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 ( ) should reflect local tissue oxygen requirements. A recent ‘foramen technique’ has derived an index of blood flow rate ( ) by measuring nutrient foramen sizes of long bones. is assumed to be proportional to ; however, the assumption has never been tested. This study used fluorescent microsphere infusion to measure femoral bone in anaesthetized non-laying hens, laying hens and roosters. Mean mass-specific 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 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 O 2 min −1 g −1 . Femoral increased significantly with body mass, but was not correlated with nutrient foramen radius ( r ), probably because of a narrow range in foramen radius. Over all 18 chickens, femoral shaft was 1.07±0.30 ml min −1 mm −1 . Mean in chickens was significantly higher than predicted by an allometric relationship for adult cursorial bird species, possibly because the birds were still growing. 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 ( ) should reflect local tissue oxygen requirements. A recent ‘foramen technique’ has derived an index of blood flow rate ( ) by measuring nutrient foramen sizes of long bones. is assumed to be proportional to ; however, the assumption has never been tested. This study used fluorescent microsphere infusion to measure femoral bone in anaesthetized non-laying hens, laying hens and roosters. Mean mass-specific 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 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 O 2 min −1 g −1 . Femoral increased significantly with body mass, but was not correlated with nutrient foramen radius ( r ), probably because of a narrow range in foramen radius. Over all 18 chickens, femoral shaft was 1.07±0.30 ml min −1 mm −1 . Mean in chickens was significantly higher than predicted by an allometric relationship for adult cursorial bird species, possibly because the birds were still growing. 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 ( ) should reflect local tissue oxygen requirements. A recent ‘foramen technique’ has derived an index of blood flow rate ( ) by measuring nutrient foramen sizes of long bones. is assumed to be proportional to ; however, the assumption has never been tested. This study used fluorescent microsphere infusion to measure femoral bone in anaesthetized non-laying hens, laying hens and roosters. Mean mass-specific 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 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 O 2 min −1 g −1 . Femoral increased significantly with body mass, but was not correlated with nutrient foramen radius ( r ), probably because of a narrow range in foramen radius. Over all 18 chickens, femoral shaft was 1.07±0.30 ml min −1 mm −1 . Mean in chickens was significantly higher than predicted by an allometric relationship for adult cursorial bird species, possibly because the birds were still growing. 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 ( ) should reflect local tissue oxygen requirements. A recent ‘foramen technique’ has derived an index of blood flow rate ( ) by measuring nutrient foramen sizes of long bones. is assumed to be proportional to ; however, the assumption has never been tested. This study used fluorescent microsphere infusion to measure femoral bone in anaesthetized non-laying hens, laying hens and roosters. Mean mass-specific 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 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 O 2 min −1 g −1 . Femoral increased significantly with body mass, but was not correlated with nutrient foramen radius ( r ), probably because of a narrow range in foramen radius. Over all 18 chickens, femoral shaft was 1.07±0.30 ml min −1 mm −1 . Mean in chickens was significantly higher than predicted by an allometric relationship for adult cursorial bird species, possibly because the birds were still growing. 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 ( ) should reflect local tissue oxygen requirements. A recent ‘foramen technique’ has derived an index of blood flow rate ( ) by measuring nutrient foramen sizes of long bones. is assumed to be proportional to ; however, the assumption has never been tested. This study used fluorescent microsphere infusion to measure femoral bone in anaesthetized non-laying hens, laying hens and roosters. Mean mass-specific 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 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 O 2 min −1 g −1 . Femoral increased significantly with body mass, but was not correlated with nutrient foramen radius ( r ), probably because of a narrow range in foramen radius. Over all 18 chickens, femoral shaft was 1.07±0.30 ml min −1 mm −1 . Mean in chickens was significantly higher than predicted by an allometric relationship for adult cursorial bird species, possibly because the birds were still growing. 