Aversion of chickens to various lethal gas mixtures

Abstract

AbstractIn the event of a notifiable disease outbreak, poultry may need to be culledin situ. This should be performed swiftly and humanely to prevent further spread of the pathogen while preserving the welfare of the animals prior to death. Here, we examined the aversion of broiler chicks(Gallus domesticus)to three lethal gas mixtures at various concentrations to determine the least aversive mix that could be used in whole-house gassing. For 1 h, individual chicks (n = 36) were allowed to place their heads inside three feeding and drinking stations (FDS) in order to access food and water. Each FDS was filled with a different gas mixture, and birds could access each FDS as much as they liked. Twelve chicks each were tested at low (50% carbon dioxide [CO2] in air, 70% argon [Ar] in CO2, 70% nitrogen [N2] in CO2), medium (55% CO2in air, 80% Ar in CO2, 80% N2in CO2) or high (60% CO2in air, 90% Ar in CO2, 90% N2in CO2) concentrations of gas mixtures. Aversion was assessed based on the time birds spent with head in each FDS (with more time indicating less aversive), and the frequency of head shakes relative to time spent with head in the FDS (with a lower proportion indicating less aversive). Data were analysed by ANOVA. On average, birds spent < 3 min with their head in any FDS. Mixtures containing 90% Ar or N2in CO2and 80% argon in CO2were least aversive and mixtures containing 70% N2in CO2and 60% CO2in air were most aversive, based on time spent with head in. Head shakes s−1were more frequent with low concentration gas mixtures compared to high concentrations, and with all CO2in air mixtures, which suggests that the intensity of head shaking is related to the concentrations of CO2. From these results, one concentration of each of the three gas mixtures (90% N2in CO2, 80% Ar in CO2, and 50% CO2in air) were chosen for assessment on a further 12 birds and the results showed that both inert gas mixtures were less aversive than 50% CO2in air based on time spent with head in. Frequency of head shakes s−1did not differ between the three mixtures. Birds found all gases aversive, however it is concluded that inert gas in CO2mixtures were least aversive compared to CO2in air and these gases also caused less signs of respiratory discomfort.