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The influence of some stressors on laying rate and selected haematological indices, and the corticosterone level in duck blood were studied. The experiment was carried out in the reproductive season (April July) on 84 of Peking ducks. One control and three experimental groups were formed. All ducks were fed standard complete diets ad libitum for 8 weeks. In the 9th week, blood samples were taken from birds and the following stress factors were introduced: in group II restricted feeding (70 g of feed per bird per day) for a period of one week, in group III addition of 20g NaCl/kg during a period of one week, in group IV withdrawal of water for two days. In the 10th week, blood samples were taken from ducks and during the next 5 weeks, all four groups were fed the standard diet ad libitum. The following parameters were estimated in blood: haemoglobin, haematocrit, red and white cell counts (proportion of granulocytes and agranulocytes) and corticosterone level. During the entire period of the experiment (14 weeks), the number of eggs laid in groups was recorded daily. Substantial decreases in the laying rate in group II (restricted feeding) and in group IV (lack of access to water) were noted. Most haematological indices in duck groups did not differ significantly. In group IV, a significant increase of the heterophil:lymphocyte ratio /HLR/ from 0.74 to 2.63 was noted, as well as the highest level of corticosterone in blood in comparison with the control and feed-restricted groups. It can be concluded that the restriction of feed exerted the highest and longest negative influence on the laying rate of ducks. Also, the two-day lack of access to water was found to have been very stressful to ducks. The 20 g of NaCl per kg added to the diet had little influence on the laying rate and also on the value of HLR.

Effects of different stressors on laying rate and selected blood indices in reproductive ducks