When some living being like dog or any mini bacteria are killed, since they are not self aware or concious do they feel the same type of pain as we do? what is the difference between their suffering and our suffering?
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Dogs don't forget pain. You only have to look at a dog that has been continuously beaten and then cringes or tries to bite anyone who tries to pet it. Yes it has become an automatic reaction but there must be some kind of memory there about humans not being trustworthy.
More primitive life forms, such as worms or fish, have a nervous system, therefore their nervous system experiences physical pain. Dogs are probably more complex and have emotions such as lust, love, *emotional* attachment; that makes them experience *emotional* sorrow & unhappiness. 

However. as we can directly experience, homo sapiens (people) have the *egoistic* attachment (*upadana*) of self-identity (*sakkaya ditthi*), which is born from thought conception. This *upadana* of *sakkaya ditthi* is the '*suffering*' ('*dukkha*') Buddhism seeks to eliminate. 

I think it is a fair assumption worms & fish cannot create the *upadana* of *sakkaya ditthi*; and probably also dogs. 

> 
> *Bhikkhu, ‘**I am**’ **is a conceiving**; ‘**I am** this’ is a conceiving; ‘**I** shall be’ is a conceiving; ‘**I** shall not be’ is a conceiving; ‘**I** shall
>  be possessed of form’ is a conceiving; ‘**I** shall be formless’ is a
>  conceiving; ‘**I** shall be percipient’ is a conceiving; ‘**I** shall be
>  non-percipient’ is a conceiving; ‘**I** shall be
>  neither-percipient-nor-non-percipient’ is a conceiving. **Conceiving is
>  a disease, conceiving is a tumour, conceiving is a dart**. By overcoming
>  all conceivings, bhikkhu, one is called a sage at peace. MN 140*
> 
> 
>