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

Abstract

The objective was to study the effects of anionic salts in a concentrate mixture on some blood and urine minerals, acid-base balance and intake of Ayrshire cows fed a grass silage based diet. Eighteen nonlactating, pregnant Ayrshire cows were divided randomly into two groups according to their expected calving date. Dietary cation-anion balance (DCAB), calculated as milliequivalents [(Na+ + K+) - (Cl- + S2-)] of the two diets was +410 mEq/kg of dietary dry matter (DM) in the high DCAB group and +81 mEq/kg of the dietary DM in the low DCAB group, respectively. The DCAB was formulated using NH4Cl, (NH4)2SO4 and MgCl2 as anionic salts. Cows received grass silage (5.2 kg 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 before the expected calving date, at calving, the day after calving and 1 week following calving. Current data indicated that it may be difficult to formulate 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 urinary pH were observed. Furthermore, it may advantageous to increase Mg intakes above current Finnish recommendations when dietary Ca concentrations are high, since 28% of experimental cows experienced hypomagnaesemia at parturition.;