Despite a brief spell as an amateur jockey in the 1980s, the king is less enamoured of horseracing than his late mother who was an equine devotee and loved both riding horses and attending race meets.
Among the mares being sold are Love Affairs and the Sir Michael Stoute-trained Just Fine.
Sir Michael's regal pedigree is well-established having trained over 100 royal winners.
“It's nothing out of the ordinary. Every year they would sell horses.,” said Tattersall's spokesman Jimmy George.
“The queen had brood mares of her own, she would breed them and sell them. You can't keep them all.”
Despite Mr George saying the sale doesn't mean the king is scaling back Queen Elizabeth's racing operation, there have been suggestions to the contrary.
While some of the royal stud would be sold each year, 14 represents a third of the queen's 37-strong collection of brood mares, a higher number than would usually be auctioned.
And earlier this month Queen Elizabeth's long-serving racing manager, John Warren, announced he was leaving the royal fold to work for Bahraini royal circles.
The much respected Mr Warren had been in post for 13 years and was a close of friend of the queen. He spoke to her before her death at Balmoral last month.
“We sat there for hours strategising and making plans going forward, I think the nicest thing for me is to know that she was surrounded by her family members,” he told the PA news agency at the time.
The queen inherited Sandringham's racehorse breeding centre from her father King George VI but Mr Warren said she would have discovered her passion for horses regardless.
Her first riding lesson was reportedly taken at age 3 at the private riding school in Buckingham Palace Mews.
She was 4 when her grandfather, King George V, gave her a Shetland pony called Peggy.
“I'm sure if the queen had not been bred into being a monarch she would have found a vocation with horses. It was just simply in her DNA,” he said.