
PLINY, Natural History, 8.20 (referring to 55 BC)

Also in Pompey’s second consulship, at the dedication of the Temple of
Venus Victrix, twenty elephants, or as some record, seventeen, fought in the
Circus, their opponents being Gaetulians armed with javelins.

CALPURNIUS SICULUS, Eclogue 7 (AD 57)

I saw a theatre that rose skywards on interwoven beams and almost looked
down on the summit of the Capitoline … Beasts of every kind I saw; here I
saw snow-white hares and horned boars … Nor did I only see monsters of the
forest: sea calves also I saw with albino bears pitted against them.

Sources on the Emperor Commodus (2nd-4th century AD)

Commodus devoted most of his life to ease and to combats of wild beasts
and men. For example, all alone with his own hands, he dispatched five
hippopotami together with two elephants on two successive days; and he
killed rhinoceroses and a giraffe.
Gladiator (2000): our hero kills animals!
But don’t be alarmed, folks –
it was only one animal, and it was only
done in self-defence!

It is not enough to have committed such wickedness:
they involve the gods in crime, and believe that the gods
above delight in the slaughter of suffering oxen! … Do
not, I beg you, and concentrate your minds on my
warnings! When you place the flesh of slaughtered cattle
in your mouths, know and feel, that you are devouring
your fellow-creature!

(1) Ovid, Fasti 4.459-62 (simile for Ceres searching for daughter):

Just as a mother cow, whose calf has been snatched from her
own udder, groans and seeks her offspring through every grove:
so the goddess Ceres did not hold back her groans and carried
herself along at speed, starting from your plains, Henna.

(2) Ovid, Fasti 4.637-8 (sacrifice at the Roman Fordicidia festival):

But when the attendants have snatched the calves from the
womb (of their mothers) and have offered the cut entrails to the
smoking hearths …
Phoenix the Calf
Civic Duty v. Emotions during the
Foot and Mouth crisis (2001)

S.J. Green (2008) "Save the Cows? Augustan
Discourse and Animal Sacrifice in Ovid's Fasti", Greece
& Rome 55, 39-54

R. Sorabji (1993), Animal Minds and Human Morals: the
Origins of the Western Debate, London, esp. 170-9

J.M.C. Toynbee (1973), Animals in Roman Life and Art,
Baltimore