Butchery was started near the beginning of Spring, with the last slaughter taking place on Slate 14. Elephants had their grazer value upped to 45 a year or so ago, but are otherwise unmodded. Weights were taken by looking at the cage with the animal and then subtracting the weight of the cage.
Adults
Weight: 1152
Description: Huge, muscular and fat
Return: 12 fat, 25 meat, 18 bone
Weight: 1428
Description: Gigantic
Return: 12 fat, 25 meat, 26 bone
Weight: 1881
Description: Enormous build but is very skinny
Return: 12 fat, 45 meat, 26 bone
Weight: 2428
Description: Gigantic and quite fat
Return: 20 fat, 36 meat, 34 bone
Weight: 2930
Description: Gigantic yet incredibly weak
Return: 24 fat, 17 fat, 64 bone
Weight: 3210
Description: Untold amounts of fat over a gigantic frame
Return: 45 fat, 25 meat, 50 bone
Weight: 3869
Description: Very fat and enormous overall
Return: 51 fat, 32 meat, 60 bone
Weight: 4236
Description: Gigantic yet weak and skinny
Return: 20 fat, 73 meat, 60 bone
Weight: 4788
Description: Gigantic
Return: 26 fat, 90 meat, 54 bone
Weight: 6098
Description: -
Return: 36 fat, 118 meat, 64 bone
Calves
Weight: 1834
Description: Gigantic and muscular
Return: 12 fat, 42 meat, 26 bone
Weight: 2100
Description: Very muscular and just gigantic overall
Return: 12 fat, 51 meat, 26 bone
Weight: 2375
Description: Enormous yet very weak
Return: 20 fat, 25 meat, 42 bone
Weight: 2543
Description: Gigantic yet weak and skinny
Return: 18 fat, 36 meat, 42 bone
Weight: 2606
Description: Gigantic
Return: 18 fat, 45 meat, 38 bone
Weight: 2671
Description: Isn't very muscular but has a gigantic build
Return: 24 fat, 36 meat, 42 bone
Weight: 2877
Description: Gigantic
Return: 18 fat, 60 meat, 34 bone
Weight: 3016
Description: Gigantic
Return: 24 fat, 53 meat, 38 bone
Weight: 3575
Description: Enormous yet very weak
Return: 30 fat, 36 meat, 60 bone
Weight: 3800
Description: Enormous build but is very skinny
Return: 12 fat, 60 meat, 50 bone
Weight: 4014
Description: Very muscular and just gigantic overall
Return: 18 fat, 90 meat, 38 bone
Weight: 4466
Description: Gigantic and muscular
Return: 24 fat, 98 meat, 42 bone
Weight: 4544
Description: Gigantic and quite fat
Return: 43 fat, 64 meat, 60 bone
Weight: 4607
Description: Gigantic yet weak and skinny
Return: 24 fat, 77 meat, 63 bone
Weight: 5182
Description: Isn't very muscular but has a gigantic build
Return: 38 fat, 81 meat, 64 bone
Weight: 5643
Description: -
Return: 32 fat, 107 meat, 60 bone
Weight: 5669
Description: -
Return: 32 fat, 109 meat, 60 bone
Weight: 5759
Description: Gigantic and quite fat
Return: 38 fat, 109 fat, 56 bone
Weight: 6822
Description: Gigantic and muscular
Return: 32 fat, 150 meat, 64 bone
A count of other butchery products, done on Slate 14.
Eye: 2
Brain: 1-6
Lung: 2-12
Heart: 1-3
Liver: 1-6
Intestines: 2-18
Tripe: 1-6
Sweetbread: 1-3
Spleen: 1-3
Kidney: 1-6
Somebody definitely ate a kidney there. In all other cases but intestines, there were enough examples of the minimum figure that I'm comfortable reporting those. For intestines, the stocks at the end of butchering were 2, 4, 4, 4, 5, 8, 8, 9, 9, 10, 10, 10, 10, 11, 14, 14, 15, 16, 16, 16, 17, 17, 17, 17, 18, 18, 18, 18, 18.
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From this it seems that raw weight is far more important than the animal's description, which controls the distribution of fat, meat, and bone to a somewhat unpredictable degree.