BY: VICTORIA O’SULLIVAN
Is it worthwhile having body condition score (BCS) as one of your selection objectives when chasing efficiency in your ewe flock?
That’s the question that provided the basis for Massey University student Isabel Vialoux’s PhD thesis, which saw her analyse pedigree-recorded sheep BCS datasets captured by stud flock breeders since 2008.
“We wanted to know whether it was possible to select for BCS in sheep,” says Isabel. “If a ewe is a certain BCS, will she pass that on to her offspring, and will those ewes be a similar BCS? And is it beneficial to go to a ram breeder that records BCS or not?”
Optimal BCS is considered to be 3-3.5 with anything outside this range generally considered inefficient. Isabel found BCS was passed on and showed similar heritability regardless of the time of year it was measured.
“It doesn’t matter if you measure it prior to mating or at weaning, there are similar genes in effect at all those different time points,” she says.
She looked at different sheep profiles and how the BCS changed through the year, and found the relationship backed up what is visually recognized on many sheep farms – the ewes that had the ability to lose more body condition could use this energy to produce milk to feed their lambs, whereas the ones that held on to condition were more likely to wean singles.
She says triplets continue to be a huge issue for many farmers so it’s important to have triplet ewes at a BCS 3.5 mating through to scanning. Isabel suggests using BCS at mating to ensure ewes have enough condition to carry them through winter and to feed the lambs up until weaning.
At weaning use BCS to draft out the lower condition ewes for preferential feeding as these are likely to have been the multiple-rearing ewes.
“As you get through the year and the foetus mass is pushing on their stomachs, they can’t make that up in late pregnancy, so it is super important to have that condition from the get-go.”
This also backs up the importance of measuring BCS and drafting into different management mobs based on BCS and pregnancy scanning results. A study conducted in New Zealand in 2016 by Corner-Thomas found only about 50% farmers actually knew the liveweight of their ewes in autumn, so were unable to make management decisions such as removing light ewes from the mob. Many feed budgeting techniques are based on ‘gut feel’ or on outdated recommendations for feed requirements, not taking into account the increases in mature ewe size.
She analysed the genetic parameters of the relationships between the BCS and the production traits like number of lambs scanned, weaned and the weaning weight of the lamb.
“The weaning weight of the lamb is what the farmers are interested in, so we tried to work out on a genetic level whether BCS is helpful to that, detrimental or has no effect at all.
She says it became evident that it is more beneficial for farmers to measure BCS on farm to influence production rather than using the genetics of BCS for selection.
“The genetics of BCS isn’t going to help in terms of increasing production”. But measuring BCS onfarm can be used to influence your production – so feeding sheep to start off with a higher BCS at mating will then have more condition to be able to lose so that they can feed their lambs, to result in heavier lambs at weaning.
A Massey research paper from 2015 looked at the tools farmers use onfarm and found less than half of farmers used BCS. For those new to BCS, she suggests taking advantage of industry workshops. Being a subjective measure, this type of learning can give farmers something to calibrate against.
“The majority of sheep probably are between 2-4 BCS, and while one step in BCS isn’t a large difference, if you’ve never done it before and you just run your hand over the back of a sheep you could be out by 1 BCS.”
She acknowledges that using BCS on sheep is a lot of extra work on top of shearing and drenching, since it can’t be done visually, but it can definitely help in terms of estimating efficiency.
“Those sheep who start with a higher BCS and have twins or triplets can actually earn you more because its higher income per ewe mated, and the highest cost is the maintenance cost to feed the ewe across the whole year.”
The flocks she worked with were Focus Genetics Romney and NZ Merino. She said due to the Romney basis of the New Zealand flock, they didn’t observe the same level of BCS variation in sheep as is typically seen in beef and dairy cattle.
From her PhD studies, Isabel recommends that there would be a benefit to using a ram breeder that records BCS and the best time for them to record BCS for genetic selection was mating to increase BCS, however it is unlikely to influence production. Measuring BCS on-farm is a valuable tool to be able to feed ewes based on BCS to lift production.
