Giani Sant Singh Maskeen Panth Rathan, Panthic Scholar and Kathavachak, explained Concept of Maas and Animal Food from Sikh History and Gurbani.
ਅੰਡਜ ਜੇਰਜ ਉਤਭੁਜ ਸੇਤਜ ਤੇਰੇ ਕੀਤੇ ਜੰਤਾ ॥
ਏਕੁ ਪੁਰਬੁ ਮੈ ਤੇਰਾ ਦੇਖਿਆ ਤੂ ਸਭਨਾ ਮਾਹਿ ਰਵੰਤਾ ॥੩॥
The beings born of eggs, born of the womb, born of the earth and born of sweat, all are created by You.
I have seen one glory of Yours, that You are pervading and permeating in all. ||3|| - 596/15 - Guru Nanak Dev
The blog contain textual material from Guru Granth Sahib, Historical Books of Sikhism and Lecture of Sikhs on said topic.