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Het emissiearm stalsysteem bleek geen invloed te hebben op het optreden van voetzoollaesies en uitval bij vleeskuikens. Het seizoen, de leeftijd van de moederdieren, het vakmanschap van de vleeskuikenhouder en bedrijfsspecifieke aspecten wel. Dit blijkt uit onderzoek van Wageningen Livestock Research.

Pest and diseases in agricultural systems reduce the yield and quality of available food and feed worldwide. To meet the global growing demand for these products, losses should be reduced, preferably in a sustainable way. Integrated Pest Management (IPM) is a sustainable method that aims to minimize economic losses due to pests and diseases. IPM is generally based on eight steps: 1) prevention, 2) monitoring, 3) Decision‐making based on monitoring and thresholds, 4) use of non‐chemical methods, 5) pesticide selection, 6) reduced pesticide use, 7) anti‐resistance strategies, and 8) evaluation. With these steps, it is possible to prevent and control pests and diseases whilst deploying pesticides only as a last resort, thus reducing issues with pesticide contamination and resistance. Implementation of IPM by farmers increases when it is clear that it is compatible with existing farm processes and that it results in benefits for them. Successful IPM is most commonly applied against pests and diseases in crop production. When comparing the number of research articles on IPM in crop production with the number of research articles on IPM in animal production, it becomes clear that a paucity of scientific papers have been published on the latter. In laying hen facilities, for example, the application of all but basic IPM is still rare, even though the benefits of IPM have been described for poultry pests and disease vectors. In laying hen facilities Dermanyssus gallinae (PRM=poultry red mite), an hematophagous parasite, is common in many parts of the world. This mite is hard to control and negatively affects hen health, ‐welfare and farm economics, with estimated costs of infestation reaching 130 million euro per year in Europe. Currently, implementation of IPM for D. gallinae in laying hen facilities is limited to some combination of cleaning between flocks, limited preventive measures, and application of chemically or physically acting products. Implementation of more advanced IPM programmes for D. gallinae should therefore be considered to improve control prospects for this pest in laying hen facilities. This thesis focuses on the knowledge necessary for advancing IPM for D. gallinae in laying hen facilities. More specifically it focuses on prevention, monitoring and population modelling of this significant pest, with preventive measures and monitoring being key in advancing IPM per se. Knowledge assessment. To develop IPM for D. gallinae in laying hen facilities, biological and ecological knowledge of D. gallinae and knowledge of the effects of biotic and a‐biotic factors on this pests’ population development are required (Chapter 2). Therefore, a seminar was organized with eighteen D. gallinae researchers, from eight different European countries, with the aim of amassing existing expertise. This seminar gave insight into the current knowledge and knowledge gaps, regarding D. gallinae, also informing future perspectives and required developments for improving control of D. gallinae in laying hen facilities. During four sessions, the researchers present discussed lifecycle issues, effects of D. gallinae on hen and egg production, monitoring methods for D. gallinae infestations in laying hen facilities and control methods for D. gallinae in laying hen facilities. It was concluded that, where the D. gallinae lifecycle is concerned, a lot is still unknown about the mites feeding behaviour and preferences, mating behaviour, survival and conditions required for reproduction, host finding, aggregation cues, and attractant and repellent substances. When focusing on the effects of D. gallinae on the hen and on egg production it was agreed that a D. gallinae infestation is likely to result in higher water intake, lower egg production, lower feed conversion, increase of the immune response and reduced feather quality. It was also suggested that these effects may be hen genotype dependent, and further noted that effects are rarely quantified and need further investigation. Though monitoring was considered to be most important to improve control of D. gallinae, it was concluded that the available monitoring methods only indicate trends and a robust monitoring plan is lacking. The participants considered heating the hen house combined with a chemical treatment to be the most promising control method. Future promising developments for control of D. gallinae were considered to be use of vaccination, predatory mites and entomopathogenic fungi. The effects of D. gallinae on human health were not extensively discussed, but it was concluded that D. gallinae can be of medical significance, either directly via reaction to mite bites, or indirectly via human exposure to the chemicals used to control D. gallinae. Prevention. To acquire knowledge on the routes of introduction and spread of D. gallinae in laying hens facilities, the Hazard Analysis and Critical Control Points (HACCP) system was used (Chapter 3). The structure of this system allows the user to identify the risk factors and the critical control points for the introduction and spread of pathogens and parasites. This method was further used to identify preventive and corrective actions against D. gallinae. Four experts identified 41 hazards for introduction and spread of D. gallinae in laying hen facilities. To prevent these hazards, these experts made several suggestions for corrective actions. The risks of 41 hazards were calculated by multiplying the likelihood (1= occurring seldomly/theoretically; 2= occurring approximately once a year; 3= occurring repeatedly/more than once a year) by the severity (1 = low / single place in the facility becomes infested with D. gallinae; 2= moderate/ facility becomes infested at more than one location; 3= high/ D. gallinae infestation occurs at almost all places within the laying hen facility) of infestation. Hazards with a risk above 3, or with a severity of 3, were regarded as Critical Control Points (CCP’s). The CCP’s with the highest risks (risk of 6 and higher) for introduction of D. gallinae in laying hen facilities were: introduction of new flocks, containers and crates, the