SOURCE: This comes from the Latin translation that accompanies De Furia's edition of the Greek Aesopic corpus, published in 1810 and available at GoogleBooks. This is fable 133 in De Furia; for other versions, see Perry 181.
READ OUT LOUD. Choose which marked text you prefer to practice with - macrons or accent marks - and read the text out loud until you feel comfortable and confident. Then, try reading the unmarked text at the bottom. It should be easy for you after practicing with the marked texts. :-)
MACRONS. Here is the text with macrons:
Agāso quīdam Asinum et Mūlam mercibus onerātōs agēbat. At Asinus quidem, dōnec in plānitiē iter processit, onerī ferendō pār fuit; ast ubī in montāna vēnēre, cum illud amplius sustinēre nōn posset, Mūlam, ut partem eius aliquam susciperet, precābātur, quō reliquum ipse perferre posset. Ea vero ipsum ōrantem cum sprēvisset, Asinus in praeceps dēlātus periit. Tum agāso, quō sē verteret nesciēns, eī nōn solum onus Asinī, sed pellem quoque Mūlae ferendam imposuit. Illa igitur vehementer dēfatīgāta, Digna patior, inquit; nam sī rogantī, ut aliquid oneris levārem, pāruissem, nunc eius sarcinam omnemque ipsum nōn gererem.
ACCENT MARKS. Here is the text with accent marks, plus some color-coding for the words of three or more syllables (blue: penultimate stress; red: antepenultimate stress):
Agáso quidam Ásinum et Mulam mércibus onerátos agébat. At Ásinus quidem, donec in planítie iter procéssit, óneri feréndo par fuit; ast ubi in montána venére, cum illud ámplius sustinére non posset, Mulam, ut partem eius áliquam suscíperet, precabátur, quo réliquum ipse perférre posset. Ea vero ipsum orántem cum sprevísset, Ásinus in praeceps delátus périit. Tum agáso, quo se vérteret nésciens, ei non solum onus Ásini, sed pellem quoque Mulae feréndam impósuit. Illa ígitur veheménter defatigáta, Digna pátior, inquit; nam si rogánti, ut áliquid óneris levárem, paruíssem, nunc eius sárcinam omnémque ipsum non gérerem.
UNMARKED TEXT. Here is the unmarked text - after practicing with the marked text that you prefer, you should not have any trouble with the unmarked text:
Agaso quidam
Asinum et Mulam
mercibus oneratos agebat.
At Asinus quidem,
donec in planitie iter processit,
oneri ferendo par fuit;
ast ubi in montana venere,
cum illud amplius sustinere
non posset,
Mulam,
ut partem eius aliquam
susciperet,
precabatur,
quo
reliquum ipse perferre posset.
Ea vero
ipsum orantem
cum sprevisset,
Asinus
in praeceps delatus
periit.
Tum agaso,
quo se verteret
nesciens,
ei
non solum onus Asini,
sed pellem quoque
Mulae ferendam imposuit.
Illa igitur
vehementer defatigata,
Digna patior, inquit;
nam si roganti,
ut aliquid oneris levarem,
paruissem,
nunc eius sarcinam
omnemque ipsum
non gererem.
IMAGE. Here is an illustration for the story (image source) from a Renaissance edition of Aesop; this version of the story shows a horse and a donkey:
Here is another illustration from the Medici Aesop, which is online at the New York Public Library website.