Although Some subjects related to professional veterinarians only yet there is need for these to have better grip on your subjects
For example
Anatomy and Physiology ( General and Comparative)
This subject might be not directly important to the exam but for understanding clinical aspects and other things better one must know at least this basic subject...
For example
Bloat is accumulation of gases and fluids in Rumen..
this statement can come in exam either not related to anatomy and physiology yet for better understanding and good memorization it is necessary..

What is Rumen?
Its Physiology??
If one knows this, he can solve hundreds of problems even he not studied them directly just by inference..

Book I suggest for this is "Anatomy and Physiology of Farm Animals by Frendson"...very basic and beautiful book...if any one needs soft copy can contact me..

@RaoRameez,
It's all true. Basic knowledge is very much necessary for success in a competitive exam. Many thanks for sharing this functional knowledge with us.
Now, the preparation will be easy for us if we follow the principles, you have mentioned.

Regards