Regional femoral bone blood flow rates in laying and non-laying chickens estimated with fluorescent microspheres

Abstract

The metabolic rate of vertebrate bone tissue is related to bone growth, repair and homeostasis, which are all dependent on life stage. Bone metabolic rate is difficult to measure directly, but absolute blood flow rate (Q̇) should reflect local tissue oxygen requirements. A recent 'foramen technique' has derived an index of blood flow rate (Qi) by measuring nutrient foramen sizes of long bones. Qi is assumed to be proportional to Q̇, however, the assumption has never been tested. This study used fluorescent microsphere infusion to measure femoral bone Q̇ in anaesthetised non-laying hens, laying hens and roosters. Mean cardiac output was 338±38 ml min-1 kg-1, and the two femora received 0.63±0.10 % of this. Laying hens had higher wet bone mass-specific Q̇ to femora (0.23±0.09 ml min-1 g-1) than the non-laying hens (0.12±0.06 ml min-1 g-1) and roosters (0.14±0.04 ml min-1 g-1), presumably associated with higher bone calcium mobilization during eggshell production. Estimated metabolic rate of femoral bone was 0.019 ml O2 min-1 g-1. Femoral Q̇ increased significantly with body mass, but was not correlated with nutrient foramen radius (r), probably due to a narrow range in foramen radius. Over all 18 chickens, femoral shaft Q̇/r was 1.07±0.30 ml min-1 mm-1. Mean Qi in chickens was significantly higher than predicted by an allometric relationship for adult cursorial bird species, possibly because the birds were still growing.