Swaledale with lambs

Feeding the Ewe in Late Pregnancy

The fourth and fifth months of pregnancy are most important to the ewe and developing lambs and influence both lamb survival and birth weight as well as placing a huge nutrient demand on the ewe due to rapid foetal growth (80-85% of growth). In addition to foetal development, udder development also occurs in the last four weeks of gestation in preparation for parturition and the production of colostrum and milk. Colostrum contains antibodies and energy that is vital for neonatal lamb survival. The quality of colostrum is dependent on the nutrition of the ewe. Undernutrition in late pregnancy may result in poor colostrum production and milk yield, whereas ewes supplied with a diet that meets nutrient requirements will produce better quality colostrum. Providing the correct balance of dietary metabolizable energy (ME) and metabolizable protein (MP) will optimise colostrum and antibody production. A direct link can therefore be made between good nutritional management of the ewe in late pregnancy and improved productivity due to better lamb survival, vigour, growth and development of offspring

In practice, in the weeks leading up to lambing, ewe nutrient requirements double but simultaneously voluntary feed intake decreases by 30%. This fall in appetite is due to the pressure placed on the rumen from the rapidly developing lambs as shown in figure.

To meet the energy and protein demands of the ewe, while considering appetite reductions, the diet provided to ewes in late pregnancy must be nutrient dense.

Body condition scoring (BCS) is a useful way to assess ewe condition from which management decisions can be made. It is recommended that ewes should enter the final trimester of pregnancy with a BCS of 3.0 or above. This ensures that post lambing, ewes can produce good quality colostrum and maintain an adequate milk yield to allow lambs to thrive without it being detrimental to ewe health in terms of use of body reserves. Feeding diets supplying inadequate energy in late pregnancy to ewes with a low BCS may lead to pregnancy toxaemia (twin lamb disease), as well as producing lambs with lower levels of adipose tissue, which is crucial in heat production, thus proving detrimental to lamb survival. It must be noted that over-feeding ewes in late pregnancy may prove equally detrimental by increasing cases of dystocia as well as reducing lamb vigour and lamb survival. Furthermore, over fat ewes are more likely to experience prolapse and are at higher risk of pregnancy toxaemia.

Maximising forage intake in ewes is the most economic strategy to meet nutrient requirements however in late pregnancy and lactation, when nutrient demands are high in the ewe and voluntary feed intake low, forage alone is unlikely to fulfil ewe nutrient demands. Therefore, there is a need for supplementation with a high quality, energy dense concentrate feed.

When selecting a concentrate feed for lambing time, a good starting point is a silage analysis as this will allow identification of the extent of shortfalls in energy and protein supply and therefore make it easier to select a feed to complement. It is important to take note of not only the ME and MP values of the feed but also the feed ingredient composition. Value should be placed on a feed with a good source of digestible undegradable protein (DUP) such as soya bean meal or rapeseed meal as this plays an important role in colostrum quality as well as milk synthesis and yield.

Nicole Welch

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