Campaigns directed toward pigs and cattle, however, could have a negative welfare effect by shifting consumption to poultry and fish products, which provide significantly less food per animal life-year. In fact, removing only poultry, eggs, and farmed fish from the diets of one hundred people would affect more animals than turning ninety-nine people vegan. If it is easier for consumers to shift consumption among animal products than to eschew all animal products, then this arithmetic has implications for both welfarist and abolitionist strategies.
That is from Natalie Cargill. And the article is informative throughout. You will note however that when it comes to environmental impact, red meat from the larger animals is typically the much larger problem. So which do you care about more, animal welfare or the environment? Or are you only willing to talk about margins where both improve? By the way:
In the United States, there are only 220 veterinarians responsible for the care of more than nine billion farm animals.