Margaret Loesch will step down as prexy-CEO of Hub Network at year’s end when her contract expires.

The kidvid vet spearheaded the launch of the joint venture between Discovery Communications and toy maker Hasbro in October 2010. The cabler, formerly Discovery Kids, has had an uphill climb in its effort to compete ratings-wise with entrenched rivals Disney Channel, Nickelodeon and Cartoon Network. Advertising dollars in the kids TV arena have also been dwindling as marketers react to the fact that younger viewers spend so much more of their time on digital platforms.

But at its core the Hub joint venture is profitable for its partners, thanks to the combination of affiliate fees, advertising and the impact that the exposure for programming tied to Hasbro brands has on retail sales. (Three words: My Little Pony.)

“I am very proud of the work we have done and the accomplishments we have achieved at the Hub. The network is now in excellent financial shape, its ratings are up year-to-year, our programming has won more than 30 awards, including 12 Daytime Emmys, and the Hub Network has become a TV home for quality programming that kids and their families come together to enjoy,” Loesch said in a statement. “I have loved my job and am proud of the achievements we’ve made. While my career has spanned over four decades, I look forward to evaluating future opportunities and writing the next chapter.”

Loesch is highly regarded by Discovery execs and her decision to step down was reached by mutual agreement.

“Margaret is a terrific executive and a terrific leader,” Discovery Communications CEO David Zaslav said. “She has done a superb job at the Hub and we are sorry to see her go. We’re confident in the team that is there now and we know that this platform has its best days ahead.”

There’s no word yet on a successor, as Discovery intends to mount a search with Loesch’s assistance.

News of Loesch’s plan to step down was first reported by Deadline.