**1. Introduction**

The control of the reproductive activity in dogs is a main issue in today's societies. Overpopulation of stray and feral dogs is an universal problem and raises public health concerns related to the increased risk of zoonotic diseases and compromise of the environmental health that may foster the permanence of diseases in other species or the degradation of ecosystems [1], as well as to the social and urban problems associated with animal-human conflicts.

At the start of this chapter, the authors would also strengthen that the best measure for a safe and definitive measure for the suppression of reproductive cycles in animals not intended for future breeding is ovariectomy (in prepubertal or young postpubertal female dogs) or ovariohysterectomy [2–4]. These procedures also have a protective effect on the incidence of uterine and mammary diseases, if performed early in the animal life. However, spaying of young animals, whether male or female dogs, is not an universal option; in some countries, it is described as an unnecessary surgical insult to the dog, and therefore must be performed only under medical indication. In other, the surgery is rejected for economic reasons, and medical contraception is regarded as a more economical alternative to surgery. The therapeutic options for mastering the companion animal reproduction substantially improved in recent decades. Also, the nonsurgical contraceptive treatments drew the attention of the industry and researchers, allowing the recent introduction of new methods in the clinical practice targeting safer long- and short-term suspension of gonadal activity in dogs. The information on the available methods alternative to progestins needs to be discussed and their advantages and disadvantages have been reviewed to disseminate basic information of their use and ease the introduction of safer products in canine medicine [5].

The suppression of canine reproductive activity includes: (1) the sterilization of both male and female, as a form to control either the ownerless or free-roaming or community-owned dogs as well as privately owned, confined or roaming dogs; and (2) the canine contraception for the periodic suspension of ovarian activity, which can also be applied on the male counterpart. This chapter focuses on the medical contraception in dogs. Moreover, as the manipulation of the ovarian activity in dogs, even if directed to its suspension, presumes the basic knowledge of the normal endocrinology of the estrous cycle of bitch, it will be reviewed, before discussing the nonsurgical contraceptive treatments available in dogs.
