Below is a summary of the ideals a rat should be :

 

General
Average Life Span	24-42 months
Body temperature	37.5-38.2oC 99.5-100.8oF
Respiratory rate	70-150/min
Heart Rate	250-480 bpm
Blood pressure	(60-90)/(75-120) mm Hg
Average Weight
At Birth	5-6 g
At 12 weeks	Female: 150-270 g Male: 200-400 g
Adulthood	Female: 250-500 g Male: 450-800 g
Reproduction And Development
Oestrus Cycle	Every 4-6 days
Oestrus Period	Approx.12 hours
Gestation	21-23 days
Duration of mating period	9-20 hours
Litter Size	6-12 (varied depending on age)
Nursing period	Approx. 28 days
Hair coat	9 days
Eyes open	10-12 days
Testes descend	15-50 days
Puberty	Females: 34-38 days Males: 42-47 days
Female Menopause	64-77 weeks

 

References : 1, 5

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