Regulatory guidelines and best practices in the care of research animals allow diets milled for laboratory animals to be used within 180 d of formulation but otherwise permit latitude and professional judgment in how and when feed is offered. As such, practices at some research institutions allow for the replenishment (‘topping up’) of fresh chow over that existing in the cage food hopper, rather than complete replacement of the diet on a regular basis. To determine the depletion rate of a pelleted diet as fed from a conventional overhead food hopper, the consumption of full hoppers of food was measured for breeding pairs of mice in production and gender-specific groups of weanlings and juvenile mice kept in ventilated cages at 71.9 ± 0.2 °F (approximately 22.6 °C) and 40% ± 5% relative humidity. Breeding pairs of mice depleted 97% of a 250-g ration within 44 d of offering and consumed diet at a rate of 4.7 ± 0.5 g per mouse daily. Gender-grouped weanling and juvenile mice housed 5 to 6 per cage exhausted more than 99% of a 500-g ration of diet in 24 d and consumed chow at a rate of 3.4 ± 0.3 g per animal daily. These findings suggest that breeding pairs and groups of mice kept 5 to 6 per cage deplete feed at such a rate that diets can be fed by using replenishment provided diet is offered within 5 mo of the milling date
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