A bird may be slaughtered as soon as it is hatched, but an animal should not be slaughtered until it is eight days old to ensure that it is viable (15:1-2; see 13:3 and 14:1,6.).

It is preferable not to slaughter an animal or bird that is about to die of natural causes (17:3;116:7) as evidenced by the fact that it cannot stand (17:1), but if its limbs moved until after the slaughtering (see 17:1-2) eating it is permitted because we may assume that the slaughtering was the cause of its death.

Slaughtering is not effective for animals or birds that had certain types of defects (TEREFAH; see 29:1) before they were slaughtered (see 26:1-2):

1. If most of the skull of an animal is fractured or significant pieces of it are missing, or if the skull of a bird is punctured (30:1-2).
2. If the membrane of the brain is punctured or if there is liquid in the brain that is in contact with the membrane (31:1-2).
3. If most of the membrane of the spinal cord is cut (crosswise) or part of the cord cannot stand up under its own weight (32:1-4). On the extent of the cord see 31:4 and 32:5.
4. If the upper jaw is removed (33:2), but not if the lower jaw or the beak of a bird is removed (33:1).
5. If the esophagus is punctured (33:3-4,6-8) or discolored (33:5) or separated from the trachea (33:10).
6. If a significant part of the crop is removed (33:11).
7. If most of the trachea is cut or it is entirely split lengthwise or a significant piece of it is missing (34:1-7,9).
8. If a lung is punctured (34:8;35:1;36:1-3,6;37:6;53:5); or (in an animal: 35:10) one of its lobes is missing or misshapen or misplaced (35:2,6-9) or (in some cases) there is an extra lobe (see 35:2-5); or a significant amount of lung is missing (36:7-8); or part of a lung cannot be inflated (36:9) or is dry (36:13); or if a lung is hard or fragile or swollen or shriveled (36:10-12,14-15); or if it has protruding abscesses that contain unclear liquid, unless they appear to be isolated and are not associated with other signs of injury (37:1-5;39:8); or if parts of a lung are discolored in certain ways (but not if it is scaly; see 38:1-5); or if there are adhesions (SIRCHOS) joining certain parts of the lungs to each other or to certain parts of the body (see 39:4-9,18-25), though some permit adhesions that can be broken by gentle pulling or rubbing (see 39:10-13). Abscesses and adhesions are not regarded as evidence of puncture in other organs (37:7) and it is not ordinarily necessary to check for the presence of defects in other organs, but the lungs of an animal must be checked for adhesions, and if they are found the lungs should be inflated to verify that they are not punctured (36:4;39:1-3). The checking should be done by a person whose observance and knowledge of the laws has been certified by a qualified scholar (1:1); on trustworthiness in these matters see 39:14-17.
9. If the heart (or a major vessel; see 34:10 and 40:4) is punctured (40:1).
10. If the liver is removed or dried up or hardened or liquefied, unless significant parts of it remain unaffected (41:1-3,5); or if its membrane is punctured (41:8).
11. If the gall bladder is punctured, unless the liver covers the puncture (42:1); or if it is missing (42:2), unless that species lacks it (42:8) or unless there is a bitter taste in the liver (42:3).
12. If the thick end of an animal’s (43:6) spleen is punctured or decayed (43:2-4), but not if the entire spleen is removed (43:1).
13. If the white part of an animal’s (44:10) kidney is injured or decayed or liquefied or discolored in certain ways (44:2-3,8-9), or if a kidney shrinks (see 44:5-6), but not if the kidneys are otherwise injured or are entirely missing or removed or have stones (44:1,4). [TO BE CONTINUED]

Shulchan Aruch, Copyright (c) 1999 Project Genesis, Inc.