FILE PHOTO: A sign sits in front of Shire's manufacturing facility in Lexington, Massachusetts July 18, 2014. REUTERS/Brian Snyder

LONDON (Reuters) - Pharmaceutical company Shire said its chief financial officer Jeff Poulton will stand down at the end of the year to join Indigo Ag, a Boston-based start-up that seeks to improve agricultural productivity.

Poulton, who joined Shire in 2003, has been CFO since January 2015, a period that saw Shire make its largest acquisition with the $32 billion purchase of Baxalta last year.

He said on Monday that it was a difficult decision to leave the rare disease drugs specialist, but he wanted to join a smaller organization where he could play a role in building a new company.

“As Shire finalizes the integration of Baxalta and focuses on paying down debt, this also presents a perfect time for me to begin this transition,” he said.

Shire’s Chief Executive Flemming Ornskov said Poulton would lead the finance team through the third-quarter reporting period and would play an active role in the search for his successor