Effects of commercial hatchery processing on behaviour and welfare of laying hens

Abstract: Around the world, more than 76.7 million tons of eggs are consumed every year. To meet this demand, billions of laying hen chicks are produced under highly industrial circum-stances. These chicks are hatched in commercial hatcheries for laying hens in a presumably stressful environment, which might affect their welfare and production later in life.   When the eggs arrive to the hatchery, they are inserted in large cabinet incubators that can hold approximately 60 000 eggs. The incubators are calibrated for optimal hatchability which includes turning of the eggs as well as fluctuating temperature and humidity over the day. This is regulated by fans whose purpose consists of removing heat and circulating the air in the incubators. However, the drawback of these fans is that their noise levels exceed 90 dB, which is equal to the sound of a passing train. After 19 days, the eggs are moved to a hatcher for the last days of incubation, in which they are exposed to formaldehyde for disinfection purposes. The eggs hatch after 21 days of incubation but are kept in the hatcher for an additional day to maximize hatchability rate. After removal from the hatcher, the racks with chicks are tilted onto a conveyer belt and separated from the shells. The chicks are then conveyed to a sex-sorting station where the males are dis-carded, and the females are further processed to a vaccination station. Once vaccinated, the animals are automatically counted and packed in transport boxes which are loaded onto a truck and transported to rearing farms.   The aim of this thesis was to investigate if and how the chickens are short- and long-term affected by this hatchery procedure, including incubation and transportation, and how this might affect their welfare. In all experiments, we have compared commercial hatchery incubated, hatched, processed, and transported White Leghorn chicks (hatchery chicks, HC) with chicks incubated and hatched in a calm environment, and gently placed in their home pens directly after hatch (control chicks, CC). In all experiments, HC and CC were from the same parental stock and kept in separate but identical pens.   In paper I, we blood sampled the chicks before and after the hatchery handling to evaluate stress hormone levels (CORT) in the hatchery. The HC had significantly higher CORT levels than the CC had at a corresponding time point, which implies that the hatchery treatment is a highly stressful experience. Our results of behaviour, HPA-axis sensitivity, and feather damages showed that the commercial hatchery treatment has a long-lasting overall negative effect on the animals up to at least 20 weeks of age.   In paper II, we aimed to compare chicks incubated, hatched, and sorted at the hatchery, with chicks incubated and hatched at the hatchery who were not sorted, to distinguish the stress effects of the actual conveying and handling. We could not find any major differences between the groups and concluded that the most stressful part in the commercial hatchery seems to be the incubation and hatching, potentially due to the high noise levels and formaldehyde exposure.  In paper III, we investigated possible welfare implications of the hatchery procedure by using a cognitive judgement bias (CJB) test that is used to measure optimism/pessimism in animals. In general, pessimistic animals perceive the same environment as more negative than optimistic animals, hence, this has a great impact on their welfare. When testing HC and CC in a CJB test, we could see that HC were consistently more pessimistic than CC, during 1st, but also during 10th week of age. This means that the hatchery treatment has a long-lasting effect on the cognitive state of the animals, implying the animals exposed to this have a poorer welfare.  In paper IV, we investigated possible effects of the hatchery treatment on production parameters. We found that HC weighed less, and laid fewer and smaller eggs than CC. HC performed more feather pecking behaviour before sexual maturity, although the feather condition after sexual maturity showed the opposite pattern. We conclude that there seems to be an effect of the hatchery treatment on traits relevant for the industry, and that this effect seems to be overall negative.   In the last study, paper V, we investigated if it is possible to buffer the hatchery stress with environmental enrichment. The enriched chicks were kept in a complex environment and imprinted on, and provided with, a stuffed mother hen. We could see a supressed physiological stress reaction to restraint in enriched HC, however, the opposite pattern was shown in CC. We found no other effects of environmental enrichment, how-ever, an overall difference between the groups where HC were more pessimistic and fearful than CC, which is in line with our previous results.   In conclusion, the hatchery procedure including incubation, hatching, conveying, sex sorting, vaccination, and transport seems to have an overall long-lasting negative effect on chicks, where HC are more fearful and pessimistic, have a more sensitive HPA-axis, show more feather pecking behaviour, and are negatively affected with regard to traits relevant to the industry. I think that these results are highly relevant, not only for the industry, but also for the welfare of the world’s most common farm animal.