Following some devastating footage via PETA of muscular dystrophy experiments on dogs, Paul McCartney is urging Texas A&M University (TAMU) President Michael K. Young to end the mistreatment. In the experiments, golden retrievers are bred to have a crippling form of muscular dystrophy that leaves them struggling to walk, swallow and breathe.

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"The video footage of golden retrievers in your university's dog laboratory is heartbreaking," the Beatle wrote in a letter on Wednesday (June 26), according to a PETA press release. "I have had dogs since I was a boy and loved them all dearly, including Martha, who was my companion for about 15 years and about whom I wrote the song 'Martha My Dear.' Please do the right thing by ending the suffering of dogs in TAMU's muscular dystrophy laboratory and switching to modern research methods instead."

McCartney has been a longtime animal supporter, as a meat-free dieter who has teamed up with PETA multiple times in the past. Learn more about the organization here.