21 Nov 2016
Louise Silk discusses the importance and impact of offering quality nutrition when feeding pregnant ewes.
Louise Silk
Job Title
A factor to consider is whether there is enough feed space for ewes to access the concentrates and forage components of their diet. Image: Fotolia/andystjohn.
Poor ewe nutrition, particularly in the final six weeks of pregnancy, will result in poor welfare, as well as reduced performance in ewes and their lambs.
Nutrition plays a vital role in the functioning of the immune system. Ewes on a poor diet will suffer a higher incidence of disease.
Of particular significance around the periparturient period would be an increased susceptibility to mastitis and increased worm egg output on to the pasture, which will have knock-on effects on lamb growth later in the season.
Conditions such as hypocalcaemia and pregnancy toxaemia would also be more likely when nutrition is inadequate. A reduction will also occur in the quality and quantity of colostrum and milk, with subsequent increased risk of neonatal disease and poor growth rates in the lambs.
Clinical and subclinical conditions associated with trace element deficiencies may also be seen.
Achieving good flock nutrition can be almost as much about how the diet is presented as it is about the diet itself. A number of factors should be considered when feeding sheep:
When considering the actual diet of ewes pre-lambing, it is important to ensure all the requirements of the ewes are being met.
This includes not only the basic components of the diet, such as energy and protein, but also minerals, trace elements and fibre.
Scanning data can be used to determine the number of lambs expected. This information can be taken alongside body condition scoring data (taken at eight weeks pre-lambing) to group the ewes, thus ensuring each ewe is receiving the correct nutrition according to her individual circumstances. Body condition scoring should be carried out at least four times per year and the nutrition of the ewe adjusted accordingly, so as to prevent major problems developing.
It is important to remember it can take six to eight weeks for a ewe to gain one body condition score on good grazing (Phillips et al, 2014). The ideal body condition scores for lowland, upland and hill ewes pre-lambing are 3, 2.5 and 2, respectively.
The major components of sheep nutrition are energy and protein. When assessing a diet, it is useful to examine the metabolisable energy (ME; MJ/kg), which is the amount of energy in the feedstuff available to the animal. ME is made up of fermentable metabolisable energy and non-fermentable energy sources (Table 1).
As the fetal lambs increase in size in the uterus, the energy requirements of the ewe increase, but the space available for the rumen decreases. As the pregnancy progresses, the diet will need to become increasingly dense in energy through improved forage quality or the addition of concentrate feed. A fine balance exists, however, between feeding too much in concentrates, which may induce a ruminal acidosis and reduce forage intakes, and ensuring the correct amount of energy is being provided.
The other major component of the diet is protein. A lack of dietary protein will result in increased susceptibility to disease (in ewes and their lambs) as well as poor colostrum and milk production, and poor production overall. It is vital protein and energy components of the diet are balanced so the rumen microbial system functions at an optimal level. The different types of protein available are outlined in Table 2.
Effective rumen degradable protein provides sufficient protein for most of the production year and, in most cases, for single bearing ewes, even in the final few weeks of pregnancy. For ewes carrying twins or triplets, it is usually necessary to provide some digestible undegradable protein (DUP) in the final few weeks of pregnancy to meet their metabolisable protein requirements.
It is also important to consider the dry matter intake (DMI) of pregnant ewes. DMI is equivalent to 2% to 2.5% of bodyweight during pregnancy (Phillips et al, 2014). It is essential any diet is formulated to maximise forage intakes of the ewes, with supplementation with other concentrate feeds being used only to make up a nutritional deficit.
The more concentrate feed fed, the greater the chance of dietary substitution, where forage intakes will be adversely affected. It should be noted some live weight loss (50g/day for the final three to four weeks of pregnancy), through the mobilisation of body fat reserves, is acceptable in ewes in late pregnancy, providing they are in good body condition. Another consideration should be the digestibility of the diet, as this will affect the rate of passage of feedstuffs through the gut.
Indoor lambing provides the opportunity to control the diet of the ewe in late pregnancy much more readily than in an outdoor lambing system. Forage analysis is a good place to start when assessing or formulating a diet for pregnant ewes. The quality of forage can vary dramatically from farm to farm and season to season.
