Have you checked if the binos have fungus in them? Fungus looks like little filaments. It is not that difficult to clean them out yourself. Professional cleaning will probably cost more than the binos are worth.
Binoculars have 2 big advantages- both eyes are used and portability.The upside down problem is corrected with a a prism.
15 x 70 s would probably be the minimum specification. All depends on how much detail you need. A novel solution to the Mak spotting scope portability problem is a gorillapod- just wrap the legs around a tree branch or the door of the ute. They come in a range of holding powers up to 5kg . I have just ordered a 5kg hold gorillapod from the USA for my 300mm f/2.8 camera rig.
A zoom eyepiece, wheras the sharpness of image will not be razor sharp, has the advantage of portability and simplicity.
Last option is a barlow type lens to bayonet on the end of a telephoto lens. This will act like a monocular. Higher quality can be achieved by adapting a telescope eypiece to the back of a decent fast telephoto lens. If you have the lens, this will be a cheap and portable rig although the image will be fairly dark.The bigger the front element size the better. Should be minimum 77mm.
***Now, very important. Do not let the P.C. brigade know that you are spying on your cattle- they will howl in protest that their privacy is being invaded and their civil rights violated. Be sure that the cattle are fully informed and consent to be spied on forms are signed in triplicate. Parental consent will be required for spying on calves. Under no circumstances should photos be taken- all hell will break loose if these images land on the net for vealophiles to slobber over
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