Effect of anionic salts in concentrate mixture on some blood and urine minerals, acid-base balance and feed intake of dry pregnant cows on grass silage based feeding with high calcium intake

The objective was to study the effects of anionic salts in a concentrate mi xture on some blood and urine minerals, acid-base balance and intake of Ayr shire cows fed a grass silage based diet. Eighteen nonlactating, pregnant A yrshire cows were divided randomly into two groups according to their expec ted calving date. Dietary cation-anion balance (DCAB), calculated as millie quivalents (Na+ + K+) - (Cl- + S2- )of the two diets was +410 mEq/kg of die tary dry matter (DM) in the high DCAB group and +81 mEq/kg of the dietary D M in the low DCAB group, respectively. The DCAB was formulated using NH4Cl2 (NH4)(2)SO4 and MgCl2, as anionic salts. Cows received grass silage (5.2 k g DM), hay (0.8 kg DM) and a concentrate mixture (1.7 kg DM) until calving. Both diets were supplemented with 100 g CaCO3 to achieve a high Ca intake (82 g Ca/d). Blood and urine samples were collected 4, 3, 2 and 1 week befo re the expected calving date, at calving, the day after calving and 1 week following calving. Current data indicated that it may be difficult to formu late a diet with a negative DCAB, if the K content of grass silage is over 30 g/kg DM. As a result, no increase in blood Ca2+ and a relatively high ur inary pH were observed. Furthermore, it may advantageous to increase Mg int akes above current Finnish recommendations when dietary Ca concentrations a re high, since 28% of experimental cows experienced hypomagnaesemia at part urition.