In the female the pituitary gland produces follicle-stimulating hormones which brings about the development of a follicle on the ovary. The follicle contains an ovum and is lined with specialized cells that produce the estrogenic hormones, estrone and estradiol. These hormones induce estrum or heat and initiate changes in the cellular lining of the uterus to prepare it for attachment of a fertilized ovum.

BEHAVORIAL CHANGES marking impending estrum
restlessness, occasionally bawling, usually clear muscus discharge from the vulva
standing to be mounted by other cows - standing heat

PHYSIOLOGICAL CHANGES occuring during the estrous cycle

• period during which the follicle is enlarging
• increase in the growth of cells and cilia lining the oviduct
• increase in blood supply to uterine lining or endometrium
• increase in mucus produced in the vagina

ESTRUM

• period during which female is receptive to the male and will stand to be mounted, often referred to as 'standing heat'
• uterus is contracted
• cervix is dilated
• mucus in the vagina is copious
• follicle ruptures, marking the end of estrus and the ovum is released, taking 5 days to reach the uterus

DIESTRUM

• several days during which the corpus luteum is developing and producing progesterone
• return to normal state, estrogen level drops rapidly and the uterus becomes soft and relaxed
• may be some capilliary bleeding from the endometrium, blood visible at the vulva or on the tail 48-72 hours after signs of estrum have passed, a useful indicator of the stage of estrous

ANESTRUM

• little uterine or ovarian activity takes place

Cattle cycle every 21 days, some may be a few days longer or shorter. When not bred cattle should cycle consistently year round.

Animals well fed will reach sexual maturity earlier and will cycle regularly. Fertility will be best when the animal is in a weight-gaining condition, although carried to an extreme, obesity can cause infertility.

First time heifers often benefit and encounter fewer calving complications by being bred to a bull that sires smaller calves.

Young bulls show sexual activity at 4 months and are usually fertile at 6 months.

• female seeks out and will only tolerate copulation during the period of estrum or standing heat
• very little foreplay involved when female in standing heat
• bull will sniff the vulva, smell increases libido
• bull mounts, interval between intromission and ejaculation averages about 7 seconds
• ejaculation occurs at the moment of a violent thrust during which the bull's hind feet actually leave the ground
• intromission or copulation terminates with ejaculation of semen at the cervical opening
• copulation will take place several times during the heat period, semen volume and concentration declines somewhat with frequency of mating
• bovine spermatozoa can reach the oviduct 2 - 4 minutes after being deposited in the cervix
• sperm rarely remain viable more than 24 hours
• the ova remains for only 12 hours

Females will sometimes attempt to mount the bull during the breeding session before she is in standing heat. If a bull is not present females will behave in a similiar manner as a bull when a female is in heat. Below are 2 females. The yellow heifer is in heat.

Heifers nuzzle.Yellow heifer sniffs and may mount.Red heifer sniffs and prepares to mountYellow heifer in standing heat.

• fertilization takes place in the oviduct at the time of ovulation
• a sperm cell penetrates the ovum and all others are blocked out
• bovines have 60 pairs of chromosomes
• cell division commences immediately following fertilization
• 3 - 5 days the zygote arrives in the uterus and attaches to the uterine lining

• average gestation 280 days
• veterinarian can diagnose pregnancy 35 days after breeding by a rectal examination, but it is recommended that examination not occur until 45 days to reduce the hazard of induced abortion
• in 60 days the fetus can be felt by the veterinarian
• rate of growth accelerates throughout gestation, greatest increase in size during the last third of pregnancy
• udder enlarges
• vulva becomes enlarged
• mucus discharged from the vulva may appear weeks before calving

• udder distended with milk
• ligaments around the tailhead relax and give a sunken appearance
• vulva distended and slack
• sticky tenacious mucus
• just before labour begins, restlessness, may seek isolated area and may refuse to feed
• placenta is forced against the cervix by uterine contractions, this helps to dilate the cervix
• placenta usually appears first, feet enter the vigina
• very strong abdominal contractions, intensity increases
• placenta ruptures
• calf born front feet first, followed by head and shoulders

Labour generally takes longer with first time mothers. A cow that labours over an hour with the front feet and nose of the calf showing and no signs of progress may need help. A cow that labours over an hour with nothing showing needs help. A veterinarian should be called.

The anterior presentation or front feet first is normal and the most common. Generally the soles of the feet are on the down side toward the dam's feet.

The posterior presentation or hind feet first is the second most common presentation frequently requiring traction for delivery and a veterinarian.. The soles of the feet are generally up toward the dam's tail if the presentation is posterior.

• dam will lick the newborn vigorously to dry it and stimulate respiration
• if dam rejects or is physically unable to care for the calf
• clear mucus from airways
• a lot of mucus - suspend the animal by the rear legs for a few minutes to help drain it out or tickling the nostril with a piece of straw may induce sneezing
• rub the calf vigorously to dry it and to help withstand temperature change
• dip the navel in tincture of iodine, kills bacteria and closes the end of the umbilical cord
• colostrum provides nutrition and disease immunity. If the calf doesn't nurse during the first hour, colostrum should be milked from the dam and fed to the newborn

The placenta is expelled and consumed by the cow. A retained placenta acts as a wick for bacterial infection and should be dealt with.