Lambing
The direct definition of lambing simply refers to the time during which ewes give birth to their young. However, lambing proves to be one of the busiest and most difficult times of year for a producer, requiring preparation beforehand and careful attention afterwards [1]. The economic viability of sheep farming relies heavily on the success at lambing. Thus, it is in the interest of the producer to not just maximize total births, but to also ensure the greatest survival rate of newborn lambs. Despite these goals, as flock sizes increase it becomes much more difficult for the producer to manage the animals [1]. To further complicate matters, sheep are seasonally polyestrus and will generally lamb together at the same time [2]. Consequently, the combination between large flock sizes and shared lambing times can lead to less than desirable survival rates. Even successful births can be thwarted by the susceptibility of newborn lambs to illness and disease [3]. These issues are reflected in the average 12-16% pre-weaning mortality rate of lambs in Canada from the last 30 years [4]. In this sense, it is a struggle for producers to balance economic interests against manageable lambing periods. These problems can be mitigated by developing a better understanding of the three main areas concerning lambing: prepartum, partum, and postpartum. By assessing the breeding cycle and gestation of ewes, an accurate prediction can be made of when lambing will occur. In doing so, necessary preparations can be carried out to elicit desirable outcomes at lambing. Appreciating the vulnerability of newborn lambs can also help to ensure that appropriate measures are taken to increase survival after birth. Together, these considerations can lead to a profitable sheep production system.
Prepartum[edit]
The prepartum period refers to the time of pregnancy before labor and birth of the neonate. This begins upon successful breeding of the ewe by a ram, followed by a period of gestation up until the moment of lambing. Before the breeding season it is best to address any flock problems, such as foot rot, as well as to give inoculations and to increase condition of the animals prior to tupping (copulation) [2]. By ensuring the health of both ewes and rams during this time, the early stages of the prepartum period are likely to be more successful.
Breeding Season[edit]
Commencement of the breeding season marks the start of the early stages of prepartum and demands careful management by producers in order to be favorable. Ewes enter into heat as a result of increased melatonin secretion as days become shorter, ultimately leading to a breeding season that is at its height during October and November [1]. As gestation usually lasts for 148 days [5], lambing traditionally occurs yearly in the Spring. However, manipulation of the breeding cycle through the use of pheromones, injection of hormones, or controlled lighting can produce lambings at any time of year [1]. Accelerated lambing programs may also be incorporated through strict management of breeding, producing 3 lambs in 2 years or, under the more intense Cornell Star system, 5 lambs in 3 years [6]. Regardless of the time of year that breeding is accomplished, conception initiates the series of events that will build up to lambing.
Gestation[edit]
Otherwise known as pregnancy, gestation consists of one of the most important stages leading up to lambing. The most crucial time during a ewe's gestation is during the first and last several weeks [7]. In the early weeks of gestation, implantation of the embryo occurs and the placenta begins to develop to later nourish the growing fetus [8]. Conversely, significant growth of the fetus takes place during the last weeks of gestation [5]. Nutritional stresses placed on ewes during these moments can compromise the pregnancy, leading to abortion of the fetus during the early stages or to premature birth of small weak lambs if nearing the end of gestation [7]. Either way, a successful lambing is reliant upon a proper gestation, which is the responsibility of producers to ensure.
Preparation for Lambing[edit]
During the end of gestation ewes will begin exhibiting signs that they are nearing time to give birth. For instance, ewes ready to lamb may withdraw from eating food and move away from the rest of the flock [3]. However, preparations for lambing should be made before such signs are observed as the lambing process will quickly follow. One of the first steps is to ensure there is adequate shelter to protect against adverse weather [2]. As newborn lambs are very susceptible to the elements, it is crucial that they are as protected as much as they can be from environmental extremes. Setting up individual pens to hold the ewe and her young after birth is also a necessary step to ensure bond formation as well as ease of routine naval dipping and tail docking [7]. Other preparations mainly involve gathering supplies that will be needed during lambing as well as for the care of the neonate after birth [1]. These proactive measures can help to ease the lambing process and provide greater success for the producer.
