Throughout the year and production cycle, the ewe goes through different phases requiring varying nutritional requirements. Part of these are minerals which are vital for growth, productivity, and immunity. Various minerals play an important role during different parts of the production cycle, therefore correct supplementation at the right time and quantity is key.
When starting to think about mineral nutrition for your sheep, the following three questions are a good place to start.
- Do you need to supplement?
- Which minerals do you need to supplement?
- What is the best supplement for your system?
The balancing act of mineral nutrition
Ensuring the animal’s requirements are met correctly without under or over supplying minerals involves a very careful balancing act. Deficiency in the animal occurs when the minerals in the feed are not meeting the requirement of the ewe, while an oversupply can cause toxicity. All minerals have a range between deficiency and toxicity, for some this can be a large range whereas for others it is small. Therefore, getting the balance correct for the animal is important to ensure their requirements are being met through the feed and if necessary, supplementing minerals. It is important to account for how the different minerals interact with each other and how that impacts their absorption and utilisation by the body.
Trace elements for sheep
Trace elements are required in small quantities of less than 100mg/kg in sheep diets, and are essential in the animal’s growth, productivity, and immunity. There are seven key trace elements that are required by the animal, these are iron, copper, cobalt, iodine, manganese, zinc and selenium. Each one is required in varying amounts and plays different roles in the animal’s enzymatic and metabolic pathways. Trace elements can play a major role in reproduction in ruminants - poor fertility can occur when one or more are deficient in the diet.
Copper is stored in the liver where it remains until it is re-directed to the cells which require it. It is involved in over 300 key enzymes in the body and its function includes energy utilisation, immune system function, fertility, and wool production. Therefore, copper is critical for growth in youngstock and fertility in lambs and ewes.
Molybdenum, sulphur and iron are antagonists of copper which can impact its absorption and utilisation by the body. Copper deficiency tends to present itself as “Swayback” in young lambs which is a hind limb weakness which leads to paralysis. This occurs due to the ewe being deficient in copper during pregnancy which causes damage to the spinal cord in the foetus. In older sheep, copper deficiency may result in reduced growth rates and poor fleece quality. Copper needs to be managed carefully to avoid toxicity which is when there is a significant build up in the liver. Supplementation of copper needs to be carefully considered and diagnostic testing should be completed to determine if there is a deficiency. White faced sheep, e.g. texels, are highly sensitive and susceptibly to copper toxicity. Blood sampling can be used as a diagnostic testing however a liver sample is preferable to give an accurate indication of the amount of copper stored in the body.
This trace element is essential for the synthesis of vitamin B12 in the rumen, so there is a tendency to discuss a vitamin B12 deficiency as well as cobalt. Cobalt plays a key role in egg development and is important in the early stages of gestation. Research has shown that a deficiency in cobalt throughout the mating period and pregnancy can impact lamb performance and viability. Previous studies have found that cobalt deficient ewes have a higher number of still births and lamb mortalities, while lambs that did survive had lower levels of vitamin B12 in their blood serum. In growing lambs, deficiency signs include poor growth rates, scaly skin behind the ears and on the face, and poor thrive (pine). Cobalt is not stored in large quantities in the body, so a consistent supply is important.
Iodine is important for thyroid development and function including the production of thyroid hormone which is vital for energy utilisation. A deficiency in iodine impacts the thyroid function which influences the production of hormones, affecting health, growth, and fertility. Fertility can be significantly impacted, causing abortions and still births in ewes. Lambs that are born alive may be weak with a higher incidence of neonatal deaths in the flock. The requirement of iodine by the animal feeding on brassicas increases by two to four-fold to compensate for the lack of iodine available for uptake by the animal due to the presence of goitrogens. Therefore, supplementation is required if ewes or lambs are being grazed on brassicas.
