By Dr Clive Dalton
Lamb mortality is the most frustrating part of keeping sheep. After planning and working all year to produce a lamb that dies soon after arrival is such a terrible waste and a killer of profit. You can get so depressed going around picking up dead lambs and worse still counting them. Your state of mind isn’t helped by the realisation that you’ll have to wait another year before you can make up for the loss.
Some farmers refuse to count lambs born dead, or that die in the first few days after birth (perinatal mortality), as it doesn’t help their morale at a busy and stressful time of year. In some areas dead lambs are collected as slinks so you can get an accurate figures of what died – if you want it! The amount earned from slinks is best not advertised in the district, and the children should also be sworn to secrecy if their bank accounts benefit. So the general feeling around sheep yards is that the subject is best not talked about, as it’s hard to know where to start to fix things.
What do we know about lamb mortality?
We know a lot, as there has been extensive research done in New Zealand on lamb mortality, and a lot of it is being (needlessly) repeated. Here’s what we know:
- We know that it’s bad! On average 20-25% of all lambs born never reach weaning but there is enormous variation around this average figure for a number of reasons.
- The lamb has low energy reserves - 3% of body weight compared to an adult at 10-15%.
- It needs energy in the first few hours to survive and it can only get this from its mother’s milk.
- The lamb has more surface area per unit of body weight than an adult.
- The birth coat has poor insulation in many breeds. The birth coat is wet and hence increases heat loss due to evaporation.
- Most of the deaths are described as “perinatal” – i.e. in the first three days after birth.
- After this killer period, deaths measured between birth and docking or birth and weaning are low – around 3-4%.
- Today because scanning is used extensively, we now know that 18-24% is a reasonable average for embryos that never become live lambs. Again there is a wide variation around this average with 28-30% in some very dry areas with poor feed.
- If you put a potential market value on all these lambs of $70 NZ from the national flock of 40 million ewes – then the waste of potential lambs from conception to market is astronomical. That’s why we don’t talk about it!
- In New Zealand the weather plays a big part in our outdoor farming systems, and severe storms over a few days at peak lambing will easily kill nearly all the lambs born while a storm lasts. This can easily put the average death rate for the flock up to 40% or more.
- Around 20% of all ewes fail to rear a lamb to weaning. This is a shock to most people who declare that it doesn’t happen on their farms – because they don’t count dead lambs.
- As fertility rises and more lambs are born – then lamb mortality increases.
- More multiples (twins, triplets and quads) die than singles. But twin survival has been often shown to be similar to singles.
- Triplets’ body temperature is 1°C lower than twins at birth, and shelter reduces thermal heat loss by 35%.
- The best birth weight for survival for both singles and twins is 3.6 – 5.6kg, but how you manipulate this is very difficult to achieve.
- Up to 80% of all lambs die (especially multiples) of a combination of starvation, mismothering and exposure referred to as SME.
- Starvation and mismothering are obviously strongly linked as these lambs at post-mortem have not fed (empty stomach).
- Exposure rapidly kills weak lambs and small multiples are certain targets for this. But even good lambs can die of exposure in storms going from 39°C inside the ewe to zero or lower on the wet ground.
- Dystocia causes birth injuries in lambs that are too big and get stuck in the birth canal. It’s the main killer of singles but birth injuries are also implicated in 60-80% of SME lambs.
- Hypothermia is the great killer of lambs in wet and cold conditions.
- Good maternal behaviour is a critical factor. Exceptional mothers don’t leave their lambs behind, and seem to be able to count them and shelter them from cold winds. Two-tooths with their first lamb can be a problem and may need extra care.
- Hoggets that have lambed and reared a lamb are good mothers at later lambings.
- Multiples are left behind to starve when ewes takes off with one lamb.
- Lambs suffocate as membranes around them have not broken at birth and the ewe has not licked them enough.
- Lambs follow other ewes away from their own mothers and are then rejected to die of starvation.
- Lambs slide down steep hillsides away from their birth site and mother. Anything steeper than 25 degrees where the sheep have made hillside tracks will cause major problems.
- Lambs die from haemorrhage when the ewe has chewed the navel or tail.
- Lambs with good thick birth coats (e.g. Drysdale or Romney) have a better chance of survival than those with thin outer birth coat (e.g. Merino).
