As the days get longer and the grass starts to grow, the mare's hormone system kicks in. Although the first heat cycle often occurs in February, there is usually a higher chance of conception in April, May, and June. This is the natural breeding season. The horses have shed their winter coat, their immune system is in order, and there is plenty of nutritious grass available.

Shift

A mare is usually pregnant for over 11 months. After the foal is born, it takes about a week for the first heat cycle (foal heat) to return. If you successfully breed the mare during this time, the foal will be born approximately three weeks earlier the following year. However, this doesn't happen often, and many breeders prefer to give their mares a bit more time after foaling. The first regular heat cycle usually occurs around 31 days after foaling. This means that the next foal will be born around the same date as this year's foal, on average a few days later. But not all breeding attempts are successful, and if it takes until the second or third attempt, you end up with a 'later' foal. After mid-August, breeding virtually stops; if it hasn't been successful by then, you have to skip a year. Because of this 'shift effect,' breeders prefer not to wait too long to breed their mares, especially if it's the mare's first breeding or if she has remained barren for a year. And if they succeed on the first attempt, they suddenly have a very early foal. This is part of the explanation for foals born in January, February, or March. Breeders want to avoid having to skip years with their mares.

Stallion approvals cause early foals

Another reason for preferring an early foal is stallion approvals and performance tests. In most Dutch studbooks (for now), the first inspection of stallions takes place at the end of the year in which the stallions turn two years old. Early foals are already 33 or 34 months old at that time, whereas foals born in July would be 27 or 28 months old. This age difference can have a significant impact on maturity and, consequently, the results of the inspection. During the first inspection, horses are led on a rope or allowed to move freely in the arena. A few months later, the performance tests follow, where they must also demonstrate their qualities under saddle or in harness. The KWPN now has a rule that horses must be at least 36 months old for a performance test, such as the performance test or the EPTM tests for mares. This means that for horses born in June or July, it takes much longer to present them for testing. Not everyone is willing to do this, partly due to the additional costs of raising the horse. In general, the ages at which young horses are evaluated have been pushed back in recent years. Studbooks no longer want very young horses in the ring, for the sake of animal welfare. This is a good thing, but it has the unintended consequence that breeders prefer to have an 'early' foal.

Consequences for the mare

If you want to breed a mare early, it is often necessary to induce her heat cycle. The estrous cycle of horses responds to daylight and sunlight, so high-quality heat cycles often occur in April, May, and June. If you want to breed earlier, the vet can administer a hormone preparation to kickstart the cycle. Some mares seem unaffected by this, while others may experience side effects such as sweating or even mild colic. These usually pass within a few hours. However, inducing heat can disrupt the cycle, and if the mare has recently been in heat, it may not always be successful. Sometimes there may be an egg present, but the uterus is not ready for pregnancy. Placing the mare at a breeding station can also cause cycle disruptions due to the stress of moving or failure to induce a heat cycle. If the mare responds well to induction, insemination can usually occur after a few days. Another common practice is to stimulate ovulation when the breeder and vet know that the mare is in heat. This is often done in early spring when some mares show signs of being in heat but may not release the egg.

Consequences for the early foal

Many hobby breeders, who breed foals occasionally for fun, do not want early foals. It is not ideal for the mare and foal and also very impractical. A foal born in January can't go outside as often as needed for proper development, especially in freezing or snowy conditions. Foals require a lot of movement for developing strong bones and preventing issues like osteochondritis dissecans (OCD). Ideally, they should spend many hours outdoors, but this is limited in early spring, and they may need a blanket when outdoors. Additionally, the mare needs extra nutrition to support her nursing foal, preferably from rich, green spring grass, which may not be available in the first few months of the year. This means more feeding, cleaning of the stables, and more work with moving the animals in and out.

Prefer a bit later

In conclusion, it is much easier and better for the mare and foal if the birthdate is slightly later. While winters are often mild nowadays and grass may start growing earlier than average, it's still a gamble. In nature, April, May, and June are the months when most foals are born. If you want to make things easier for both yourself and your horse, increase your chances of successful breeding, and have a healthy and strong foal, it's better to breed a bit later.