Getting an electric shock in this manner is not as obvious as it may first seem, it might be better to explain it in terms of two dimensions.
If you have an electrical system where the primary earth point is an electrode driven into the ground, if a fault current occurs, it passes throught the earth electrode and is distributed into the earth mass.
If you take the electrode as being the supply conductor in this case, what happens is that you get a potential(voltage) between it and any other point on the ground, the closer you are to the electrode, the lower the potential between them.
You can plot this on a chart and what you get is concentric rings of voltages of a particular voltage around the electrode.(imagine contours of voltages around the electrode)
So you might get a circle of voltage of perhaps 10 volts between any point ten feet away from the electrode, this is just an example.
Lets continue to imagine that for every 10 feet, the voltage drops by 10 percent from the previous reading and the electrode is at 240Volts - you’ll note that the change in voltage decreases with every ten feet as this is an itirative solution.
If you were to take two points one ten feet from the electrode, the other 100 feet, you would also measure a potential between them, I’m not going to do the maths, but you can see how quite a large potential will develop between them.
If you then joined those two points with a conductor then a current would flow, following the various electrical laws, but also including the supply impedance which would tend to limit the current flow…
It happens that in some conditions, this is a real problem, for a human with only a short distance between contact points, the feet, and with footwear, the chances of standing such that the potential between those feet is even large enough to feel is very small.
However, when we are dealing with farm animals, this situation is very differant.
The supply systems to farms often entails the use of earth electrodes, and a fault on the system can drive a large current throught the earth electrode.
There is a real possiblility that if the earth electrode is situated in an area where farm animals are nearby, they are of such length, and their heart is directly in the path of current flow, that they can get a 50-70volt shock between foreleg to rear leg, and it will kill them.
You note that in such a scenario, the animal has not even touched the earth electrode, it has just formed a conducting path parallel to the ground plane.
This is the same situation when we deal with swimming pools and immersion, except we are dealing with three dimensions, you do not get a shock directly from the conductor itself, but rather, you form a lower resistance path between two points at differant distances from the source of the electricity.
The purer the water is, the wider is the spread of potential and hence the more dangerous, the more contaminated, or perhaps even salty, the smaller is the spread of electrical potential, and also it is much more likely to be a better conductor than the human body.
As for distances, well, I have personally used salt water for fire fighting purposes directly onto 440volt conductors at less than 10 feet, this was done during damage control training when I was in the Royal Navy, so it would seem to me that you have to be pretty damn close to get yourself a shock in this manner