- Birth fluids are only attractive to ewes around the period of birth.
- Skinny ewes produce small miserable lambs that are very keen to die! Ewes should have a condition score of 2.5 at mating and be 3.5 for lambing.
- Varying gestation length has little effect on lamb mortality.
Previous practice in New Zealand developed for old-fashioned Romney ewes was to flush them for the three weeks up to joining them with the ram, and then feed them on a level plane for a few weeks after mating until pregnancy was well established.
For the middle part of pregnancy you made them work by going out to the back of the farm to eat fern and scrub and do it hard for a while, and if they lost weight nobody worried. Then they were fed on a rising plane again, but for the three weeks before lambing they went back on to almost starvation rations to cut down the size of the lambs and prevent lambing problems. Fertility levels were so poor that most ewes had singles.
Today’s sheep have changed their complete genetic makeup and the above practice is certainly not recommended any more. But unfortunately what is recommended now is more confusing, because the results of research have been confusing. Current recommendations seem to be based on which research paper you believe. Here is a summary of the key points from all this:
- The majority of research shows that altering feeding levels has little effect on lamb birth weight or survival. This is after years of believing and preaching that it did.
- But most consultants still recommend that you feed today’s sheep well for the whole of pregnancy. In any case, manipulating feed levels is far too complicated and has animal health risks too. You need to keep thing simple, so:
- CONCLUSION – Feed sheep well during the whole of pregnancy.
- If you severely restrict feed in the first 60-100 days of pregnancy you’ll reduce the weight of the placenta and foetus, so:
- CONCLUSION – Don’t do this and feed them well all the time.
- Shearing during mid-pregnancy can increase the birth weight of lambs provided the foetus is small. Initial University research results were positive but later on-farm trials have been very variable and of course have not been published in scientific journals. The subject seems to have gone off the radar!
- In any case shearing before lambing is too risky and has big animal welfare impacts that are not worth taking with the present value of ewes, and with international eyes on how we treat our sheep in New Zealand.
- The 2009 computer modelling work showed pre-lamb shearing to be very bad for lamb survival, and it was recommended that ewes should be shorn no later than mid pregnancy.
- CONCLUSION – Don’t risk it.
- The heritability of lamb survival is low (2-16%). Nevertheless breeders have made progress by selecting for easy-care sheep before they knew this.
- CONCLUSION – Breed for easy-care sheep with determination.
- Scanning allows you to identify and feed ewes carrying multiples well so feed them well all the time. Ewes carrying singles, especially if they lamb late, can have their feed restricted before lambing to prevent Dystocia.
- CONCLUSION – scan the flock and give the feed to the multiple-bearing ewes.
Increasing fertility and multiple births
As overall flock fertility goes up, this has important practical implications for managers as the number of singles, twins and triplets changes. Here’s a brief summary of what happens from resent research:
- In high-fertility ewes, deliberately not flushing before mating will only reduce lambs born/ewes lambing (LB/EL) by 1-2%.
- Up to 1.6-1.7 LB/EL, singles decrease and the number of twins increases. Twins substitute for singles.
- Around 1.7 LB/EL twins level off and triplets go up rapidly.
- Around 1.8 LB/EL twins decline and triplets show a rapid increase. Singles remain stable at low levels.
- At 2.2 LB/EL quads increase, twins decline and triplets level off at 30-40%.
- Above 2.3 LB/EL with so many quads, any extra lambs are not worth the bother as they have lower survival and lower growth to weaning, as a ewe cannot feed them all.
- Some farmers with 10-20% triplets or even up to 40% triplets leave them on the ewes. Above this you have to look at removing one lamb to mother on to another ewe, rearing it artificially or letting it die. The recent good prospects for lamb have changed attitudes considerably regarding putting more work into saving lambs.
- The increasing fertility in modern sheep breeds has led to higher numbers of triplets and quads in commercial flocks.
- As a ewe only has two teats, inevitably there are higher death rates in these multiples and if they are reared, either on the ewe or artificially, it leads to many smaller lambs at weaning.
- Some farms now get up to 40% triplets and once litter size (number of lambs born/100 ewes lambing) gets over 2.2, an increasing number of quads are born which cannot be reared by the ewe.
