A quick lamb post- mortem can be a valuable tool for identifying any underlying diseases or ewe management issues that could be contributing to lamb losses.
Speaking at a recent Beef + Lamb New Zealand Lamb Survival Focus Group in North Canterbury, vet Ginny Dodunski says while post-mortems are “another thing to do” at a busy time of year, she encourages farmers to look for external clues before getting the knife out.
The first of these is the feet. If the lambs’ feet still have soft jelly tips, the lamb won’t have walked.
If they have walked, the cause of death can often be starvation or exposure.
Other external clues include a swollen head, which indicates dystocia, and a hard and thickened area where the naval enters the body, indicating a possible navel infection.
Lambs born ‘orange/yellow’ have passed their meconium on the way out. Meconium is the lambs’ first poo – the more meconium staining, the more prolonged the birth process was, which can be a sign of low energy supply to the ewes.
It is lambs that die without any obvious cause that can be worth taking a closer look at.
Carrying out a post-mortem examination – what to look for?
Place the dead lamb on its back and make two cuts under the armpits to let the shoulder blades fall away from the body. This ensures the lamb lies flat and makes the job a lot easier.
Then pinch the skin of the belly to pull it up and away from the organs, and remove the belly and lower third of the chest (cutting through the ribs) in a single cut. This single incision allows everything to be seen at once.
Look at the stomach and intestines to see if they contain milk (whether or not the lamb has drunk). Milk looks like cottage cheese; mucus can look ‘milky’, but it’s clear and won’t be clotted. Then look for brown fat reserves that sit around the heart, kidneys and other abdominal organs.
While it’s called ‘brown fat’, it is more a pale tan colour, says Ginny.
This fat is metabolically important as it generates heat and helps keep the lamb alive for the first 24-36 hours. If the lamb has used up all its brown fat, what’s left behind will appear dark red due to blood vessels.
Lungs and pneumonia
To determine whether the lamb has breathed or not, look at the lungs and place a piece of lung in water.
If the lamb has breathed, the lungs will be pale pink and the lung tissue will float.
If not, the lungs will be dark red and the tissue will sink.
Pneumonia can set in very quickly in a lamb that is suffering from exposure. Lesions of pnuemonia start in the front lobes of the lungs and appear as uneven shaped, dark red, consolidated lung tissue, which will also sink if cut out and placed in water.
Thyroid glands
The thyroid glands are two kidney-bean shaped glands that sit either side of the trachea just under the angle of the jaw. As a rule of thumb, these glands should be no bigger than a little fingernail. Enlarged thyroid glands can indicate a possible iodine deficiency and a vet should be contacted to carry out a definitive diagnosis.
White spots on the liver of a lamb that was dead at birth can be a sign of campylobacter. Liver abscesses are more common in older lambs as a consequence of navel infection.
Maintaining ewes in optimal body condition
Studies have shown that ewes in optimum body condition (BCS 3-3.5) have lambs faster, the lambs have more brown fat reserves, the ewes are better mothers, have plenty of colostrum and milk and lamb survival is much higher than lambs born to ewes in sub-optimal condition.
Ginny stressed that feeding was the single most important factor affecting lamb survival and the overall performance of the ewe flock.
She says while trace elements need to be adequate, there was not a lot of good trial work supporting the use of ‘luxury’ amounts of these.
“Figure out what trace elements you are short of and supplement in the most cost-effective way possible.”
Ginny also cautions farmers against the risk of yarding old, multiple-bearing ewes immediately before lambing to administer their pre-lamb treatments.
The metabolic stress of bringing them into the yards can outweigh any possible benefits of a pre-lamb vaccination. Even two hours off feed for an older triplet ewe, close to lambing, can affect lamb survival. A solution for these is to administer their treatments further out from lambing when their rotation is coming past a set of yards, or to take portable yards to the ewes. Their lambs can be vaccinated at tailing if pulpy kidney before weaning is likely to be a risk.
Bearings
Ginny said it is ewes that gain weight at or immediately after mating that can be at greater risk of having bearing problems in the lead up to lambing.
While there are a lot of unknowns about bearings, the greatest risk period appears to be immediately after fertilisation when over-feeding can potentially lead to bearing issues at lambing.
Ideally, farmers should be aiming to get ewes back up to mating weight as soon as possible after weaning and then maintaining them at an optimum body condition (BCS 3-3.5) through into mating. This can eliminate the need for flushing and reduce the risk of bearings.
Alternatively, ewes can be flushed up until mating and then put straight back onto maintenance about 10 days after the ram joins. This also allows pasture covers to be built over autumn.
Ginny says there was no correlation between bearings and the feed levels at or just before lambing. Ewes should be fed as well as possible in late pregnancy, with sudden changes in feed volume or quality avoided if possible. New Zealand and international work has shown that ewes losing weight before lambing are at higher risk of bearings than those being fed to maintain their condition.
Salt is considered a bearing risk in some parts of the country and a possible mitigating factor in others - similarly, swedes are also considered a risk factor in some areas.