Potassium carbonate as a potassium source and dietary buffer for lactating Holstein cows during hot weather.

Twenty-four lactating Holstein cows were offered diets containing .93, 1.29, and 1.53% potassium during hot weather. Cows fed 1.53% potassium consumed more dry matter than cows fed either .93 or 1.29% potassium. Milk production and composition were not different. Potassium intake and fractional excretion increased, and fecal output as a percentage of intake declined with diets containing 1.29 and 1.53% potassium. Magnesium fractional excretion was least and fecal output greatest in cows fed 1.29% potassium. Fecal sodium output and fecal output as a percentage of intake was reduced by 1.53% dietary potassium. During comparison period 2, potassium carbonate at 0, .5, or 1.0% had no effect on feed consumption or milk yield, but buffered diets increased milk fat percentage and depressed milk protein percentage. No effects of buffers on ruminal pH, volatile fatty acids, or digestibility of dry matter or fiber were noted. Cows responded favorably during hot weather to potassium supplementation at 1.53% of the diet, but with high dietary potassium, effects on other minerals must be considered. Chloride, although present above requirements in all diets, was greater in the highest potassium diet.