Partum[edit]
Once gestation has reached its conclusion, the lambing process itself is ready to take place. This is the moment in which producers have spent much of their time and resources towards achieving. The initiation of lambing is largely controlled by hormones. Specifically, increases in cortisol lead to a decline in progesterone, which has up to this point prevented contractions of the uterus [1]. Concomitantly, estradiol begins to increase and causes the uterus to become more responsive to oxytocin, which elicits contractions [5]. In response to these strong uterine contractions, prostaglandins stimulate cervical dilation [5].Onset of these hormonal changes can be observed through behavioral modifications within the ewe. In particular, ewes that are nearing their lambing will usually have a developed udder, may show interest in other lambs, will often become restless, and typically have a swollen vulva [1][9]. At this point, the lamb is ready to be delivered.
Natural Lambing[edit]
Most often ewes are able to birth their young naturally without having the producer to intervene [5]. This process generally follows 3 major steps: cervical dilation, delivery of lamb, and passing of afterbirth [10]. The fluid filled membranes are the first to pass through the cervix, followed by the forelegs and head of the lamb if it is in the correct presentation [3]. Once all lambs have been delivered, the afterbirth is expelled as it no longer serves any purpose [10]. The completion of this final step marks the termination of the lambing process.
Assisted Lambing[edit]
Occasionally ewes have trouble during lambing where the progression of delivery does not go smoothly. In these situations it is vital that producers offer assistance to avoid losing the lambs or even the ewe itself. Ideally, producers should not intervene if do not have to as their involvement may cause undo stress. However, there are signs in which can be an indication that assistance is mandatory. For instance, the appearance of only a single body part, the lack of progress after the fluid filled membrane has passed, or excessive delivery time can be causes for concern [8]. Consequently, at this point producers should assess the situation by checking on whether the lamb is alive and if it is in the correct presentation [3]. If any issues are identified or progress has still not been made, then further action is needed.
Supplies[edit]
Various supplies may prove to be necessary when assistance is needed during lambing. These supplies should have been readied beforehand. At its bare minimum, there needs to be access to warm water, disinfecting soap, disposable gloves, lubricant, and rope.[11]. Using these supplies will help ensure a hygienic entry, the ability to correct presentation if it is abnormal, and easier delivery for the ewe [10]
Likewise, a collection of supplies should also be available once the delivery of the lambs has been completed. Namely, there should be towels to dry off the newborns, a thermometer to check temperature, infra-red lamps for heat, iodine to dip navel cords, rubber rings for tail docking, antibiotics and nutritional supplements to be given as needed, and a supply of colostrum if nursing initially proves ineffective [1]. Although all supplies may not be needed in every instance, it is good practice to have them on hand in case they are.
Presentation[edit]
One of the most common causes for the need of intervention during lambing is due to abnormal presentation within the uterus. Abnormal presentations may be characterized by either the forelegs facing backwards, the head being tucked down, the entire body facing backwards with hindlegs facing out, or a breech in which both the body and hindlegs are facing backwards [8]. Regardless, in any of these cases assistance will likely be needed. Even a normal presentation may prove difficult for the ewe to deliver, especially if it is a single lamb that is large [1]. Thus, by correcting presentations and assisting in the delivery of lambs a delivery can be prevented from becoming detrimental.
Techniques[edit]
In correcting presentations, or simply aiding in the delivery of the lamb alongside the contractions of the ewe, there are generally a series of steps that must be taken. Hygiene is of upmost importance to prevent infection of the ewe; thus, it is necessarily for the producer to clean any dirt and manure from the vulva and to wear gloves before proceeding into the birth canal [10]. Plenty of lubrication and gentle movements will ensure minimal strain and injury to the ewe [3]. If presentation proves to be the issue, it is best to push the lamb back into the uterus where there is more room to correct its position directly or with ropes [8]. Once a normal presentation has been achieved, the lamb is ready to be delivered. The ewe may be able to do this on her own now, although assistance might still be required. In the latter case, the legs are located and pulled, one at a time, until the lamb can be easily removed from the birth canal [9]. Attention must now be given to the neonate, especially as it has likely gone under additional stress from the assisted lambing.
Early Care of Neonate[edit]
Upon birth the lamb is very susceptible to various ailments; thus, quick action by the ewe and producer is needed to ensure the lamb is taken care of. Producers should check on newborn lambs, regardless of whether they came from a natural or assisted lambing [10]. Cleaning of mucous from the lamb's nose and air passageways is crucial in enabling it to take its first breath [11]. Likewise, drying off the lamb is also important to prevent a drop in temperature; however, the ewe will often do so through licking the lamb soon after birth [10]. The ewe's teats should be stripped in order to determine she is producing milk, which at this point will contain colostrum that is important in building the lamb's initial immune defense [9]. If the lamb is unable to nurse immediately, it may be necessary to force feed colostrum [7]. Once the lamb is comfortably with the ewe, no other immediate actions are needed at this point. For the following days, producers must monitor the newborn lambs closely as they are still very vulnerable.
