By Ludwig Burger and Frank Siebelt

FRANKFURT, Dec 3 (Reuters) - Switzerland's Novartis is letting Bayer and other rivals have a look into the books of its animal health business to whet prospective buyers' appetite for the unit, four people familiar with the matter told Reuters.

The financial sources said the suitors were conducting a due diligence assessment of the Novartis business.

Combining Bayer's roughly $1.7 billion in veterinary drugs sales with Novartis' $1.1 billion would lift the German company to the number three or four spot in the global animal health market, where Zoetis, a former Pfizer unit, is in pole position.

"We are interested in growing our animal health business," Bayer Chief Executive Marijn Dekkers told Reuters at a pharmaceuticals conference in London on Tuesday. He declined to comment on whether Bayer was looking at the Novartis assets.

A Novartis spokesman declined to comment.

Bayer is seeking to bolster its position as a diversified life science company while Novartis Chief Executive Joe Jimenez and new Chairman Joerg Reinhardt have both stressed they will only hang on to businesses that are among world leaders.