| Abstrakt: |
Forage‐based rations with a low dietary cation anion difference (DCAD) should be fed to dairy cows 2 to 4 wk prepartum to prevent hypocalcaemia or milk fever. We evaluated the DCAD of two to four cultivars of five grass species at three locations in Québec, Canada. Orchardgrass (Dactylis glomerataL.), meadow bromegrass (Bromus ripariusRehmann), tall fescue (Festuca arundinaceaSchreb.), smooth bromegrass (Bromus inermisLeyss.), and timothy (Phleum pratenseL.) were harvested twice a year during two production years. Forage mineral concentrations were measured and the DCAD was calculated with a short equation [DCADS= (Na++ K+) − (Cl−+ S2−)], and a long equation [DCADL= (Na++ K++ 0.15Ca2++ 0.15Mg2+) − (Cl−+ 0.6S2−+ 0.5P3−). The five species had, respectively, DCADSof 656, 540, 510, 490, and 384 mmolckg−1DM (dry matter) in spring growth, and 633, 569, 496, 447, and 332 mmolckg−1DM in summer regrowth. Orchardgrass had the highest DCAD and timothy the lowest while the three other species were intermediate in both spring growth and summer regrowth. Species differences in DCAD were primarily related to differences in K concentration. Timothy was the only species that decreased significantly in DCADS(by 52 mmolckg−1DM) and DCADL(by 35 mmolckg−1DM) from spring growth to summer regrowth. Cultivars did not differ in DCADSand DCADLexcept for tall fescue. Locations did not differ in DCAD. Among the grass species in this study, and because of its low DCAD, timothy is the best suited for producing forages fed to dairy cows in the weeks preceding calving. |
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