Descriptive, comparative, and functional anatomy of the facial musculature in cattle (Bos taurus).

Facial expressions can provide insight into animal emotions and pain, but no standardized system for assessing the entire facial display in cattle (Bos taurus Linnaeus) exists. The Facial Action Coding System (FACS), originally developed for humans, identifies distinct facial movements based on mimetic muscles. Developing a cattle-specific FACS requires mapping and comparing cattle mimetic musculature with that of humans and related species, which was the aim of this study. Dissection of three heads-using skinning and facial mask preparation on opposite sides-identified 30 mimetic muscles and revealed notable fiber blending in the lower face and ear region. The method helped clarify subtle anatomical discrepancies in previous literature that are important for interpreting muscle function. Muscular differences with humans and horses suggest a slightly less diverse or different facial repertoire in cattle. Robust lips and a different lip-muscle arrangement likely restrict the marginal, upper lip, and lip-corner movements described in one or both comparison species. A broad insertion of the M. levator labii superioris indicates involvement in both upper lip and nostril movements, and several muscles appeared to influence nostril shape. The eyebrow region-served only by a broad M. frontalis-suggests fewer eyebrow movements than in humans and broader ones than in horses. Cattle also possess musculature supporting movements not described in one or both comparison species, including upper lip retraction, nostril lifting, cheek raising, and diverse ear movements supported by well-developed ear muscles. The findings provide a basis for developing a FACS for cattle, pending validation in live animals.