17 Dec 2018
Valentina Busin discusses management strategies to maximise newborn lamb survival, animal welfare and farm profitability.
Valentina Busin
Job Title
Figure 1. Ewe nutrition is key to neonatal survival.
After birth, the first 24 hours are the most crucial of a lamb’s life, with the risk of death at its highest. The ability and speed at which the lamb stands and moves to the udder is directly linked to its survival. Our role as vets is to make sure every lamb born is given the best opportunity to survive in a potentially very harsh environment. Ewe nutrition – both as they prepare for tupping as well as throughout pregnancy – is one of the crucial keys for success.
Good quality and quantity of colostrum is the other main factor that will give every lamb the best possible start in life. The most common causes of neonatal mortality are dystocia, hypothermia/hypoglycaemia and septicaemia, which, for the most part, are directly related to management issues. To achieve the highest possible neonatal survival and, therefore, run a successful enterprise, flock health planning and good management are key.
Lambing is one of the most stressful and exciting times of the year – not just for the farmer, but for everyone involved, and, obviously, for the sheep themselves.
It is also, for the vast majority of sheep farms, a crucial time for making the enterprise profitable, as the main purpose of keeping sheep on pasture is to produce lambs that can be sold fattened or retained for breeding. Neonatal survival is, therefore, the primary goal at lambing time and something that needs to be addressed in every flock health plan.
Obviously, it is impossible to expect all lambs born on farms to survive, but we need to be aware of what is reasonably achievable and what is definitely unacceptable. National figures on lamb mortality show 15% to 20% of lambs are lost between scanning and sale or retention1, with most losses occurring during pregnancy or in the first week of life.
This has two major implications: welfare – as one of the pillars of animal welfare is “freedom from pain, injury and disease” – and profitability, as while costs for running the farm are kept the same, the output is considerably reduced. Neonatal mortality should, therefore, be used as an on-farm welfare measure2 and could be used in assurance schemes to inform consumers of welfare on farms.
Looking at figures on the economic cost of neonatal mortality, the Agriculture and Horticulture Development Board has estimated each lamb that dies in the neonatal period would cost the farmer around £20 to £253. It is interesting to notice, similar to almost all species, males are at higher risk of dying. Unsurprisingly, lamb triplets are also more at risk4. A sensible and realistic target for a well-managed flock should, therefore, be for losses below 5%.
The most important indicator of lamb survival and viability is their birthweight, and this is directly linked to optimal ewe nutrition (Figure 1). A crucial balance exists between low birthweight – which is associated with mortality due to starvation and exposure – and too high a birthweight, which is associated with increased mortality due to dystocia.
Planning for ewes to be at their optimal condition pre-tupping (on average at a body condition score [BCS] of three out of five) is the starting point of a well-managed flock. Therefore, the supplementation of ewes in poor body condition in advance (at least three weeks) of the breeding season is proven to increase neonatal survival. If nutrition is well planned throughout pregnancy, ewes will, therefore, be at the optimal BCS at lambing (on average at 2.5 out of 5). They will produce heavier and more vigorous lambs with a bigger chance of survival, as lambs born from ewes that lost significant body condition are at greatest risk of dying5.
The golden rules about colostrum apply to sheep as much as they do cattle (Figure 2). Placenta in sheep is epitheliochorial, which means large molecules (such as antibodies) are not transferred between mother and fetus. Lambs are, therefore, born without any defence to infectious agents. Colostrum, however, is the most powerful source of immunoglobulins, as well as energy. If colostrum management is right then we are on top of the game.
But how much, how soon and how often? The guidelines are on roughly 200ml/kg within 18 hours of birth, with a maximum of 50ml/kg intake on each occasion and, ideally, a first intake within 2 hours of birth6. The quality of colostrum is also fundamental. Colostrum should have a specific gravity of at least 1.05 and more than 60mg/ml Ig, but six hours after birth, Ig has already significantly declined. Furthermore, within 36 hours from birth, closure of the intestinal cells starts and, by day four, no capacity to absorb macromolecules, such as Ig, exists. It is also reported the bodyweight of a ewe has a direct correlation with the concentration of Ig in colostrum samples.
Hygiene is the other pillar for success in rearing healthy and happy lambs. A properly cleaned pen (Figure 3), with bedding carried out daily, navel treatment with iodine solution as soon as they are born and provision of an isolation pen for sick lambs are all fundamental requirements to reduce neonatal mortality.
Other measures to consider are more compact lambing, which will avoid mixing ages and a more focused time; although this has to be balanced with labour availability. Frequent lambing supervision, in particular, plays a fundamental role since ease of delivery has a great impact on lamb survival. Fostering seems to be connected to increased lamb mortality, either because too many triplets exist or because of poor milk production. Again, data on fostering numbers should be evaluated as they might indicate an underlying problem.
Vaccination is obviously another major factor. A good protocol would be for all animals on farm to be vaccinated for clostridial diseases, with lambing ewe booster carried out annually four to six weeks pre-lambing. Another thing to consider is the frequency of ewe replacement. High ewe replacement is linked with higher lamb mortality. This can be explained by either general poor ewe management, which leads to a high culling rate4, or the fact lambs from primiparous ewes are more likely to die (due to either a less maternal/inexperienced behaviour, smaller lamb birthweight or lower quality colostrum production)5.
