Bottle Feeding A (Smart) Elderly Dog

First off, you're working under a completely wrong assumption: that sucking milk from a teat or a bottle is less work for the tongue than lapping up water from a bowl.

Puppies don't have the muscles necessary to suck from a nipple in their lips. Instead, they curl their tongue around the nipple in a U-shape and suck the liquid with their tongue, as opposed to their lips. And they can create quite a lot of suction like that.

Nipple size

The nipple must be the correct size in relation to your dog. Puppies are tiny, so they need tiny nipples. If your dog is bigger. you need a bigger nipple.

The nipple must fit between the canines of your dog and have a little extra room for the tongue to wrap around it. I doubt the shape makes much of a difference, but I would go with straight and tubular, if available (basically an oversized puppy nipple).

How to induce the instinct to suckle?

A funny experience I had with my dog lets me assume that the instinct to suckle never fully vanished. I was holding a CD (for those youngsters around here: shiny disk with a hole in the middle, where music used to be stored ;) and I had my finger poked through the hole. My dog was interested in the object so I held it down for him to sniff it, but instead he suckled on my finger.

I can only assume here, but I think the sensation of a little appendage poking out of an otherwise flat surface might have triggered it (like a nipple poking out of mummy dog's otherwise flat-ish stomach). He was first sniffing the CD, so his nose bumped into the flat surface and then my finger touched his mouth.

You could simply take a piece of cardboard and cut a hole the size of the nipple into it. Stick the nipple through the hole and see if she starts suckling. Her nose must press against the cardboard, so the nipple must not stand out too far.

If she doesn't suckle, maybe she isn't capable anymore.

Is this really the solution to your problem, though?

If your dog already has problems with her tongue, she probably won't have the muscle strength left to actually suckle liquid from a bottle. But then there are human babies with a similar lack of strength, so you can use some baby bottle hacks for your dog as well:

• Instead of having a hole in the tip of the teat, carefully cut an X into the tip with an X-Acto knife. That still holds the liquid without (much) leaking but makes sucking much easier due to the big opening. It should also release some liquid if she bites instead of suckling.
• Poke a second tiny hole into the top (!) of the teat at the very edge where it's connected to the bottle. That second hole will allow air to be sucked into the bottle while the liquid is being sucked out, reducing the negative pressure inside and thereby the force you need to suck more liquid out. Many modern teats already include this second hole, my parents still had to poke it themselves.

Please be aware that both hacks combined may lead to leaking.

Alternatives

The type of syringe you describe is hard to control. A rubber balloon syringe or baster syringe is much easier to control and far less likely to cause aspiration. Just make sure to never use a glass syringe! They are available in plastic, metal and silicone as well.

Turkey baster syringe

It might be easier for her to drink from a source at eye level and let the water trickle down her throat.

One idea is the type of water dispensers commonly used for small mammals like rabbits or chinchillas.

Small pet water dispenser

The problem is that they only work up to a certain size and even the biggest size is probably too small for your dog. But it never hurts to try.

Another idea is to put a cat water fountain at her nose level so she can lap the water from a higher point than the ground. Since these include a water pump that is close to impossible to clean, I wouldn't fill it with anything but clean water.

Cat water fountain