How Long Are Cows Pregnant? A Guide To Cow Gestation Period

Gestation periods vary depending on the breed of cattle and the gender of the calf. The most frequent duration is 283 days, with an average lower range of 279 days to an average maximum of 287 days. Bull calves usually have a more extended gestation period than heifer calves.

In this article, we’ll help you better understand how long your cow will stay pregnant.

Typical Cow Pregnancy Durations

Cows268 days / 9 months (on average)
Humans283 days / 9.5 months
Shortest GestationAberdeen Anguses (273 days)
Longest GestationBrown Swiss/Braunvieh (292 days)

The gestation length depends on the sex of the calf and how many calves the cow carries.

The average time is 283 days. 95% of calves are born within 9 days (plus or minus) of the expected due date.

The majority of cattle producers control pregnancy periods using methods of planned impregnation. Breeders might choose to use the clean-up bull option if artificial insemination (A.I.) has not been successful. A farmer will place clean-up or tidy-up bulls in a pen or corral with any cow that has failed to conceive after A.I.

A typical clean-up bull would be expected to impregnate 40% to 50% of the cows it is placed with. Clean-up breeding usually starts 2 to 4 weeks after A.I. and lasts approximately a month and a half.

What Can Impact A Cow’s Pregnancy Duration?

Congenital deformities (or birth defects) in the adrenal and pituitary glands can lead to prolonged gestation. Most of these deformities are connected to abnormalities in the pituitary gland.

The pituitary gland is the size of a pea and sits at the base of the brain. It manufactures the Adrenocorticotropic hormone (A.C.T.H.), among others. A.C.T.H. controls the production of the vital hormone cortisol. Corticosteroids or cortisol aid the control of stress, immunity, and inflammation, amongst other things.

Pituitary Gland Abnormalities

Scientific opinion is that aplastic (or non-functioning) pituitary glands result from a recessive gene. Cattle breeds such as Ayrshires, Guernseys, Jerseys, and Holstein-Friesians have exhibited these irregularities.

Afflicted fetuses stop growing after six to seven months in the uterus. The resulting calves are consequently undersized compared to a calf from a non-affected dam.

Spontaneous parturition (or giving birth) fails to occur due to the pituitary gland not functioning normally, and calves are generally still-born. They sometimes display severe defects of a craniofacial nature (skull and face).

Adrenal Gland Abnormalities

A fetal adrenal gland malfunction caused by an autosomal recessive gene can lead to prolonged gestation in Holstein-Friesian cows. “Autosomal” means that a specific gene is a numbered chromosome and not a sex chromosome, leading to inherited genetic disorders.

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Fetal A.C.T.H. would usually trigger these glands into producing corticosteroids at term, controlling growth patterns. The malfunction in the fetal adrenal gland means no corticosteroids are produced and the fetus grows without regulation until its blood supply is no longer sufficient. The result is fetal gigantism.

“Dysgenesis” or defective development of the adrenal gland can prolong gestation – anything up to 465 days – and cause fetal gigantism.

Combined Pituitary and Adrenal Gland Abnormalities

An organ or tissue lacking the prerequisite number of cells is hypoplastic. The condition, hypoplasia, causes pituitary and adrenal gland abnormalities in cattle.

Holstein-Friesians, Ayrshires and some Swedish cattle breeds have demonstrated this phenomenon. It can prolong gestation by 21 to 150 days, and produce pronounced abdominal enlargement.

Parturition can fail to occur and the unborn calf may die due to the natural blood supply being insufficient. Cervical relaxation is deficient, almost always resulting in dystocia.

The calf can weigh 105 to 185 lb at birth (the average is 48 to 62 lb), a clear case of fetal gigantism. It will show indications of postmaturity, such as loose, prominent hair and longer hooves.

If the calf survives, there will be dyspnea or shortness of breath, and the cow may grunt and froth around the muzzle area. Dyspnea occurs from insufficient surfactant release from the lung cells, and the subsequent collapse of alveoli can result in death.

A necropsy or post-mortem examination usually reveals evident hypoplasia of the cranial pituitary and adrenal glands.

