With increasing lambing percentages comes increased triplet-bearing ewes, therefore, in addition to the mis-mothered orphan lambs, there are also triplet lambs adding to this.
Triplet-bearing ewes have the potential to increase flock productivity, however, there is a lack of information in this space. This is a summary of a review paper which aims to summarise all the studies to date on triplet lambs.
The triplet lamb is lighter, more metabolically challenged and lower in body temperature in comparison to its twin counterpart
Triplet lambs receive less colostrum and milk which combined results in lower survival rates and weaning rates.
Total litter weaning weight is greatest when all three lambs are weaned.
Ensure triplet-bearing ewes have the most shelter and the highest quality feed for optimal survival and growth.
There is limited scope for increasing triplet survival and growth, perhaps there is a need to look into intensive triplet lambing systems, mothering triplets onto single-rearing ewes or hand-raising triplet lambs.
Birth weight and heat production
Triplets have shown to have a lower rectal temperature within the first few hours of birth than twins and singles which is associated with lower survival. It was also found that the lightest triplet lamb has the lowest temperature out of the three triplet lambs. As birth weight increases in triplets so does their total maximal heat production, however, on a per kg basis they are no different indicating that weight is associated with heat production.
The birth weight of triplet lambs was approximately 81% of the average twin lamb birth weight and 66% of the average single lamb birth weight. For example, the average single lamb weighed 5.5 kg and the average triplet lamb weighed 66% of that which was 3.6 kg.
An increase in triplet lamb birth weight would increase the chances of survival, however, there are a small number of studies that have tried to improve triplet birth weights with little success.
Offering alternative feeds, such as herb-clover mix, kale or barley mix, to triplet-bearing ewes in late pregnancy did not increase birth weights in comparison to grazing ryegrass white clover pastures. A few studies have shown that mid-pregnancy shearing can increase lamb birth weights, but must be used alongside adequate body condition score while feeding high quality feed. Both of which are not always present with triplet-bearing ewes. Mid-pregnancy shearing of triplet-bearing ewes would also compromise the ewe in having her off feed for a period of time to empty out prior to shearing.
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Lamb survival to weaning
Lamb mortality can vary from 5% to 30% under both pastoral and indoor conditions with increasing mortality rate in those with greater litter sizes. The average lamb survival in singles was 89.5%, for twins was 85.5% and for triplets was 67.5%.
Most lamb deaths occur within 3 days of birth, however, triplet lambs can have a higher loss rate after this time period. Most likely due to the ewe not producing enough milk for all 3 lambs.
It has been found that survival only marginally increases above a birth weight of 3 kg as can be seen in the graph below.
However, around 25% of triplets in the studies reviewed were under 3 kg.
There is likely an optimum birth weight for survival for all litter sizes, however, triplet lambs struggle to reach this optimum birth weight. The heavier the average litter birth weight the greater the survival. This suggests that it would be best to have all the lambs within a triplet set to be of similar birth weight.
Cause of triplet lamb deaths
The graph below indicates the proportion of the cause of triplet deaths. These include; prenatal death, dystocia, starvation/exposure, a combination of these or other (another cause or unknown death).
Dystocia can be a major cause of death in triplets. Dystocia has traditionally been thought of as a birth weight/size and pelvic opening mismatch, however, it can also be caused by disturbance during lambing, foetal entanglement, mis-presentation, ewe weakness and prolonged birthing process, ewe nutrition and sire selection. Dystocia seems to be a common cause of death for litter sizes of 4 and above.
Starvation and exposure are interrelated and are often considered together. Starvation is where a lamb fails to drink enough milk to survive and exposure occurs when the lamb is subjected to unfavourable conditions where the lamb cannot produce enough body heat to survive regardless of milk intake.
Most triplet deaths are either dystocia, starvation/exposure or a combination of both; potentially dystocia leading to starvation/exposure.
Ewe-lamb bonding and behaviour soon after birth
The behaviour of the lamb after birth is critical for survival. This behaviour includes progression through standing, udder seeking and suckling, which are all influenced by ewe behaviour. The ewe behaviour includes grooming, suckling and bleating. Lambs that are slow to stand or ewes that spend less time grooming the lamb are more likely to be mis-mothered and less likely to survive.
Triplet lambs have a slower progression of the lamb behavioural traits than singles and twins and triplet-bearing ewes show a longer period of restlessness prior to lambing, therefore, both influencing the lower survival rate of triplet lambs.
Milk production of triplet-bearing ewes
Triplet bearing ewes produce less milk in the first 24hrs after lambing than than ewes with twins. It has been suggested that when the lambs are 3 weeks old the milk production of the ewe is less than the theoretical demand of their lambs.
A study indicated that triplet-rearing ewes produce 21% more milk and are more efficient in converting feed to milk than twin-rearing ewes of similar weight. Feeding a herb-clover mix increased milk production in comparison to a ryegrass based pasture, however, this is likely to be due to the higher herbage quality (protein and energy content). Triplet-bearing ewes must be provided with a high quality diet to maximise milk production.
As triplet lamb receive less milk than singles and twins, they are slower growing and have lighter individual lamb weaning weights. However, total litter weaning weight is greatest when all 3 lambs are weaned.
What needs to be done?
There are some potential options to increase lamb survival that have not been investigated in triplets. These include but are not limited to:
Change in ewe behaviour (seeking shelter)
Increased ease for lamb finding the teat
Increased dam awareness of the lamb
Fewer ewes failing to stand after lambing
Increase ewe milk production
Improved lamb vigour and thermoregulation
As sheep farming systems in New Zealand can be vastly different, it is unlikely that there is a 'one size fits all' approach to increasing lamb survival. Most of the studies reviewed show conflicting relationships or no relationship with lamb survival and growth, therefore, there is limited scope for increasing triplet survival and growth. Some other options to consider could be to have intensive triplet lambing systems, mothering triplets onto single-rearing ewes or hand-raising the third lamb. All of these options will increase labour requirements and potentially lamb feed requirements, however, weaning three lambs per ewe could significantly increase farm profitability.
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