While the focus in most mid-season lambing flocks at present is the management of late-pregnancy nutrition, planning for early lactation nutrition also merits consideration.

The milk production ability of the ewe will be the key driver of lamb performance during the first seven weeks after lambing and can have knock-on effects on lamb performance for the remainder of the year.

There are a number of factors that will influence the ewe’s ability to produce milk, including her age, genetic make-up and litter size. However, ewe body condition score (BCS) and her potential to mobilise her body reserves during periods of energy deficit, along with the diet offered, will have a major influence on milk production and lamb performance.

The first seven weeks of lactation place a number of stresses on the lactating ewe.

Firstly, in many mid-season lambing systems, the ewe will undergo a change of diet and environment as she is turned out to grass after lambing.

Secondly, and importantly, her nutrient requirements are rapidly increasing during the first month of lactation to produce sufficient milk to support lamb growth.

A typical twin-suckling ewe will need to produce between 2.5 and 3.0 litres of milk per day to support lamb growth rates of 300g/day.

Lambs are highly efficient at this stage of their lives and can convert one kilogramme (kg) of milk dry matter (DM) into 1kg of liveweight during early lactation.

Ewe milk is approximately 20% DM, meaning the lamb must consume 5kg of milk in order to increase liveweight by 1kg. This level of production has been equated to a cow producing 25 litres of milk per day.

Table 1 shows the metabolisable energy (ME) and metabolisable protein (MP) requirements during the first two months of lactation for an 80kg ewe rearing two lambs.

In order for her to produce 3kg of milk, she requires approximately 34.3MJ of ME and 309g of MP. This is assuming she does not mobilise body reserves, which is rarely the case.

The early lactation ewe is physiologically and physically unable to consume enough feed to meet these requirements during the first month of lactation in most situations.

The ewe’s intake capacity drops during late pregnancy due to the physical encroachment of the uterus on the rumen and her intake capacity does not reach its full potential again until approximately six weeks after lambing.

Demands of production

At the same time, the demands of milk production greatly increase her energy and protein requirements. This forces the ewe to mobilise her body reserves in order to compensate for this nutrient deficit in an effort to maintain milk production.

Body reserve mobilisation is a key element of flock nutrition during periods of high demand, particularly during late pregnancy and early lactation. While some level of BCS loss can be tolerated during late pregnancy, this BCS is better utilised during early lactation when demands are highest.

Supplementation, if necessary, is also usually easier to manage during pregnancy as opposed to early lactation.

It is recommended that the average BCS of a lowland flock should be 3.0 at lambing and the ewe can afford to use approximately 0.5 of a BCS unit during lactation. A 0.5 BCS unit drop is the equivalent to 100MJ of ME. Spread over a seven-week period, the daily energy supply coming from this level of BCS change is equivalent to the energy content of 150g of barley.

Performance

How the ewe is managed during late pregnancy is crucial to ensuring she has adequate body reserves available during lactation.

Ewes that are either too fat or too thin at lambing will have an altered pattern of body reserve mobilisation during early lactation compared with ewes lambing at the correct BCS, which can negatively impact flock performance.

As can be seen in Table 1, allowing the ewe to lose either 50g or 100g of liveweight per day during early lactation will reduce the energy required in the diet.

This energy allows the ewe to compensate for her reduced intake potential during the first five weeks after lambing and to maintain performance.

Excessive mobilisation of body reserves is dangerous and can severely affect the health and performance of the ewe, meaning feed intake must be maximised, regardless of the level of body reserves available for mobilisation.

Meeting the intake requirements of the lactating ewe can be difficult given the potential volatility in spring grass growth and indeed DM content.

One of the key questions around this time is often if there is a need for concentrate supplementation and what are the benefits to supplementation during lactation?

In terms of energy content, spring grass compares quite favourably to barley. Good-quality spring grass usually contains between 12.2 and 12.4MJ ME/kg DM, while barley contains around 13.2MJ ME/kg DM.

Attractive option

But the comparison is not quite so close on price. The cost of producing 1kg DM of grass will vary from farm to farm, depending on inputs etc, but will cost approximately 8c. On the other hand, barley will cost close to 15c, making grazed grass a much more attractive option on price.

Supplying ewes in the correct BCS with adequate quantities of good-quality grazed grass has the potential to support flock performance during early lactation without the need for supplementation.

Research carried out at UCD in recent years on housed lactating ewes offered zero-grazed grass would suggest that where ewes have access to sufficient quantities of good-quality grass, ewe milk production during the first five weeks of lactation will not be improved from supplementing the lactating ewe with concentrates.

Concentrate supplementation also appears to reduce the grass DM intake of the ewe while not improving total DM intake.

However, this work needs to be repeated again with ewes grazing in a normal environment before any final conclusions can be drawn on the ability of grass alone to maintain ewe performance.

The substitution rate of concentrates in place of grass is also linked to grass quality, particularly fibre content, and where grass quality or supply is poor, concentrates have the potential to increase total DM intake.

Further work is also needed in this area to assess the role of concentrates when grass supply is limited or of poor quality.

Maintain performance

The ability of the ewe to maintain performance from grass is subject to the ewe mobilising BCS to meet energy deficits.

Body reserves must be available to supply energy and allow the ewe to maximise the utilisation of nutrients, especially protein, coming from grass.

In our research, where ewes received some level of concentrate supplementation during early lactation, they were heavier at weaning.

This is most likely as a result of the energy supply coming from the concentrate reducing the level of body reserve mobilisation required for energy.

The highest rate of BCS loss will also be during the first two to three weeks of lactation when demand is highest and intake ability is still increasing.

The potential of grass to meet the ewes’ nutrient requirements during early lactation is also very much reliant on the ewe having access to high-quality grass, not being forced to over-graze (post-grazing sward heights of between 3.5cm and 4cm) and the dry matter content of the grass.

As grass dry matter decreases, the dry matter intake of the ewe will also decrease, reducing the nutrients available to the ewe from grass. Concentrate supplementation may be necessary to maintain DM intakes.

Our research would also indicate that any changes or stresses placed on the ewe during the first six weeks of lactation, such as health problems or extreme weather conditions (remember March 2013) which reduce or affect feed intake, can quickly lower the ewes’ milk production levels.

One clear message coming from our research, and indeed from research in other institutes, is that in order to give the ewe and her lambs the best chance during early lactation, it is vital to ensure she has adequate body reserves available at lambing time.

Frank Campion is in the final stages of his PhD at UCD Lyons Research Farm. Tommy Boland is senior lecturer in ruminant nutrition and sheep production.