Do I turn left or right? Effects of sex, age, experience and exit route on maze test performance in sheep.

Brain development and function are susceptible to perturbation by environmental factors. Sheep are increasingly being used as a neurodevelopmental model due to timing similarities with humans, but effects of age, experience and sex on cognition are not well characterised in this species. We therefore studied memory and reversal learning in sheep using a modified Y-maze at two ages: naive 18 weeks old (18N: 23 male, 17 female), experienced 40 week old sheep that had previously been tested at 18 weeks (40E: 22 male, 17 female), and naive 40 weeks old (40N: 4 male, 10 female). Younger naive animals (18N) required more trials and time to solve the first reversal task (task R1) than 40E (P=0.007 and P<0.001 respectively). Experience also improved outcomes, with 40N sheep requiring more time to solve tasks L (P=0.034) and R1 (P=0.002) than 40E. Increasing age (40N cf. 18N) decreased bleat frequency in tasks R1, M2 and R2 (each P<0.05). In 40N females, outcomes also differed by exit method in task R1, with those that exited via an indirect route taking less time to pass tasks R1 (P=0.009) and R2 (P=0.015) than those that used a direct route. Age plus experience improved learning outcomes, demonstrating knowledge retention for 22 weeks in this species, whilst age alone affected mostly behavioral responses. These results provide comparison data, and can be utilised to improve experimental design, for studies of neurodevelopment in the sheep.