One thing that might need clarification is what we define as the neonatal period. Conventionally, this goes from the moment the lamb is born to a more flexible timeline from one to seven days.
For the purpose of this article, the common causes will be considered for up to two days. However useful it is to ascertain the case definition for neonatal mortality, it is fundamental to remember what affects neonates might have occurred during the fetal stage (for example, abortifacient agents or impaired placental development and poor fetal growth due to undernutrition).
The three most common causes of neonatal mortality in lambs are intrapartum hypoxia/dystocia, hypothermia/hypoglycaemia and septicaemia (Table 1). Intrapartum hypoxia/dystocia is either due to unsupervised prolonged labour or because of ewe-lamb disproportion. The complex hypothermia/hypoglycaemia is usually related to a lack of colostrum (starvation), rather than direct cold exposure (apart from specific situation), while septicaemia is usually a combination of a lack of hygiene, poor colostrum management and infectious agents present on farm. Less common causes include congenital malformations and trace elements (mainly selenium) deficiency.
Congenital malformations are mostly due to either genetic or environmental factors (toxic plants or teratogenic compounds). Usually, they account for a very small percentage of neonatal losses. However, the appearance of Schmallenberg virus (SBV) has shown how intrauterine virus infection can present in the form of outbreaks of neonatal malformation. Also, wide access to a toxic compound (for example, Veratrum californicum or the use of benzimidazole in pregnant sheep) could cause outbreaks of malformed lambs as well as a single sire carrying a lethal gene, but these tend to be fairly rare.
The most common lethal congenital malformations of neonates are ventricular septal defects, schistosomus reflexus and CNS defects (anencephaly, hydrocephalus and hydranencephaly). The latter one should always raise prompt investigation for intrauterine viral infections (bluetongue virus, border disease virus and SBV), but it is also important to remember not all of them would be due to these aetiological agents.
The first step to improve neonatal survival is to gather reliable data and attempt a diagnosis for the most common causes of neonatal mortality in each specific farm. The most important data are the actual number of lambs expected (calculated from scanning data), the number of lambs born alive, dead or stillbirth, the time frame of losses (beginning versus end of lambing or throughout), and the age group/location of ewes where losses are occurring.
Gathering reliable information is probably the most challenging part of our job – data are often recalled by memory or scribbled on a piece of paper. It is worth investing some time explaining the power and necessity of gathering information, then looking at them.
A very valuable and cost-effective tool is on-farm postmortem of a percentage (rather than a single case) of dead lambs. Cases of dystocia will often present with fractured ribs or limbs, ruptured liver, internal bleeding or petechiation of the myocardium – while meconium staining, and swollen head, neck or tongue are often signs of prolonged labour. It is also important to estimate when death occurred – pulmonary inflation will provide an indication if the animal was born alive (pieces of lungs will float in water) or dead (pieces of lungs will sink).
Tissue decay (if carcases are examined fresh) will also suggest death in the uterus a few days before examination. Hypothermia/starvation are usually presented with a complete lack of brown fat around the kidneys, which is replaced by red gelatinous fluid and an empty stomach (no milk clots in abomasum).
Finally, assess the navel and, in particular, evidence and location of iodine staining. Blood samples can also be collected up to a week after birth to assess failure of passive immunity transfer (insufficient colostrum intake). Available tests are to measure total protein using a refractometer (with guidelines of less than 20mg/ml showing failure), a quantitative zinc sulphate turbidity test (less than 15 units indicative of relative failure) or gamma glutamyl transferase (with less than 277U/L indicative of failure). Ideally, serum IgG should be more than 1,600mg/dL (with levels under 600mg/dL indicative of passive transfer failure, and between 600 and 1,600 of inadequate transfer)7.
For the common infectious causes of neonatal mortality, gross pathology alone would be suggestive, but will likely require a collection of samples for further diagnostic tests (Table 1). If, however, the confidence or time for on-farm postmortem are limited, submitting carcases to the regional laboratory for further investigation would be a valid alternative.
Once data have been gathered and analysed, discussion will focus on the target area(s) for improvement (pre-tupping, pregnancy period or neonatal period). If problems seem to be related to pre-tupping and tupping, consider reviewing the replacement policy (young animals and sire size/genetics), BCS of ewes in advance of the breeding season and ewe management after weaning.
Within the pregnancy period – since most will be related to ewe nutrition – a BCS of ewes should be carried out throughout pregnancy (or at least in the last trimester), and a pre-lambing metabolic profile could be carried out to evaluate energy and protein levels. Finally, lambing management – the frequency of supervision, experience and number of staff, lambing pen facilities, hygiene measures, colostrum management, and vaccination history.
Although many interventions will be aimed at the next crop of lambs, some measures can be put in place in the current lambing season (for example, lambing management).
Lambing is the most crucial and stressful period for any sheep enterprise. Although problems are identified at this time (high neonatal mortality), factors leading to it are likely to have occurred even before pregnancy. To increase flock welfare and profitability, careful planning and good animal management are, therefore, paramount and should be addressed well in advance of lambing season.
