Basic Rat Facts Average Life Span: 2.5 years Weaning Age: four to six weeks Beginning Age of Reproduction: 5 weeks Body Temperature: 99.5 to 100.6 degrees fahrenheit Heart Rate: 260 to 600 beat a minute Breathing Rate: 65 to 115 breaths per minute Average Weight: female - 13oz......male - 20oz Optimum Environmental Temperature: 72 degrees fahrenheit Average Daily Food Consumption: .7 - 1.5oz Average Daily Water Consumption: 1 - 2oz A rat's skeletal system.