This is an animated version of Yanase Takashi's picture book featuring the friendship between a mother dog, Muku-muku, who lost her puppy, and the baby lion Buru-buru, who lost her mother. Although Tezuka Osamu planned to create an entire musical animated series for this story focused on the feelings of the mother dog and baby lion, this animated production was the only one never completed. 
(Source: en.tezuka.co.jp) 
Note: In 1998, a renewed version was produced that changed some dialogue and re-recorded the audio with new voice actors. The last scene was also modified.