Seasonal animals have evolved diverse variations in physiology and behaviour to accommodate yearly changes in environmental and climatic changes. These changes are initiated by changes in photoperiod (daylength). Here we investigated the effect of photoperiod and high fat diets on the cognitive deficits, as measured by novel object recognition, in the photoperiod sensitive F344 rat, which exhibits marked natural changes in growth, body weight and food intake in response to photoperiod. 32 male juvenile F344 rats were housed on either long day (LD, 16 hrs light per day) or short day (SD, 8 hrs light per day) photoperiod conditions and fed either a high fat diet (HF, 45% fat by kcal) or a chow diet (nutrient matched). 8 rats/group were tested in the novel object recognition test before photoperiod and diet intervention and re-tested after 28 days of intervention. Briefly, rats were permitted to explore 2 identical objects for 3 minutes (acquisition trial); they were then taken out of the arena and returned to their homecage for a 1 min inter-trial interval (ITI). This was followed by a 3 min retention trial were rats were exposed to a familiar object and a novel object. The exploration time spent at the objects was recorded by an experimenter blind to the intervention group. In both tests during the acquisition trials there was no significant difference in exploration levels of the left and right objects in any of the groups. Before the intervention, all 4 groups showed a significant increase in exploration of the novel object compared to the familiar object: SD-chow (11.6±1.7 sec vs. 5.9±1.5, P<0.05), SD-high fat (11.6±2.4 sec vs. 7.6±2.3 sec, P<0.05), LD-chow (9.9±2.3 sec vs. 3.6±0.9 sec, P<0.05), LD-high fat (8.1±1.5 sec compared to 3.8±0.6, P<0.01). However, following the photoperiod and diet interventions the retention trial revealed that only rats in the LD-chow group explored the novel object significantly more than the familiar object (8.6±2.5 sec vs. 5.3±1.6 sec, P<0.05), whereas all the other 3 groups showed no significant preference. These results suggest that changing rats to SD impairs their ability to differentiate between the normal and familiar objects regardless of whether they eat chow or a high fat diet. The rats on LD-chow were still able to perform the task therefore their short-term recognition memory remained intact, whereas the high fat diet in the LD group induced an impairment in memory. These findings suggest that rats exposed to long photoperiod have different cognitive responses to rats exposed to short photoperiod and high fat diet.