A point to consider is that every category of animal, animal abuse or advocacy can be called "single issue," whether the category is chickens, kaporos chickens, farmed animals, furbearing animals, aquatic animals, whales, whaling, dog fighting, squirrel shooting, circuses, rodeos, SeaWorld, mountain lion protection, anti-welfare campaigns, save the elephants, spay & neuter, vivisection, or whatever.
Campaigns on behalf of specific human groups have been waged throughout history. Was the campaign to end apartheid in South Africa a "single-issue" campaign that thwarted the overall effort to liberate all people everywhere on earth from legalized discrimination? What about the suffragist movement or the civil rights movement or the gay rights movement in the United States? Don't these constitute "single issues" within the universal drive for social justice? And do they not break down further into specific campaigns for voting rights, equal opportunity in education, anti-housing discrimination, affirmative action, and so forth?