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Group size and phenotypic appearance: Their role on the social dynamics in pullets

By Irene Campderrich, Guiomar Liste, Inma Estevez

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Abstract

Non-caged production systems offer greater freedom of movement and behavioural opportunities to pullets, which may also include the occurrence of undesired behaviours. The incidence of such behaviours may be affected by group size but also by the group memberś phenotype. This study was designed to explore the effects of group size and phenotypic appearance in the social dynamics of pullets. A total of 1050day old Hy-line Brown was randomly assigned to 45 pens at 3 group sizes (GS), 10, 20 and 40 birds (constant density 8 hens/m2). For all GS treatments, the phenotypic appearance (PA) of different bird proportions was modified with a black mark at the back of their head. Two types of populations were studied: homogenous (0, 100%) with all pen members presenting the same marked (M) or unmarked (U) phenotype, and heterogeneous (30, 50, and 70%) were the two phenotypes (M and U) coexisted in the same pen. All pens were observed during rearing on alternate weeks. Aggressive and affiliative social interactions performed among group members were registered together with their PA (M or U). The observed and expected mean frequencies for all phenotype combinations involved in the social interaction were calculated: MM, MU, UU and UM, where the giveŕs phenotype is indicated by the first letter and the receiveŕs phenotype by the second letter. Data were analysed with mixed model ANOVAs that included GS and PA as fixed factors for the general model, and GS, PA and type of interaction (MM, MU, UU, UM) to determine the direction of the interaction in the case of heterogeneous groups. Both aggressive (threats) and affiliative interactions (exploratory pecking and beak pecking) were more frequent in small (10) than in large (20, 40) GS (P0.05; GS×PA, P>0.05). Aggressive interactions however, occurred at a higher than expected frequency in heterogeneous GS 20, and were predominantly from U towards M birds (UM; P

Publication Title Applied Animal Behaviour Science
Volume 189
Pages 41-48
ISBN/ISSN 0168-1591
DOI https://doi.org/10.1016/j.applanim.2017.01.014
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Tags
  1. Aggression
  2. Group size
  3. Hens
  4. Interactions
  5. phenotypes