Effects of Zinc, Manganese, and Taurine on Egg Shell Microstructure in Commercial Laying Hens After Peak Production.

Much strive has been made to improve egg shell quality in laying hens. This study was conducted to evaluate the effects of two microminerals, zinc and manganese, besides taurine semi-essential amino acid on eggshell quality after peak production of Hy-line laying hens. A total of 720 laying hens were assigned to 18 treatments in a completely randomized design (3 × 3 × 2 factorial) at week 71. Experimental period included 8-week adaptation and using 18 dietary treatments for about 6 weeks. Dietary treatments included Zn (0, 80, and 160 mg/kg), Mn (0, 90, and 180 mg/kg), and taurine (0 and 1960 mg/kg). Supplementation of 90 mg Mn and 1960 mg taurine in laying hens' diet after peak of production improved egg shell quality without any negative effect on the internal quality of the egg. Egg specific gravity significantly increased in response to Zn, Mn, and taurine in comparison with control treatment (P < 0.05). Applying 1960 mg taurine/kg diet significantly improved calcite crystal's structure and eggshell strength in comparison with control treatment (P < 0.05). It was concluded that adding Mn and taurine can positively affect eggshell quality of laying hens post peak period.