Inherited adrenal cortical and adenohypophyseal (the anterior section of the pituitary gland) hypoplasia can occur in Belgian Blues. Except for some hirsutism, afflicted calves have a normal appearance. Live, but non-viable fetuses can be born more than 30 days after insemination.

An inherited genetic recessive disorder is responsible. Despite this disorder, calves can survive even when born over 30 days after insemination but are non-viable and will be slaughtered.

Unilateral Adrenal Gland Dysgenesis

Unilateral adrenal gland dysgenesis can also affect Swedish Reds. It can lead to prolonged gestation periods of up to 465 days, and the consequent fetal gigantism.

Sometimes, prolonged gestation periods can be iatrogenic (caused by medical examinations or treatment), such as somatic cell cloning in fetal calves. Low quantities of A.C.T.H. produced by the fetal pituitary gland or the abnormal placenta not responding to cortisol secreted in the fetus when the calf is close to birth can lead to overlong gestation in some of these clones.

Natural parturition may not take place, and gestation will continue until manually terminated.

Pestiviruses and Arboviruses

There is an established association between prolonged gestation and materno-fetal infection with pestiviruses. These viruses potentially spread by mucous or other nasal secretions, such as bovine viral diarrhea virus. Arboviruses (mosquito/tick-borne viruses, such as Rift Valley fever and Bluetongue virus) are also responsible for these afflictions.

Although the virus that causes bovine viral diarrhea can provoke abortion in cattle, it can also result in congenital fetal defects. These afflictions include cerebellar hypoplasia (brain-cell deficit), anencephaly (a severe birth defect involving the absence of parts of the brain and skull), and hydrocephaly (build-up of cerebrospinal fluid in the brain ventricles or “water on the brain”).

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There can be prolonged gestation if the pituitary function is affected, and calves may have severe central nervous system defects.

The Akabane virus of Africa, Australia, and the Middle and Far East is an insect-transmitted disease affecting pregnant cattle and sheep. Bovine fetuses exposed to the virus during the gestation period of 76 to 104 days may develop hydranencephaly (sacs filled with cerebrospinal fluid replacing absent cerebral hemispheres in the brain).

Exposure to the akabane virus at 105 to 174 days of pregnancy may cause both hydranencephaly and arthrogryposis (joint stiffness and muscle weakness). It can also affect pituitary function leading to prolonged gestation.

The Bluetongue virus found in Africa, Australia, North and South America, and Europe is also an insect-borne infection. The infection has caused suspected cases of prolonged gestation.

Rift Valley fever is prevalent in mainland Africa and Madagascar. Infection can lead to very high rates of abortion in cattle.

Plant Toxins

Plant toxins may cause prolonged gestation and deformities in fetuses if eaten inadvertently or fed to cattle experimentally. Viscum album, for example, has caused these two phenomena in Japanese Holstein-Friesian cows.

Other Factors

Many factors can affect gestation length. International dairy and beef cow research on this topic by Andersen and Plum, 1965) found that a dam’s age at calving affected gestation periods.

In addition, about 50 percent of the studies showed that parity (the number of times a cow has calved) affected gestation periods. Older cows carried calves for greater than or equal to one day longer than younger cows.

Cows under four years of age that had undergone embryo transfer demonstrated a gestation length of nearly less than three days than older ones with the same treatment.

Reports showed that high summer temperatures could also reduce gestation times for beef cattle.

Hageman et al., 1991, found that the gestation period was a day longer for high genetic milk production line cows in a University of Wisconsin research herd than cows from the average line. Indeed, there could be an overall positive correlation between milk yields and gestation periods (Silva et al. 1992).

Stages of Cow Pregnancy

Cattle pregnancy consists of three trimesters. Each trimester contains a variety of different circumstances which may catch inexperienced breeders off-guard. It is essential, therefore, to carry out proper research beforehand to ensure you act accordingly and introduce any relevant safety measures to pre-empt potential emergencies.

Stage One

The first trimester lasts from weeks 1 to 12 when the fetus begins to form. During this phase, the cow’s uterine muscles relax to accommodate the growing calf and keep it protected.

