4 reasons for high lamb mortality
Mortality rate in sheep is still high with 15% and we are still not close to the target of lower 3% . The first day is the most critical day: Up to 50 % of lambs' mortality during the pre-weaning, takes place on the first day! . Consequently, risk factors must be defined and targeted strategies for a successful lambing period are needed.
But what are the main reasons for lamb mortality?
- Birth difficulties
- Refusion of the lamb by the ewe
- Infectious diseases
- Congenital malformations
(According to Dwyer et al., 2016 )
Which risk factors can we define?
There are several risk factors, which have an influence on these causes for death. The birth weight of lambs is an important factor, which can be influenced by the feeding of the prepartum ewes. High birth weights or big litter sizes can result in birth trauma and severe lack of oxygen intrapartum. Hypoxic brain injuries affects the behavior of lambs which might not be able to stand, suckle or vocalize . Additionally, the hygiene management, vaccination routines and housing enormously affect the pathogen pressure and the risk for infectious diseases.
Directly after birth lambs are faced to low temperatures. They need to regulate their body temperature which can be difficult with such a small body surface area exposed to low outside temperatures. The newborn lambs maintain the body temperature by using brown fat energy reserves and by increasing the muscular activity by shivering . The size of the fat reserves depends on the body weight of the lambs affected by the feeding of the ewe prepartum, too .
You can already see how important the feeding management of pregnant ewes is as maternal undernutrition can influence the neonatal lamb mortality .
Prepartum, the transfer of antibodies from the ewe to the lamb is not possible due to the placental structure. The immunization has to be performed by the intake of colostrum in the first hours of life. The success of the passive immunization depends mainly on the time and the quality of the colostrum. Lambs with reduced teat-seeking behavior, disabilities to stand early after birth or lambs that are not allowed to suckle by scared ewes might not be able to acquire an adequate passive immunity. Considering that 22% of ewes have poor colostrum quality (<50 g Immunoglobulin G/l)  and that twin-bearing ewes often show a low colostrum quality , the demand for additional support is obvious.
How to support lambs in the best way?
To ensure an optimal birthweight of lambs a balanced diet to the ewes must be fed  (figure 1). Very light lambs have impaired thermoregulatory ability whereas heavier lambs have a higher risk for dystocia . Ultrasound scanning for litter size evaluation and assessing of body condition scores can help to adapt the diet.
A guidance how to react if low body temperatures or weak lambs are born is shown in figure 2. Hypothermia of lambs should be prevented by providing shelters, isolation and by reducing the group size. Small group sizes might also help to improve the bonding between lamb and ewe so that an early suckling is possible.
Additionally, an adequate colostrum intake needs to be secured as the consequence of insufficient colostrum intake is far-reaching. Insufficient intake increases the risk of hypothermia and the susceptibility to pathogens. At least 50 ml colostrum/kg bodyweight should be ingested by lambs within the first 18 hours after birth but at low temperatures this amount can increase up to 280 ml/kg . Furthermore, the young lambs are faced to different microorganisms directly after birth and some might be pathogenic. If the pathogen pressure is high and the colostrum supply is inadequate the risk for the development of several diseases is higher. Diarrhea is the most common clinical symptom in neonatal died lambs  and it can be associated to a failure of passive immunity transfer.
However, sometimes management structures on the farms cannot be changed very easily despite all efforts. We are often faced to low quality colostrum or lack of colostrum due to a huge litter size. In these situations, a good preparation can help.
There are different ways to support with dietary feed supplements depending on the on-farm situation:
Pastes rich in bovine colostrum, energy, trace minerals, vitamins and prebiotics which can be easily applied and deliver extra energy and immunoglobulins.
Colostrum replacer should be available in emergency cases when no colostrum is available.
The quality of the colostrum should be checked. If the quality is poor, the colostrum needs to be enhanced with colostrum enhancer.
If colostrum replacer or enhancer are used, not only high immunoglobulin but also high fat concentration should be ensured to prevent hypothermia. These high concentrations are essential for a colostrum replacer for lambs and goat kids because they are able to ingest only small volumes per feeding (up to 250 ml, depending on the body weight). Small volumes should be applied for several times on the first day of life. Yeast products can help to promote an early development of a well working intestine to be prepared against pathogens.
Our aim: Improving the survival rate in newborn lambs! You are interested in strategies for a successful lambing period? Contact our experts!