Warren Buffett's conglomerate, Berkshire Hathaway Inc., now owns more than 10 percent of dialysis clinic operator DaVita Inc., after adding to its position at the end of last month, according to a filing with the U.S. Securities and Exchange Commission on Monday.

DaVita was a longtime favorite of Ted Weschler, the fund manager Buffett hired in 2011 to help oversee Berkshire's investment portfolio. Berkshire began building a stake in the company roughly around the time Weschler was hired.

Berkshire added another 282,403 shares last week for between $100.42 and $103.76 each, the filing indicated. It now holds about 10.2 million DaVita shares, for a stake of about 10.8 percent of the company, nearly twice that of the next-largest holder.

The majority of the investment is held by Berkshire auto insurance unit Geico, with the rest held by the pension plans of various subsidiaries, according to the filing.

DaVita shares closed at $103.61 on Friday. Berkshire first disclosed a position in the company on February 14; the stock is up 22 percent since then.