MTV Networks announced approximately 50 layoffs that will significantly affect development and programming at its various channels, though the company does plan to hire some replacements in reconfigured positions.

The company ascribed the layoffs, which include but are not limited to employees at MTV and VH1, largely to a search for efficiencies in the down economic climate. But a spokesperson added that MTV is looking to redefine its “development and programming teams by bringing in new areas of expertise, including animation, scripted, hybrid reality (and) long- and shortform.”

“The development execs we had in place are terrific and have done a great job, but as we reinvent the brand, it is important to bring in new voices that will help us reflect our audience,” the spokesperson said.

While not disclosing a specific number, MTV indicated that it was laying off 1% of its workforce, which was previously calculated at slightly more than 5,000.

The layoffs come days after word came of the departure of MTV Networks veteran programming czar Brian Graden, effective at the end of 2009. Graden oversees programming for MTV, VH1, CMT and Logo.

MTV has seen a 20% decline in ratings in April and May among young adults. According to Credit Suisse, the channel has showed ratings declines for the past two years, with the exception of the fourth quarter of 2007. Credit Suisse estimates that Viacom’s ad-supported channels will see a 7% decline in ad revenue for 2009.

Some but not all of the layoffs will be effective immediately. The downsizing does not affect MTV Networks entertainment group or the company’s kids and family group.

(Claire Atkinson of Broadcasting and Cable contributed to this report.)