Why is pig iron called so?

Pig iron is the intermediate product of smelting steel ore with coke and resin. Pig iron has a high carbon content, typically 3.5-4.5%, which makes it brittle and not useful directly as a material except for limited applications. The traditional shape of moulds used for these ingots was a branching structure formed in sand, with many individual ingots at right angles to a central channel. Such a configuration looks similar to a litter of piglets suckling on a sow. When the metal had cooled and hardened, the smaller ingots (the pigs) were broken from the much thinner runner (the sow), hence the name pig iron.