the final product produced from thi

the final product produced from this production cycle.
Discussion
It has been known that the main route of Salmonella spread in the broiler production chain can be either vertical or horizontal transmission (vd Giessen et al., 1991; Heyndrickx et al., 2002). However, in this study we did not find any Salmonella positive in the egg samples, indicating that the vertical transmission was not the main route of Salmonella contamination in this integrated broiler production. It was possible that the attenuated and killed vaccine used in the second and third breeder flocks were highly effective since no Salmonella was detected in either of the breeders or in the eggs produced from these flocks. According to previous studies, an effective vaccination program can prevent vertical transmission of Salmonella to eggs as well as prevent colonization in internal organs and shedding in feces (Okamura et al., 2007; Penha Filho et al., 2009). For the first breeder flock, although no egg was positive for Salmonella, the breeders and farm environment were contaminated with S. Albany. It is possible that only attenuated vaccine used in this flock may not be enough to protect the breeders from the infection. In addition, the age of the breeders which were older than others (55 weeks old) may also contribute to the higher chance of contamination from the environment.
In the hatchery, Salmonella was found in the environment and equipment before being used indicating insufficient cleaning and disinfection of this production unit. Transfer of Salmonella from the contaminated hatchery environment and equipment to the baby chicks and subsequent production units was evident from the third production cycle. In this production cycle, the most frequent serotype contaminated in this hatchery was S. Corvallis, which was also found in the baby chicks and persisted throughout the rearing period and whole carcasses. A previous study demonstrated that contaminated egg trolleys and trays in a hatchery can lead to widespread dissemination of Salmonella within integrated poultry production (Davies et al., 1997). However, in the current study, no contamination in the egg trolleys was found. In addition, although the hatching trays were found contaminated on several occasions, they were positive with the serotypes different from those in the baby chicks and subsequent production units. In this work, the possible source of contamination were the worker’s hands and transferring belts, which were contaminated with S. Corvallis before work, and the same serotype was found in the baby chicks from this production cycle.
In the broiler farms, various serotypes of Salmonella were isolated from water on several occasions. For example, in the first sampling cycle, the water was contaminated with S. Albany at farm preparation step and suspected to be the source of contamination of this serotype in the house and other equipment during cleaning and disinfection. During subsequent production steps, the water was found occasionally contaminated with S. Derby, S. Weltevreden and S. Falkensee. These results indicated that there was a problem in the water treatment system. However, there is no direct evidence that water was the source of Salmonella contamination in