A method and arrangement for determining a gut fill level of the rumen of an animal uses a three-dimensional camera and an image processing system. The three-dimensional camera is located in a station, wherein the animal is forced to stand essentially still during recording of the three-dimensional image. The three-dimensional camera is located on the left side of the animal at a height above the rumen triangle of the animal, longitudinally in essence in level with the rumen triangle, and is directed downwards towards the rumen triangle during the image recording. The image processing system automatically determines a depth and/or volume of a convexity or concavity of the rumen triangle, and determines the gut fill level of the rumen of the animal based on the determined depth and/or volume.
