The 2014 Hungarian film White God featured many scenes involving live dogs, including scenes of dogfights and other types of animal abuse. The director, Kornél Mondruczó, did not want to use CGI to create the animals because he felt it would be inauthentic, an invention of the human creators rather than a genuine observation of the dogs' behaviour. So he worked with dog trainer Teresa Ann Miller to find and train real live dogs and coach them through the various scenes the film required.
This video is an interview with Mondruczó and Miller in which they discuss the techniques they used to create the disturbing scenes. For the most part, they used careful editing and what Mondruczó calls "dramaturgy and illusion" to create the impression of cruelty and suffering while not actually harming the dogs at all.
The dogfight scenes, for instance, are very hard to watch as they seem so realistic, but if you carefully observe what is actually on screen, you can see that you are never shown the dogs' teeth impacting each others' bodies. The editing is very fast, and there are a lot of sounds of growling and snarling to cover up the fact that the dogs do not ever bite each other on-screen. (The growling and snarling is not real, either: the sounds were recorded by humans and dubbed in afterwards.)
It is of course very common for dogs to play-fight in a way that does them no harm, and the trainer exploited this, as she explains in the video linked above. She introduced two dogs to each other, got them to be friends, then separated them so that when they met, they would run towards each other in excitement and play-fight with great energy. The footage of several sessions of this play-fighting could then be cut together with fake growls on the soundtrack to give the impression of a vicious and brutal fight. This was enhanced by adding CGI blood on the dogs' muzzles. One of the dogs was happy to "play dead" in a very dramatic-looking way, which worked pretty well since he was the one who was supposed to lose the fight!
Now, White God is an unusual film because of the large number of animals used, and the director's strong commitment to using live animals when CGI was a possible alternative. Nonetheless, unusual as it is, it seems most likely that the techniques used by Miller and Mondruczó have been used in other films: careful editing, fictitious sound effects, and exploiting the natural behaviours of the animals.