It's always hard to diagnose a plant issue from photo's.
Possibly, your tree is infected with a 'coffea' specific disease but this is unlikely, given relative isolation and the lack of multiple plants.
The symptoms, from a look at what you have posted, could be anything from a nutrient deficiency,
a toxicity in the soil, a general fungus disease, or water logging.
Coffee trees like a lot of water but if your soil has poor drainage then the roots will suffer.
Normally, symptoms which first show up in the growing tip relate to an issue with the roots/soil.
Some nutrient deficiencies show up first below the shoot tip, in newly expanded leaves while other deficiencies manifest in older leaves as the
plant 'steals' nutrients to maintain new leaf production.
Fungal or mildew problems will show up first on soft new leaves, near the growing tip but not at the very tip and generally don't trouble older leaves.
You may have a nutrient deficiency.
Do the cattle urinate on the root zone? Urea toxicity may be the problem.
Here is a link to a diagnostic chart:
http://landresources.montana.edu/NM/Modules/Module9.pdf
The other thing you can do is put some leaves in a SEALED, clear, plastic bag and take them to
an agricultural chemical reseller who generally have agronomists or horticulturalists in their employ
and who have access to agricultural extension services.
You could also try getting in touch with a coffee grower in Byron Bay/ North Queensland but you will need more detailed, close-up photos.