Lamb loss is a major source of wastage in the NZ sheep industry. About 17% of lambs (foetuses) present at scanning don’t make it to docking (average). The majority of these are lost in the perinatal period (around birth).
The main drivers of lamb losses under our control are:
- Ewe condition and feeding (lambing date, farm stocking rate etc.)
- Trace element deficiencies
- Paddock choice, set stocking rates
Performing a basic post-mortem is a quick and easy way to understand lamb wastage on your property. Lamb post-mortems don’t necessarily need to be performed by vets. We are more than happy to do them for you, or to train you to do them yourself. Following a simple protocol can give you a general cause of death. Perform at least 10 post-mortems on freshly dead lambs to have an understanding of what may be causing your losses.
Weigh the lamb, it should be at least 4kg. A large portion of underweight lambs can reflect poor nutrition during crucial stages of pregnancy. Lamb birthweights do have a correlation with lamb survival.
Check the lambs feet. Lambs that have not walked will have a jelly like slipper on their hooves. If these are present, they were likely dead at birth, or very weak.
Cut away the skin over the head, neck, and rump of the lamb. If the lamb suffered from dystocia (got stuck), there will be oedema/bruising under the skin. This appears as jelly like swelling/haemorrhage. You can also cut away the skin on the legs to see if there was a leg stuck back.
Locate, remove, and weigh the thyroid gland. Iodine deficiency causes enlargement of the thyroid. The thyroid weight (grams) to lamb body weight (kg) ratio should be less than 0.4 (grams thyroid weight: kg body weight). Any larger than this indicates iodine deficiency.
Finding the thyroid glands can be the most difficult part of a lamb post-mortem. It may require some googling or having a vet show you. This gland is located on either side of the windpipe, quite close to the Adam’s apple.
Open the chest cavity. A lamb that has breathed air will have lungs that look normal to anybody who has cut up an animal before. They should be bright pink. If there is any doubt, put the lung in a bucket of water. If the lamb was born alive and has breathed air, the lungs will float in the water but if the lamb that was dead on arrival, the lungs will sink.
Look at the heart and kidneys. Lambs that have not starved to death will have fat around these two organs. Lambs that have died of starvation will have brown jelly like material where the fat should be. Look in the stomach, is it empty?
Record all findings. Contact the vets for a simple lamb post-mortem sheet that makes all these findings easy to record and assess. If we have at least 10 dead lamb post-mortems we can start to draw some conclusions and make attempts to increase lamb survival for next year. Take photos of anything you’re not sure about, we might be able to help.
It’s a good idea to collect information every year about numbers scanned and docked from each paddock, to give an idea of which your best lambing paddocks are. They might not be the paddocks you expect.