hens is the most important nutritional factor determining eggshell quality. Also, replacing fine limestone with coarse limestone provides a more uniform availability of calcium to the bird due to its longer retention time in the gizzard. Additionally, the inclusion of insoluble fibers in the diet of laying hens appears to have a significant effect on the bioavailability of calcium particles, as insoluble fibers mechanically stimulate the gizzard wall, leading to an increase in its relative weight and functional activity. The objective of this study was to investigate the effects of different sources of insoluble fiber (no fiber, sunflower hulls, rice hulls – each at 4% of the diet) and calcium carbonate particle size (3 and 5 mm) on the productive performance and egg quality of laying hens.
Materials and methods: In this experiment, 216 Hy-Line W-80 laying hens, 70–80 weeks of age, were used for 10 weeks (including 2 weeks of adaptation and 8 weeks of data collection) during the late production phase in a cage system. The hens were randomly allocated to 36 experimental units, consisting of 6 treatments and 6 replicates (6 birds per replicate), in a completely randomized design with a 3×2 factorial arrangement. Egg production and egg weight were recorded on a daily basis, while feed intake was recorded weekly. To evaluate egg quality characteristics, two eggs from each replicate were labeled and transferred to the laboratory at the end of the fourth and eighth weeks.
Results and discussion: The results showed that there was no significant interaction between fiber source and calcium carbonate particle size on feed intake (P>0.05). However, sunflower hulls significantly increased feed intake (in the first week, second week, and overall: 116.8, 130.9, and 142.2 g; P<0.05). Fine calcium carbonate increased feed intake by 7% in the second week and by 4.5% over the entire period compared with the coarse type. Despite the identical inclusion of an insoluble fiber source in the diets, the differences in feed intake are attributable to the distinct physical characteristics of the fiber sources. Sunflower hulls, due to their coarser structure and greater susceptibility to fragmentation, exert a stronger physiological effect on gizzard activity, which may consequently lead to increased feed intake. Coarse particles of calcium carbonate appear to provide a more stable and effective calcium supply for eggshell formation due to their longer retention time in the gizzard, gradual dissolution, and slow release of calcium. The importance of this phenomenon is greater in older hens, as bone calcium reserves decline with age, increasing the reliance on the gradual release of dietary calcium. Therefore, although fine calcium carbonate particles may increase passage rate and stimulate feed intake, calcium provision from coarse particles is a key factor in maintaining egg production and shell quality in these birds. A fiber-free diet combined with fine calcium carbonate resulted in the lowest egg weight (P<0.05). Sunflower hulls increased egg mass throughout the entire period (57.3 g). Sunflower hulls also led to an increase in feed conversion ratio (1.9 in the first week and 2.19 overall). Eggshell strength and eggshell percentage were higher in the groups receiving coarse calcium carbonate (7% and 5% in the second week and overall, respectively). Given the differences in solubility among calcium carbonate particle sizes, coarse calcium carbonate appears to provide greater calcium availability to hens, thereby resulting in increased eggshell deposition. The highest yolk color score was observed in the diet containing rice hulls and coarse calcium carbonate. The increase in yolk color observed with the use of rice hulls may be attributed to enhanced mechanical activity of the gizzard and a reduced feed passage rate. Similarly, coarse calcium carbonate, due to its longer retention time in the gizzard, exerts a comparable effect. The combination of these two factors improves digestion and increases the bioavailability of lipophilic pigments (xanthophylls), ultimately leading to greater deposition of these pigments in the yolk.
Conclusions: The results indicated that the inclusion of 4% insoluble fiber—especially sunflower hulls—improved feed intake, increased egg mass and egg weight, and enhanced eggshell thickness in laying hens, without negatively affecting the rate of lay. Additionally, the use of coarse calcium carbonate improved eggshell quality.