- With triplets, observant farmers have noticed that between 10-15 days after birth, the ewe decides that she cannot feed all her lambs so she starts to leave one behind.
- The two that get to the udder first can soon drink all the milk so when it’s the turn of the third lamb, there is no milk left. The neglected third lamb is found motherless in the paddock and will die if not removed and fed which may not be economic.
Selecting only for twins
To avoid the problems mentioned above, geneticists are now working on the genetic variation they have found in ewes that twin regularly. This they say will allow improved twinning without producing triplets and quads. It’s clearly a complex trait with low heritability with many environmental factors involved to confuse things. It cannot be done by just selecting rams and ewes that were born as twins. We want ewes that consistently produce two eggs every time and they all survive. It will take a long time to achieve this in a flock unless aided by gene technology.
What can be done about lamb mortality?
Researchers have been telling farmers about the statistics of death for at least three decades, but both have failed to come up with good cost effective practical solutions to cut down the waste.
Admittedly from the national flock we dock and wean more lambs now than ever before, but this is because more lambs are born through introduced higher fertility breeds like the Finn which have been crossed into other breeds. But the problem of perinatal lamb mortality remains.
All we’ve been good at over the years is talking about it, doing more endless post mortems and reporting what’s already been done! We hoped that more practical answers would come out of all this but they haven’t. So what can be done? The truthful answer is “not a lot” but here are a few thoughts:
On big commercial sheep farms
- Don’t plan to have the first lambs in the district – lamb when the feed is going to be there.
- Pay special attention to feeding. Feed high producing ewes on a good plane of nutrition for the whole of pregnancy. They should be going into 1200kg DM/ha (4cm high) in the four weeks before lambing.
- Condition score is important. At mating they should be CS 4 and lamb at a minimum of CS 3-3.5.
- Scan the ewes at 80-90 days of pregnancy, and lamb all those carrying multiples separately in good level paddocks and with shelter if available.
- Accept the fact that a lot of good lambs will die, and don’t wait for research to come up with any solutions to do anything practical about saving them.
- Select ewes intensively for “easy-care” (non-assisted) lambing. The trait has low heritability (0-15%) but if you put enough emphasis on it, then progress although slow will bring results. Many farmers who have made spectacular improvements have certainly backed the theory.
- Buying rams from breeders recording on SIL who can show genetic gains in lamb survival is a high priority, and if you cannot find any that meet your needs, start and breed your own rams.
- Remember this easy-care approach has welfare implications and you’ll need to meet the requirements of the sheep code of welfare, where any ewes in need must be helped to lamb. These ewes and their offspring should be marked for subsequent culling.
- Give ewes plenty of undisturbed space to lamb and leave them on their birth sites till they want to move away.
- Get them used to you moving through the paddock on foot, by bike and with a dog before lambing or keep right away from them.
- Any shelter must be at ewe and lamb level. You may have to fence off popular areas where ewes camp and lamb when they get dirty.
- Watch out for ewes with multiple lambs needing assistance, and lambs that seem motherless and are not getting a feed. At current prices it’s worth mothering them on to other ewes if you can streamline the process – normally it is not.
- Put covers on weak lambs in cold wet spells or if one is forecast. Don’t rely on the general weather forecast – get regular reports on the one for you local area.
- Give ewes carrying singles different care with controlled feeding to prevent oversize lambs.
- Give ewes a good pre-lamb crutch taking plenty of belly wool off in front of the udder if it’s long so newly-born lambs can easily find the udder and teats.
- If time permits, check for cast ewes and lambs with stuck-down tails.
- Euthanase ewes with bearings that are too difficult to treat and make them for culling.
- Before lambing, check with your vet about the mineral status of the flock incase any extra supplementation is needed.
- Lamb on the flattest paddocks you have, and try to avoid steep country above 25-30°.
- Provide intensive care for the flock and try to save every lamb. It will be a lot of work so don’t count your hours and charge them at business rates! Take the view that you are saving lives and costs are not the main issue.
- Scan the ewes at 80-90 days of pregnancy and lamb all those carrying multiples separately in a level paddocks and with good feed and shelter.
- Get the sheep used to disturbance by shepherd, farm bike and dog and the children before lambing.
