Abstract: A hydrometer for determination of immunoglobulin content of mare colostrum comprises a container having a top wall, side walls and an open bottom. An elongate, emergent stem is carried by and projects from the top wall, and the stem is provided with a scale along its length to indicate the specimen specific gravity when the device is immersed in water. A partition wall for the container is positioned between the top wall and the open bottom dividing the container into an upper air chamber and a lower specimen chamber. A removable closure member is used for the open bottom of the container. The closure member is sized to adjust the specimen chamber to a predetermined volume when fully inserted in the open bottom of the container. A bleed vent contained in the side wall of the closure member, allows excess specimen and air bubbles to escape.