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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I think that (according to Buddhism) humans, animals, ghosts, and residents of hell all belong to the same kind of category: all "[sentient](https://en.wikipedia.org/wiki/Sentient_beings_(Buddhism))", all composed of the five skandhas, and all subject to suffering.

Since all belong to the same continuum (i.e. samsara), I expect that they all "lose memory" and that their "suffering finishes" in much the same way.

I don't consider a dog as like a bacterium, by the way: IMO a bacterium is more like a plant than an animal. I think different schools of Buddhism differ on whether plants are "sentient" and have any "consciousness".

**don't they just forget or loose the momory of their suffering after it is finished?**

Isn't that more-or-less true (or untrue) of people too?
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*
> 
> 
>