Abstract
The objective of this study was to investigate the effects of dietary iron (Fe) on reproductive performance of Chinese Yellow broiler breeder hens during the egg-laying period. A total of 480, 55-wk-old hens were balanced for laying rate and then randomly allotted into 5 groups, each with 6 replicates (8 cages for each replicate with 2 birds per cage). The trial was for 10 wk. Birds were fed diet with 44, 58, 72, 86, or 100 mg/kg Fe contained feed. Laying performance, biochemical indices and reproductive hormones in plasma, egg quality, ovarian and oviductal variables, tibial breaking strength, and hatching performance were determined. The key performance variables hematocrit, hatchability of live embryos, and tibial breaking strength were selected for analysis by quadratic polynomial (QP) and broken-line (BL) regressions to better determine optimal dietary Fe level. Qualified egg (excluding those with double-yolk, soft-shell, cracked, very small malformed, etc.) rate tended to decrease with the lowest and highest dietary Fe levels. Hematocrit was affected (P = 0.003) by dietary Fe, along with linear (P = 0.017) and quadratic (P = 0.002) effect. There was a significant effect (P = 0.034) of dietary Fe level on tibial breaking strength of breeder hens with a quadratic (P = 0.044) effect. Breeder hens fed inadequate (44 mg/kg diet) or excess (100 mg/kg) Fe both had lower (P < 0.05) tibial breaking strength compared to that of hens fed 86 mg/kg Fe. Hatchability of live embryos was affected (P = 0.004) by diet; with both linear (P = 0.014) and quadratic (P = 0.001) effects. Maximal hatching of live embryos occurred with diets of breeder hens containing 72 mg/kg Fe. From the QP and BL models fitted to hematocrit, tibial breaking strength, and hatchability variables, the optimal dietary Fe level for Chinese Yellow broiler breeder hens in the laying period was 70-90 mg/kg. The daily Fe fed (allowance) was about 8-11 mg.