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Due to the massive nutritional demand on ewes in late pregnancy and the importance of having sufficient colostrum at lambing, it is vital both the energy and protein content of late pregnancy diets are up to the mark.
Starting with energy first, a ewe’s energy requirement will start to increase from seven to eight weeks before lambing and follow a rising trend.
The increase in nutritional demand is occurring at the same time as the animal’s intake capacity is coming under pressure due to a rapidly growing foetus/multiple foetuses. It is for this reason that the energy content of the feed, which is generally dictated by ingredient choice and inclusion level, is critically important.
Soya bean meal is the Rolls Royce of protein sources
The energy content can be classified by two measurements: the net energy system (UFL) and the metabolisable energy system (MJ ME).
Looking at the net energy system to classify the value of feed ingredients, one unit is called a UFL, with the standard comparison for one UFL being 1kg of barley as fed.
As can be seen from the table, cereals such as barley, maize and wheat are all good energy sources. The pulps, such as molassed sugar beet pulp and citrus pulp, are also good sources of energy and have the benefit of being safer from a point of view of being higher in fibre.
At present, however, citrus pulp is not readily available and the volumes available represent poor value at current prices.
Oats and soya hulls are also strong ingredients from the point of view of being safer when included in a mix or fed at high quantities, although they possess lower energy content.
Protein content
The desired protein content in a ration will be influenced by the feeding rate, protein content of forage and litter size. The protein content of a ewe’s diet is generally not an issue until the final weeks of lambing, with weeks two and one pre-lambing the most critical (protein requirement typically increases from about 130g to over 200g/day).
An 18% crude protein content is the most common feed type sold for ewes in late pregnancy or early lactation. This is generally adequate in most situations, with the exception of very poor-quality forage or higher litter sizes.
In the latter case, some recent recommendations by Teagasc suggest protein content may need to be increased to 19% to 21% for high-prolificacy flocks.
However, it is also important to note that where the concentrate feeding rate increases and comprises a higher percentage of the diet, the overall protein intake will be greater and may be sufficient to meet an animal’s requirement. An example of this is all-concentrate diets where forage quality may be poor, but volumes fed are not significant.
As is the case with energy ingredients, there are significant differences in the feeding value of protein ingredients.
Soya bean meal is the Rolls Royce of protein sources as it has a very high energy content and is a good source of bypass protein – important for udder and milk development in late pregnancy.
While sunflower has a high protein content, it is very low in energy and as such should be avoided. Rapeseed meal also comes into this bracket, with the added complication of palatability issues but with the correct formulation, it may be use succesfully.
Some of the distillers grain ingredients are relatively good protein and energy sources, but there is also a warning point about the possibility of variable copper and mineral levels that could lead to issues at high inclusion rates (not recommended above 25% to 30%).
Feed selection
The advice on feed selection boils down to investigating ingredients and inclusion rates. The target is greater than 0.9 to 0.94 UFL or an ME of 12 MJ ME to 12.5 MJ ME. Some millers or feed labels do not list inclusion rates. By law, ingredients have to be listed in order of their inclusion rate.
Watch out for low-value ingredients being present at the start of the ingredient list and, likewise, do not let a high protein feed that is based on low energy ingredients mask low energy content.
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