Abstract

This study examined the effect of the different group sizes on the titers of some immunological indicators and signs of health in two strains of lohmann layers. A total 558 layers (279 lohmann brown and 279 lohmann selected leghorn), aged 50 weeks were homogenously classified into four groups, where 360 birds (180 lohmann brown and 180 lohmann selected leghorn) in 6 cages (60 layers/cage “5 m2”) and 198 birds (99 lohmann brown and 99 lohmann selected leghorn) (33 layers/cage “2.8 m2”) with the same floor space relatively. The antibody titer of avian encephalomyelitis, avian meta-pneumonia, infectious bronchitis and mycoplasma synovia were higher in small group (33 birds) than large group size (60 birds). However, the differences didn’t reach the significance. In the other hand, the lohmann selected leghorn was more susceptible to avian encephalomyelitis, infectious bronchitis and mycoplasma synovia due to the increase in its antibody titers, while the antibody titers of avian meta-pneumonia and mycoplasma gallisepticum were higher in lohmann brown. In large group size, the scores of plumage condition were referred to the best, especially in lohmann brown. Furthermore, the changes in feet condition in lohamman brown were better than lohmann selected leghorn, especially in large group. In order to achieve the full genetic growth potential, layers must be reared under optimal group size. Therefore, any deviation of the managemental condition of layers may impair their performance, cause immunosuppression, and change their physiological responses leading to increase their susceptibility to diseases.

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