Postpartum[edit]
After delivery the ewe takes on maternal instincts to look after the newborn lamb. New mothers may offer poor care due to inexperience, whereas as older ewes may be incapable of providing sufficient milk [1]. Soon after birth the ewe learns to recognize the scent of the newborn lamb, which is an important first step in establishing a bond [5]. Once a maternal bond has formed through scent and sound [2], the ewe can discriminate her lambs from others, which is important in preventing cross-sucking [5]. Without proper postpartum care, even healthy newborn lambs may not be able to thrive.
Nursing[edit]
One of the most essential aspects of maternal care is proper nursing. If a lamb cannot get sufficient colostrum after birth as well as milk later on, then a decline in health is inevitable. A ewe nursing triplets or one that is under-producing milk likely cannot meet the nutritional demands of the lamb [8]. In these cases, it is possible to foster a lamb onto another ewe; although, milk replacer can serve as an alternative if the lamb is not accepted [7]. Consequently, producers must be prepared to deal with issues surrounding nursing after lambing.
Lamb Health[edit]
Lambs ultimately face two challenges to their health: complications from birth and vulnerability to environmental conditions. During delivery lambs may experience trauma in the form of brain damage, hypoxia, liver rupture, and fractures [1]. While some of these outcomes may be severe enough to lead to death, those lambs that do survive are further disadvantaged during their first weeks of life. Temperature and infectious disease are two of the more prominent environmental aspects that can be detrimental to lambs. Heat loss is substantial in newborn lambs; thus, hypothermia can easily set in if the lamb cannot get sufficient shelter or does not consume enough energy to produce more heat [8]. Although colostrum provides useful antibodies to protect the neonate, these are temporary and only protect against infectious diseases that the ewe has come into contact with [3]. Consequently, if further protection is not provided by producers lambs run the risk of falling ill. While the health of newborn lambs is sensitive, good management systems should have no problem in addressing these concerns.
References[edit]
- ↑ 1.00 1.01 1.02 1.03 1.04 1.05 1.06 1.07 1.08 1.09 1.10 Henderson, D.G. (1994). The Veterinary Book for Sheep Farmers. Ipswich: Farming Press Books. ISBN 0-85236-189-0. Search this book on
- ↑ 2.0 2.1 2.2 2.3 Johnston, R.G. (1983). Introduction to Sheep Farming. London: Granada Publishing Ltd. ISBN 0-246-11962-4. Search this book on
- ↑ 3.0 3.1 3.2 3.3 3.4 3.5 Eales, A.; Small, J. (1986). Practical Lambing: A Guide to Veterinary Care at Lambing. London: Longman Group Ltd. Search this book on
- ↑ Kennedy, Delma (2012). "Understanding Lamb Mortality". Ontario Ministry of Agriculture, Food, and Rural Affairs. Retrieved November 27, 2019.
- ↑ 5.0 5.1 5.2 5.3 5.4 5.5 5.6 Sheep Production Handbook. Fort Collins: ADS/Nightwing Publishing. 2003. ISBN 0-9742857-0-6. Search this book on
- ↑ Menzies, P.I. "Breeding Programs of Sheep". Merck Manual Veterinary Manual. Retrieved November 27, 2019.
- ↑ 7.0 7.1 7.2 7.3 7.4 Fell, H.R. (1979). Intensive Sheep Management. Suffolk: Farming Press Ltd. ISBN 0-85236-101-7. Search this book on
- ↑ 8.0 8.1 8.2 8.3 8.4 8.5 Eales, A.; Small, J.; Macaldowie, C. (2004). Practical Lambing and Lamb Care. Oxford: Blackwell Publishing Ltd. ISBN 1-4051-1546-7. Search this book on
- ↑ 9.0 9.1 9.2 Johnson, J. "Guide to Lambing Season Success". Purina Mills. Retrieved November 27, 2019.
- ↑ 10.0 10.1 10.2 10.3 10.4 10.5 Martin, J. (April 15, 2010). "Assisting the Ewe at Lambing". Ontario Ministry of Agriculture, Food, and Rural Affairs. Retrieved November 27, 2019.
- ↑ 11.0 11.1 Hides, S. (July 2008). "Lambing Difficulty". Agriculture Victoria. Retrieved November 27, 2019.
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