Wang (1982) relates this word to 羖 (OC *klaːʔ, “(black) ram”), 牯 (OC *kaːʔ, “male bovine”) and 麚 (OC *kraː, “stag”); thus, this word is likely a general word for “male animal”. However, Schuessler (2007) considers 牯 (OC *kaːʔ) to be a post-classical loanword from Austroasiatic, and 羖 (OC *klaːʔ) a cognate to 羯 (OC *kad, “wether”). See these entries for more.
The common word for “pig” in most modern varieties of Chinese, 豬 (OC *ta), is likely a derivative. See there for more.