Sheep, like many mammals, form a strong bond with their offspring shortly after birth. However, a mother sheep, known as a ewe, may sometimes reject one or more of her lambs. This behavior is a known occurrence and stems from various factors. Understanding these reasons helps in appreciating the complexities of maternal care.
Common Reasons for Rejection
Several scenarios can lead to a ewe rejecting her lamb. First-time mothers, or primiparous ewes, often show a higher tendency for rejection due to inexperience and stress during their first lambing. They may be less adept at initiating bonding behaviors or find the birthing process overwhelming.
Multiple births also present challenges. Ewes giving birth to twins, triplets, or more may struggle to bond with or adequately care for all lambs, sometimes leading to the rejection of the weakest or an overload where she cannot manage the needs of all offspring. Environmental factors, such as loud noises, human interference during lambing, or relocation immediately after birth, can stress a ewe and disrupt the bonding process.
A lamb’s condition can also influence rejection. A lamb that is weak, cold, ill, or has an unusual scent might be perceived as unfit by the ewe, triggering her to reject it. This can be an instinctive prioritization of resources towards stronger, more viable offspring.
Odor confusion, where a lamb’s natural scent is masked by human handling or other foreign smells, can prevent the ewe from recognizing it as her own. A painful or difficult birth experience might also cause the ewe to associate the lamb with negative sensations, contributing to rejection.
The Role of Hormones and Senses
Maternal bonding in sheep is a complex process with significant biological underpinnings. The hormone oxytocin plays a central role in initiating maternal behavior immediately after birth. Its release, triggered by the stimulation of the vagina and cervix during labor, is crucial for the ewe to develop maternal instincts and bond with her lamb. Stress during or immediately after birth can interfere with the proper release or effectiveness of oxytocin, hindering bond formation.
Olfactory recognition, or the sense of smell, is important for a ewe to identify her lamb. Within the first few hours after birth, the ewe learns the unique scent of her lamb, often by licking the amniotic fluid from its body. This scent recognition forms the primary basis of their bond. Interference with this sensory connection, such as human handling that transfers foreign scents to the lamb, can cause the ewe to fail to recognize her offspring, leading to rejection.
The bonding process typically occurs within a narrow window, often within the first two to four hours after birth, sometimes extending up to 24-48 hours. This period is often referred to as the critical bonding period. If the bond is not established during this time, perhaps due to separation or other disruptions, the ewe may become selectively maternal, accepting only lambs with whom she has bonded and actively rejecting others.
Supporting Rejected Lambs
When a ewe rejects her lamb, the consequences for the lamb can be severe. Rejected lambs face a high mortality rate if they do not receive intervention. Starvation and hypothermia are common causes of death for these lambs, highlighting the urgency of addressing the situation.
Several intervention strategies can support rejected lambs. Fostering, also known as grafting, involves attempting to have another ewe adopt the lamb. This can be achieved through scent transfer techniques, such as rubbing the rejected lamb with the amniotic fluid or membranes of the foster ewe’s own lamb, or using the skin of a deceased lamb from the foster ewe to mask the orphan’s scent. Vaginal stimulation of a foster ewe who has recently given birth can also encourage her to accept an additional lamb by mimicking the birthing process and renewing her maternal drive.
When fostering is not possible or unsuccessful, hand-rearing the lamb becomes necessary. This involves bottle-feeding the lamb with milk replacer, ensuring it receives colostrum—the first milk rich in antibodies—within the first few hours of life. Early detection of rejection signs, such as a ewe butting or ignoring a lamb, is important for successful intervention, as it allows for prompt action to ensure the lamb’s survival and well-being.