Animal Reproduction The Reproductive Process in Mammals

Steps in Reproduction 1 - Estrus 2 - Ovulation 3 - Breeding 4 - Fertilization 5 - Pregnancy 6 - Parturition 7 - Estrus

Estrus Defined as the heat period. The time that the female is receptive to the male & physiologically capable of becoming pregnant. The time of estrus is determined by season or cycle depending on the species of livestock. Regulated by the female sex hormone estrogen.

Duration of Estrus in Livestock Sow: range = 1-5 days, average = 44 hours Ewe: range = hours, average = 30 hours Cow: range = hours, average 18 hours Mare: range = 3 – 8 days, average 5 days

Signs of Estrus in Livestock Sow –pays little attention to feed –grunts more than usual –vulva will be swollen & congested –becomes immobile when pressure is applied to back

Ewe –Wags tail and stands to be mounted –swollen vulva

Cow –Restlessness –Does not eat –Bawls in search of a bull –Attempts to mount, and stands to be mounted, by other cows –Mucus secretions from vulva

Mare –Restlessness –Mucus secretions from vulva –“Winking” of the vulva –Frequent urination –Elevated tail –Change in disposition

The estrous cycle is the period of time from the beginning of one heat period (estrus) to the beginning of the next. Also known as oogenesis Duration of estrous cycle differs among various species of livestock.

The estrous cycle begins with the ripening or the maturing of a follicle on the ovary in a non-pregnant female. At this time, the follicle containing the maturing ovum secretes the hormone estrogen which begins the heat period. Heat period = the time the female will accept a male.

Length of Estrous Cycle in Various Livestock Species Sow: range = days, average 21 days Ewe: range = days, average 17 days Cow: range = days, average 21 days Mare: range = 18 – 23 days, average 20 days

Ovulation During heat, or shortly after, the follicle will erupt resulting in ovulation. After ovulation, the follicle that erupted becomes a corpus hemorrhagicum and then a corpus luteum, which secretes the hormone progesterone. The release of progesterone causes the absence of a heat period until the next follicle matures completing an estrous cycle.

Breeding After ovulation, the ovum is received by the infundibulum & funneled into the fallopian tube (oviduct). This is the time that breeding should occur. Breeding can be done by two methods –Natural breeding –Artificial insemination

Natural breeding - allowing the male to physically copulate with the female. Artificial insemination - ( AI ) inserting sperm cells into the uterine horn by artificial methods.

Fertilization Is defined as the union of the haploid gametes, restoring the diploid chromosome complement and initiating the development of a new individual. Involves penetration of the large sessile egg by a small motile spermatozoon, completion of the maturation process of the ovum, and fusion of the nuclei to form the zygote nucleus.

Pregnancy After fertilization, the ovum begins a process of cellular division and becomes an embryo. The embryo attaches to the uterine wall, at which time it becomes a fetus. The embryo is encompassed in a fluid filled membrane called the embryonic vesicle, which develops raised button-like nodules on its surface called caruncles.

At the time of attachment to the uterus, these nodules attach themselves to raised portions of the uterine wall called cotyledons. The caruncles and cotyledons make up the umbilicus. During fetal attachment, the fetus is fed by the mother through the attachment of the caruncles with the cotyledons. The period of pregnancy is called the gestation period and varies within different livestock species.

Gestation Times of Livestock Sow: range = days, average = 112 days. Ewe: range = days, average = 150 days Cow: range = days, average = 283 days Mare: range = 340 to 345 days, average = 342 days

Parturition Defined as the birthing process. A normal pregnancy is terminated by birth. At the time of parturition, the fetus is expelled from the uterus and passes through the cervix and vagina out of the reproductive tract.

After parturition, the corpus luteum on the ovary begins to digress, decreasing the production of progesterone. At this time, another follicle will begin to develop on one of the ovaries, and the estrous cycle begins once more.