Energy needs of triplet bearing ewes
In New Zealand the average litter size per mated ewe has increased resulting in more triplet-bearing ewes. This increase in litter size, although should result in greater profit, is also associated with higher mortality of lambs. We have done a previous summary that gives an overview of the research on triplet lamb mortality.
The paper we are looking at in this summary is a Norwegian study published in 2020 that looked at improving triplet-bearing nutrition during late pregnancy to improve lamb performance.
In Norway, sheep are farmed outdoors in extensive systems and the inland sheep farms house and feed their sheep indoors during winter. This likely makes it slightly easier when compared with New Zealand farming systems to supplement the triplet-bearing ewes with concentrates during pregnancy.
The ewes fed above their energy requirements had the greatest increase in live weight prior to lambing, but also had the greatest decrease in live weight during lactation compared with the other two treatment groups.
There was no significant difference of feed treatment on lamb birth weight.
When only complete triplet litters (lambs born and reared as triplets) were compared at weaning, the lambs born to ewes fed above their energy requirements were heavier than lambs born to ewes fed at their energy requirements, but did not differ from the lambs born to below energy requirement ewes.
Twenty-seven triplet-bearing Norwegian white ewes were allocated to 1 of 3 dietary treatments based on INRA (Jarrige, 1989) recommendations.
The Norwegian white sheep is a dual purpose crossbred sheep, likely with similar characteristics to crossbred sheep in New Zealand.
Ewes were offered a ration of either 85% (below), 100% (at) or 120% (above) of recommended net energy lactation requirements from mid pregnancy to lambing.
Lets call these treatment groups:
"below" feed requirements
"at" feed requirements
"above" feed requirements
Ewes were individually fed and the feed requirements were individually calculated for each ewe.
Diets consisted of a restricted portion of grass silage from early harvest and an adjusted level of concentrate.
The triplet bearing ewes showed that they are able to ingest feed above their requirements, however, during the last two weeks before lambing they refused the grass silage so were solely eating concentrate.
The graph below shows the average BCS for each treatment group. As expected, increasing feed allowance increased the ewe body weight gain and body condition score (BCS) prior to lambing.
The above feed requirement ewes lost more body condition in lactation compared with the ewes feed at their requirements.
This greater BCS obtained by the above feed requirement ewes prior to lambing likely allowed for more fat reserves to be mobilised to use as energy for milk production during lactation. This is shown by the significant drop in BCS between early and late lactation.
In the graph below we have the weaning weight (kg) of the 3 treatment groups if only the triplet litters that were born and weaned as a triplet litter were considered. Only the triplet litters are considered here because some ewes can be scanned as triplet bearing but only rear 1 or 2 lambs due to the high rates of lamb mortality in the first 3 days. The ewes that were fed below requirements are in blue, at feed requirements are in purple and above feed requirements are in grey. The above feed requirement lambs were heavier than lambs born to at feed requirements ewes, but did not differ from the lambs born to below feed requirement ewes.
This could be partially explained by the drop in BCS of the above feed requirement group, allowing for more energy for lactation, resulting in lambs with greater weaning weights (kg). The authors state that there was a small number of triplets that were remaining at weaning in the below feed requirement treatment group so that could have increased the error of this result, making the weaning weight not significantly different from the above feed requirements group.
The early live weight gain from birth and weaning weights of lambs increased alongside increasing pre-lambing energy allowance of their mother. However, only lambs in complete triplet litters had significant increases in live weight gain until weaning which is why these are the only results presented above. So the lambs that were born as a triplet, but were reared as a twin or single due to lamb mortality, had weaning weights that were no different between treatment groups.
The following behaviour scores were measured:
There was no effect of feed treatment on any of these behavioural scores showing that it is likely all triplet lambs have a similar rate of birth assistance, lamb vigour and suckling assistance no matter what the feed intake is of the ewe. There was also no effect of ewe nutritional treatment on the lamb birth weight.
The authors of this study concluded that it is possible for triple-bearing ewes to meet the increased feed demand and gain BCS in late gestation but only when the feed quality is high. The need for high energy concentrates in this study mean that achieving this on farm could be an expensive exercise as New Zealand sheep farms are mainly pasture based and do not often have the infrastructure to feed out concentrates with high utilisation.
The authors also stated that the high energy intake in ewes during late pregnancy increased energy mobilization during lactation that seemed to benefit lambs in triplet litters with better growth to weaning. Perhaps this is an option for farms that leave all three lambs on the ewe. The ewes that were scanned as triplet-bearing but raised twins had lambs with similar live weights at weaning. This means that the ewes that rear twins are unlikely to need the extra feed as they are raising one less lamb.
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Dønnem I, Granquist EG, Nadeau E, & Randby ÅT (2020) Effect of energy allowance to triplet-bearing ewes in late gestation on ewe performance, lamb viability, and growth. Livestock Science, 237, 104027.