Metabolic Profiling in the Sheep Flock – Why and How to Do It
17 October 2024What is metabolic profiling?
Metabolic profiling involves blood testing sheep at key times in the production cycle, such as pre-tupping and pre-lambing or for lambs post-weaning. It is a common management tool used to assess the nutritional adequacy of a ration and to help reduce the risk of metabolic diseases and suboptimal fertility or performance.
Management practices such as body condition scoring, weighing, forage analysis and ration formulation are all necessary to put together an accurate nutrition plan. Metabolic profiling is a useful management tool, that can provide insight at the time of sampling, if the ration is adequate. Blood testing can also be used as part of a mineral audit to assess the mineral and trace element status of the ewes or lambs. While analysing forage for minerals is also important, due to the antagonism that often occurs between minerals, blood testing is another way to assess if the mineral and trace elements are being absorbed.
Reasons to test
In the final 6 weeks of pregnancy 75% of the lamb’s growth occurs, hence there is a massive demand on the ewe at this critical stage. Metabolic profiling can identify potential problems in the run up to lambing including:
- Pregnancy toxaemia (twin lamb disease)
- Hypocalcaemia and hypomagnesemia (staggers).
It can also assess if the energy and protein supply is sufficient which is important for colostrum production and quality. This allows you to take preventative action and correct the issue. Blood testing before mating is useful to identify if there are any trace element deficiencies that may cause sub-optimal fertility.
When to sample
The timing of sampling is important alongside interpretation as some blood parameters will only give you information about the nutritional adequacy at the point of sampling, whereas some blood parameters will provide more historical information.
Sheep should be on their current ration for at least 3 weeks before sampling without any changes. It’s important to ensure they have sufficient access to feed in the period before blood sampling. Any restricted access to feed in the previous 24-48 hours will affect the results with many blood parameters sensitive to changes in short-term feed intake. Avoid sampling straight after concentrate feeding, ideally you want to time sampling before concentrate feeding or 3-4 hours after feeding.
Pre-lambing
Blood testing ewes pre-lambing should be sampled around 3-4 weeks before lambing is due to start, ensuring that the earliest lambing ewes in an average body condition for the flock are selected. The reason for sampling at 3-4 weeks pre-lambing is due to the increase in energy demands in this period, and if sampled earlier then energy problems may be missed. It is not advisable to sample any later than this as making any nutritional adjustments close to lambing would have limited benefits. Groups of at least 6 ewes should be sampled from each management group (single, twins and triplets), sampling is also beneficial on unscanned- flocks as the same principles apply.
Pre-mating
For ewes and rams blood sampling for trace elements can be a useful tool in late summer. This is a key time in the production cycle and the focus is on groups of ewes and rams to assess that they are in optimum condition for mating. Samples should be taken from 4-6 animals.
Post-weaning lambs
It is beneficial to check lambs post- weaning, particularly if there has been a prolonged check in growth rates. This can provide another piece to the puzzle to ensure trace elements are not affecting growth rates. Samples should be taken from 4-6 lambs.
Additional information to provide
When submitting samples for analysis the more information you can provide the more you will get out of the interpretation. Therefore, provide as much information as you can including:
- Average weight and condition score of groups
- Number of lambs carried (if scanned)
- Breed
- Ration formulation for each group including forage analysis if applicable
- Any additional minerals or compounds provided
Tests and analysis
A range of parameters can be measured to assess energy, protein and mineral status, as well as picking up indications of disease. The following are most commonly tested for, but other tests are also available upon request such as plasma inorganic iodine (PII) to assess iodine status.
Depending on the type of management group you are testing, the blood parameters most commonly tested include:
- Energy status: beta-Hydroxybutyrate (BOHB). Note non-esterified fatty acids (NEFAs) are not usually used as they are difficult to interpret in ewes as they are likely to be elevated in late-pregnancy due to the high demands of the growing lamb.
