Photoperiod is known to cause physiological changes in seasonal mammals, including changes in body weight and reproductive status. The objective of this study was to determine the effect of increased photoperiod (longer days) on voluntary physical activity levels, resting metabolic rate, food intake required to maintain body weight, and fasting serum leptin and ghrelin concentrations in adult cats.
Eleven healthy, adult, neutered, male domestic shorthair cats were used in a randomized crossover design study. During two 12-week periods, cats were exposed to either a short-day (SD) photoperiod of 8 hours light: 16 hours dark, or a long-day (LD) photoperiod of 16 hours light: 8 hours dark. Cats were fed a commercial diet to maintain baseline body weight.
In addition to daily food intake and twice-weekly body weight, resting metabolic rate (via indirect calorimetry), body composition (via dual-energy X-ray absorptiometry-DEXA) and physical activity (via Actical activity monitors) were measured at week 0 and 12 of each period. Fasting serum leptin and ghrelin concentrations were measured at week 0, 6 and 12 of each period. Average hourly physical activity was greater in LD versus SD cats, which was primarily due to increased dark period activity. This corresponded to higher daily metabolizable energy intake and increased resting metabolic rate in LD cats. Body composition, serum leptin and serum ghrelin were not altered by photoperiod.
More research is needed to determine potential mechanisms by which these physiological changes occurred and how they may apply to weight management strategies.