Nutrition hugely affects all aspects of sheep health and production. Poor nutrition has negative effects on ovulation rate, early embryonic loss, lamb vitality, peri-natal metabolic disease and passive transfer of antibodies through colostrum.
Nutrition hugely affects all aspects of sheep health and production. Poor nutrition has negative effects on ovulation rate, early embryonic loss, lamb vitality, peri-natal metabolic disease and passive transfer of antibodies through colostrum. A reduction in any or all of these factors will ultimately affect the number of lambs sold and therefore the profitability of the farm.
The main limiting factor affecting nutrition is how much a ewe can eat. It is generally thought that a ewe can eat 2-2.5% of its body weight in dry matter. This equates to about 1.5-1.8kg dry matter for a mule ewe per day and all the nutrient requirements need to be included in this small amount of feed. A ewe in the last few weeks of pregnancy will have a reduced dry matter intake (DMI) due to the growing lambs in the abdomen. Another factor affecting DMI is the access to feed, for housed sheep on ad lib forage there should be 15cm feed space per ewe and 45cm feed space for concentrate feeding. DMI is also affected by body condition score, lameness, access to water, amount and type of fibre in the diet, palatability and water content of the diet. Maximising DMI will mean it will be easier and cheaper to get all the nutrient requirements into the ration.
The main nutrients are protein and energy; the requirements for both of these increases dramatically in the last third of pregnancy, just when DMI goes down! For a typical ewe, scanned for twins, the energy requirements increase from 11.4 MJ/day 50 days before lambing to 18.3MJ/day 1 week before lambing (note this increases further still in lactation); the protein requirements increase from 112g/day to 150g/day.
Energy is vital for lamb growth and milk production. Energy comes in many forms, for example molasses which is rapidly digested, slower digested starchy feeds and digestible fibre which takes much longer to release its energy but is vital for rumen health. Any deficiencies in energy intake will lead to the breakdown of fat which releases ketones and the development of twin lamb disease (ketosis). This can be easily diagnosed by a vet with a ‘pen side’ ketone meter; levels over 1.6mmol/l indicate an energy deficit.
Dietary Protein is essential for udder development, improved immunity, reduced worm egg production, milk/colostrum production and increased birth weights. It has been shown that a good source of bypass protein (DUP) such as soya, is preferable in the last third of pregnancy and has the most beneficial effect on production traits. Rumen degradable protein (RDP) such as urea, does not have the same effect on these production factors but is vital for rumen health. Therefore, when assessing a diet, it is not enough to assess the crude protein percentage but also to assess the protein source and whether there is adequate DUP.
Getting it right
Assessing nutrition in the flock begins with assessing the forage for protein and energy and then balancing the ewe requirements with concentrates and anticipated DMI. This is fine on paper and a good starting point, but what actually happens may be totally different. Actual intakes should be assessed, if they are not eating the anticipated amount then there will be a nutrient shortfall.
The ewes themselves should be assessed for nutrient levels, this can be done by:
- Energy: measure ketones (BHB) from several animals in each management group 2-4 weeks prior to lambing to ensure adequate energy intake
- Protien: measure albumin and blood urea 4-8 weeks prior to lambing to assess protein intake. (This should be done 3-4 hours after a concentrate feed
If there are any problems detected with intakes or nutrient status then the diet should be ‘tweaked’ appropriately or the way that it is fed improved so as to improve DMI and therefore nutrient intake.
Energy and protein are the main nutrients and most commonly involved in cases of poor flock performance however other nutrients are also required by ewes during pregnancy/conception.
- Vitamin E contributes to lamb vigour at birth
- Selenium is involved in thyroid function, immunity and embryo survival
- Cobalt is involved in immunity, milk production and lamb vigour
- Iodine is required for thyroid function, embryo survival, lamb vigour and brown fat utilisation
- Copper is required for nervous system development
- Calcium required for normal ewe metabolism
These nutrients/trace elements are important but it is vital that they supplemented appropriately as toxicities can easily occur (especially copper). It is always worth assessing the mineral status of several animals prior to tupping and about ideally 100 days into pregnancy. Only supplement if it has been shown there is a deficiency in the flock.