- Give them plenty of undisturbed space to lamb and leave them on their birth sites till they want to move away.
- Provide plenty of shelter with hay or straw bales in the paddock. Any shelter must be at ewe and lamb level.
- You may have to fence off popular areas where ewes camp and lamb when they get dirty.
- Try a zigzag temporary fence across the lambing paddock for both shelter and to restrict the mobility of ewes and lambs in the first day after lambing – especially if they have multiples.
- In storm conditions get newly-lambed ewes into cover, especially if they have multiples. Use a shed or an old-fashioned lambing pen made of hay bales and a sheet of corrugated iron for a roof – with a large rock on it to stop it taking off in the wind! It’s a handy place for the shepherd to have a snooze after lunch!
- Put covers on all lambs at birth unless it’s brilliant weather. You can buy plastic or wool ones or use old bread and supermarket bags. But buy some decent covers as remember what each lamb is worth, and you can use them again.
- Code mark multiple lambs at birth with raddle to remind you which they are and which ewe they belong to. Check they are correctly mothered up during the day and particularly at night.
- Be prepared to foster all spare lambs or rear them artificially.
- Check for cast ewes and lambs with stuck-down tails.
- Get the vet to deal with any ewes with bearings.
- Select replacement ewes and rams for high survival (See breeding).
- If you have lambing problems that you can’t fix, don’t delay in getting experienced help.
- Before lambing, check with your vet about the mineral status of the flock incase any extra supplementation is needed.
Where's this lamb's mother? Be wary of single lambs on their own that don't have full belly. They could be dead next morning
Temperature of a 'starving"
- 39-40 degrees C - normal healthy lamb
- 37-39 degrees C - lamb is at risk and needs feed and shelter
- Below 37 degrees C - Lamb is in grave danger and needs urgent emergency treatment.
For a lamb that has not fed, is starving and cold, it's important to get some energy into it before you warm it up as warming it up will increase the demand for nutrients. If they are not available, then the lamb may die faster. An injection of glucose is worth a try.
- Use 30ml of 40% dextrose and mix it with 30ml of boiled (and cooled) water. You can buy ready-to-use product.
- Disinfect the injection site.
- Use a 3/8 inch needle (sterilised by boiling and then storing in meths).
- Hold the lamb up by the front legs and insert the needle in front of the navel.
- You will hear a 'pop' sound if the needle goes through the body wall, and to confirm this the syringe will empty easily. If you get a lump appearing at the end of the needle, then the needle has not gone through.
- Some folk find this better than 'tubing' a lamb with less risk of lung damage.
- After treatment, warm the lamb in an old electric blanket and feed colostrum to keep it going. Feeding rate is 50ml of colostrum/kg of body weight, for at least three days.
- Bonding of the ewe and lamb is very rapid at birth – it only takes a few minutes. Once the ewe has smelled the lamb, she will not take another lamb that smells differently.
- To foster lambs on to ewes, there are a few tricks but realise that some ewes are more determined than others not to be fooled.
- For guaranteed success, you really need to confine the ewe so she has little room to move away from the lamb, and the lamb is in constant physical contact with the ewe. Special mothering-up pens are commercially available.
- Tying a ewe to a fence or to a peg in the ground by her front leg, and expecting the fostered lamb to mother itself on is a waste of time.
- To add a lamb to a ewe that already has a single, have the lamb ready and cover it in the ewe’s birth fluids so both lambs smell the same. The fostered lamb will be more active so make sure the ewe licks her own lamb well and it gets a suck. It’s best to stomach tube it to make sure it gets enough colostrum.
- For a ewe with a dead lamb, skin the dead lamb and make it into a suit with holes for legs to fit on the fostered lamb.
- Use strong smelling oil or commercial product to put on the lamb and up the ewe’s nostrils. This is not always effective.
- Put the ewe in a headbail in a pen and leave the lamb with her till she accepts it. This may take a few days and some ewes will still win the battle.
- Some people recommend washing the fostered lamb to remove all the smell and then rub it on the dead lamb or the ewe’s own lamb. Ewes are not that stupid and can still smell an alien lamb.
- This is the first milk produced by the ewe and is thicker and more yellow than normal milk. It’s often more like glue.
