Abstract: A method of regulating the reproductive functions of animals, preferably domesticated ruminants, and veterinary implants for use in such a method are provided. The veterinary implant tablet comprises about 2-15% by weight of a fatty acid salt compression binder, about 25-50% by weight of a directly compressible vehicle selected from the group consisting of calcium phosphate and derivatives thereof, about 1-5% by weight of a granulating agent, and an amount of melatonin effective to maintain blood melatonin at, or above, a natural nighttime level of an animal to be treated for a period of time effective to accelerate an onset of breeding activity in mature animals or to delay an onset of puberty in prepubescent animals. The implant tablet provides a substantially continuous release rate of melatonin so as to maintain blood melatonin at, or above, the stated level. A method for preparing such a veterinary implant tablet is also described.