A calf (: calves) is a young domestic cow or bull. Calves are reared to become adult cattle or are slaughtered for their meat, called veal, and their hide.
Terminology
"Calf" is the term used from birth to weaning, when it becomes known as a weaner or weaner calf, though in some areas the term "calf" may be used until the animal is a yearling. The birth of a calf is known as calving. A calf that has lost its mother is an orphan calf, also known as a poddy or poddy-calf in British. Bobby calves are young calves which are to be slaughtered for human consumption. A vealer is a calf weighing less than about which is at about eight to nine months of age.The Land, Rural Press, North Richmond, NSW, 7 August 2008 A young female calf from birth until she has had a calf of her own is called a heifer (). In the American Old West, a motherless or small, runty calf was sometimes referred to as a dodie. Cassidy, Frederic Gomes, and Joan Houston Hall. Dictionary of American Regional English. , Referenced via Internet Archive June 4, 2009
Early development
Calves may be produced by natural means, or by artificial breeding using artificial insemination or embryo transfer.Friend, John B., Cattle of the World, Blandford Press, Dorset, 1978,
Calves are born after nine months. They usually stand within a few minutes of calving, and suckle within an hour. However, for the first few days they are not easily able to keep up with the rest of the herd, so young calves are often left hidden by their mothers, who visit them several times a day to suckle them. By a week old the calf is able to follow the mother all the time.
Some calves are ear tagged soon after birth, especially those that are stud cattle in order to correctly identify their dams (mothers), or in areas (such as the EU) where tagging is a legal requirement for cattle. Typically when the calves are about two months old they are branded, ear marked, castrated and vaccinated.
Gestation In cows, gestation generally lasts between 280 and 284 days.
Endocrine control of gestation The production of progesterone by the corpus luteum is essential to sustain gestation. The corpus luteum, formed during ovulation leading to fertilization, remains present throughout gestation, preventing the onset of a new reproductive cycle. For this reason, cows do not go into estrus during pregnancy. To maintain the corpus luteum and thus gestation, the embryo produces a specific signal that prevents luteolysis, which would otherwise occur at the end of the estrous cycle. Bovine embryos produce and release very early a gestation-specific protein, interferon-tau. This protein inhibits oxytocin receptors in the uterine epithelium and prostaglandin synthesis, which are necessary for the destruction of the corpus luteum.
Fetal development +Fetal development during gestation Month of gestation Fetal weight (kg) Fetal height (cm) Gravid uterus weight (kg) Stage of development2nd month0.1–0.26 –71.3Limb outline4th month0.8–114–286.5Appearance of external genitalia6th month3–825–5020Hair on ears, forehead and tail8th month8–1540–6040–45Hair on limbs9th month20–5065–8545–80Full body hair
Premature calving: Abortions Abortions are unusual in cattle. They are often preceded by the death of the fetus, which may be directly affected or impacted by a placental issue. Abortion can be linked to trauma experienced by the animal, the misuse of treatments, or an unbalanced diet containing toxins that could harm the fetus's health. However, the most common cause is contamination by an infectious agent. Brucellosis used to be the leading cause of abortion, but extensive efforts to combat this disease, which could be transmitted to humans, have led to its eradication in some countries, such as France. Salmonellosis does not necessarily cause abortion, and when it does, it typically occurs during the 7th month of pregnancy. Aspergillosis is caused by a fungus found in moldy hay or beet pulp. It can reach the placenta via the bloodstream, sometimes crossing it to directly affect the fetus and cause its death. Listeriosis causes abortion 3 to 4 weeks after the animal becomes infected. Certain venereal diseases, such as trichomoniasis and campylobacteriosis, can also cause abortions. Leptospirosis can shorten gestation, as can bovine viral diarrhea (BVD), chlamydia, or Q fever. Another disease to add to this list is a parasitic infection, neosporosis, whose prevalence in cattle is still not well understood. This disease is caused by a protozoan and was long underrecognized in livestock. Currently, it is considered one of the most common explanations for abortions in cattle.
Preparation of the cow before calving At the end of pregnancy in cows, the development of the udder begins to be observed. This development is early in primiparous cows (about one month before calving) and later in multiparous cows (about one week before calving). The udder appears congested, sometimes even edematous. Under the action of hormones, especially relaxin, the ligaments soften. Thus, a relaxation of the sacroiliac ligaments, located at the base of the tail, and a sagging of the udder are typically observed in the 24 hours preceding calving.
A temperature variation is also noted in females ready to calve. In the weeks leading up to calving, the animal's temperature is abnormally high, usually reaching 39 °C instead of the normal 38 °C. Approximately 24 hours before calving, there is a sudden drop in temperature of at least 0.5 °C, lowering it to around 38.4 °C. Farmers commonly use this characteristic as a tool for predicting calvings.
