Farm Animal Reproduction 101

Spring is notably a time when farm animals have their babies. It’s an exciting, joyful, and sometimes stressful time. But not all livestock gestation (pregnancy) is the same. How do farm animals gestate and have their babies?


Cattle, like humans, have a gestation period of nine months (283 days). Different breeds of cattle have much different average sizes, but a new calf can weigh somewhere between 70-100 pounds. For beef cattle producers, cows will be made to cycle (go into heat) at the same time so that new calves will be born at roughly the same time. Producers generally choose to either calve in the spring or in the fall, depending on feed availability, climate, building accessibility, etc. For dairy producers, calves are born year-round to keep a certain amount of cows at their peak milking potential at all times.

Cattle are also like humans in that they usually only have one offspring at a time. In fact, it is preferred that cows only have one calf as that is much easier on the mother. There is also a phenomenon when twin male and female calves are born that the female is likely to be sterile. This calf is called a “freemartin”. So, while it may seem more efficient to want cows to have multiple calves, their bodies simply don’t handle it as well as other species, and can cause major problems and even death.


Pigs are very efficient at reproducing. Their gestation period is three months, three weeks, and three days, meaning they can have two litters per year. Sows (mama pigs) average around 7 piglets per litter, but can have a dozen or more. A new piglet will weigh only a couple of pounds.

Sometimes in large litters in many species, there can be siblings that are more aggressive or more weak than others. If sows have variation in litter size, some of those siblings can be moved around to other sows to get a better shot at equal nutrition. Farmers will keep records of each animal so they can track progress, health, and development.


Sheep have a slightly shorter gestation period at 142 – 152 days, or about five months. Lambs, similar to calves, are born in the spring. This is partly because they are one of the animal species whose estrous cycle is dependent on seasonal changes. For sheep, the most natural time to breed is late fall. However, this can vary breed to breed.

Sheep are also interesting in litter size. The first time a ewe (mama sheep) lambs, she will likely have only one offspring. For later pregnancies, she will likely have two or maybe even three. Sheep are unlike cattle in this way, and twins are really more preferred.


Chickens are different as they are not mammals and are instead birds. However, their reproduction cycle is commonly misunderstood. Chickens are oviparous, meaning they lay eggs. Chickens will cycle to develop and lay an egg about once a day. They do this with or without a rooster present. The cycle can be impacted based on the amount of light (natural or artificial) present. This means that backyard, outdoor chickens will likely lay fewer eggs during the winter than they would in the summer because the natural length of daylight changes. For commercial production, laying hen barns will likely have artificial lights on for the same length of time everyday to keep the birds’ cycles more consistent year-round.

When a fertilized egg (which does require a rooster) is laid, the hen will incubate it for 21 days, at which point the egg will hatch as a fully developed chick. Though it is possible for an egg to hatch twin chicks, it is rare.


Goats are a lot like sheep in many ways. They are similar sizes, have similar gestation periods (about 150 days), and also tend to have twins. They, too, have estrous cycles impacted by day length, meaning they are more likely to cycle during the short days of the fall or winter and kid (give birth) in the spring. Times when they do not cycle is called anestrous. A new baby kid can weigh between 4 and 12 pounds, depending on the breed.


Donkeys have an interesting anomaly in gestation length. There’s a normal three-month window where the jenny (female donkey) could foal. Donkeys can gestate between 11 to 14 months. To me, a mom with more experience working with cattle and pigs, this seems highly inconvenient! Imagine being full-term for three months! But, that’s just how they are built.

Donkeys tend to have single births, but twins do happen on occasion. A donkey foal will weigh in between 19 and 30 pounds.


A mare (female horse) will have a gestation period of 11-12 months. Horses are similar to donkeys in many respects, but do mark some differences in twin occurrences (notably fewer than donkeys) and maternal instincts (less so than jennys). Horses, like cattle, are also not well-equipped for multiple births. According to the American Association of Equine Practitioners, almost all twin pregnancies will result in the death of both foals.

Horses are also impacted by seasonal estrous cycles, but unlike sheep and goats, their breeding season will occur in late spring (April-May). If the different seasonal estrous cycles seem to not make sense, just think about when the offspring will be born. It’s common for an animal’s natural cycle to give birth in the spring, when temperatures are not so harsh on the young and there is grass and water available for the offspring. For horses, the mares can expect to give birth in March, April, or May to a foal that weighs about 40 pounds.

Why is there such a difference between species on gestation? The short answer is that different species are very different. The long answer may be that different animals have different uterine types that lend themselves better to multiple or singular births; different species have different estrous cycles that time their fertile windows and seasons differently; and there are differences in farms, climates, and facilities available on an individual farm level that impact reproduction management farm to farm.

Then what?

Before, during, and after birth, livestock species require lots of care. Pregnant and nursing mothers require adequate nutrition and monitoring to be sure things are progressing normally. During birthing times, farmers will monitor their livestock closely and only interfere if the mother needs help. If a mother is having trouble giving birth, this is called dystocia. Farmers pay attention to these occurrences and try to breed for animals that will not have trouble giving birth.

After the baby is on the ground, one of the first things they will need to do (in mammal species) is find their way to their mom for food. The first milk is called colostrum and includes very important nutrients and antibodies. Newborn animals lack strong immune systems, so this first milk is extremely important.

On the occasion that the mother doesn’t claim the young or doesn’t survive, the farmer will take care of the young by using store-bought colostrum or milk replacer, or by pairing the offspring to a different mother in the herd. Mothering ability is another trait that farmers will keep tabs on with the females in their herd.

Are there other species you have questions about? Let us know in the comments!


One thought on “Farm Animal Reproduction 101

  1. Pingback: Farm Animal Reproduction 101 – Aerospace

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