Epidemiology of influences on the performance in broiler flocks--a field study in Germany.

To establish which factors influence performance and bird welfare during a fattening period and to identify those factors to be investigated during routine monitoring of farms by veterinary authorities, a questionnaire-based field study was conducted in districts of Lower Saxony, Germany, with the highest density of broiler chickens. Mortality and BW of farms with different stocking densities (≤33, 33.1-39, and >39 kg/m(2)) were investigated. Analyses of 79 farms with 176 stables and 634 fattening periods revealed that flock mortality and BW appeared to be greatly influenced by weather conditions and litter material. In general, it is an advantage to grow broilers under warm weather conditions. However, the longer the fattening period lasts the more important it becomes that the outside weather conditions are not too warm. Therefore, weather conditions should be considered when determining the length of the fattening period, especially before the background of the growing demands of broilers regarding ventilation, absorption of feces by the litter material, and so on. Apart from the length of the fattening period, the weather conditions determine the choice of the litter material, as well. Under cold-humid weather conditions, it is better to use litter material other than wood shavings. In particular in older buildings it is not possible to provide the required conditions, which results in a lower weight gain the longer the fattening period lasts. The study identified differences in the final BW of flocks, which indicate different (farm) management policies. Regardless of the underlying policy, the performance of a fattening period can be improved by optimizing the farm management according to the prevalent conditions. Future routine monitoring, which should be cost effective regarding personnel and finance, should be generally risk based and consider weather conditions, litter material, the age of the building, and the length of the fattening period.