title: Effect of different potassium levels in hay on acid-base status and mineral balance in periparturient dairy cows.
abstract: Forages commonly used in dry cow rations contain high K concentrations. This results in a high dietary cation-anion difference (DCAD), which can compromise the calcium homeostasis of periparturient cows. The aim of this study was to determine the effect of 2 types of hay, fed during the prepartum period and differing in their K concentrations, on the peripartum acid-base status and mineral balance of dairy cows. During the prepartum period, the cows of group K(33) (n = 6) received a diet based on hay with a high K concentration (33 g/kg of DM), whereas the cows of group K(13) (n = 6) received a diet based on hay with a low K concentration (13 g/kg of DM). Both experimental diets were formulated to be isoenergetic and isonitrogenous. After calving, all cows received the same diet based on hay K(33). Blood and urine samples were taken on d 14, 7, and 3 before parturition, at parturition, and then daily during the first 8 d after calving. Concentrations of minerals were analyzed in both blood and urine. Creatinine was also measured in urine for the calculation of the mineral:creatinine ratio. The acid-base parameters in blood (pH and HCO(3)(-) concentration) and urine (pH, net acid-base excretion, and base-acid quotient) were determined on d 14, 7, and 3 before parturition, at parturition, and on d 1 after parturition. The use of hay K(13) reduced the DCAD value of the prepartum diet by half (195 vs. 514 mEq/kg of DM). No significant differences between the 2 groups were observed for blood acid-base indicators or plasma minerals except for the Mg plasma concentration, which tended to be higher in group K(13) from d 3 prepartum to d 2 after calving. In group K(13), urinary Ca excretion tended to be higher from d 3 prepartum to d 1 after parturition than that in group K(33). On d 3 before parturition, urinary pH and net acid-base excretion were significantly lower in group K(13) than in group K(33). On d 14, 7, and 3 before parturition, base-acid quotient was significantly lower in group K(13) than in group K(33). In group K(13), daily feed intake and hence daily intake of Ca, P, and Mg during d 3 and 4 after parturition were higher than in group K(33). The decrease of the DCAD in positive ranges by feeding a low-K hay before parturition induced a reduction of the metabolic alkalotic charge, as observed in acid-base parameters in urine, and increased the availability of Ca and P as a result of higher feed intake at the onset of lactation.
authors.affiliation: Agroscope Liebefeld-Posieux Research Station ALP, PO Box 64, CH-1725 Posieux, Switzerland. michel.rerat@alp.admin.ch
authors.forename: M
authors.initials: M
authors.lastname: Rérat
authors.forename: A
authors.initials: A
authors.lastname: Philipp
authors.forename: H D
authors.initials: HD
authors.lastname: Hess
authors.forename: A
authors.initials: A
authors.lastname: Liesegang
mesh_terms: D000136:Acid-Base Equilibrium / Q000502:physiology*; D000821:Animal Feed / Q000032:analysis*; D000818:Animals; D002118:Calcium / Q000097:blood / Q000652:urine; D002417:Cattle / Q000378:metabolism / Q000502:physiology*; D003612:Dairying; D004435:Eating / Q000502:physiology; D005260:Female; D006863:Hydrogen-Ion Concentration; D008274:Magnesium / Q000097:blood / Q000652:urine; D008903:Minerals / Q000378:metabolism*; D036801:Parturition; D011188:Potassium / Q000032:analysis / Q000097:blood / Q000378:metabolism* / Q000652:urine; D011247:Pregnancy; D014556:Urine / Q000737:chemistry
chemical_list: D008903:Minerals; D008274:Magnesium; D011188:Potassium; D002118:Calcium