Flock Focus: Feeding the ewe throughout pregancy

Lamb death rates average about 15% in the UK – something which could be slashed by better feeding of ewes in late pregnancy, according to recent trials.

John Vipond, senior sheep specialist at the Scottish Agricultural College, is convinced that changing the formulation of ewe rations could dramatically improve flock productivity.

“Having carried out trials and spoken to technical people who understand rations, we are all in agreement that the current sheep feeding strategies are underfeeding protein in late pregnancy.

“The current figures are based on lamb birth weights in the 1960s – but sheep are much more productive now, and lambs are bigger, so we need to reanalyse those figures.”

In the last three to four weeks of pregnancy, ewes need high levels of good quality protein to help the lambs develop and grow a decent covering of wool – with those carrying triplets clearly in need of even greater help. Without sufficient protein levels, the lambs’ growth rates will suffer, both before and after birth.

Preventing poor immunity

If the ewe is not receiving sufficient balanced food, she will prioritise what is available, first for the lamb, then for her own maintenance, says Dr Vipond. “If she doesn’t have enough left over for immunity, she will become immuno-compromised, and that’s when you see a massive increase in faecal egg counts in late pregnancy, when a ewe can produce enough worm eggs to infect 15 lambs.”

A ewe with poor immunity will not be able to pass on beneficial antibodies to her lamb via colostrum, leaving the lamb vulnerable to sickness – particularly clostridial diseases – in its first few weeks of life. “About 15% of lambs die in the perinatal period, which is a very disappointing figure. If you increase the birthweight and colostrum quality that will improve.”

Colostrum is formed in the last four to six weeks of pregnancy – and antibodies from the clostridial vaccine will be passed on to provide passive immunity for the lamb. “Better feeding will boost antibody levels by 25% – that is a big difference. In the first 12 hours after birth, those antibodies will provide the lambs with immediate protection against disease.”

Of course, if the ewe’s immunity is compromised, she is more likely to succumb to diseases around lambing time herself. “We try to keep ewe deaths to 2% a year, but on a lot of farms it’s up to 5% or more. Cull ewes are worth £115-120, so you really don’t want to be losing them due to inadequate feeding. Anything we can do reduce lamb and ewe deaths has got to be worth investing in.”

Providing correct protein type

However, it is not just the protein content of the ration that producers must consider – it is the type of protein that is important. “This is not about feeding more of what you used to feed, it’s about feeding better quality feed. Crude protein tells you nothing about the quality of the protein; what is required is digestible undegraded protein (DUP), which cannot be broken down inside the rumen.”

Most protein in compound feeds is rumen degradable, not all of which can be readily used by the ewe, says Dr Vipond. Feeding higher levels of this kind of protein will not only be ineffective, it will actually use up the equivalent of 150g of barley a day, as the ewe must use energy to convert it into urea to excrete.

Instead, producers should feed soya bean meal or specialist products with protected amino acids. “Soya has about 130g of DUP a kg, whereas products which protect that protein can have 260g/kg.” As a rule of thumb, they should supplement 100g of soya a day for each lamb carried, depending on the sheep breed and ration quality, for the last three or four weeks of pregnancy. In trials, this slashed worm burdens by 60-70%, and associated egg output by 80% or more. “It is a good alternative to anthelmintics.” Feeding the equivalent of 40g of DUP extra a day in the late stages of pregnancy also boosted birthweights by 500g each for twin lambs. And continuing with 100g of DUP extra during early lactation increased lamb weight gain by about 20%, says Jos Houdijk at the SAC. “Carry-over effects of late pregnancy feeding are small, so most benefit is gained by continuing supplementation during lactation.”

At a cost of about £4 a head, farmers will get a potential return of £10-12 by reducing ewe and lamb mortality. And with lambs reaching slaughter weights earlier, producers can secure premium prices, adds Dr Houdijk.

Maximising feed efficiency

For maximum efficiencies, producers should be feeding home-grown, high quality silage or grass throughout pregnancy, says Dr Vipond. “There is plenty of rumen-degradable protein in silage, to keep the rumen bugs healthy – and this year there is a lot of good quality silage about. If you have silage with metabolisable energy (ME) of 11 MJ, and crude protein of 14-15%, you really don’t need to feed any extra energy – all the ewe will need is the DUP supplement.”

In trials, he looked at adding barley to grass silage feed in 200g a day increments. “With a silage ME of 11.3 MJ, I found that all the barley did was increase the fatness of the ewe at lambing – it did nothing to the birthweight of the lamb.”

The trials also achieved high levels of silage intake, but to replicate this on farm, producers need to pay attention to trough space and pushing up the silage twice a day. “Ewes will eat 1.4% of their bodyweight in late pregnancy. If you have an 11 ME silage, that’s 15.5MJ a day – add 200g of soya and you’re up to 17MJ. But you need to make sure the silage is readily available, and sort out ewes carrying twins and triplets four weeks prior to lambing. For ease of use, just sprinkle the soya on top.”

For growers with poorer quality silage, it is simply a case of formulating a balanced ration using cereals, he adds. “It’s very important to have your silage analysed for ME, protein and trace elements. If you have a trace element deficiency, you need to supplement that element. Balancing your ration and feeding more DUP is effectively the same thing. Let’s use the science and see how to supplement our sheep better. And don’t just buy the cheapest compound you can find – buy the one that provides the best value for your sheep.”

This year’s dry summer has meant some parts of the UK have struggled with poor grass yields. “If your sheep are a bit thin, feed some concentrates prior to scanning, so they are all in good condition at 70-80 days. But if you have had lots of grass and the sheep are in good condition, feed silage four or five days a week, and straw over the weekend. If you put a big bale in the pen they will eat it and bed themselves down at the same time.

Correct diets can boost ewe and lamb immunity and reduce worm burdens.

Assessing sheep condition

“The important thing is to go through the sheep, assess their condition, and try to do something about it if necessary.” Ewes lambing in February or March should be at condition score three at lambing time, and may need extra feed due to the lack of grass at that time of year, says Dr Vipond. “They will need good body reserves to produce sufficient milk.” Those lambing at grass later in the spring should be at condition score 2-2.5, as there will be more than enough grass to meet their requirements.

Producers who make red clover silage may need to feed even less soya in late pregnancy. “You don’t want to feed red clover in early pregnancy as it contains oestrogen which affects placenta development. But it is safe in late pregnancy, and contains a PPO enzyme which helps to reduce the degradability of protein – so you have a better protein supply and higher feed intake as red clover is so palatable.”

• Read more from our Flock Focus series

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