Potassium Requirements of Dairy Cows in Early and Midlaction

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Abstract
Two trials with lactating Holstein cows were to determine the percent K required in the ration. A midlactation study compared 3 K percentages (.46, .69 and .97% of dry matter) for 5 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 1 of 3 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 1st trial but not in the 2nd trial. Blood serum K was significantly different due to treatment in the 2nd trial with changes in percent K of -.6, -.4 and +1.1 for the 3 treatments. A K content of .7% appears to be adequate for cows in mid to late lactation. The feed intake and K in serum indicate that .7% may not be optimal for high producing cows in early lactation.
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