The maturation of lambs is measured according to their complete independence from their dams and when they reach puberty. Until the age of one year, lambs are called ewe lambs or ram lambs, depending on their gender. After that, they are referred to as fully-grown ewes or rams.
Lambs are considered mature and fully grown by the age of six months. By this time, they would have been weaned from their mother and started entering puberty. However, it is by 48 months that sheep have developed all their incisors and are known as "full-mouth" sheep.
Depending on the husbandry practices employed, lambs can start breeding when they reach puberty. However, some farmers prefer to allow their ewes to reach eighteen months before breeding. This helps to ensure that ewes are physically strong enough to survive their first pregnancy and lambing.
How Long Before A Lamb Becomes A Sexually Mature?
Lambs reach puberty and become sexually mature at different ages, depending on if they are ewes or rams. Ewes can reach puberty from six to twelve months old, while rams can reach sexual maturity as early as four to six months. Ewes begin their first estrus cycle in puberty. When a ewe is in estrus, it means she is in heat and sexually receptive.
The estrus cycle of ewes is every 16 to 17 days. During this time, they emit pheromones and show readiness through physical displays toward rams. Free-roaming sexually mature rams begin to contest with other rams to earn dominance for mating with ewes. Rams' hormones can make them quite aggressive. Hence, sheep farmers tend to keep only one ram to cover their ewes.
Other factors determining when a lamb reaches puberty include breed and nutrition. When lambs are well-nourished, they are more likely to be highly fertile and better developed sexually. To tell if a ram is expected to be fertile, his testicles should be a good size by around 49 days old
A Lamb's Life From Birth To Sexual Maturity
When lambs are born, they are already at an advanced stage of behavioral and physical development. Their advanced development lets lambs stand within 30 minutes after birth and interact with their respective mothers.
By the time they are a day old, lambs can distinguish their dam (their maternal ewe) from an alien ewe using sight, sound, and smell. The bond lambs have with their dams helps them feel safe, secure, and protected until they are weaned.
Lambs can be weaned as early as three months with human intervention. However, left to their own devices, dams will naturally wean their lambs by six months. Weaned lambs that a farmer wishes to keep should be separated according to gender to prevent early breeding.
Despite pubescent lambs being able to reproduce, premature breeding can lead to stock loss and low body condition scores (BCS) in lamb ewes.
What Is The Earliest A Ewe Should Be Bred?
Even though lambs can breed at the onset of puberty, it's not advisable to breed a ewe lamb or ram lamb too early. Ewes should only reproduce when they are 65 to 70% of their adult weight, while rams should be 50 to 60% of their adult weight . This said, many dairy operations breed their ewe lambs early, so the ewe lambs have their first lambs when they are about a year old.
Generally, however, ewe lambs are mated when they are 8 to 9 months old. They are usually bred one or two months after mature ewes for the following reasons:
- Increased lambing percentages,
- Better chance of conception because mature ewes will dominate the ram,
- If the ewe lamb is young and pregnant, she will need up to 25% more energy than a mature ewe. This is because the ewe lamb is still growing yet must supply energy for her fetus to grow.
- Ewe lambs are at a higher risk of dystocia,
- Ewe lambs don't produce much colostrum for their offspring,
- Mature ewes would have lambed before ewe lambs, freeing up labor to help ewe lambs with their first lambing.
- Ewe lambs can be more readily assimilated into the milking parlor routines as they can "learn" from the mature ewes already in the routine.
How Can You Tell The Age Of A Sheep Or Lamb?
If you haven't got a record of a sheep's lambing date, you can estimate its age by assessing its teeth. For instance, the number and condition of the teeth and the order of the permanent incisors' eruption are used as a guideline . This said, a sheep's teeth will be affected by its overall health and nutrition, breed variation, strain, and environment.
For example, on long feed, a sheep's teeth will remain in good condition and not wear down too quickly. However, on short feed where rocks or gravel are present, the teeth will wear down or be damaged faster.
A healthy and mature adult sheep's teeth will be as follows:
- Lower jaw: Eight permanent incisors in the front, with six molars on either side.
- Upper jaw: Six molars on either side of the jaw. In the front of the upper jaw is a hard, dense, fibrous patch.
The following table is a guideline for aging sheep based on the number of incisors they have.
Age of lamb or sheep
Description of teeth
A newborn lamb has no teeth.
1 week to two months
The lamb starts to grow temporary milk teeth on the front lower jaw.
12 to 18 months
18 to 24 months
24 to 36 months
36 to 48 months
Estimation becomes difficult
Estimation is difficult, but culling might be necessary.
Table 1: How teeth are used to Tell The Age Of A Sheep
A sheep is considered a lamb when it is younger than one year. However, because lambs can reach sexual maturity before then, they are considered mature. A significant factor in a lamb reaching maturity is proper nutrition. Therefore, sheep breeders should keep a detailed account of their flock to track the maturity of their sheep and identify patterns or problems.