It is crucial to ensure the cow is well cared for and closely observed during the initial period, as sudden and unanticipated abortions are possible in the first three weeks of pregnancy. However, once six weeks have passed, the incidences of miscarriage fall sharply to just six percent.

Stage Two

This phase spans until the 26th week of pregnancy and is a critical period, especially regarding the supply of nutrients that the cow has to feed its fetus. The quality and quantity of this nourishment will determine the future health of the calf and the probability of dystocia, i.e., complications while in labor.

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Stage Three

Phase three is the final stage and the one that sees the most rapid growth rate. An estimated 70 percent of the calf formation occurs during these last 13 weeks. You will need to increase the feed and supplements to ensure your cow supplies the nearly full-grown calf with all the nutrients it requires.

A healthy newborn calf can weigh anything between 50 and 100 lbs, so plenty of high-quality food is essential for good health and body condition.

Cervical expansion takes up most of the birthing process and lasts from two to six hours. The expectant mother will most likely be a little nervous and anxious, so careful handling and a suitable environment are paramount.

The rest of the birth then takes about 30 minutes to 2 hours.

How Long Before Cows Can Get Pregnant Again Post-Partum?

Post calving, the point at which a cow will start its next estrous cycle (or estrus) depends on its physical and mental health, body weight, and nutrition. Follicular activity, i.e., estrogen creation, can resume after fewer than 10 days if the cow displays an increase in the production of a transient follicle-stimulating hormone within five days of birthing.

Well-nourished dairy cattle normally recommence ovulation about 2 weeks after the calving process. A beef suckler cow would take approximately 30 days. Female beef cattle with poor physical characteristics might not ovulate for up to 100 days.

Ovulation can take time to re-establish itself. Suckling, decreased physical condition after providing the gestating calf with adequate nutrition, and the exertion of calving can suppress the luteinizing hormone pulses that spark ovulation.

Progesterone (P4) from the corpus luteum is a vital component in achieving a series of productive pregnancies. It is a significant factor in regulating secretions from the endometrial gland, which supplies essential nutrients to the conceptus or embryo in the uterus throughout the first trimester.

Placental membrane retention and uterine infections can also play their part in prolonged delays in ovulation. Dystocia or calving difficulty, particularly common in Holsteins, is a further complication.

To sum up, the fundamental requirement of an effective breeding program is that post-partum cows should resume ovulation in the shortest time frame possible. To achieve this end, they should be at absolute peak physical condition pre-partum.

F.A.Q.s

Do dairy farmers have a set date to get their cows pregnant for the first time?

Farmers plan for dairy cows to calve for the first time at around two years of age. Consequently, first-calf heifers (young female cows pregnant for the first time) should conceive when they reach about four months old.

Are more mature cows less likely to conceive than younger ones?

Cows decline in fertility at about 8 years of age. This decline is more pronounced when the cow reaches the age of 12.

Are there differences in udder behavior with older cows?

With first-time pregnant cows, their teats begin to fill with milk around two months before birthing. With dams, it takes a bit longer for this to happen.

How many calving seasons are there?

Generally speaking, there are three breeding seasons: spring, summer, and fall. The most popular one is spring; calving in April or May allows ranching operations to obtain the maximum weights for weaned calves when the summer grass season finishes.

What external indications are there that my cow is about to enter labor?

As a cow or heifer is about to enter labor, the vulva will swell and “flop” while walking. There will also be a discharge of clear fluid. The gradual expulsion of the “water bag” from the vulva indicates that stage two labor is about to commence.

Do pregnant cows lactate?

Yes, a cow lactates (produces milk) immediately before or directly after giving birth. A “lactation” is when she makes milk between each calf.

Is there any difference in the gestation length for male or female calves?

Heifer calves usually have a slightly shorter gestation period compared to bull calves.

Adam

Adam has always had a fascination with farmyard animals, no doubt sparked by the farm in Devon he used to visit every summer when he was a young pup. He became close friends with the farmer’s children, two of which were about his age, and they allowed him to help out with cattle milking, herding and tagging. Being a fondly magical experience, he recently jumped at the opportunity to help the team at Cow Care Taker.

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