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Caro caedes est.
One may even omit the copula “est”, to attain that charming compactness characteristic of Latin. 
I think there might be more of an ‘oomph’ with ‘est.’
I think not! 
Yet, whether or not the presence of the copula is desirable with a view to apportioning that “oomph” to the little sentence, we may leave to the judgement of the topicstarter. I didn’t intend to prejudice on the aesthetic merits of omitting the copula, but merely sought to point out that, if one would consider the omission of the copula more attractive, the rules of grammar would not impede this desire. 
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My dictionary says that homicidium means “homicide” and “manslaughter” in addition to “murder.” I would personally not use that word because it would seem to imply cannibalism.
My dictionary also says that interfectio means just “killing.” I think you want it to seem more evil than that, if that’s a good way to put it.
Of course, I could be totally incorrect on both counts. Maybe my dictionary isn’t the best one.
Which one do you use, Dacice? If I had a a few hundred $$ to spare, I think I’d go for Glare’s…
Well, this is an interesting discussion. As Dacicus wisely pointed out, “homicide” specifically refers to the killing of a man, as opposed to an animal. Therefore any phrase with the Latin term homicidium does not fit your intended meaning. Yet these may be salvaged by replacing the word with a synonym for murder.
Fortunately, Latin has an abundance of words for murder! caedes is probably the most emphatic choice, meaning “carnage, slaughter, massacre, brutality”, even used sometimes of animals. nex is “violent death, murder”. occisio also means “slaughter/massacre”, literally “a cutting down”. homicidium literally means “killing of a man” homo “man” + -cidium (caedere) “killing”. interfectio is pretty weak, “a putting of an end to someone/something’s life”, but much more common as a verb (interficere) than a noun. clades and strages also mean “slaughter, carnage, etc.”. So basically, your realistic choices for murder are:
caedes, nex, strages, clades and occisio; I think caedes seems most prudent.
“deer/venison in abundance is man-killing” - sort of a silly thing to say
CARO INTERFECTIO EST
“meat is a killing” - pretty much the same thing as caro caedes est, but with a less probable choice of words.
Carnificium est Homicidium >
“murder is the trade of executioners” (roughly) - I think the person meant to use lanius “butcher” rather than carnifex “executioner” (literally “meat-maker”, but not used in that sense). Replacing homicidium with a more appropriate word for animal killing, this could definitely be a phrase to consider.
e.g. lani(i) (ars) est caedes “brutality is a butcher’s trade”
or probably better with a verb: lani(i) (ars) est caedere/necare “a butcher’s trade is to kill”.
Are any of these correct? If so, which do I use? I like ‘caro cadaes est’ it’s nice and short and much less painful as a tattoo!! >
caro caedes est is perfectly fine grammatically, though the idea is a bit foreign sounding and the idea abstract. Meat itself is not murder, the act of getting the meat is what is being argued about, so it is a bit illogical without an understanding of modern word usage. The phrase lani est caedere/necare circumvents this ambiguity entirely, so it may appeal to you in that regard.
There seems to be some contention as to whether the word murder can apply to animals, or just to humans. Does this make any difference? I really must get it right!
“murder” can apply to humans or animals, but "homicide’ and its Latin counterpart homicidium apply only to humans.
Which one was used in law courts? If you killed a person, and later were tried and convicted under the law, which crime were you guilty of?
It seems to me the criminal act of killing is the most relevant. All of these below miss the point just slightly:
meat is slaughter
meat is butchery
meat is killing
meat is an execution
meat is a slaying
meat is brutal(ity)
The fact that meat involves slaughter is not news. “Meat is murder” asserts that meat is tantamount to an unlawful or unethical killing.
Which one do you use, Dacice? If I had a a few hundred $$ to spare, I think I’d go for Glare’s…
I have The New College Latin & English Dictionary, published by Bantam Books. Saying that maybe it’s not the best was a major understatement. I probably won’t get a better one anytime soon, since I’m not a Classics major or anything like that.
The problem is that in a court of law it is always homicide to which they refer. Does necare fit your criteria? There is also the adjective internecinus, e.g. interneciva est caro (edenda) “meat is murderous (to eat)”.
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caro really is literally “meat” or “flesh”, see for yourself if you like: Lewis & Short Latin Dictionary. You wouldn’t recognize it in the form caro, but most of its other forms begin in carn-, hence “carnivore”, “carnage”, and a little more remotely, “carnival”.
Are you planning to sell Meat Is Murder T-shirts at the Colossium? Maybe you could get the gladiators to wear them! (Well, after we’ve perfected that time machine thingy.)