Using body condition scores to maximise ewe potential
Understanding the body condition score (BCS) of a ewe gives the farmer a wealth of information to best manage a flock at every point of the year.
But it is particularly important at scanning time as it will dictate how the flock is managed to maximise its potential over the lambing period.
Scanning is important when it comes to segregating ewes for their requirements over the last few months of pregnancy. The number of lambs scanned in ewe is also a key performance indicator which can be used to plan the next production year and benchmark against previous years and other farms.
Results are influenced by many factors, so they can also highlight wider problems such as the fitness of rams, the weather and management during pregnancy.
Eblex beef and sheep scientist Liz Genever says segregating the flock by litter size and condition score will help farmers manage their ewes.
She says: “Do not forget, thinner ewes will need to be moved up a group so their condition will improve. Regular assessment of BCS within the flock over the last month of pregnancy and relevant movements of ewes within groups will ensure ewes are fed optimally.”
In terms of BCS, a shift in the condition score of a ewe at certain stages of pregnancy will affect lamb growth.
Early during pregnancy, there is no requirement to adjust the diet. As ewes move into the second month of pregnancy, ewes tupped in adequate condition are able to lose 0.5 BCS as long as this happens gradually.
Larger losses of ewe BCS will impact on foetal growth and birth weight. Equally, ewes should not gain more than 0.5 BCS at this time.
“Later in pregnancy, it is critical the condition of the ewe is actively managed, because during the last six weeks of pregnancy, 70 per cent of foetal growth occurs and the udder develops,” says Dr Genever.
An Eblex-funded project on sheep performance indicators has found a positive relationship between ewe BCS at lambing and lamb weaning weights. Early results predict every one unit increase in BCS at lambing is associated with a 5.4kg increase in weight of weaned lamb.
Work from New Zealand has shown lamb survival decreases by five per cent for every half BCS lost in the four weeks prior to lambing. During lambing, every half BCS less than three equates to a further five per cent reduction in terms of lamb survival.
Ewes at BCS 3.5 also produce twice as much colostrum as a ewe at BCS 2.5.
In most systems, supplementary feed is required to maintain condition in late pregnancy, as it helps ensure the ewe receives sufficient energy, protein, minerals, vitamins and trace elements.
Dr Genever says: “As the foetus grows, it takes up more room within the ewe and her appetite reduces by about 30 per cent. This is the reason why concentrates are generally needed to supplement forage.
“Therefore, understanding the value of forage is important, so supplementary feed requirements can be planned. Simply supplementing with the same feed you have always used will not necessarily work because forage quality will differ year-on-year.
“For some systems, grazing alone can be sufficient as long as stocking rate is appropriate. The target sward height prior to lambing is about 30-40mm and after lambing 40-60mm is ideal.”
In-lamb ewe lambs must be segregated because they require 20 per cent more feed than mature ewes in order to sustain their continuing body growth throughout pregnancy. In terms of growth rate, a ewe lamb should be growing at 250g per day for the first two months from when the ram is introduced.
After then and until six weeks prior to lambing, a growth rate of at least 150g per day is optimum. Ensuring ewes are at optimal condition (BCS 3) six weeks prior to lambing and only feeding for maintenance and growth of the foetus in the last stage of pregnancy is important.
Dr Genever reminds producers to consider trough space, as allowing 450mm per ewe when planning a supplemented diet should ensure intakes are similar.
Why do sheep need it?
During pregnancy, ewes need protein for maintenance, lamb growth, udder development and milk production.
What kind of protein?
Ewes will need two different types of protein during the latter stages of pregnancy:
- Rumen digestable protein – Bacteria in the rumen require this to break down forage and produce a protein the ewe can digest in the small intestine.
- Digestable undegradable protein – This type of protein avoids breakdown within the rumen and is absorbed in the intestine of the sheep.
Good sources of protein:
- Rapeseed meal
- Sunflower meal
- Soya bean meal
- Maize gluten