I'm going to chime in on this one, seeing as I'm currently an animal technician (not with dogs - however I know and network with other techs who do). I've obviously name changed for this for security as yes the crazies are a real risk to us, and the researchers/users.
Labs that use animal models are highly legislated. We're visited by the home office - and randomly too - if something is going on that shouldn't be, we would be in big trouble.
I'm not going to do a song and dance about how animals in labs have vast quantities of space - they do not, not at least in the sense pet owners would like to see (I say that as a pet owner). However, there are legal minimums. As a tech, I push my users to utilise the most space possible for the animals, usually with the argument that healthier, happier animals, will result in better research. Unfortunately from a legal standpoint - they don't have to, they only have to adhere to legal minimums. This is something I will address honestly, I WOULD honestly like to see it change, however it also has to be financially viable for all parties for it to work. You absolutely have more to worry about with the space farmed animals bred for meat get to live in though - I assure you.
The comment about the underfeeding is ridiculous - animal techs would NOT have animals underfed. Neither would researchers - unhealthy animals effects the legitimacy of their research. Researchers are often working on tight budgets and since they pay to use the animals, will not be happy if they are paying for unhealthy animals which will in turn, negatively affect their research. Animals used for research are fed extremely high quality diets - that, just for info's sake, tend to cost an absolute fortune. If for some reason you had evil animal abusing technicians and researchers who would be happy for the animals to be underfed or malnourished - the home office would certainly not. This may be different for feeding trials or nutritional experiments, - however all studies do need to be cleared first so any suffering has 'humane endpoints' that need to be followed. For all experiments and research however, the feeding is very carefully controlled, managed and a lot of research goes into the best possible diet and feeding regimes used by labs.
With regards to exercise - research dogs are socialised, played with, and exercised. Are they taken for a leisurely stroll down the road? Absolutely not. Animal units NEED to be biosecure because the procedures are scientific. The dogs could easily pick up pathogens that again, could and WOULD effect research, and potentially spread disease and parasites to all the other animals in the facility, in which case, if the pathogen is severe enough, would mean to need to cull entire lines of animals - this doesn't bode well with home office, users who have extremely important lines, or the reduction aspect of the 3 R's (replacement, refinement and reduction).
On the rehoming aspect - whilst the animal species used are (usually, but not definitely not always) domesticated, they are not pets in the way most owners think of pets. They are usually friendly enough (despite the 'torture' many think they endure) but it needs to be understood these animals are bred for specific purposes. A fair amount will be genetically modified in some way - this won't be visually apparent but will affect for example their natural immunity, antibodies, predisposition to certain illnesses - and above all they have been bred in biosecure units. Once you take that animal out into the 'real world', well you can imagine.
The rules around rehoming lab animals is very strict - and not by the labs themselves, but by governing bodies. And there is justified reason for it. Sure enough though, I know some animals have been rehomed.
Labs, like zoo's, were guilty of having atrocious standards in the past. This has massively changed as our entire society's attitudes to animal welfare have changed.
I'm afraid you're incredibly misinformed and I dare say biased.
I'm an animal lover, and an animal technician in a lab - funny that. I certainly couldn't do it if there was quite the torture many seem to imagine goes on. Are some of the experiments unpleasant? Of course. Is it carefully controlled, and managed, and where possible, pain relief etc given? Absolutely.
You will not find people who care more about animals than the technicians that work with them, and are responsible for their care on a daily basis. Many of the increased standards of welfare are a direct result of technicians. I work in the industry I do because I want to be a part of making sure the animals are treated the very best that is possible, and I've been responsible for positive changes to welfare myself, and pushed bloody hard for it.
Everything in the scientific field has to be 'justified'.