This mineral is vital for the growth of the animal through their muscle development and is important for supporting immune system function. Selenium plays a key role in fertility - for ewes it is important for egg production and quality, in tups it is vital for sperm quality. A deficiency in selenium can influence the ewe’s reproductive performance with a higher risk of early embryonic loss. Symptoms in lambs include poor growth rates, born weak and white muscle disease which is a sudden stiffness. If an animal has a selenium deficiency, they tend to have a poorer immune system which increases their risk to other diseases.
Macro minerals for sheep
Macro minerals are required in relatively large quantities in the diet of sheep and are vital for bone development and nervous system health. Macro minerals include calcium, phosphorus, magnesium, sodium, chloride, potassium and sulphur, with each mineral playing a vital role within the body. Generally, grass tends to have sufficient levels of macro minerals for sheep therefore supplementation is not always required.
This mineral is the most abundant in the body with 99% of storage occurring within the skeleton. Calcium is involved in the production of milk, nervous system function, skeletal production and muscle contractions. Other minerals can impact the absorption of calcium by the body, there is a link with vitamin D3 as it is required for calcium absorption, whilst excess phosphorus can lower calcium absorption. In ewes, a deficiency is most likely to be seen during the last six weeks of pregnancy due to the increased demand for calcium. Ewes in late pregnancy are sensitive to sudden changes in diet, housing, bad weather or gathering which can bring on milk fever. Signs of milk fever in ewes include weak ewes which are unable to stand steady and, in some cases, ewes may prolapse.
70% of this mineral is stored in the bones while the other 30% can be found in soft tissues and fluids. Magnesium has multiple functions in the body and is important for nervous system health, bone formation, enzyme system function and metabolism of carbohydrates. Magnesium is particularly important for muscle contractions and important for the rumen microbiome. A key relationship is between magnesium and potassium - increased levels of potassium lower magnesium absorption by locking it up.
Grass staggers, magnesium deficiency, is typically seen in the spring in the first six weeks post lambing due to the low levels of magnesium in the blood of the ewe. It is a risk in the spring due to the grass growing rapidly with low concentrations of magnesium, but potassium levels are high. Other factors which may increase the risk of grass staggers include low body condition, malnutrition, and poor weather. The symptoms include muscle tremors, excitability, shaking or seizures which can be rapidly followed by death. If sheep are being moved onto lush grass, then it is important to observe them and provide adequate magnesium supplements either through mineralised concentrates, licks, or buckets.
Mineral testing and diagnostics
To determine whether mineral supplementation of your sheep is required, it is vital to spend some time piecing the jigsaw together to figure out which minerals may be deficient in the flock. Forage and grass samples can be tested to determine the quantity of minerals that are available for the animal to uptake through their diet. Accurate mineral status of forages and grasses will allow rations to be formulated or supplementation to occur to meet the requirements of the sheep.
Determining whether the animal has a deficiency or toxicity can be done through blood sampling or liver testing. Blood sampling should occur in a select number of animals from each group, once results have been received then suitable supplementation requirements can be established.
There are a variety of different methods that can be used on farms to supplement minerals to support the animal throughout the production cycle. Depending on the regularity of handling, supplementation can be given as a long or short-term treatment. There are a variety of options available such as boluses, drenches, mineralised concentrates or powdered minerals, and each method can provide a consistent supply of minerals to your sheep.
- Buckets can be used, however there is a reliance on each animal utilising the bucket every day which is not guaranteed so there may not be a consistent supply of minerals.
- Powered minerals can have variable intakes if offered as free access unless they are mixed in with some feed which will be dependent on your system.
- Boluses are administered and sit within the reticulorumen of the animal and slowly dissolve and release trace elements over time.
- Drenches may be an option if the sheep are handled on a regular basis to allow the drench to be administered regularly, which can be as often as four to six weeks.
- It is important to remember that boluses and drenches will not cover the macro minerals like calcium or magnesium so you may need to consider an alternative way of ensuring that these are not deficient in the diet.
Author: Dr Cara Campbell
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