William D. Fortney, DVM
Average puppy and kitten deaths during the first 12 weeks of life approach? 11%-34%. Still births or death within the first 24 hours account for 5% of the losses; an additional 5% loss occurs during the neonatal period; and 0%-5% loss in transitional & socialization periods. Infectious diseases are not the most common cause of neonatal or transitional period mortality.
The neonatal period is the first 4 week of life. During this critical period, the puppy or kitten has a different physiology and rate of development and than during the rest of the pediatric period. Once the puppy or kitten is 6- 8 weeks of age, then all of the development is complete and the youngster can be considered a "growing" adult.
Aging in dogs and cats is associated with gradual and progressive deterioration in the delicate body systems that eventually results in anatomical changes and decreased physiological functions. At some stage in the progressive decline, a "tipping point" is reached, where all of the physiological reserves are exhausted resulting in altered biochemical parameters; overt changes in diagnostic screening tests; and/or the onset of clinical symptoms of age-related disease occurs.
An animal's life can be divided into four stages; pediatric, adult, senior (middle age), and geriatric (senior / super senior). The senior / middle age years represents the transition period between the usually uneventful "healthy" adult years and the traditional "geriatric" age period where serious age related diseases are much more prevalent.