FACTORS INFLUENCING FLOOR-LAYING BY HENS IN MODIFIED CAGES

Hens in modified cages, which incorporate nests, lay a variable proportion of eggs on the floor. This reduces the acceptability of this system as an alternative to the conventional battery cage. Observations were noted to determine if floor-laying was influenced by rearing hens in cages or on litter, by their age at transfer to the modified cages or social interactions. Cage- and litter-reared birds were obtained at 97 days of age and housed either immediately in modified cages or at 112, 129 or 145 days of age, after further time in conventional cages or on litter. Once all hens were housed in the modified cages, a 28-day observation period was conducted. Of the total eggs, 14% were laid on the floor, although the percentage of floor-eggs declined significantly during this period. A step-wise multiple regression revealed that age at transfer, rearing conditions and days since start of observations, together accounted for 40% of the variability in the percentage of floor-eggs laid per cage- Age was the most important contributory factor in the regression, with a significant positive relationship between age at transfer and percentage of floor-eggs. Litter-reared hens laid significantly more floor-eggs, made significantly more transitions in nest-site choice for reasons not obviously explicable by social interactions and made more transitions overall. These results indicate that litter-reared hens were less stable in their oviposition behaviour. During 9 consecutive days of the 28-day observation period, the majority of hens (69%) laid all their eggs in nests; a further 19% laid only 1-2 floor-eggs. Few hens used the floor consistently for laying. During the period of darkness the proportion of eggs laid on the floor was significantly greater than expected, but not during the morning or afternoon periods. The majority of hens used only one nest site; social interactions apparently influenced nest choice by others. Approximately equal numbers of the hens were gregarious or solitary in their nesting behaviour and this must be considered in future designs of modified cages.