A plug of an artificial insemination tube for livestock breeding includes a leading portion and a viewing portion, each having different color layers or different hardness layers, and being formed by stacking and combining different foam layers. In an artificial insemination for livestock breeding, the plug installed at the front of a sperm delivery duct is inserted into a reproductive organ of the livestock, and secretion or fluid is attached and shown on surfaces of the plug leading portion and the viewing portion with different colors to achieve the effect of detecting the physical and physiological conditions of the livestock. In addition, the leading portion is a foam layer with relatively greater hardness, density, and smoothness, so that the plug may be entered into the female livestock body more easily, and the injection hole will not be deformed easily, so as to improve the smoothness and efficiency of the artificial insemination.
