The main features of breeding dogs
The laying and formation of the genital glands and organs in dogs occurs during embryonic development. However, puberty, i.e., the growth, formation and formation of the function of the sex glands, continues for a fairly long time and is an important period in the prenatal development of animals.
In males, the process of sexual development includes an increase in the size of the testes and, normally, lowering them from the abdominal cavity into the scrotum. In the blood during puberty, the concentration of male sex hormones (androgens) gradually increases, upon reaching a certain level of which the process of converting primary germ cells into spermatozoa begins. This process, very delicate and complex, is controlled by the mechanism of the formed positive feedback between the testes, adrenal glands and the parts of the brain that are responsible for the secretion of various hormones and maintenance of a certain level in the circulating blood. At the beginning of puberty, a small amount of spermatozoa forms in the male dog , some of which have structural anomalies that impede the process of fertilization.
However, at this point, the level of androgens in the body is already high enough to include a complex of behavioral mating reactions. The young dog is not only interested in bitches, but also actively mates. When examined under a microscope of the sperm of such males, it is often found that their ejaculate (seminal fluid) does not yet contain sperm and is, in fact, the secret of the accessory sex glands. It is with this that low fertility, even infertility in young dogs is associated. Thus, preventing breeding of males under the age of 2 years is quite reasonable from a scientific point of view. The opinion that early mating stops male growth is erroneous. Slowing growth is possible only with very large sexual loads and poor feeding, but these reasons will also adversely affect the health of an adult male. Interestingly, in natural conditions in large family groups of dogs consisting of animals of different ages and sexes, males begin to mate at the age of two – two and a half years, having gained a rather high hierarchical rank in the pack. Sexual development of bitches is no less difficult, although the onset of puberty is much easier to determine. Unlike the male gonads, the ovaries of a newborn female contain a huge number of already formed eggs. Each egg is immersed in ovarian tissue and is surrounded on all sides by epithelial cells, which protect it from damage and provide nutrients. The approach of puberty is also accompanied by an increase in the level of sex hormones in the body of a bitch, but these hormones have a different chemical structure and therefore function and are called female sex hormones (estrogens). With an increase in the level of estrogen secretion and with the formation of a positive feedback mechanism, the adrenal ovaries – hypothalamus – pituitary gland, follicles grow, i.e., vesicular formations from the epithelial cells surrounding the egg. Follicle growth is uneven: some become very large, others grow slowly, and often generally undergo a reverse growth and resolve. The largest follicles eventually burst, and the eggs move along the oviduct into the uterus. Typically, an egg cell is found with a sperm and is fertilized in the oviduct. We note in passing that the fertilization mechanism is such that an egg can merge and give rise to a new organism with only one sperm; all other sperm that have reached it die in the membranes surrounding the nucleus of the egg. It follows that when mating a female with several males, each puppy nonetheless comes from only one father, and not from several.
Fertilization can occur only in a strictly defined period, the external manifestation of which is called “estrus”. In the scientific literature, the term “estrus” is used to denote this state of the female organism. It is during this period that the female is ready to accept the male and is actively looking for a meeting with him. The physiological process of rupture of the follicle and the release of the egg is called ovulation, in dogs it simultaneously (but not simultaneously) ovulates up to 10 – 15, sometimes more than the eggs, but usually 5 – 8. Estrus, the onset of which is determined by the presence of a certain concentration of estrogen in the blood, is not always accompanied ovulation. This may be due to diseases or insufficient sexual development of young bitches, as well as the use of hormonal drugs and may be one of the causes of sterile mating.
The first estrus in a bitch occurs at about the age of 6-8 months. However, in dogs of large breeds, the physical development of which takes longer than in small ones, the first oestrus may occur later, sometimes at the age of 1 – 1.5 years.