Late pregnancy nutrition: Have you tested your silage?

Late pregnancy is a critical period on sheep farms, as 85% of all foetal lamb growth occurs in the final two weeks of pregnancy, according to UCD’s Prof. Tommy Boland.

Speaking at the recent Teagasc National Sheep Conference, he said: “If ewes are lambing on March 15, those lambs are about 25% of their final birth weight at the moment.

“The ewe needs to do a huge amount of work over the next six weeks to get that lamb to a good birth weight. At the same time, that ewe is facing a major challenge.

In the period of eight weeks prior to lambing up to the point of lambing, the ewe’s nutrient requirements double. It doesn’t matter if we are talking about energy, protein or calcium – they all double.

“However, the ewe’s intake capacity reduces by about 33% and the only way we can compensate for that is to increase the quality of the diet we feed.

“And, in most systems, this is where we need to supplement with concentrates – particularly in housed, grass silage feeding systems,” he said.

Feeding the ewe

For a housed system, these requirements can be met by forage, concentrates or body reserve mobilisation. The latter is not recommended. Forage quality is central to a successful late feeding programme, he said, and higher-quality forage reduces the requirement for concentrate supplementation.

When silage quality reduces from 79% DMD (dry matter digestibility) to 64% DMD, a three-fold increase in concentrate supplementation rates is required to meet the ewe’s nutritional requirements.

This arises from two issues with low DMD silage. Firstly, intake is restricted and secondly, for each gram of silage consumed, the energy supply is reduced as less of that silage is actually broken down. This results in a situation where extra concentrates are required to meet the ewe’s requirements.

Table: The effect of silage quality and processing on total concentrate requirement during late pregnancy

Source: Adapted Keady, 2017

Boland also stressed that it’s important for farmers to test the quality of silage being offered to ewes.

“Average quality silage will provide about 10.5MJ of ME (metabolisable energy) in late pregnancy. That’s about enough to maintain an 80kg ewe without giving her anything for the lambs.

“If the silage is of higher quality, we will have higher energy intakes and less concentrate supplementation will be required.”

Touching on the physical attributes of silage, he said: “If we feed single-chop or long-chop silage compared to precision-chop silage, intake is reduced by 25%. Sheep are just not as good at processing that long fibre as cattle.”

farm fodder

He added: “Concentrate feeding also has the capacity to negatively influence forage intake. My recommendation would be to not go over 500g of concentrate in a single feed and to space those concentrate feeds out as much as possible across the day.”

If feeding more than 500g of concentrates per day, he recommended, split into two feeds. If about 1kg/day, split into three feeds.

This is especially important where forage quality is poor. Poor-quality forage spends a long time in the rumen, as it takes the microbes more time to break it down.

When concentrates are consumed, the rumen pH drops and the microbes in the rumen responsible for digesting the forage are negatively impacted. This means it takes longer to break down the forage. By spreading out the concentrates as described above we reduce this negative impact on the rumen.

Key considerations in late pregnancy forage feeding:
  • Conduct a forage quality test;
  • Offer high-quality forage in the final six weeks of pregnancy;
  • Provide continuous access to the forage with adequate feed space (minimum of 150mm/animal);
  • Avoid low dry matter silage;
  • Avoid silage with clay contamination;
  • Big bale or single chop silage will reduce intakes by 25%;
  • Poorly-preserved silages (high ammonia and butyric acid contents) are less acceptable to sheep.

Energy and body reserves

Boland also urged farmers to weigh their ewes, adding: “If we underestimate the liveweight of the ewe, we underfeed our ewes.

“If we think our ewes are actually 60kg when they are really 80kg, we can be underfeeding those animals by as much as 6.5MJ of ME or 0.5 UFL.

“In terms of concentrates, that’s about 0.5kg/day that we are underfeeding the ewe by. If we do so, the ewe is going to mobilise body reserves, which are needed for the day the ewe lambs down.”

spring lamb

At lambing, Boland recommended that ewes should be in a body condition score of three.

“If we fail to hit that target, it has an effect on the future performance of our lambs. If the ewe has body reserves to mobilise, it means that the ewe does not need to consume as much energy post lambs.

“The biggest barrier to our ewes in early lactation is consuming enough energy.”

When ewes are in adequate body condition at lambing, he said, they can mobilise body reserves post-lambing to produce milk for the lambs.

“For each 100g of body weight that the ewe mobilises, it’s an energy saving of about 4MJ/day, which is the equivalent of feeding 300g of concentrates per day.

“I wouldn’t like to see the ewe mobilising more than 100-150g/day, but clearly she needs to have those body reserves to mobilise it.”

Boland also discussed research carried out in Lyons Estate, which looked at the effect body condition score at lambing has on the future performance of the lambs. The study compared ewes with a body condition score of 2.3, 2.5 and 2.8 at lambing.

Commenting on the results, he said: “If we take the two extremes (2.8 verses 2.3), where the ewes had a higher body condition score at lambing, the lambs grew about 45g/day faster than their counterparts when the ewe had a body condition score of 2.8.

“It does pay to have that condition there to mobilise in early lactation,” he said.