It's an enviable part of the doggy lifecycle unfortunately....after the cute puppy dog days your dog grows into an adult...has hopefully a good decade or longer and then starts to slow down once they enter into the geriatric age...
Sometimes this is a slow and obvious process and other times it can creep up on you pretty quick. With older age, in almost all dogs, comes some level of joint discomfort or pain...especially in the bigger dogs. It's important to understand the symptoms of joint pain so you can catch it early and take preemptive measure to slow it down or even hopefully prevent it.
Here are some of those symptoms...
For most of us we're pretty used to the (best part of having a dog right) exuberant tail wagging and barking when we get home from a long day. If your dog suddenly decides he's not going to get up to happily greet you anymore, it's probably not that he grew to hate you overnight, but more likely that it's getting pretty painful to get up.
When it's increasingly difficult to get up and move around dogs generally slow down or stop exercising...they walk less, they stop running around, and at the same time (as most of us know) they don't stop eating. So like many humans they start packing on the pounds pretty quickly in their old age. It's important to curb this though as the heavier the dog is the more pressure he puts on his joints...which may perpetuate the problem.
If your dog doesn't have the same energy or willingness to get up and go do things they're used to doing it could be because join pain. Similarly if your dog has grown increasingly irritable, it could mean he's been fighting off some pretty serious pain...dog's obviously can't tell us verbally so it's important to monitor their non-verbal communication and behavior in this case.
If you ever notice your dog suddenly licking, biting, scratching, or chewing you should always dig into what's going on. There are several different things that can be causing the discomfort, but joint pain can certainly be one of the culprits.
A more obvious sign of joint pain is if you notice your dog walking (more bow-legged) funny and/or limping...this is pretty common in older dogs so make sure not to push them too much if you're taking them on a run. This is also true for the dog park or other outdoor activities....most dogs always want to go 100mph...it's later that they'll feel the pain so it's important to temper them and their activities so they don't make it worse.