Seatrah Ji,
Sikhi/Gurmatt is NOT about the PHYSICAL....so much as about the MIND/MANN/SOUL.
Thus Guru nanak ji, the Founder on Page 15 of Sri Guru Granth Sahib Ji discusses this and declares thta EXCESSIVE ATTACHMENT to anything is bad....Excessive attachment to Gold, silver, wealth, palaces, mansions, beautiful women, perfumes and soft bedding, ostentatious transport like elephants and horses, SUGAR, MEAT ..etc etc etc is NOT "Healthy" - BOTH for the Mann and Body. Everything must be done in MODERATION..SEHAJ...for full benefits to be attained.
ON Meat Guru Ji terms it as foolish argument as to what is vegetarian and what is animal based..
TO Illustrate Guru nanak ji gives a Graphic account of how a Sugar cane is treated to give us SUGAR..for our SWEET TOOTH...Bhai Gurdass Ji gives a similar account of the lowly goat which siurvives on cactus and grasses leaves and its flesh is found to be tasty....according to Gurbani there is LIFE even in WATER...and AIR..
The Sikh Rehat maryada allows MEAT that is NOT slaughtered the Muslim Way (hallal) or Sacrificial Meat (kosher) Khalsa can consume meat that is killed for FOOD purposes and NOT as Sacrificed meat to a Diety.Thus even a JHATKA sacrificed at the Kali Mata Mandir of a Hindu is NOT allowed to Sikhs. Hence its NOT a question fo how an animal is slaughtered..but SACRIFICE...Kabir Ji says..WHY KILL the lowly Chicken..to PLEASE Him when its HIM that gave it life..you are being cruel, zalim by taking what you didnt give.
Reference:: Sikh Philosophy Network http://www.sikhphilosophy.net/showthread.php?t=25634
For more sustained information there is a Thread in our archives....Only Fools wrangle over Flesh. Enjoy a thoroughly explored matter in that Thread.