Reproduction of dogs in the tropics

Dog overpopulation is considered a serious problem in developing countries and a threat to human health. To be successfully implemented, official dog control measures have to be in accordance with regional beliefs and practices of an area. For these reasons local municipal authorities, veterinarians and dog owners need to have information about the structure, size, and dynamics of growth of the canine population, as well as the prevalence of reproductive diseases. They also need to be well informed about methods for the control of reproduction in this species. The aims of this thesis were to provide this information, and to test a non-surgical method of castration of male dogs. It was found that dogs are popular pets in urban and rural Yucatan with 72.8% of households in Merida owning a dog and 63.3-71.1% in rural communities, respectively. Households of medium socio-economical status, with large families and adequate fences were more likely to own dogs. In the city owners provided better husbandry, health care and feeding of their dogs. This was reflected in a lower mortality rate and lower rate of unwanted matings and litters. Free roaming dogs in urban or rural communities may reproduce to their maximal capacity. This is more evident in rural communities due to less supervision, and to that only 1.8% of the dogs are neutered or spayed, compared to 3.1% in the city. The veterinary practitioners did little to promote the control of dog breeding or to reduce the relinquishing of unwanted dogs in the city. Better client education and promoting the sterilization of pets at low cost would improve the situation. Female dogs under tropical conditions may cycle throughout the year but a marked increase was found in December. Females in estrus attract males and the testosterone concentration of the males is increased during those periods. Healthy male dogs in tropical conditions constantly produce viable sperm capable of impregnating a receptive female. Pregnant bitches, therefore, can be found all through the year. During periods of high environmental temperature, however, the percentage of pregnant females was lower. Underweight animals are less likely to become pregnant. Ovulation may also be influenced by the climatic conditions of the tropics, with a higher number of oocytes being ovulated during the summer time. Although the environmental temperature can modify seminal traits and sperm morphology in male dogs, those changes are of low grade and males remain fertile throughout the year. Day length and temperature probably induced the circannual changes in prolactin secretion found in the male dogs, but the physiological role of this hormone is incompletely known. A high environmental temperature was found to induce seasonal subfertility in bitches, probably due to an increase in the rate of embryo resorption. Epidemiological data revealed a high prevalence of genital pathologies in both sexes. The pathologies most frequently found in the bitches, however, did not adversely affect the capacity to come into estrus or to become pregnant. In males, most of the reproductive pathologies seem to affect the spermatogenesis, and depending on the amount of testicular interstitial tissue damaged the production of testosterone may also be affected. Aged dogs, as expected, are at higher risk to suffer testicular degeneration or to develop testicular tumors. A new non-surgical method for neutering dogs was evaluated as an alternative method for surgical mass sterilization. Crushing of the spermatic cord leads to vascular damage and cellular hypoxia of the testis and, consequently, to infarction. The method proved to be quick, efficient and of low cost, with minimal damage to the patient. However, long-term studies are needed to prove it has no adverse reactions