Effect of dietary potassium and anionic salts on acid-base and mineral status in periparturient cows

Dry cow diets based on grassland forage from intensive production contain high amounts of K and could be responsible for a reduced ability to maintain Ca homoeostasis. The aim of this study was to determine whether a moderate anionic salt supplementation to a forage-based pre-calving diet with varying native K content affects the mineral and acid-base status in transition cows. Twenty-four dry and pregnant Holstein cows, without antecedent episodes of clinical hypocalcemia, were assigned to two diets during the last 4 weeks before estimated calving date. Twelve cows were fed a hay-based diet low in K (18 g K/kg DM), and 12, a hay-based diet high in K (35 g K/kg DM). Within each diet, six cows received anionic salts during the last 2 weeks before the estimated calving day. After calving, all cows received the high K diet ad libitum. Blood samples were taken daily from day 11 pre-partum to day 5 post-partum. Urine samples were taken on days 7 and 2 pre-partum and on day 2 post-partum. The anionic salt did not alter feed intake during the pre-partum period. Serum Ca was not influenced by the dietary treatments. Feeding pre-partum diets with low K concentrations induced a reduced metabolic alkalotic charge, as indicated by reduced pre-partum urinary base-acid quotient. Transition cows fed the low K diet including anionic salts induced a mild metabolic acidosis before calving, as indicated by higher urinary Ca, lower urinary pH and net acid-base excretion. Although serum Ca during the post-partum period was not affected by dietary treatment, feeding a low K diet moderately supplemented with anionic salts to reach a dietary cation-anion difference close to zero permitted to obtain a metabolic response in periparturient cows without altering the dry matter intake.