Also stress has a role to play in laying hens that are kept in free-range systems. When stress hormones were measured, birds that interacted a lot with other chickens did not necessarily have less stress than animals that lived in separation. Changing animal contacts and the interaction with the environment for feed and water turned out to be rather stressful.
This all led to the return of outbreaks of several old diseases, such as worm infections, blackhead (Histomonas), Salmonella gallinarum, coryza, Pasteurella multocida, E.coli and Avian influenza. “Comparing the outbreaks of high pathogen aviary influenza in 2003 and 2014, the situation 2003 was a reassortment of low pathogen strains to a high pathogen strain, spreading in a poultry dense area. In the fall of 2014 it concerned an introduction of a high pathogen virus in closed housing systems, which didn’t spread.” De Bruijn’s findings are not restricted to old diseases alone. Also a few new illnesses appeared. “Since the new decade, we saw significantly more chronic and clostridium related enteritis, Mycoplasma synoviae and AIS in laying hens.