When I was a teen I boarded and did chores at a place with very lax grain management and a dirt floors in the stalls. The rats dug holes under the stalls so they could get to the corner under the feed troughs unseen. My dog, a Aussie who was bred at the farm, was super people-shy but a cold blooded rodent killer. One day a younger girl was getting her picking up her riding boots which sat along a long barn aisle next to her tack box. A rat popped out of her boot and scared her half to death. The next day I was walking by the end of the aisle and saw my dog near there. All the sudden she leapt and death-bit a rat that lie there squealing. I said "good dog!" and distracted her so much she didn't finish the job! Luckily her mom, an older dog at the barn came running and killed it.
Next story is about 10 years later. I'm a working student another barn, an old dairy barn with dirt and gravel floors with mats over top and a cement aisle. Again, we had a rat problem and the tunnels in the corners of the messy eating horses' stalls were unmistakable. We had cats, but the rat problem was out of control. We used a combo of rat traps with locked stalls overnight and the black boxes with rat poison that keep other animals from getting to it. The worst part was finding the rats drowned at the bottom of a horse's water bucket as you dumped it out.
I learned then that the internal bleeding caused by the rat poison makes the rats incredibly thirsty and they search for water and fall in and drown when ordinarily they wouldn't. But I never saw live rats really, only dead ones and evidence of them. They eventually were knocked down and they didn't have a problem for many years after. The cycle of country life.
This may have been covered, I skipped to the end -- there are different kinds of rats. Native cotton rats are very different that Norway or black rats. Your best friends, if you would not like to see them, are snakes. Rodents are their Krispy Kremes!
My little rat terrier, all 11 lbs of her, has no problem dispatching mice and the occasional rat, some half her size!
Of course, since there are not many around she can get to, she doesn't make a dent in their population.
She sure will indicate if one is hiding somewhere, like in a pipe and is relentless after them, best she can get to them.
That is why she has been bitten by rattlers twice now, sticking her nose where she should not into rat holes that also had a guest in there.
By the way, we don't feed any grain, just hay, but rodents like to live in, to them, warm, well protected structures and hay stacks.