Mechanisms of calving onset The calving onset is triggered by a complex hormonal mechanism. The fetus initiates the hormonal cascade leading to its expulsion through the production of ACTH by its hypothalamus. This hormone stimulates the fetal adrenal glands to produce corticosteroids, which act directly on the cow's placenta, prompting it to produce estrogen instead of progesterone. Estrogen, in turn, stimulates the synthesis of relaxin, a hormone produced by the corpus luteum that facilitates the gradual opening of the cervix and the loosening of the sacro-sciatic ligaments. Estrogen also promotes the production of prostaglandins: type E prostaglandins contribute to cervical softening, while type F prostaglandins lyse the corpus luteum, halting its progesterone production. This triggers the first myometrial contractions once progesterone ceases to inhibit parturition. The sharp drop in progesterone levels explains the temperature decrease observed before calving. Myometrial contractions progressively push the fetus through the pelvic canal, further stimulating cervical dilation and the release of oxytocin. Oxytocin amplifies the myometrial contractions, ultimately leading to the expulsion of the fetus.
Moment of calving
Contractions The uterine muscle contractions, or myometrium, facilitate the calf's progression through the pelvic canal during calving. These contractions, known as "colic," begin approximately six hours before delivery. Initially, they are infrequent (every seven minutes) and brief, lasting only a few seconds. As calving progresses, the contractions become closer together and longer. Near the critical moment, they last about one minute and are spaced similarly. These repeated contractions gradually move the calf through the pelvic canal, allowing it to pass the cervix and reach the vulva. Internal tension causes the allantoic sac to rupture, releasing the "first waters."
Fetus expulsion Shortly after the rupture of the allantoic sac, the amniotic sac appears at the vulva. This sac also tears under the cow's expulsive efforts.Sometimes, the amniotic sac does not rupture, which ultimately results in the death of the calf, trapped inside this sac and unable to breathe. The head and front legs are soon present at the vulva, which gradually dilates to allow their passage. This stage of calving is the most painful for the cow, requiring significant expulsive effort. Once the chest has passed through the pelvic canal, only a few more contractions are needed to expel the entire calf, followed by the remaining fluids from the amniotic and allantoic sacs.
The umbilical cord breaks only after the fetus has completely exited the vulva.
Calving is relatively slow in cows, especially first-time mothers. It can last between 30 minutes and three hours. The separation of the maternal cotyledons from the fetal cotyledons occurs slowly, allowing circulatory exchanges between the mother and calf to continue until the fetus is expelled. This explains why longer deliveries in cows do not significantly reduce the calf's chances of survival.
Calf presentation Typically, the calf is positioned in the "dorso-sacral" posture, with the forelegs and head emerging first through the pelvic canal. However, in 5% of cases, the hind legs present first. This variation slightly prolongs calving and reduces the calf's survival chances, as the umbilical cord may break prematurely, potentially causing asphyxiation.
Twin births
Multiple births are relatively uncommon in cattle, with the natural twin birth rate estimated at 3%. Twin pregnancies are generally associated with a reduction of 3 to 6 days in the gestation period. However, twin gestations can also have specific consequences on the calving process. While the risk of a size mismatch between the fetus and the mother's pelvis is lower, there is a higher probability of fetal malposition or simultaneous presentation of both fetuses. Furthermore, excessive uterine dilation caused by carrying twins can lead to uterine inertia and insufficient contractions. In twin pregnancies, it is common for one fetus to be in an anterior presentation while the other is in a posterior presentation. Twin calves are often weaker and more prone to neonatal conditions such as anoxia. The rate of stillbirths is also higher in twin pregnancies.
In cases of fraternal twins of different sexes, testosterone production by the male fetus can hinder the normal development of the female fetus's reproductive organs, leading to an increased incidence of sterility in heifers from such pregnancies. This issue is particularly pronounced when both fetuses develop in the same uterine horn, as it increases the likelihood of placental connections. The occurrence of freemartinism is estimated at 90 to 95% in twin pregnancies involving fetuses of different sexes. These mixed-sex twin pregnancies account for 42 to 46% of all twin cases.
Dystocia The term "dystocia" refers to any calving that occurs with difficulty and generally requires human intervention to varying degrees, from simple traction to a cesarean section or . Dystocia can be attributed to the calf in 60% of cases, the cow in 30% of cases, and in 10% of difficult calvings, it cannot be attributed solely to one or the other.
Maternal causes Maternal dystocia can, for example, result from dysfunction of the cow's reproductive organs. One such dysfunction is uterine inertia, which is the inability of the myometrium to contract sufficiently to expel the fetus. This condition may be caused by underdevelopment of the myometrium or insufficient production of prostaglandin F2alpha, a hormone that controls the initiation of uterine contractions. A mineral deficiency in calcium or magnesium can also lead to a lack of contractions, as these ions are involved in the muscle's response to prostaglandin stimulation. Normal fetal progression may also be obstructed by failure of the cervix to open, which is often related to a deficiency in calcium ions (Ca²⁺). Additionally, in first-time calving cows (primiparous), parturition may sometimes be delayed by vaginal and vulvar atresia, a condition that very rarely requires surgical intervention.