Anionic salts in the feeding of dairy cattle

A feeding trial with dairy cows was conducted to assess the effect of different calcium concentrations in diets without or with the supplementation of anionic salts on mineral metabolism and acid-base balance in periparturient cows. Twenty-four Holstein cows were assigned to four groups. From day 263 of gestation until parturition, each group was fed a different diet. Groups A and B received a low calcium diet (3 g/kg DM) and groups C and D received a high calcium diet (7 g/kg DM). Additionally, groups B and D were supplemented with anionic salts. The dietary-cation-anion difference (DCAD) was calculated as DCAD (mEq/kg DM) = (0.2 Ca2+ + 0.16 Mg2+ + Na+ + K+) – (Cl- + 0.6 S2- + 0.65 P3-). The diets A, B, C and D presented a DCAD of +190, -48, +222 and +22, respectively. Independent of the Ca level in the diet, the supplementation of anionic salts increased Ca excretion with urine prepartum without affecting Ca retention pre- or postpartum. In contrast, P retention prepartum was decreased by supplementation of anionic salts. With the exception of bicarbonate concentration and standard base excess, which indicated a slight metabolic acidosis in group B, blood parameters were not affected by dietary Ca concentration or supplementation of anionic salts. In group B, urinary pH around parturition was significantly lower than in the remaining groups (7.0 vs. 8.5). However, it remains unclear to which extent this slight acidosis could prevent the incidence of milk fever.