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LAMB SURVIVAL 

The initial focus of sheep reproductive efficiency is getting the maximum number of lambs born.  The next challenge for sheep producers is to manage these lambs through the following stages of suckling, weaning and turnoff.  According to the Meat & Livestock Australia report on cost of endemic disease, neonatal mortality costs the Australian sheep industry A$540m annually.  It was estimated that Merino producers on average lose 17% of singles and 30% of twin lambs between scanning and weaning.  Attention to lamb survival will have important economic benefits to sheep producers, especially since lamb survival and health can be strongly influenced by management and animal health inputs. 

Infographic

Causes of lamb loss

Studies have shown that 80% of lamb deaths in Australia occur in the first 48 hours after birth1,2. 

In a trial that determined cause of death in 3198 lambs across Australia, starvation/mismotherment was found to be the highest single cause, accounting for 25% of deaths. Stillbirths were next at 21%, followed by birth injury (19%) and dystocia (9%). Predation accounted for 7% of lamb deaths and cold exposure 5%, while infection and misadventure accounted for only 1% each. Four percent of deaths went undiagnosed. 

Single lambs were more likely to die from stillbirth or dystocia, while twin lambs had a higher chance of dying from starvation or birth injury.

How to diagnose cause of death

Cause of death can be determined by collecting lambs and submitting them for post mortem examination. Your veterinarian can assist with how to diagnose causes of death. Dead lambs should be collected each day and stored in a cool room immediately after collection, or examined within 12 hours of death. There are many tell-tale signs that provide evidence to determine the reason why the lamb did not survive. Bodyweight, girth and crown-rump length are recorded, along with external signs, including the presence of membranes on the feet that would indicate if the lamb had walked or was dead at birth. 

Internal organs are examined and the presence of milk in the stomach, air in the lungs and haemorrhage in various organs can help piece together whether the lamb had starvation, birth trauma or was unable to breathe.

More information on lamb mortality diagnosis can be found at the website https://www.agric.wa.gov.au/livestock-biosecurity/ewe-abortion-and-newborn-lamb-deaths-surveillance-program

Nutrition

Ewe nutrition will determine several important behavioural and physiological factors: 

Hungry ewes will walk away from lambs leading to high rates of mismotherment, particularly in twin births

Ewes with low body condition score or under-nutrition will fail to provide adequate volume and quality of colostrum

Liveweight at weaning and survival of Merino weaners (45 kg SRW) to 12 months

Graph 1

The relationship between lamb birth weight and survival

Graph 2

(source: Lifetime ewe manual)

Shelter and cold resistance

Low bodyweight lambs struggle to maintain body temperature.  All lambs have a high surface area to bodyweight ratio, but particularly those under 3-4kg rapidly lose energy if left exposed. Lambs that suckle strongly can survive well in cold conditions, but in general lambs are not tolerant of wind.  Pasture height greater than 10cm improves lamb survival as it allows lambs to take shelter from wind, particularly in cold, wet conditions. Shelter belts and windbreaks can be maintained in lambing paddocks to improve ewe and lamb comfort. 

Stocking density and husbandry at lambing

Twin-bearing ewes have higher rates of lamb survival if lambing in smaller mobs (100 to maximum 200). This is especially important for maidens, as they are inexperienced and more likely to ignore the lamb’s attempts to suckle. Pasture availability should be highest for twin-bearing ewes (>2000 kg DM/ha preferable) to avoid ewes needing to walk away from lambs looking for feed. 

Improving ewe-lamb bonding (maternal characteristics) 

Mothering ability is repeatable across years, so a ewe that fails to rear a lamb one year is a good candidate for culling. Also, good maternal characteristics are enhanced within a flock by:

Choosing ewes that are early to conceive and bear twins (determined by ultrasound scanning and/or observation at lambing)
Wet/drying ewes at lambmarking to remove ewes that failed to rear a lamb and tag the ewes that did not conceive, or had pregnancy loss. 
Avoid interruptions to lambing such as chasing with dogs, driving into paddock if ewes aren’t accustomed, loud noises
Select and manage ewes for low rates of dystocia
Good predator control through fencing, baiting, shooting or trapping

Sheep

Wet/drying ewes

Wet/drying ewes can be done by looking at and feeling each ewe’s udder at lambmarking. Ewes fall into one of three categories depending on udder characteristics. 

Category Physical features Comment Action
Wet+wet Udder is swollen, with milk easily squeezed from the teat, often with saliva on the teat Ewe is rearing a lamb Keep ewe for continued production
Wet+dry Udder is swollen but has no or little milk and no saliva on the teat The ewe has lambed but lost the lamb Tag the ewe for culling
Dry Udder is small, flaccid, empty The ewe has not lambed, either due to failure to conceive or pregnancy loss Tag or immediately draft the ewe for culling
Table 1.7: Categories of ewes based on udder examination at lambmarking (wet/drying)

References

  1. Western Australia Department of Agriculture. Growing Weaner Sheep. Available online: www.agric.wa.gov.au/managementreproduction/Growingweanersheep Accessed 29/4/15.
  2. Neonatal lamb mortality: factors associated with the death of Australian lambs. G. Refshauge, F. D. Brien, G. N. Hinch, and R. van de Ven,  Animal Production Science 56(4) 726-735
  3. Lamb Post-Mortem Protocol for Use on Farm: To Diagnose Primary Cause of Lamb Death from Birth to 3 Days of Age. J.M. Everett-Hincks and S.J. Duncan  HYPERLINK "https://www.researchgate.net/journal/1874-3188_The_Open_Veterinary_Science_Journal" The Open Veterinary Science Journal 2(1) · June 2008 

Further Reading

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