Terms of Reproduction

10.2.3 Terms of Reproduction Sperm Sperm are tiny cells present in the male's testicles at birth, which mature when the animal reaches puberty. The sperm move from the testicles into the epididymis, where they become mature. When a male animal sees or smells a female animal in heat, he usually wants to mate (or breed) with her. His penis becomes rigid and is inserted into the vagina of the female. At the moment of breeding, many sperm travel from the epididymis, through the vas deferens, and into the urethra. Certain glands (e.g. prostate and seminal vesicles) secrete fluid into the urethra to combine with the sperm, and form semen. The semen flows from the penis into the vagina of the female near the cervix. The sperm then move through the cervix, into the uterus, and up the oviduct.

‘Heat’ or ‘Estrus’ From birth, females have many eggs (ova) in their ovaries. Following puberty, an egg (ovum) matures inside a fluid-filled bubble called a “follicle” on the surface of the ovary. The ovum produces the hormone “estrogen” which enters the bloodstream and reaches the brain, causing the female to come into 'heat' or 'estrus', and to stand still while mating. Estrogen also causes ova to mature inside a follicle and prepares the uterus for pregnancy. In animals that usually have only one baby at a time, only one ovum develops during each estrus. In animals that have litters, such as dogs, many ova develop during each estrus.

Ovulation Ovulation is when the follicle ruptures and releases the ovum. Ovulation usually occurs at the end of estrus. After ovulation, the ovum enters the oviduct.

Fertilization If sperm are present in the oviduct at the time of ovulation, the egg might combine with a sperm cell. This process is called “fertilization.” If the egg is fertilized, the mother becomes “pregnant.” The new cell formed by fertilization contains everything needed to form a baby, which will have characteristics of both the mother and father. The new cell divides and multiplies millions of times throughout pregnancy to form a baby.