Thermische manipulatie tijdens de incubatie van vleeskippen: Implicaties voor hitte resistentie, performantie en gedrag
Year: 2022
Type: dissertation
Abstract: The poultry production sector is being challenged and a lot of pressure is placed on its producers. Together with the increasing demand for animal welfare, there are many and necessary restrictions and environmental standards. Since most of the poultry production takes place in warm climate areas such as China, Brazil, Latin America and the Asia-Pacific regions, both outdoor as indoor bred animals are threatened by rising temperatures. Meat-type chickens, called broilers, are more sensitive to heat stress than egg-type chickens, called layers, due to their higher body weight and faster growth. Thermal discomfort from the heat poses a serious challenge for sustainable broiler production. Even in more moderate climate regions such as North America and Europe, heat stress occurs more often due to the increase in the number and intensity of heat waves. Several heat stress alleviating techniques are available ranging from management to genetic strategies. One of the more promising strategies is a process called thermal manipulation in which broiler eggs are exposed to high temperatures during their incubation. Epigenetic adaptations will prepare these animals for later life when challenged by heat and this by lowering their body temperature and basal metabolism. Despite the plethora of research conducted, it appears that thermal manipulation affects not only the thermoregulatory system but also performance parameters such as chick quality, hatchability and growth. Contradicting effects are found for similar or even identical treatments indicating the lack of knowledge about the functioning of thermal manipulations and the thermoregulatory system. Additionally, it has been shown that thermal manipulation influences fear and social behaviour in reptiles and the first indications in layers are found. Therefore, it is important to assess these effects as well. In this work, the potential of thermal manipulation is further explored by looking into the mechanisms behind it, investigated from a molecular level as well as evaluating its effects on fear and social behaviour. All of this while monitoring performance parameters. In the first part of this work, the mRNA expression levels of 22 potentially thermosensitive ion channels are measured in the brains of developing broiler embryos. Several of these channels were TRP (transient receptor potential) ion channels as these are known to be thermosensitive and responsible for peripheral and brain temperature sensing in mammals. However, very limited research is conducted in poultry. To study these channels in broilers, eggs were incubated in different temperature profiles (T1 and T2) during which brain samples were collected from incubation day 15 until hatch. We found 8 of the ion channels to be affected by treatment or by the interaction of treatment and day. In general, the expression of potentially heat sensitive ion channels was increased in both T1 and T2. However, the more intense T2 treatment managed to change the expression of more channels than T1. It seems that both treatments had an acclimatisation effect, probably as a result of epigenetic mechanisms, to adapt the animal to a life in which heat stress can occur. As validation, a heat challenge test in later life showed a numerical lowering for the number of mortalities for both T1 and T2, although the difference was not statistically significant. To evaluate the effects of T1 and T2 on fear and social behaviour, seven behaviour tests were conducted throughout the rearing period of 42 days. Both T1 and T2 increased social stress during isolation with T1's effects visible from week 4 onwards, whereas T2 increased the stress levels only in week 6. Interestingly, the social motivation to be with conspecifics of T2 males was increased from week 1 onwards. Prosocial behaviours are crucial for good animal welfare, especially as a high sociality can aid in coping with other stressors. The behaviour effects of two cold incubation profiles were also researched with one referred to as IT treatment, designed to increase performance variables, and the other one referred to as NT, designed to represent a nature like incubation. IT was found to increase the fear of a novel environment whereas NT males showed increased levels of social stress when in isolation. For all treatments, a variety of effects were found on performance parameters. The same as in literature studies. It is likely that the background of the broiler breeder farm and age of the breeders, the exact storage conditions and uncontrolled elements in the incubators such as humidity, O2 and CO2 interfered with the results. Even though some treatments had a negative effect on hatch performance such as lowering hatchability or chick quality, none of the treatments affected their growth during the full rearing period. All in all, treatment T2 seems like a potentially commercially applicable treatment due to its promising heat resilience improving effects, improvements in social motivation and no decrease in performance. Still, many questions are remaining especially concerning the more fundamental research on thermal manipulation, thermosensitivity, integration of signals etc. Epigenetic research is just starting to elucidate further mechanisms behind thermoregulation in general and the way thermal manipulation influences it. Many opportunities remain open in this field of research. The combination of epigenetic studies with computer supported data analysis such as Precision livestock farming techniques analysing biological data in real-time could be valuable for future monitoring and control of the incubation process concerning its temperature profile.
Source: Lirias
Author: Verlinden, Sara
Institution: KU Leuven
Language: English
Subfield: Animal Science and Zoology
Domain: Life Sciences
SDG: Zero hunger
Open Access status: green
OpenAlex ID: W7034396054