Effect of photoperiod on body weight in the vole, Microtus montanus

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Abstract
Body weight in voles exposed to various photoperiodic treatments is shown to be significantly affected by the length of the photoperiod. Animals raised under a long (18 h per day) photoperiod gained weight more rapidly than animals raised under a short (6 h per day) photoperiod. Body weight of animals maintained outdoors appeared to fluctuate as a function of decreasing and increasing day length. Adults lost weight and subadults stopped gaining weight during the fall and early winter. All animals gained weight following the winter solstice during the coldest part of the winter. Thyroxine levels as determined by radioimmunoassay were significantly lower in voles maintained under a short (8 h per day) photoperiod than in voles maintained under a long (16 h per day) photoperiod.