Effect of Dietary Zinc Level on Egg Production Performance and Eggshell Quality Characteristics in Laying Duck Breeders in Furnished Cage System

Dietary zinc supplementation affects eggshell quality and ultrastructure in commercial laying ducks by influencing calcium metabolism

This study evaluated dietary Zn supplementation on productive performance, eggshell quality and ultrastructure, and calcium metabolism during eggshell formation in laying ducks. A total of 360 Longyan laying ducks (45-wk) were randomly divided into 5 treatment groups with 6 replicates of 12 birds each and fed for 20 wk. The 6 treatments fed the basal diet supplemented with 0 (control), 20, 40, 80, or 160 mg Zn/kg (ZnSO4·H2O). Dietary supplemental level at 80 mg/kg increased egg production (4.3%) and mass (5.7%), and decreased FCR (2.9%) compared to the basal diet, and these indices increased quadratically with increasing Zn supplemental levels (P < 0.05). The shell breaking strength (15.8%) and fracture toughness (10.6%) were higher with the supplementation of Zn at 80 mg/kg than the basal diet, and increased quadratically with Zn supplementation (P < 0.05). Dietary supplementation of Zn at 80 mg/kg improved shell ultrastructure by increasing total (9.0%) and effective thickness (14.2%) and decreasing mammillary thickness (12.0%), and their responses were quadratic with increasing Zn levels (P < 0.05). The supplementation of Zn affected the calcium contents in plasma, tibias and ulna, ulna phosphorus content, and linear and quadratic effects were observed, and higher values were observed with 160 mg/kg Zn supplementation than control (P < 0.05). The supplemental Zn level at 80 mg/kg increased shell effective thickness in growth stage (P < 0.05), and shell calcium and phosphorus content in initial and growth stages (P < 0.05). Dietary Zn supplementation did not affect the gene expression of Ca2+ transporters in the eggshell gland, but affected the expression of HCO3- exchanger in initial and growth stage (P < 0.05). Overall, dietary Zn supplementation could improve productive performance and shell quality in laying ducks at late phase of production, and calcium metabolism and deposition were modulated by Zn influencing HCO3- secretion and thus affecting shell ultrastructure and quality. A supplemental level of 80 mg/kg Zn in the diet with a basal content of 34.0 mg/kg was optimal, and higher level (160 mg/kg) decreased shell calcium deposition by depressing its metabolism.

Mineral requirements in ducks: an update

Mineral nutrition plays a critical role in growth and bone mineralization in meat ducks as well as reproductive performance in duck layers and duck breeders. In addition to improving production performance parameters, minerals are also essential to support several enzymatic systems to enhancing antioxidant ability and immune function. This review explores the biological function and metabolism of minerals in the body, as well as mineral feeding strategy of various species of ducks. Topics range from mineral requirement to the physiological role of macroelements such as calcium and phosphorus and microelements such as zinc and selenium, etc. As with the improvement of genetic evolution and upgrade of rearing system in duck production, mineral requirements and electrolyte balance are urgent to be re-evaluated using sensitive biomarkers for the modern duck breed characterized by the rapid growth rate and inadequate bone development and mineralization. For duck breeders, mineral nutrition is not only required for maximal egg production performance but also for maintaining normal embryonic development and offspring's performance. Therefore, the proper amounts of bioavailable minerals need to be supplemented to maintain the mineral nutritional state of duck species during all phases of life. In addition, more positive effects of high doses microelements supplementations have been revealed for modern meat ducks subjected to various stresses in commercial production. The nutritional factors of mineral sources, supplemental enzymes, and antinutritional factors from unconventional ingredients should be emphasized to improve the effectiveness of mineral nutrition in duck feed formulation. Organic mineral sources and phytase enzymes have been adopted to reduce the antagonistic action between mineral and antinutritional factors. Therefore, special and accurate database of mineral requirements should be established for special genotypes of ducks under different rearing conditions, including rearing factors, environmental stresses and diets supplemented with organic sources, phytase and VD₃.