Mineral imbalances in finishing lambs primarily impact growth rates and therefore time to finishing and slaughter. There are several reasons why mineral problems arise in finishing lambs, here we discuss ones that are commonly seen on farms.

One of the reasons that problems arise is due to the lamb running out of minerals from the stores that are developed during pregnancy. When the ewe is pregnant, she will transfer minerals to the foetus through the placenta and that lamb will be born with a certain amount of minerals. Ewe mineral status during pregnancy will determine the amount of minerals that the lamb will be born with in their stores. Similarly, in the early stages of life, the lamb relies entirely upon minerals to be transferred through colostrum and milk until it begins to eat forages. So, the ewe has a direct effect on what happens to that lamb from birth to finishing. How much and to what extent some of these minerals have been stored can influence how effectively the lamb reaches finishing.

Lambs have a maintenance requirement for minerals as well as a growth requirement, therefore their demands for minerals are higher than ewes. During the period from birth to finishing, the requirement for the lamb to grow rapidly is significant and certain minerals are important for growth, including selenium which is involved in muscle development.

Disease and parasite burdens can impact growth rates in lambs. At times it can be difficult to separate whether a nutritional imbalance is causing the disease and parasite burden or vice versa. Therefore, it is important to tackle both in tandem and remember that minerals are strongly involved in the immune system, such as helping immune response and adaptive immune defence, and anti-inflammatory and antioxidant functions.

A quite simple reason for problems in lambs is poor quality diets which are not providing sufficient energy and protein required for growth of the lamb. Similarly, antagonism within the diet, particularly between minerals can cause reduced uptake and therefore, reduced growth rates. Antagonism within the diet is complex, there are many factors which can influence the interactions between minerals and uptake including soil pH, grass growth rate, plant species and fertiliser. This is particularly important to consider if out-wintering lambs on certain crops, e.g. kale which is goitrogenic.

Balancing act

A key way to consider minerals is to think about it as a mineral imbalance rather than deficiency or toxicity. Getting the balance right in the diet is important as an undersupply can lead to deficiencies or an oversupply can lead to toxicity. Each mineral has a different level of risk - some minerals have a wide range whilst others are significantly narrower. A prime example would be copper which has a narrow range - if it is under supplied, lamb growth rates decrease and in replacements there may be issues with fertility. Whereas in certain breeds, particularly white-faced ewes, like Texel, there is a higher risk of oversupply of copper which is stored in the liver and is released into the bloodstream, causing the animal to become poorly and in worst case, potentially death.

In finishing lambs, there are three main minerals which are considered important for growth and a strong immune system, these are cobalt, selenium and copper. Generally, in finishing lambs, these are the three most common mineral problems which arise on farm.

Cobalt/B₁₂

Lambs do not actually have a requirement for cobalt, their requirement is for vitamin B₁₂ and due to their microbiome inside the rumen, the microbes convert cobalt ingested in feed into vitamin B_12. The role that vitamin B₁₂ plays in the lamb is the efficient conversion of feed into glucose, if there is insufficient vitamin B₁₂ being produced in the rumen then this will affect feed efficiency and therefore, weight gain. In finishing lambs, a deficiency in cobalt and therefore, vitamin B₁₂ is one of the most common mineral issues seen each year.

Selenium and vitamin E

Selenium and vitamin E work in tandem, both are vital for lamb growth by developing muscle and are important in correct liver function. Selenium is a mineral which is important for the immune system and therefore, antioxidant function. Ensuring selenium and vitamin E are balanced ensures that weight gains are met in finishing lambs, if these are outbalanced then performance can be impacted.

Copper

In sheep, copper is a particularly important mineral as it is involved in over 300 key enzymes within the body. It plays a key role in fertility, growth and once again, the immune system of a lamb. Normally, copper issues are associated with young lambs which may have sway back due to the ewe being deficient in copper during pregnancy. Copper is stored in the liver, released into the bloodstream and the body will keep the amount of copper within a narrow range. In continental breeds, due to their genetics, supplementation needs to be carefully considered and ideally, blood or liver samples should be completed to determine whether copper needs to be supplemented.

Goitrogen crops

If finishing lambs are being outwintered on goitrogen crops then quality of diet needs to be considered - are energy and protein requirements being met to achieve appropriate growth rates? Goitrogens in forage crops act as an antagonist of iodine, so when finishing lambs are outwintered on these crops, there is a requirement to supplement. The requirement for iodine can increase by two to four-fold to compensate for the lack of iodine available from the forage crop.

Getting minerals correct in your finishing lambs is key to getting good growth rates and finishing times to slaughter.

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Growing and Finishing Lambs in Autumn and Winter | Helping farmers in Scotland | Farm Advisory Service