Effects of Food Deprivation and Seasons on Circadian Rhythm in Body Temperature and Bodyweight in Rouen Ducks under Tropical Conditions

Background: The present study investigated the effects of four days of fasting on colonic temperature (CT) and body weight responses in 20 adult male Rouen ducks (Anas platyrhynchos domesticus) during the hot-dry (12:12 light/dark cycles) and cold-dry (harmattan) (11:13 light/dark cycles) seasons under natural light/day cycles in tropical conditions. The ambient temperature and relative humidity of the pen and the CT of the ducks were recorded bihourly for four days before fasting and subsequently for another four days during fasting. During the fasting period food was completely withdrawn from the ducks at 06:00 h for four days (96 h), but the ducks were given access to clean drinking water ad libitum throughout the fasting period. Results: A major finding in the present study was that four days of food deprivation, photoperiods, season and duration of fasting did not induce hypothermia or changes in circadian rhythmic pattern of CT in the Rouen ducks. The result, for the first time, suggests that circadian modulation of fasting-induced hypothermia was lacking in Rouen ducks. The mesor and amplitudes of CT obtained during both the harmattan and hot-dry seasons before fasting were not different (P > 0.05) from those obtained during fasting. The acrophases in both seasons before and during fasting were restricted to the photophase at 14:00 h, except for the acrophase in fasted ducks during the hot-dry season, which was delayed to 16:00 h. Body weight of the ducks decrease significantly (P > 0.05) only on the 4th day of fasting. Conclusion: Overall, unlike other birds and mammals, the Rouen ducks showed greater starvation resilience, apparently due to an unknown component of fasting resistance or regional heterothermy. Future studies to elucidate the mechanism by which Rouen ducks were resistant to fasting are still required.