Why they did it
Little information in the veterinary literature exists about changes in mineral metabolism that affect laboratory parameters in growing cats.
What they did
The authors of this study evaluated changes in laboratory parameters for calcium (total and ionized), phosphorus, magnesium, whole and intact parathyroid hormone (PTH), calcitriol (vitamin D), and calcidiol (a precursor to calcitriol) in 14 young cats. The European shorthaired cats had blood samples drawn every three months from age 3 to 15 months. The cats were housed in an animal care facility and were fed a commercial kitten diet throughout the study period.
What they found
Calcium, phosphorus, and magnesium concentrations all decreased with age. Phosphorus concentrations decreased at 12 months and were at their lowest by 15 months (5.3 mg/dl ± 0.1), while magnesium concentrations did not demonstrate a decrease until 15 months of age (2.7 mg/dl ± 0.1). Albumin concentrations were below normal at 3 months of age but were then stable throughout the study period.
The ratio of whole (biologically active) PTH to intact PTH declined progressively throughout the 12-month sampling period. Calcitriol concentrations declined beginning at 9 months of age and continued to decrease until 15 months, while calcidiol concentrations climbed between the 3- and 15-month sampling times. The authors propose that these changes are likely a result of changes in demand for calcium and vitamin D during the decline in the rate of skeletal growth.
Blood parameters related to mineral metabolism change throughout the growing process, and these values appear to stabilize by or shortly after 1 year of age. Age-related changes in vitamin D concentrations are particularly important when attempting to formulate a diagnosis in a patient suspected of having vitamin D-dependent rickets and highlight the need for age-specific laboratory parameters for analytes relating to mineral metabolism.
Pineda C, Aguilera-Tejero E, Guerrero F, et al. Mineral metabolism in growing cats: changes in the values of blood parameters with age. J Feline Med Surg 2013;15:866-871.
Link to abstract: http://jfm.sagepub.com/content/15/10/866.abstract