Effects of population size and cage area on agonistic activity and social structure of White Leghorn layers.

Four caging environments consisting of two population sizes (4 vs. 6 birds/cage) and two cage area allocations (316 vs. 406 cm2/bird) were evaluated for their effects on agonistic activity, social structure, and egg production of Single Comb White Leghorn layers. Wire battery laying cages were designed and constructed to study these effects in a nonconfounded approach while maintaining feed trough space constant. Agonistic activities and dominance structure for the treatment groups were assessed during Weeks 23 to 26 and 37 to 40; egg production was obtained for Weeks 20 to 40. Cage groups demonstrated a high degree of linearity (K) for dominance hiearchies during both observational periods. Values for K ranged from a low of .69 during Period 1 to as high as .91 during Period 2. Cage groups were also very stable over observation periods; correlation coefficients for dominance ranks between Periods 1 and 2 averaged .95 and .89 for the four and six-bird groups, respectively. Greater cage area and population size resulted in more agonistic activity during Period 1, but only in the 6/406 cm2 treatment during Period 2. The alpha individual was responsible for the most aggressive acts committed in all cage groups (40 to 50%). Aggressive activity was observed to decline in a linear manner with declining dominance rank. Egg production was significantly affected by population and density treatments during Period 2; however, correlations between aggressive acts per cage and egg production were not generally significant.