The herd - 107 French Charolais cattle and 53 Highland - is to be auctioned at short notice in two weeks' time at Lichfield, Staffordshire. Farming experts think it is worth up to pounds 500,000.
Mr Montague, who lives on a 1,300-acre estate near Pusey, Oxfordshire, has also made seven of his farming staff redundant and is sending much of his equipment to auction, including a relatively new pounds 100,000 combine harvester.
A spokesman for Tiphook said the herd and equipment were being sold and the staff laid off because Mr Montague was switching from mixed farming to arable: 'It is part of a business plan.'
However, farming experts said that the timing of the sale, its short notice and the absence of reserve prices suggested it had been hastily arranged. Graham Kirk, pedigree livestock correspondent of Farming News, said the auction of so large a herd would usually be arranged many months ahead so that the relatively small number of interested buyers from around the world could arrange to attend. But it was advertised in the farming press only a few weeks ago.
The timing is also unusual since it comes only a month after Britain's main pedigree cattle sales, in Perth.
Mr Montague started to breed pedigree cattle six years ago at his former home, Rushmore Hill House, near Pratt's Bottom in Kent. He has been a successful breeder, winning a number of prizes.
Pusey House, which was formerly the ancestral home of Sir Simon Hornby, the outgoing chairman of WH Smith, was sold to Mr Montague for a rumoured pounds 8.4m three years ago, and local people estimate that he has spent at least another pounds 1m on it and the farm since then.
Rushmore Hill House was put on the market at pounds 5.3m, but a year ago the asking price was slashed to pounds 3.5m. It has since been sold, but the agents will not disclose the price.
Tiphook deal, page 2