Reproductive cycle in farm animals

Reproduction in female is a complicated process, and normal reproduction ivolves synchronization of many functions. It is subject to many adverse effects at certain stages. Different aspects of reproduction in cows and buffaloes along with the physiological mechanisms involved are discussed in the following paragraphs.
Puberty or sexual maturity
Puberty is defined as the age at which reproduction becomes possible. In the female this is usually considered to be the age of first estrus. Puberty occurs before full mature body size is attained. The average age at puberty in cows is average 34 months and in buffaloes is 38 months. In cross breeds, the age at puberty is 9 - 18 months.

Sahiwal Cow
Holstein Cow
Age at first service (days)
Gestation Period (days)
Dry Period (days)

Service Period (days)

Calving interval (days)

Length of estrus cycle (days)
Duration of estrus (hours)
4-8 Days
Post-estrus time ovulation (hours)
1-2 Days
Best time to Breed
Late estrus or shortly after Estrus
Late estrus or shortly after Estrus

Middle of Estrus

Every other day beginning 2nd day of Estrus
Fertile life of sperm in the female genital tract (hours)


Fertile life of ovum (hours)

The onset of puberty depends upon a change in the balance between the output of gonadotropins from the gonads and growth hormones secreted by the anterior pituitary gland. The pituitary gland is located in a bony depression at the base of the brain. It consists of two distinct parts, known as the anterior (front) and the posterior (rear) pituitary glands. The pituitary is controlled by certain physiological functions involving the gonads and the anterior pituitary gland, and is influenced by several environmental (season, temperature, nutrition) and genetic factors.
Breeding season
The term breeding season refers to the period of time during the year when females of a species come into estrus. Most species of wild animals have a definite breeding season which is initiated at a time when environmental conditions are conducive to the survival, growth, and development of the young one after birth. For example, the gestation period in sheep and goats is 144 - 152 days, and the breeding season in these species starts in fall so that the young are born in spring. In cattle, where pregnancy on average lasts for nine months, the female breeding season occurs in the early summer so that the calves are born in the spring when the temperature is optimum for the growth of the newborn. Green fodder and forages are also available, which support sufficient milk production by the dams.
Domestication of farm animals has resulted in some variation of breeding season. Due to the intervention of modern production techniques, farm animals are now capable of breeding throughout the year. Among the farm animals, cows and buffaloes are polyestrous, showing diestrous cycles throughout the year. Mares, ewes, and does are seasonally poly estrous, showing diestrous cycles during a definite breeding season. The breeding season of ewes and does is confined largely to fall and winter. In Indian sub continent, buffaloes breed from October to December, when day length is decreasing. The stimulus for the initiation of reproduction during certain seasons results from the action of light, via the eye and optic nerve, on the pituitary gland. This stimulus causes the pituitary to release gonadotropic hormones, which activate the functioning of the gonads. One of the limiting factors influencing the productivity of the buffalo is the seasonality of breeding, which may be due to either anestrus or silent estrus during the hot, dry months of summer.
Estrus Cycle
Estrus occurs in non-pregnant females in characteristic rhythmic cycles. The interval between two consecutive estrus periods is known as the estrus cycle. The estrus cycle in farm animals is characterized by cyclic changes in the morphology of the reproductive organs as well as in the behavior of the animals.
The estrus cycle is divided into four different phases; these are known as proestrus, estrus, metestrus and diestrus. 
Proestrus is the phase of estrus in which the reproductive system is beginning preparation for the release of the mature ovum from the ovary. Estrus is defined as that phase of the cycle when females are receptive to coitus. Metestrus is the short transitional stage following ovulation in which the effects of estrogen are declining. The recently ruptured follicle is reorganized, and the secretion of progesterone is rising. During this phase, the uterus gets prepared for the implantation of the embryo. If pregnancy does not occur, the reproductive tract goes into a period of rest called diestrus. In cows and buffaloes the estrus cycle averages 21 days in length. Sheep and goats usually have a shorter estrus cycle ranging from 16 - 21 days.
Signs of estrus are somewhat similar in females of different species. In cows and buffaloes, estrus is characterized by the manifestation of heat. The cows may bawl frequently, become very active and restless, or mount other females and remain mounted. The vulva swells and the vestibule may be come deep-red. The swelling subsides with the end of estrus. There is marked discharge of clear, viscid mucus secreted by the cervix from the vulva. The excessive secretion at estrus acts as a lubricant during copulation.
Ovulation: Ovulation may be defined as the discharge of the ova from the Graafian follicle. Ova develop from germ cells in the ovaries. Numerous germ cells are present in the ovaries at birth, but few of the follicles surrounding them mature to rupture and shed ova. Follicles grow under the influence of the follicle stimulating hormone (FSH). The layers of follicular tissue become thinner with growth, the follicle rupturees and ova are released. This process is stimulated by the luteinizing hormone (LH). The released ova are swept by muscular and ciliary movements into the oviduct towards the uterus. If mating or articficial insermination takes place, spermatozoa and ova meet in the oviduct.
Esturs and ovulation are more or less synchronized in females to increase the chances of fertilization, the union of an ovum with a spermatozon. Synchronization of ovulation and insemination is essential because the life of the ovum once it is shed and that of the spermatozoa in the female reproductive tract is limited to a few hours.
Gestation: Gestation is the process that begins with the fertilization of the ovum by the sperm and terminates with the birth of a young one. The period of gestation varies considerably among species of farm animals. The average gestation period of cattle is 282 days, buffaloes 310 days, and sheep and goat 151 days. Generally, male calves are carried one day longer than female calves.
Parturition: Parturition is the physiological mechanism that enables the uterus to expel fetus after a certain period of development and nourishment. The process is called "foaling" in mares, "calving" in cows and buffaloes, "lambing" in ewes, and "kidding" in goats.
Signs of Parturition. The dam shows a number of signs of approaching parturition, which are usually divided in to following four stages.
(a) Preliminary stage: This stage may last for hours or even days. The ligaments in the pelvic region and around the tail head begin to relax and sink a few days before calving. The dam exhibits difficulty in movement. The external genitalia are swollen, enlarged, and flabby, and strings of mucous are seen. The mammary glands are enlarged and become tender. A clear, waxy fluid oozes out of the teats when pressure is applied.
(b) Dilation of the cervix: This stage merges with preliminary stage. Uneasiness increases and the animal may lie down and get up frequently. Frequency of micturition (urination) increases. At this time the cervix is fully dialted, and the next stage follows without any appreciable break in the sequence of events.
(c) Expulsion of the fetus: This staage begins with the fetus entering the dilaated cervix and the birth canal. During this time, uterine contractions occur at about two-minute intervals and the amnion is not ruptureed. There is a rush of fluid from the uterus when the water bag rupturees, and the animal appears relieved. Normally, the forefeet, with the muzzle lying behind and over them, appear at the vulva. The young one is expelled from the fetal membranes by a forceful and painful effort by the mother.
(d) Expulsion of membranes: The expulsion of the fetal membranes is commonly known as the delivery of the afterbirth. COntinued contractions of the uterus disjoin the fetal cotyledons, and the placenta is expelled within half an hour to eight hours after partuirition.