Blood oxygen binding in double-muscled calves and dairy calves with conventional muscle conformation

Objective-To assess in vivo blood oxygen binding in double-muscled calves a nd dairy calves with conventional muscle conformation. Animals-58 dairy and 48 double-muscled calves. Procedure-Calves were classified as neonatal (24 hours old) or older calves (2 to 26 days old). Venous and arterial blood samples were collected, and hemoglobin concentration, pH, P-CO2, and P-O2 were determined. Blood oxygen equilibrium curves (OEC) under standard conditions were constructed, and t he oxygen exchange fraction (OEF) and the amount of oxygen released at the tissue level by 100 mi of blood (OEF Vol%) were calculated, Results-In each breed, partial pressure of oxygen at 50% saturation of hemo globin (P-50) under standard conditions was significantly higher in older t han in neonatal calves, indicating a right shift in OEC with age. Venous P- 50 was significantly lower in neonatal double-muscled calves than in neonat al dairy carves, but arterial and venous P-50 were significantly higher in older double-muscled calves than in older dairy carves, in double-muscled, but not in dairy, calves, OEF was significantly higher in older than in neo natal calves. In neonatal carves, OEF Vol% was not significantly different between breeds, but OEF Vol% was significantly higher in older double-muscl ed calves than in older dairy calves, Conclusions and Clinical Relevance-The lower OEF in neonatal double-muscled calves, compared with dairy calves, could contribute to the higher sensiti vity of double-muscled calves to hypoxia, Blood oxygen affinity decreased w ith age, but OEF and OEF Vol% were unchanged with age in dairy calves, wher eas they increased with age in double-muscled calves.