Pain and suffering are certainly visited upon animals in such practices as the castration of cows. In Britain an anesthetic must be used, unless the animal is very young, but in America anesthetics are not in general use. The procedure is to pin the animal down, take a knife, and slit the scrotum, exposing the testicles. As Singer remarks of this kind of thing, it is typical of what happens to your dinner when it is still an animal. Unnecessary for the achievement of any justifying end.
People like to eat meat.
They enjoy it. By inflicting cost-saving pain and suffering on animals we enable humans to satisfy a dietary preference at an affordable price. Beyond that no good comes of it in Singer's view. Our heavy consumption of meat is not healthy. Furthermore our agricultural practices, geared as they extensively are to the production of meat, are environmentally unsound.