My father and I want to develop a cow pedometer to measure a cow's activity. The idea is that if you can measure a cow's activity you can detect when she enters heat. Detecting heat with sensors will help us increase the probability to choose offspring sex depending on insemination time since heat detection, and increase insemination rates since we are not relying on humans to detect cows in heat.
Commercial options are too expensive for us so we have decided to develop the sensors ourselves. I have no EE background, just CS. I come to you for guidance on how to proceed with the project.
Project background
We want to create a pedometer that can be attached to a cow's feet and is powered by a battery. The pedometer must be able to send the accelerometer's data to a central system for data logging and processing. The maximum distance a cow can be from the central system is 1.5km. There are about 400 cows. The farm is on flat ground and doesn't have a clear line of sight (trees block the sight, although it's just a few of them). We also have a mountain overlooking the valley where the farm is (maybe to but up the main receiver?) SEE FARM MAP. Trees in green, farm limits red, circle of radius 1.5 with center in house covers the whole farm. 
Here are the questions I have, any question you could give feedback on would be great.
How can I achieve a low power long range transmitter? I suppose it will be low bandwidth (only sending sensor id, x accel, y accel, z accel)
Are there any available systems I can use to reduce development time?
At first I will be prototyping with Arduino.
Best Answer
According to me using moteino with accelerometer module like MPU6050 would do the trick. One use was able to get a range of 1.5Km using moteinos(https://lowpowerlab.com/forum/moteino/rfm69hw-driverange-test/). You will have to decide the frequency of data that you get, so accordingly the system can go in low power mode and give a longer battery life.