farmer and their employees. The CCP’s with the highest risks (risk of 6 and higher) for spread of D. gallinae between laying hen facilities were mice, rats and flies, wild birds, the feeding system, shared material and equipment, the egg conveyer belt, manure aeration pipes, removal of cadavers, visitors and external personnel, the farmer and their employees. The critical limits, a procedure step of the HACCP system which will be followed by a corrective action when the limit is exceeded, could not be determined as a result of lack of knowledge about thresholds. Subsequently, suggestions were made for monitoring the mite population and for documentation and validation. A checklist was devised using the corrective action from the CCP’s with the highest risks. This management tool for layer farmers was evaluated by UK and Dutch layer farmers as feasible and useful. Monitoring. The approach of Reflexive Interactive Design (RIO) was used to design an automated monitoring tool for D. gallinae, including an automated mite detection sensor (Chapter 6). The approach generated effective and technically feasible solutions for the key functions of the automated mite detection sensor, these being 1) the assessment of the D. gallinae population, 2) localizing the location and assessing the time of detection and 3) removal of mites from the detection area. Three different design concepts were designed using these solutions. As an additional, albeit proven essential step to the RIO approach, the main solutions were tested with live mites ensuring the alignment of solutions with the biology and behaviour of D. gallinae in vivo. A combination of the best solutions were developed in two different prototypes. These prototypes were subsequently tested in the laboratory and on farm. The prototype situated under the perch, with a through beam sensor and a pump to remove mites from the sensor after recording, was the most successful model. The designed automated mite detection sensor, or automated mite counter, for D. gallinae was subsequently validated in experimental laying hen cages with live birds and a growing population of D. gallinae (Chapter 5). The study resulted in 17 data points, each being a combination of ‘number of mites counted’ by the automated mite counter and the ‘number of mites present’ in the experimental laying hen cages. The regression line between the ‘number of mites counted’ and the ‘number of mites present’ demonstrated that the automated mite counter was able to track the D. gallinae population effectively. Population modelling. Step 2 of IPM describes not only pest monitoring in the field, but also ‘scientifically sound warning, forecasting and early diagnosis systems, where feasible, as well as the use of advice from professionally qualified advisors’. To advance this step for D. gallinae we developed and demonstrated an operational model, forecasting the mite population dynamics and evaluating and forecasting the effect of a treatment application for D. gallinae in laying hen facilities. For IPM this model and the required inputs need to be 1) labour‐extensive with minimal staff input, preferably automatically implementing “real time” measurement data into models; 2) operational, providing easily interpretable data, forecasting pest population dynamics and the moment a threshold will be exceeded; 3) able to compensate for different locations and time‐specific‐interactions and variables (e.g. management and temperature), enabling the handling of variability of the parameters of interest; 4) able to identify pest hotspots; 5) able to estimate and forecast treatment efficacy; and 6) applicable for different monitoring methods and therefore able to correct for monitoring measurement errors. Prior to the development of the population dynamics model a high variation in population growth was found which could be only partly explained by temperature, flock age, treatment, and compartment/laying hen facility. A substantial part of the total variation remained unexplained, or was found to be temporal. As a result of this partly temporal variation, a dynamic approach was suggested to improve the forecasting quality of a population dynamics model. With the input of population monitoring data, temperature data and information of the dates of any D. gallinae treatment interventions, the developed model was able to forecast the population dynamics of D. gallinae post treatment and without treatment while compensating for location and time specific interactions, handling the variability of the parameters. Moreover, this population dynamics model was able to forecast the D. gallinae population using data from different monitoring methods. Together with the models compatibility with different housing systems and its ability to forecast the mite population dynamics (requiring only three relative easy obtainable parameters), this model is an improvement over existing approaches for forecasting D. gallinae that could contribute to steps 2 and 8 of IPM for D. gallinae in laying hen facilities. The results from this study directly facilitate advanced IPM programmes for D. gallinae in laying facilities. The new ‘products’ developed are tools for prevention, monitoring, forecasting population dynamics and evaluating treatment effects, representing the requirements of IPM steps 1, 2, and 8. Indirectly the results may accelerate the development of new control measures, with knowledge acquired through use of the developed products it also is likely to contribute to IPM steps 3, 4, 6 and 8 in the future; e.g. the determination of an action threshold, and a tool advising farmers on the most effective and economic time for applying a corrective action or hotspot treatment for D. gallinae. With the obtained knowledge and new products implemented to control D. gallinae in laying hen farms, major advances can be made in IPM for this pest. More specifically, as a result of this work IPM for D. gallinae in laying hen facilities can be advanced by the identification of preventative control measures, the development of an automated monitoring tool and a model forecasting mite population dynamics and evaluating applied treatments. Consequently, the results of this study can be expected to improve hen health, welfare and farm economics for the egg production industry. In the future, advances in other IPM programmes can be expected when the obtained knowledge, tools and methods are transferred to other pest species in multiple sectors.

Informatie over omvang en grootte van kippenhouderijen in Nederland en de verdeling per bedrijfssysteem.

The course for later life immune responses is set early in life during the developmental phase of the immune system and accordingly disturbances of immune development may have long-term consequences for host health. In terms of immune activation and immune development the gut microbiota play an important role and consequently disturbances of early life microbial colonization may affect host immunity later in life. In chickens, disturbances of microbial colonization may be caused by various early life conditions which in turn may affect robustness of the chick in the long term. The aim of this thesis was to assess the effects of several early life factors including time of access to feed post hatch (immediately or 72 hours delayed), housing conditions, antibiotic treatment, and intestinal pathology on the intestinal microbiota composition, immune development, and specific antibody response later in life in chickens. Additionally, possible differences between broilers and layers were taken into account as unintentional co-selection of immunological traits may have taken place during the selection process for different production traits. Delayed access to feed and administration of antibiotics early in life led to a shift in early life microbiota composition, which seemed to be restored quite quickly in both cases. Microbiota composition in response to DSS was not investigated, but based on rodent studies was expected to be influenced. Ileal immune development, which was assessed in terms of relative cytokine and immunoglobulin mRNA expression levels was not affected by feeding strategy post hatch (early vs. delayed), but a downregulation of ileal immunoglobulin expression levels could be observed during DSS treatment. All early life factors investigated affected the specific antibody response towards an immunological challenge later in life. Interestingly, there seemed to be an interaction between immediate access to feed post hatch and immune responsiveness towards the environment, thus early feeding may influence the adaptive capacity of chickens in different environments. Regarding the differences between breeds it is interesting to note that broilers seem to have developed a more humoral oriented immune strategy, while layers seem to react in a more pro-inflammatory way. Taken together, results suggested that early life conditions may influence priming of the immune system during its developmental phase, leading to altered antibody responses later in life. Furthermore, broilers and layers seem to have developed different immune strategies. Early life conditions as well as possible differences between breeds should therefore be taken into account in future immunological studies.

The course for later life immune responses is set early in life during the developmental phase of the immune system and accordingly disturbances of immune development may have long-term consequences for host health. In terms of immune activation and immune development the gut microbiota play an important role and consequently disturbances of early life microbial colonization may affect host immunity later in life. In chickens, disturbances of microbial colonization may be caused by various early life conditions which in turn may affect robustness of the chick in the long term. The aim of this thesis was to assess the effects of several early life factors including time of access to feed post hatch (immediately or 72 hours delayed), housing conditions, antibiotic treatment, and intestinal pathology on the intestinal microbiota composition, immune development, and specific antibody response later in life in chickens. Additionally, possible differences between broilers and layers were taken into account as unintentional co-selection of immunological traits may have taken place during the selection process for different production traits. Delayed access to feed and administration of antibiotics early in life led to a shift in early life microbiota composition, which seemed to be restored quite quickly in both cases. Microbiota composition in response to DSS was not investigated, but based on rodent studies was expected to be influenced. Ileal immune development, which was assessed in terms of relative cytokine and immunoglobulin mRNA expression levels was not affected by feeding strategy post hatch (early vs. delayed), but a downregulation of ileal immunoglobulin expression levels could be observed during DSS treatment. All early life factors investigated affected the specific antibody response towards an immunological challenge later in life. Interestingly, there seemed to be an interaction between immediate access to feed post hatch and immune responsiveness towards the environment, thus early feeding may influence the adaptive capacity of chickens in different environments. Regarding the differences between breeds it is interesting to note that broilers seem to have developed a more humoral oriented immune strategy, while layers seem to react in a more pro-inflammatory way. Taken together, results suggested that early life conditions may influence priming of the immune system during its developmental phase, leading to altered antibody responses later in life. Furthermore, broilers and layers seem to have developed different immune strategies. Early life conditions as well as possible differences between breeds should therefore be taken into account in future immunological studies.

In de komende jaren moeten stallen voldoen aan de eis van maximale ammoniakemissiewaarden volgens de AMvB huisvesting. Om een idee te krijgen van de kosten die gemoeid zijn met het terugdringen van de ammoniakemissie op pluimveebedrijven heeft het Praktijkonderzoek een inventarisatie uitgevoerd naar de extra investeringen en het extra energieverbruik van de systemen die voldoen aan de maximale emissiewaarde van AMvB huisvesting, met een onderscheid in stallen voor leghennen, voor vleeskuikenouderdieren en voor vleeskuikens

De Wageningse projectgroep "Houden van Hennen" heeft twee ontwerpen gemaakt voor houderijsystemen, het Rondeel en de Plantage, voor leghennen waarin de wensen van kippen, pluimveehouders en burgers samenkomen

Het projectteam van het project "Houden van hennen" heeft zich bezig gehouden met het "Programma van Eisen". In dit artikel wordt ingegaan op de behoeften van de leghen en de pluimveehouder en de daaruit voortkomende eisen en mogelijke oplossingen

Door Het Spelderholt werd een proef gedaan naar een overdekte buitenuitloop voor vleeskuikens in de tweede helft van de groeiperiode. De proef geeft aanwijzingen voor een welzijnsverbetering, maar vervolgonderzoek moet dit uitwijzen

Het effect van huisvestings- en managementmaatregelen op de ammoniakemissie bij leghennen, vleeskuikens, kalkoenen en eenden is door Wageningen UR Livestock Research onderzocht.

De kostprijzen liggen ruim 40 eurocent per hen hoger dan in de vorige berekening uit 2010. De kostprijs per afgeleverde hen staat in tabel 1. In de 2e tabel staan de investeringskosten per hen en de kuikenprijs. In de 3e tabel staat de gevoeligheidsanalyse kostprijs 17-weekse hen.

Dust, both coarse and fine (PM10), is emitted mainly through the exhaust fans of livestock housing and especially through the exhaust fans of poultry housing. There is little known about the dispersion of the emission plume of an exhaust fans of funnel ventilation systems at a short distance of the housing (30 to 40 m). It is known that a hedgerow has a profound effect on an emission plume as both wind speed and wind direction are affected. However, up till now it is not clear how an emission plume is changed. Stof, grof en fijn, wordt vooral via de ventilator van veehouderijbedrijven in de lucht gebracht en in het bijzonder via de ventilatoren van kippenstallen. Het is niet bekend hoe een emissiepluim van ventilator(en) van lengteventilatiesystemen eruit zien op korte afstand van de stal (tot 30 à 40 m). Wel is bekend dat een groenelement invloed heeft op de emissiepluim, doordat de pluim door een groenelement zowel van richting als van impuls verandert. Het is echter onbekend wat deze veranderingen zijn.

In this report the results of the project ‘Implementation of the broiler welfare assessment protocol’ are summarised and presented for the participating broiler farmers, slaughter plants and veterinarians. The following topics are discussed: validity and feasibility of measures, which measures need to be improved; possibility for simplification of the assessment protocol (reduction of assessment time); management changes and the effects: is the assessment protocol suitable to support farmers’ management?; feedback from the participants.

Dust, both coarse and fine (PM10), is emitted mainly through the exhaust fans of livestock housing and especially through the exhaust fans of poultry housing. There is little known about the dispersion of the emission plume of an exhaust fans of funnel ventilation systems at a short distance of the housing (30 to 40 m). It is known that a hedgerow has a profound effect on an emission plume as both wind speed and wind direction are affected. However, up till now it is not clear how an emission plume is changed.

In the current report, two topics related to our study on the implementation of the Welfare Quality® broiler assessment protocol are discussed. First, animal-based measures for broiler welfare, currently included in the Welfare Quality® broiler assessment protocol, are discussed with respect to their suitability as outcome-based measure in future legislation or regulations. Practical experiences with the measures and supporting literature are used to judge the various animal-based measures. Second, the Welfare Quality® broiler assessment protocol is discussed with respect to a simplification, the relevance of the various measures and the aggregation model, and it is suggested how the assessment protocol can be applied in practice.

Het emissiearm stalsysteem bleek geen invloed te hebben op het optreden van voetzoollaesies en uitval bij vleeskuikens. Het seizoen, de leeftijd van de moederdieren, het vakmanschap van de vleeskuikenhouder en bedrijfsspecifieke aspecten wel. Dit blijkt uit onderzoek van Wageningen Livestock Research.

Door middel van een case-control studie is onderzoek gedaan naar veronderstelde risicofactoren voor introductie van laag-pathogene aviaire influenza (LPAI) virus op pluimveelegbedrijven met vrije uitloop. Onder een LPAI virus werd in dit onderzoek verstaan: een aviair influenza virus van elk subtype (H1 tm H16), met uitzondering van de hoog pathogene aviaire influenza (HPAI) virussen. Veertig bedrijven met een LPAI virus introductie in het verleden (cases) zijn vergeleken met 81 bedrijven waar geen introductie heeft plaats gevonden (controls) om te onderzoeken of potentiële risicofactoren voor een besmetting met een LPAI virus geïdentificeerd kunnen worden. Vragen over aanwezigheid van potentiële risicofactoren zijn door middel van enquêtes voorgelegd aan de pluimveehouders.

In this report the results of the project ‘Implementation of the broiler welfare assessment protocol’ are summarised and presented for the participating broiler farmers, slaughter plants and veterinarians. The following topics are discussed: validity and feasibility of measures, which measures need to be improved; possibility for simplification of the assessment protocol (reduction of assessment time); management changes and the effects: is the assessment protocol suitable to support farmers’ management?; feedback from the participants. Dit rapport is de eindrapportage van het project welzijnsmonitor vleeskuikens voor de deelnemende vleeskuikenhouders, slachterijen en dierenartspraktijken. In het rapport komen de volgende onderwerpen aan de orde: praktische ervaringen: welke metingen zijn valide en goed uitvoerbaar en welke metingen behoeven verbetering; mogelijkheden om de monitor te vereenvoudigen (minder tijdrovend te maken); managementaanpassingen en het effect daarvan: is de monitor geschikt als instrument om het management te ondersteunen?; terugkoppeling vanuit de deelnemers.

In this study the diurnal variations in bacteria and endotoxin concentrations and emissions in houses for finishing pigs and broilers were determined.

This report describes the result of a field study in which the effects of low emission housing systems on mortality rate and footpad dermatitis score of broilers was studied. Dit rapport beschrijft de resultaten van een onderzoek waarbij de effecten van het emissiearme huisvestingsystemen op uitvalspercentage en voetzoollaesiescore bij vleeskuikens werd bestudeerd.

In this study the diurnal variations in bacteria and endotoxin concentrations and emissions in houses for finishing pigs and broilers were determined. De doelstelling van dit onderzoek is om de binnen-dag variatie in bacterie- en endotoxineconcentraties en –emissies vast te stellen. Dit is gedaan voor twee belangrijke diercategorieën, namelijk vleesvarkens en vleeskuikens.

Andere verwarmingssystemen, ander type kuiken. Het is misschien wel tijd om de minimale ventilatiebehoefte te herzien. WUR Livestock Research deed daarom onderzoek.

Door middel van een case-control studie is onderzoek gedaan naar veronderstelde risicofactoren voor introductie van laag-pathogene aviaire influenza (LPAI) virus op pluimveelegbedrijven met vrije uitloop. Onder een LPAI virus werd in dit onderzoek verstaan: een aviair influenza virus van elk subtype (H1 tm H16), met uitzondering van de hoog pathogene aviaire influenza (HPAI) virussen. Veertig bedrijven met een LPAI virus introductie in het verleden (cases) zijn vergeleken met 81 bedrijven waar geen introductie heeft plaats gevonden (controls) om te onderzoeken of potentiële risicofactoren voor een besmetting met een LPAI virus geïdentificeerd kunnen worden. Vragen over aanwezigheid van potentiële risicofactoren zijn door middel van enquêtes voorgelegd aan de pluimveehouders.

