Alternative rib bone biopsy measurements to estimate changes in skeletal mineral reserves in cattle

Rib bone biopsy samples are often used to estimate changes in skeletal mineral reserves in cattle but differences in sampling procedures and the bone measurements reported often make interpretation and comparisons among experiments difficult. ‘Full-core’ rib bone biopsy samples, which included the external cortical bone, internal cortical bone and trabecular bone (CBₑₓₜ, CBᵢₙₜ and Trab, respectively), were obtained from cattle known to be in phosphorus (P) adequate (Pₐdₑq) or severely P-deficient (Pdₑfᵢc) status. Experiments 1 and 2 examined growing steers and Experiment 3 mature breeder cows. The thickness of cortical bone, specific gravity (SG), and the amount and concentration of ash and P per unit fresh bone volume, differed among CBₑₓₜ, CBᵢₙₜ and Trab bone. P concentration (mg/cc) was closely correlated with both SG and ash concentrations (pooled data, r=0.99). Thickness of external cortical bone (CBTₑₓₜ) was correlated with full-core P concentration (FC-Pcₒₙc) (pooled data, r=0.87). However, an index, the amount of P in CBₑₓₜ per unit surface area of CBₑₓₜ (PSACB; mg P/mm²), was more closely correlated with the FC-Pcₒₙc (pooled data, FC-Pcₒₙc=37.0+146×PSACB; n=42, r=0.94, RSD=7.7). Results for measured or estimated FC-Pcₒₙc in 10 published studies with cattle in various physiological states and expected to be Pₐdₑq or in various degrees of Pdₑfᵢc status were collated and the ranges of FC-Pcₒₙc indicative of P adequacy and P deficiency for various classes of cattle were evaluated. FC-Pcₒₙc was generally in the range 130 to 170 and 100 to 120 mg/cc fresh bone in Pₐdₑq mature cows and young growing cattle, respectively. In conclusion, the FC-Pcₒₙc could be estimated accurately from biopsy samples of CBₑₓₜ. This allows comparisons between studies where full-core or only CBₑₓₜ biopsy samples of rib bone have been obtained to estimate changes in the skeletal P status of cattle and facilitates evaluation of the P status of cattle.