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This study was conducted in two steps to determine the effects of in ovo injection of zinc acetate (ZAC) on some gene expression associated with embryonic growth and development, and with growth and carcass characteristics of the resultant chicks. In the first step the effect of in ovo injection of ZAC on the expression of insulin-like growth factors (IGFs:IGF-I and IGF-I), myogenic regulatory factors (MRFs) and metallothionein (MT) genes was examined, and in the step two, the associations between genes expression with fertility, embryonic mortality, hatchability, body weight (BW) and relative organ weight on day of hatch, and body weight (BW) and feed conversion ratio (FCR) a week after hatching were investigated. Seven hundred twenty fertile eggs (n=720) were randomly divided into 4 treatment groups consisted of: 1) noninjected (NI) group, 2) sham group (group injected with deionized water (DW)), and 3) and 4) groups injected with 3.64 and 5.23 M ZAC, respectively. On day 3 of incubation the eggs were injected with 50 µL of each treatment into the albumen. On day 5 of the incubation and on hatch day, liver and breast muscle of the chicks were removed and immediately stored at -80 °C until RNA extraction and real time-PCR analysis. In ovo ZAC injection increased myogenic differentiation factor both in embryo and breast muscle. MT mRNA expression was also increased by ZAC injection. Hatchability was lower in ZAC groups and early embryonic mortality was higher in sham control (SHC) and ZAC groups. Injection of ZAC improved both BW and FCR during the first week of rearing, and increased the relative weights of liver and breast muscle. In conclusion, in ovo injection of ZAC increased some of gene expressions of tissues and BW7 during the first week, but decreased hatchability. Hence, lower doses of ZAC are recommended to use in further experiments. [ABSTRACT FROM AUTHOR]