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 ( ) should reflect local tissue oxygen requirements. A recent ‘foramen technique’ has derived an index of blood flow rate ( ) by measuring nutrient foramen sizes of long bones. is assumed to be proportional to ; however, the assumption has never been tested. This study used fluorescent microsphere infusion to measure femoral bone in anaesthetized non-laying hens, laying hens and roosters. Mean mass-specific 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 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 O 2 min −1 g −1 . Femoral increased significantly with body mass, but was not correlated with nutrient foramen radius ( r ), probably because of a narrow range in foramen radius. Over all 18 chickens, femoral shaft was 1.07±0.30 ml min −1 mm −1 . Mean in chickens was significantly higher than predicted by an allometric relationship for adult cursorial bird species, possibly because the birds were still growing. 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 ( ) should reflect local tissue oxygen requirements. A recent ‘foramen technique’ has derived an index of blood flow rate ( ) by measuring nutrient foramen sizes of long bones. is assumed to be proportional to ; however, the assumption has never been tested. This study used fluorescent microsphere infusion to measure femoral bone in anaesthetized non-laying hens, laying hens and roosters. Mean mass-specific 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 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 O 2 min −1 g −1 . Femoral increased significantly with body mass, but was not correlated with nutrient foramen radius ( r ), probably because of a narrow range in foramen radius. Over all 18 chickens, femoral shaft was 1.07±0.30 ml min −1 mm −1 . Mean in chickens was significantly higher than predicted by an allometric relationship for adult cursorial bird species, possibly because the birds were still growing. 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 ( ) should reflect local tissue oxygen requirements. A recent ‘foramen technique’ has derived an index of blood flow rate ( ) by measuring nutrient foramen sizes of long bones. is assumed to be proportional to ; however, the assumption has never been tested. This study used fluorescent microsphere infusion to measure femoral bone in anaesthetized non-laying hens, laying hens and roosters. Mean mass-specific 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 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 O 2 min −1 g −1 . Femoral increased significantly with body mass, but was not correlated with nutrient foramen radius ( r ), probably because of a narrow range in foramen radius. Over all 18 chickens, femoral shaft was 1.07±0.30 ml min −1 mm −1 . Mean in chickens was significantly higher than predicted by an allometric relationship for adult cursorial bird species, possibly because the birds were still growing. 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 ( ) should reflect local tissue oxygen requirements. A recent ‘foramen technique’ has derived an index of blood flow rate ( ) by measuring nutrient foramen sizes of long bones. is assumed to be proportional to ; however, the assumption has never been tested. This study used fluorescent microsphere infusion to measure femoral bone in anaesthetized non-laying hens, laying hens and roosters. Mean mass-specific 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 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 O 2 min −1 g −1 . Femoral increased significantly with body mass, but was not correlated with nutrient foramen radius ( r ), probably because of a narrow range in foramen radius. Over all 18 chickens, femoral shaft was 1.07±0.30 ml min −1 mm −1 . Mean in chickens was significantly higher than predicted by an allometric relationship for adult cursorial bird species, possibly because the birds were still growing.

Nutrient arteries enter limb bones through discrete foramina on the shafts. They are required for bone remodelling in response to mechanical loading and dynamic forces imposed by locomotion. The cross-sectional area of the nutrient foramen of the femur represents an index of blood flow rate to the shaft and thus provides insight into the animal's level of activity. Morphometric data on femoral length, mass and foramen size from 100 extant bird species and eight extinct moa species were analysed allometrically and phylogenetically. The nutrient foramen blood flow index ( Q i ) and femur mass ( M f ) increase with body mass ( M b ). At 1 kg body mass, cursorial species have approximately 2.1 times higher Q i and 1.9 times heavier M f than volant species. The scaling of Q i on M f is independent of the primary mode of locomotion, but the ratio Q i / M f decreases significantly in larger birds, although absolute Q i increases. The overall avian equation for Q i on M b is not significantly different from previous data from mammals, but when differences in blood pressure are accounted for, estimated blood flow to the femur is approximately 1.9 times higher in cursorial birds than in mammals, possibly in relation to bipedalism and quadrupedalism, respectively. Femoral bone blood flow in both endothermic groups is estimated to be 50–100 times higher than in ectothermic reptiles.