The relationship between dietary cation-anion difference and nitrogen metabolism in lactating dairy cows
Wildman, Christopher Dwayne
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Positive dietary cation-anion difference (DCAD) enhances blood bicarbonate concentrations in lactating cows, improving blood buffering which may improve animal health and performance. The objectives of this research were to determine the effects of DCAD on nitrogen metabolism in lactating dairy cows, including changes in amino acid (AA) metabolism that may be influenced by DCAD. Potassium:sodium ratios were compared to elucidate interactions between 2:1, 3.5:1, and 5:1 dietary K:Na ratios within DCAD treatments of 45 and 60 meq / 100 g dry matter (DM). No differences were observed for DM intake (DMI) or milk yield (MY) for DCAD treatments. Milk yield was lower for the 3.5:1 K:Na ratio. Blood bicarbonate was similar among treatments, but blood urea N declined as DCAD increased from 45 to 60 meq Na + K – Cl / 100 g suggesting reduced systemic protein catabolism because of reduced need for protein in systemic buffering. No differences were observed for blood urea N concentration among potassium:sodium ratios. In late lactation cows, serum total AA and total essential AA concentrations were greater for DCAD of 50 meq / 100 g DM compared with 25 meq / 100 g DM. Milk yield declined as DCAD increased although no difference in DMI was noted. Blood bicarbonate concentration was greater for high DCAD diets, indicating improved blood buffering with high DCAD. In early lactation cows, improved DMI, MY, and urinary uric acid, which is indicative of microbial crude protein yield, was observed for cows fed diets low in dietary crude protein when DCAD was increased from 25 to 50 meq / 100 g DM. Blood bicarbonate concentrations were also higher. Improved DMI, MY, total blood AA, and total essential AA concentration was observed in diets low in dietary crude protein and rumen degradable protein when DCAD increased from 25 to 50 meq / 100 g DM. Results of this research indicate that increasing DCAD enhances amino acid status in lactating dairy cows. The mechanism is not known, but could be a result of decreasing systemic buffering role of amino acids.