Billionaire investor Warren Buffett donated more than $750 million in Berkshire Hathaway stock to the four foundations run by his family Wednesday, but unlike his annual gifts to charity each summer, the recipients didn't include the Bill & Melinda Gates Foundation.

Buffett has been making annual donations to the same five charities every year since 2006 when he unveiled a plan to give away his fortune over time, with the Gates Foundation receiving the biggest donations. Wednesday's donations mark the first time the 92-year-old has made a second major gift within the same year.

A filing with the Securities and Exchange Commission showed Buffett gave 1.5 million Class B shares in the Omaha, Nebraska-based conglomerate he leads to the Susan Thompson Buffett Foundation, named for his first wife. He also gave 300,000 Class B shares apiece to the three foundations run by his children: the Sherwood Foundation, the Howard G. Buffett Foundation and the NoVo Foundation.

In June, he gave 11 million Class B shares to the Gates Foundation, 1.1 million B shares to the Susan Thompson Buffett Foundation and 770,218 shares apiece to his children's three foundations.

It wasn't immediately clear what prompted the new donations this week, and Buffett didn't immediately respond Wednesday to questions about them. The Gates Foundation and the Buffett family foundations that received the gifts also didn't immediately respond to questions.

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The only other major change Buffett has made to his giving plans over the years came a decade ago when he significantly increased the amount pledged to the foundations his children run because he was pleased with what they had done with his money.

The Susan Thompson Buffett Foundation keeps a low profile, but over the years it has been a major supporter of abortion rights, making large gifts to Planned Parenthood and other groups. Buffett hasn't announced any changes in his giving plans since the U.S. Supreme Court overturned Roe v. Wade earlier this year.

Susie Buffett, 69, uses her Sherwood Foundation to strengthen early childhood education and support a number of projects around Buffett's hometown of Omaha where she also lives. Howard Buffett, 67, is helping farmers in impoverished nations produce more and working to end world hunger with his namesake foundation. Peter Buffett, 64, has dedicated his NoVo Foundation to empowering women and girls worldwide through education, collaboration and economic development to end violence against women.

Even after these latest gifts, Buffett still controls more than 31% of Berkshire’s voting power.

Berkshire Hathaway is an eclectic conglomerate that owns more than 90 companies including BNSF railroad, Geico insurance, several major utilities and an assortment of manufacturing and retail firms including Precision Castparts, Dairy Queen and Helzberg Diamonds. In addition to the companies it owns outright, Berkshire owns major investments in Apple, Bank of America, Coca-Cola and other companies.

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(Edited by : Asmita Pant)