Rearing laying hens: Environmental complexity and genetic strain affect pullet but not chick performance in a T-maze learning task

Laying hens require well-developed cognitive spatial skills to find and retain the location of resources in a complex housing environment. Spatial skills develop early with a sensitive period in the first few weeks of life. We aimed to test whether the performance of laying hen chicks/pullets in a two-dimensional spatial learning task was affected by the degree of spatial complexity experienced during the first few weeks of life. We hypothesised that 1) increased spatial complexity during early life would improve the performance of laying hen chicks/pullets in a T-maze, 2) chick/pullet performance in the task would differ between genetic strains, and 3) genetic strain and rearing environment would have an interactive effect on performance in the task. Four flocks of brown and white feathered chicks were raised in conventional cages (Conv), and rearing aviaries with low (Low), intermediate (Mid), or high complexity (High) during the first six weeks. Chicks were tested during week four in a simple spatial task (T-maze) and given five trials to locate a mirror (social reward). In this test, the number of correct choices and the latency to choose were recorded. Pullets of flocks three and four were habituated, trained, and tested in a more extended spatial task (T-maze) during weeks 13 and 14. In the testing phase, they were given a maximum of 15 trials to learn the location of a reward (food plus the option to escape). The learning criterion was defined as four correct choices within five consecutive trials. Test performance of chicks, while overall poor, was mostly affected by flock (x2 = 19, p = 0.0003). In support of our hypotheses, pullets from High and Mid demonstrated improved learning performances (x2 = 12.98, p = 0.005). As expected, strain differences were found in both age groups, with white chicks being faster in choosing a side (x2 = 4.11, p = 0.04), and white pullets being quicker to reach the learning criterion than their brown-feathered counterparts (pullets: x2 = 28.44, p < 0.0001). There were no consistent genotype by environment interactions. In conclusion, laying hen spatial skills appeared to be sensitive to the degree of early life complexity as well as genetic strain.