Author
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GOFF, JESSE |
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HORST, RONALD |
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Submitted to: American Dairy Science Association Abstracts
Publication Type: Abstract Only Publication Acceptance Date: 6/23/2003 Publication Date: N/A Citation: N/A Interpretive Summary: Technical Abstract: Manipulating diet cation-anion difference to reduce milk fever and hypocalcemia in the periparturient cow is now commonly practiced on dairies. However, how lowering DCAD improves calcium status remains uncertain. Previous work in our lab suggested tissue responsiveness to parathyroid hormone is impaired in cows fed diets that are high in cations. Some studies dispute this theory and suggest acidifying diets cause bone dissolution directly as the bone is used to buffer the blood pH. We fed 7 older Jersey cows a low or high DCAD diet during late gestation. Urine pH in cows fed the low DCAD diet were between 5.3 and 6.2, while cows fed the high DCAD diet had urine pHs between 8.2 and 8.5. Cows were then treated with 0.35 mg synthetic 1-34 parathyroid hormone (PTH) intramuscularly every 3 h for 48 h. In low DCAD cows, plasma calcium concentrations increased significantly by 8% in 6 h and by 13% at 15 h. In high DCAD cows, a significant increase in plasma calcium concentration (10% above pretreatment) was not seen until 15 h of PTH treatment. Diet DCAD significantly affects the speed with which PTH can improve blood calcium concentration. Implications of plasma 1,25-dihydroxyvitamin D and urine hydroxyproline concentration changes, which also can be used as indicators of tissue PTH sensitivity, will also be presented. |