Forage analysis is often carried out for free by feed manufacturers, but it is important to take a representative sample (three core samples from a silage clamp or five cored samples from a stack of big bales; Phillips et al, 2014). Home mixing of the diet is another option for housed animals. A huge array of feedstuffs can be used to make up a sheep ration, but it is essential the diet has been correctly formulated to ensure it delivers on all aspects of nutrition.
For an outdoor system, as a guide, young spring grass can provide ME of more than 12.5 MJ/kg dry matter (DM) with crude protein at 19% to 24% and DUP greater than 5%. However, it is important to note, in wet weather, the DM of spring grass can be very low and it may then be necessary to supplement the ewes with dry feedstuffs, such as hay or feed blocks.
The other factor to note, if relying on grazed grass in late gestation, is the quality of the grass decreases as the sward height increases. The optimal sward height would be 4cm to 6cm and good management is required to maintain swards at the optimal height for grazing (Phillips et al, 2014).
Supplementary compound feeds can vary considerably in their constituents. It is important to check the full formulation sheet, rather than rely on the information on the outside of the packaging.
The way feed is delivered can be almost as crucial as the feed itself. Concentrate feeds can be fed at a flat or step rate pre-lambing (ensure no more than 0.5kg concentrates per head, per feed) and may be fed in troughs (ensure feed space is adequate) or on the floor. It is important farmers choose the most practical option for their farm. This may be a TMR (ideal for optimal rumen health if chop length and formulation are correct) or feed blocks (good for outside lambing supplementation, but can be expensive, with variable intakes).
Another way to assess the adequacy of pre-lambing nutrition is by carrying out metabolic profiling on a sample of ewes. This will give a more immediate assessment (in comparison to looking at body condition changes) of the nutritional status of the ewes and determine the risk of pregnancy toxaemia.
Metabolic profiles look at the energy reserves of the ewes (beta-hydroxybuterate), as well as both long-term and short-term indicators of protein intake (albumin and urea, respectively). Metabolic profiling involves sampling at least five ewes per group of twin and triplet-bearing ewes, at three to four weeks before the expected start of lambing.
This ensures a representative sample for the flock is taken and sufficient time is available to effect a change in the diet, should it be necessary, before lambing commences. It is important to sample ewes before feeding, or at least four hours after feeding, if concentrates are used, as feeding can influence urea levels.
While metabolic profiling can be a useful tool, it should be used in conjunction with regular body condition scoring, scanning, ration analysis and grouping of ewes, such that their management and nutrition may be tailored to their individual requirements.
The mineral composition of the pre-lambing diet is also important. Hypocalcaemia in ewes generally results from poor calcium mobilisation from the bone, rather than low calcium (Ca) intakes. Excess Ca in the diet can lead to reduced Ca mobilisation and, ultimately, inadequate mobilisation when Ca is in high demand for skeletal calcification in late pregnancy and for colostrum production (Sykes and Russel, 2000).
Excess phosphorus (P) in the diet, relative to its calcium content, will reduce bone resorption and act as a predisposing factor for hypocalcaemia (Treacher and Caja, 2014).
The dietary Ca to P ratio should be in the region of 1.5:1 to 2:1. Sudden diet changes, including inadequate feed access and other stressors (handling, transport, shearing, vaccination and inclement weather), should be avoided as this could precipitate hypocalcaemia in ewes in late pregnancy.
An array of trace element supplements are available for sheep – from boluses, to injectable or oral preparations, to pasture dressings. Supplementation can be costly, particularly if carried out unnecessarily. Many farmers supplement with one or a number of trace elements, despite no evidence it is necessary. Equally, flocks may exist where production losses go unnoticed or unaddressed where the trace element status may play a role.
The pre-lambing period may not be when trace element supplementation is occurring, but its need may become apparent in the immediate postnatal period – for example, high still birth rates associated with iodine deficiency. Vitamin E and selenium are key to lamb viability, as well as immune function. Selenium also interacts with iodine to influence thyroid function (Robinson et al, 2002).
When assessing key trace elements in ewes, and whether there is a need for supplementation, some key points to remember are:
