Humane methods of killing for laboratory animals are expected by society and are essential for maintaining public trust in science. Robust application of the 3Rs and cost-benefit analysis underpins ethical approval of research involving animals, ensuring minimal harms are weighted against optimised benefits. Schedule 1 killing describes certain approved, assumed to be humane methods, commonly applied as part of scientific studies for tissue collection, to fulfil legal requirements on conclusion of the research work, or as a routine part of breeding of transgenic lines.
Domestic fowl (chickens) are the primary bird species used for experimental procedures in the UK, with 124,078 birds bred and used in experimental procedures in 2019 (Home Office, 2019). Large numbers of chicks are killed in the first week of life after genotyping, for husbandry management, or in research targeted at the neonatal stages of development. Current permitted methods for despatching newly hatched chicks are cervical dislocation, exposure to carbon dioxide (CO2) in a rising concentration, concussion of the brain and anaesthetic overdose. While these Schedule 1 methods have been assessed in rodents, the evidence base for their use and reliability in small birds is extremely limited or absent. In fact, there is a dearth of published studies evaluating Schedule 1 killing methods in birds of less than 7 days of age in research contexts, and despite the scale of the global poultry industry, relevant research in agricultural settings is also limited. Even studies on older birds have taken place in the farm animal context, where numerous practical and food safety constraints apply - most of which are not relevant to laboratory settings. For example, there is a lack of research on the welfare implications of exposure to a rising concentration of CO2 and the issue of CO2 exposure in general is becoming increasingly controversial. Overdose of anaesthetic via intravenous injection has been associated with good welfare outcomes, but it is difficult to perform in small and/or young birds and the handling involved can cause fear and distress. Intraperitoneal injection is associated with tissue irritation and extended time to death in rodents. Exposure to inert gases and hypobaric hypoxia (via exposure to gradual decompression) have been positively assessed in adult birds within the food chain and appear promising for chicks, but these are not currently available Schedule 1 killing methods. The remaining physical methods: concussion and cervical dislocation (which is most commonly used) are associated with significant issues in terms of reliability and training standards in adult chickens and their welfare implications in newly hatched chicks are unknown. In short, there is either limited or no evidence that current Schedule 1 methods for chicks are associated with acceptable welfare outcomes.
The aim of this project fills this knowledge gap by systematically evaluating the welfare implications of current and novel methods of killing of newly hatched chicks (of both broiler and layer strains), to (i) validate or reject current methods, depending on welfare outcomes; and (ii) underpin the addition of new humane methods to Schedule 1. We will integrate behavioural, physiological, neurophysiological and pathological data to assess the types and severity of suffering prior to loss of consciousness for each tested method, a robust approach that we have validated in previous work.
This project will result in detailed, scientifically sound guidance for killing methods of newly hatched chicks, ensuring humane deaths. Such guidance will be tailored to strain and age, improving the welfare of newly hatched chicks in research facilities. It is also likely that the findings will have important implications for routine procedures in poultry meat and egg production, where chicks are regularly culled.