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In today's modern chicken production, breeder and layer flocks are typically used in one production cycle. However, the hen species is able to produce eggs for a much longer period of time, which can be achieved by interspersing moulting periods. From an economic point of view, it should be considered that the hen flock produces two egg production cycles with one investment cost. The moulting is one tool of keeping breeder flocks economically.

Moulting in birds is a complex and intricate physiological process, that not only change of plumage, but also affects the neuroendocrine system, the structure and function of reproductive tissues and influences egg production.

Artificial moulting is based on the temporary deprivation of feed and drinking water, as well as a marked reduction in the time and light intensity. These changes stress the hen, which induced hormonal changes that trigger and accelerate moulting.

We investigated how two different moulting programmes influence and which one is more effective in Cobb 500 female line grandparent broiler flocks. We monitored in 3 and 4 barns on two farms under the same conditions. Both programmes lasted 12 weeks, which started at 53 weeks old.

During the first week of two moulting programmes, we uniformly withdrawn the feed, but we made a difference in the length of the watering and the lighting period. In the „A” program, we put 2 thirst qienching days with constant 4 hour light and 5 lux light intensity. In the „B” program, we did not deprive the drinking water, here the lenght of lighting and drinking period were reduced in parallel and then increased. In the following weeks, we changed the drinking and lighting time, the light intensity and the feed ration in almost the same way.

Based on our results, in the „A” program, the body weight loss during the week of feed withdrawal was smaller. Before resuming feeding, we aim for the birds to lose at least 20 % of their body weight. The weight loss of birds ranged between 8-13% in „A” program and 12-18% in „B”. Since feed cannot be withheld for longer than 7-10 days, we started feeding with a small head ration, which was gradually increase. At a variable rate, the 20% body weight loss occurred in all barns except only by the 3rd week. We determind the mortality data of the flocks as the succes of moulting program. The weekly breakdown of hen mortality was around 1-6 %. For the 12 weeks of moulting program, the total death is 22% for „A” and 32% for „B”.

In conclusion, in the „A” moulting program the body weight loss started more slowly, caused less stress. However, in accordance with the „B” program, the flock lost 20% by the 3rd week. Based on the mortality data, the death rate was higher in the „B” program, so the „A” proved to be more effective.

In summary, the „A” program showed better survival results, despite the fact that we used 2 days of water deprivation. Therefore, withholding water with a maintained lighting program causes a milder stress effect.