• by Mark Walsh  @markfwal, July 9, 2013

LinkedIn’s slow rollout of ads in the news feed means the new format is unlikely to reach significant scale until late 2013 or the first quarter of 2014, according to a new research note by Macquarie Securities analyst Tom White.

While the gradual ramp of LinkedIn’s Sponsored Updates should boost ad sales over time, it likely means slower growth for its ad business the rest of the year as it pulls back on custom and ad-hoc marketing programs. LinkedIn began testing the new in-stream ad unit earlier this year with a handful of brands.

During its first-quarter conference call in April, the comp said it had expanded the number of high-profile advertisers using Sponsored Updates to 20 including Shell, Intuit, Xerox, Telstra and American Express. The ad pilot program was extended to smartphones as well. The Macquarie report pointed out that 30% of LinkedIn’s traffic now comes from mobile, meaning almost a third is “under-monetized.”

Looking at desktop usage, the research note cited comScore figures showing page view growth slowed for the second straight month in June to 9% from a year ago. That compares to a gain of 18% in May and 25% in April. Unique users grew 22%, down slightly from 27% in both April and May. LinkedIn has a total of 225 million registered users.