Potassium requirement of dairy cows in early and midlactation

Two trials with lactating Holstein cows were to determine the percent potassium required in the ration. A midlactation study compared three potassium percentages (.46, .69, and .97% of dry matter) for five cows assigned to each treatment for a 10-wk experimental period. In an early lactation study, 15 cows were assigned at 2 wk postpartum to one of three treatments (.51, .75, and .99%) for an 8-wk experimental period. Feed intake was changed by treatment from a control period (all cows fed the high K ration) +1.3, -.3, and +.1 kg for the .46, .69, and .97 treatments and +3.4, +1.0, and +.5 kg for the .51, .75, and .99 treatments. Milk production and change in body weight differed significantly in the first trial but not in the second trial. Blood serum potassium was significantly different due to treatment in the second trial with changes in percent potassium of -.6, -.4 and +1.1 for the three treatments. A potassium content of .7% appears to be adequate for cows in mid to late lactation; however, the feed intake and potassium in serum indicate that .7% may not be optimal for high producing cows in early lactation.