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

Summary 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 C a 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 C a 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 C a, lower urinary pH and net acid–base excretion. Although serum C a 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.