Relationship Between Bicarbonate Retention and Bone Characteristics in Broiler Chickens

Determination of the bicarbonate retention factor (BRF) is an important step during development of the indicator amino acid oxidation technique for use in a new model. A series of 4-h oxidation experiments were performed to determine the BRF of broilers aged 7, 14, 21, 28, 35, and 42 d using 4 birds per age group. A priming dose of 1.2 μCi of NaH14 CO3, followed by eight half-hourly doses of 1 μCi of NaH14 CO3 were given orally to each of 4 birds per age. The percentage of 14 C dose expired by the bird at a steady state was measured. These birds, as well as 12 additional birds matched for age and BW, were killed, and femur bone mineral density was measured by quantitative computed tomography to determine the relationship between bone development and bicarbonate retention at each age. There was a correlation (r = 0.50; P < 0.05) between total cross-sectional femur bone mineral density and bicarbonate retention at each age. A prediction equation (Y = 6.95 × 10−2 X − 3.51 × 10−5 X2 + 27.58; P < 0.0001, R2 = 0.79) where Y = bicarbonate retention and X = BW was generated to predict Y as a function of X. Bicarbonate retention values peaked at 28 d, during the stage of the most rapid bone deposition and the highest growth rate. A constant BRF was found from 1,900 to 2,700 g of BW of 35.15 ± 1.095% (mean ± SEM). This retention factor will allow the accurate correction of oxidation of 14 C-labeled substrates in broilers of different ages and BW in future indicator amino acid oxidation studies.