- Protein status: urea/urea-N, albumin, globulin
- Major minerals: Magnesium and calcium
- Trace elements: copper, GSHPx (as a marker of selenium) and vitamin B12
Interpreting results
Energy and protein status (optimum levels based on pre-lambing):
| Blood Parameter | Optimum levels | Interpretation |
|---|---|---|
| Beta – hydroxybutyrate (BOHB) mmol/litre | <1.1 – scanned ewes <0.8 – unscanned ewes | High levels will indicate if the ewe is in negative energy balance. Sheep with high BOHB’s may develop twin lamb disease and be at risk of poor colostrum production. |
| Urea Urea- N mmol/litre N.B Urea = Urea-N x 2.14 | >2 – group average >3- individual >4 | Low levels of urea may arise where there is reduced availability of rumen degradable protein. Poor protein availability results in poor colostrum quality and yield. Elevated levels are an indicator of excess rumen degradable protein. |
| Albumin g/litre | >30 | This is a measure of long–term protein status. Albumin is produced by the liver therefore if levels are low this could suggest liver damage e.g. by fluke, disease or the ewe has been protein deficient in their diet for a prolonged period. |
| Globulin g/litre | 25-50 | High levels indicate a chronic inflammatory condition such as lameness, liver fluke and Johnes disease. |
Mineral and trace element status (optimum levels for all sheep categories):
| Blood Parameter | Optimum levels | Interpretation |
|---|---|---|
| Magnesium mmol/litre | 0.7-2.0 | Important for calcium mobilisation at lambing to help maintain muscle function, reducing the risk of slow lambing, retained foetal membranes and milk fever, as well as hypomagnesaemia (staggers) during lactation. There are no body stores of magnesium so low levels in the diet will result in low blood levels very quickly. |
| Calcium mmol/litre | 2-3 | Values below this range are suggestive of hypocalcaemia. |
| Copper (µmol/litre) | Serum: 3.0 -8.0 Plasma: 3.0 -9.0 | Important role in health, fertility and immunity. Blood levels tend to be relatively constant unless excessive overfeeding or underfeeding. Liver copper analysis will give a more accurate indicator of copper status. |
| GSPHx (Selenium) iu/ml PCV | >50 | Selenium is essential for growth and fertility and also plays a vital role in immune function. Blood test Indicates the selenium status of the animals over the past few months. Low levels at mating results in early embryonic loss, therefore reduced ewe productivity. |
| Vitamin B12 (cobalt) pmol/litre | Suckling: >350 Weaned: >500 | Vitamin B12 is produced in the rumen from dietary cobalt. It is required by the enzymes which regulate energy metabolism. Cobalt deficiency in ewes is implicated in increased stillbirths and neonatal mortality. |
| Plasma inorganic iodine (PII) (µmol/litre) | 80-300 | Pooled iodine results give an indication of the overall iodine status in the group tested. Results are indicative of dietary intake in the previous 24 hours. Less than 80 µmol/l would indicate a dietary deficiency in the majority of the group at the time of sampling. |
These values are only a guide and should be interpreted alongside the individual ewe or lambs information including health status, body condition and stage of pregnancy if applicable.
Thanks for subscribing! Please check your email for further instructions.
How the metabolic status of ewes and lambs affects survival
A study in 2020 by Edinburgh University into lamb survival, looked at the metabolic status of ewes and found that protein deficiency and negative energy balance in ewes can have an affect on both lamb mortality in the first 24 hours of life and growth rates until weaning. The trial used the university’s March -April lambing lowland flock of 250 ewes, which had been scanned and where in the target body condition score for lambing.
The key findings from this study showed that ewes with lower blood albumin levels (a long-term protein indicator) were more likely to lose a lamb in late pregnancy or the first 24 hours of life. In this study they found half of the flock had low albumin levels going into lambing, despite being rationed according to their energy and protein requirements and predominantly being in good energy balance. This highlights the importance of year-round management of the ewe throughout her production cycle, regular body condition scoring and health management of issues such as fluke.
The study also showed that ewes in negative energy balance (detected by high BOHB levels) were five times more likely to have a lamb with insufficient antibody levels. This is associated with poor colostrum transfer and meant lambs were five times more likely to be poorer growers until weaning.
Body condition scoring is also strongly linked to metabolic status and hormone levels in ewes. FAS technical note has more information on body condition scoring and targets at key production stages: https://www.fas.scot/downloads/tn702-body-condition-scoring-mature-sheep/
Conclusion
Metabolic profiling in sheep is a useful nutritional tool to objectively assess the animals nutritional status and allow fine-tuning of the diet to ensure optimal performance and fertility. Alongside ration formulation, forage analysis and body condition scoring it provides another layer of information to ensure the ewes energy and protein requirements are being met for the stage of pregnancy. It can also be used to identify mineral and trace element deficiencies in ewes, rams and lambs.
Mary Young, SAC Consulting
Sign up to the FAS newsletter
Receive updates on news, events and publications from Scotland’s Farm Advisory Service