- Colostrum is full of antibodies that help protect the lamb from infections, and also has a laxative effect to remove the meconium (foetal faeces).
- It helps keep the lamb warm because it is rich in energy.
- It is easy to digest and it helps the lamb strengthen and grow. It can work miracles on weak newborn lambs.
- If lambs don’t get enough colostrum in the first hours of life, they will be very susceptible to infections for months afterwards.
- Be aware that many orphan lambs haven’t had sufficient colostrum in their first few hours of life and are prone to die. They are very susceptible to infections like diarrhoea and pneumonia.
- It is very important that every lamb gets colostrum during the first 24 hours of life.
- Ideally they should get a good colostrum feed between 1 hour and 6 hours of birth. After this time, the ability of the gut to absorb the antibodies decreases rapidly.
- It’s best to let the lamb suckle naturally from its mother. And if you can supervise without causing distress, make sure the lamb has found the teat and is sucking properly, and not just wasting time pretending and wagging its tail.
- Colostrum varies in quality. The quality decreases quite rapidly after birth, and some ewes produce better quality colostrum than others.
- The following recommendations apply when colostrum is given by bottle or stomach tube.
- Depending on their size, lambs should get about 100-200 ml colostrum per feed (600ml in total in the first 12 hours of life), and larger newborn lambs need up to 1500 ml daily. Only the really heavy-milking breeds of ewe would produce this much milk if well fed – so you may need to supplement their feed if they are not milking well.
- Colostrum feeding should continue for at least 4 days if at all possible.
- Then get the lamb on to a good quality powder lamb milk replacer and follow the instructions on the bag to the letter! If in doubt make it weaker rather than richer and watch for sticky tails and constipation.
- Generations of orphan lambs have been fed on cows’ milk after getting minimal colostrum, and sometimes it was even diluted with water to cut costs! Lambs will not die on this but don’t grow very well.
- Without doubt, the lamb is best left on its mother to suckle colostrum naturally.
- However if the lamb is too weak to suck naturally, colostrum can be milked from its mother or from other newly-lambed ewes and fed by stomach tube. If it’s weak it won’t be able to suck fast enough if at all.
- f you have stored sheep colostrum in the freezer, don’t thaw it in the microwave oven as this will destroy the antibodies.
- If colostrum from ewes is not available, newly calved cow colostrum can be used.
- Try to get some sheep colostrum into the lamb before you try the cow colostrum.
- Good quality colostrum substitutes can be purchased, but it is important to use only the type of colostrum that contains antibodies.
- Beware of old home-made colostrum substitutes that use egg yolks and cod liver oil. These don’t contain protective antibodies.
Feeding by stomach tube
- Colostrum can be given to newborn lambs by stomach tube when they are too weak to suck.
- A rubber stomach tube made especially for lambs should be used (obtainable from rural suppliers or your vet). Tubes that are too large can cause damage.
- Extend the head so the mouth, throat and gullet (oesophagus) are in a straight line.
- Gently thread the tube through the mouth into the throat, then down into the gullet, taking care to ensure it hasn’t gone into the lungs.
- If the tube is correctly inserted, you will see it distend the gullet a little on the left of the windpipe as it goes down into the stomach.
- Warm the colostrum to body temperature before pouring it down the stomach tube.
- Never warm or thaw colostrum in the microwave because the important antibody proteins will be damaged and will congeal.
- If colostrum is not immediately available for the first feed after birth, give electrolyte solution with no protein added (see your vet). Feeding non-colostrum proteins to newborn lambs results in subsequent impairment of their ability to absorb colostrum proteins.
- A ewe’s lactation peaks at about 3-4 weeks after lambing.
- How much milk she gives depends greatly on the number of lambs she is suckling.
- If her udder is emptied often, then the milk producing cells (alveoli) in the udder are stimulated to produce more milk.
- Ewes suckling multiple lambs will have a later lactation peak in production.
- Grazing ewes suckling singles will produce about 2 L/day and 3L/day suckling twins.
- Ewe milk is especially high in fat and protein compared to the goat and cow.
This material is provided in good faith for information purposes only, and the author does not accept any liability to any person for actions taken as a result of the information or advice (or the use of such information or advice) provided in these pages.