This report describes the results of emission measurements of ammonia, odour, PM10, methane and nitrous oxide from broiler houses bedded with white wood shavings (=control), fresh silage maize or pre-dried silage maize.

This report describes the result of a field study in which the effects of low emission housing systems on mortality rate and footpad dermatitis score of broilers was studied.

This report describes the results of emission measurements of ammonia, odour, PM10, methane and nitrous oxide from broiler houses bedded with white wood shavings (=control), fresh silage maize or pre-dried silage maize. Dit rapport beschrijft de resultaten van emissiemetingen van ammoniak, geur, fijnstof (PM10), methaan en lachgas uit vleeskuikenstallen ingestrooid met witte houtkrullen, verse snijmaissilage en voorgedroogde snijmaissilage.

In the current report, two topics related to our study on the implementation of the Welfare Quality® broiler assessment protocol are discussed. First, animal-based measures for broiler welfare, currently included in the Welfare Quality® broiler assessment protocol, are discussed with respect to their suitability as outcome-based measure in future legislation or regulations. Practical experiences with the measures and supporting literature are used to judge the various animal-based measures. Second, the Welfare Quality® broiler assessment protocol is discussed with respect to a simplification, the relevance of the various measures and the aggregation model, and it is suggested how the assessment protocol can be applied in practice. Dit rapport bediscussieert twee onderwerpen in relatie tot het onderzoek naar de implementatie van de Welfare Quality® vleeskuikenassessment protocol. Als eerste worden dierkenmerken, die op dit moment onderdeel zijn van het Welfare Quality® vleeskuikenprotocol, besproken met betrekking tot de geschiktheid om als doelkenmerk te worden opgenomen in toekomstige wet- of regelgeving. De beoordeling van de dierkenmerken is gedaan op basis van ervaringen met het meten van de diverse kenmerken en een literatuurstudie. Vervolgens wordt de welzijnsassessment protocol besproken in relatie tot een vereenvoudiging, de (on)bruikbaarheid van de indicatoren en het integratiemodel, en wordt een advies gegeven met betrekking tot de toepassing van de assessment protocol in de praktijk.

Bij legkippen ontwikkelt zich vaak verenpikken, het beschadigen of uittrekken van veren van soortgenoten, en soms ook kannibalisme, het verwonden van soortgenoten en het consumeren van bloed of vlees. Het uittrekken van veren levert pijn en ongemakt op voor het dier dat gepikt wordt. Het slachtoffer krijgt kale plekken op haar lichaam, hetgeen kan resulteren in problemen met de warmtehuishouding. Ook zijn de kale plekken aantrekkelijk voor soortgenoten om naar te pikken. Dit kan leiden tot ontwikkeling van kannibalisme, hetgeen gepaard gaat met een sterk verminderd welzijn en hoge uitvalspercentages. In het proces van domesticatie is de kip vanuit de vrije natuur naar het boerenerf verplaatst, vervolgens naar een afgesloten kippenren, en tenslotte naar de legbatterij, waar de dieren in kleine groepjes in kooien worden gehouden. Deze verhuizing van de vrije natuur naar de legbatterij heeft voor- en nadelen voor de kip gehad. Wat betreft de beschikbaarheid van voedsel en bijvoorbeeld bescherming tegen ziekte en predatie is de kip erop vooruit gegaan, maar wat betreft levensruimte en mogelijkheid tot het vertonen van het complete gedragsrepertoire, biedt de legbatterij weinig ruimte en mogelijkheden

'Welzijn bestaat niet', is een gevleugelde uitdrukking van één van mijn collega's. Deze weliswaar ietwat ongenuanceere stelling geeft het probleem weer waarmee een gedragsbioloog in het welzijnsonderzoek geconfronteerd wordt: welzijn is niet direct meetbaar. Want de aanname is dat een dier zelf uitmaakt hoe het met zijn welzijn gesteld is. Dat hangt af van de omstandigheden waarin het dier zich bevindt. Maar hoe komt een etholoog te weten hoe een dier de eigen situatie beoordeelt? Je kunt er niet naar vragen. Nou ja, je kunt er wel naar vragen, maar een antwoord zul je niet krijgen. Of misschien toch wel? Het promotie-onderzoek van Patrick Zimmerman richtte zich op de vraag of het welzijn van leghennen te meten is op basis van geluiden die ze maken