While this is the case for almost all animals and their meat in Japanese, oddly enough lamb meat is ラム肉 ramu-niku, where ramu is loaned from English "lamb". The animal is 羊 hitsuji, but while 羊肉 youniku is possible, you'd rarely if ever use that in speech (and I had to look up the onyomi reading!).
That said, lamb is quite rare in Japan, it's eaten primarily up north in Hokkaido.
That said, lamb is quite rare in Japan, it's eaten primarily up north in Hokkaido.