Cattle Mineral Supplementation

Throughout the year and production cycle, the cow goes through different phases with varying nutritional requirements depending on her stage of production. Minerals are an essential part of a cow’s diet, important for growth, productivity, and immunity. It is vital that supplementation of minerals takes place at the correct time and quantity throughout the cycle to ensure that the cow’s requirements are met.  

When starting to think about mineral nutrition for your cattle, 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 

Mineral nutrition requires careful balancing to ensure that the cow’s requirements are met without under or over supply. An undersupply of minerals can cause deficiency in the animal whilst an oversupply can cause toxicity. Some minerals have a wider range between deficiency and toxicity than others, therefore getting the balance correct is important to ensure the requirements are being met through the feed and if necessary, supplementing minerals. Part of the balancing act also involves the way in which the different minerals interact with each other and how that impacts the absorption and utilisation of the minerals by the body.  

Macro minerals for cattle 

Macro minerals are required in relatively large quantities in the diet of cattle, 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.  

Calcium is the most abundant mineral 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. High levels of calcium can impact the absorption of magnesium, zinc, copper, and cobalt by lowering absorption, whilst it may increase molybdenum absorption.  

At the onset of milk production, there is a sudden increase in demand for calcium which needs to be carefully managed as the cow transitions from the dry period to milking. On the day of calving, the requirement of calcium in a dairy cow will increase four-fold (400%) due to the production of colostrum. This large draw of calcium into milk production causes a sudden drop in the amount of calcium in the body which, if the cow becomes deficient, can result in hypocalcaemia (milk fever). If a cow’s diet is deficient in calcium, she will pull the calcium from her bones to maintain the levels within the blood and milk. If there is not enough calcium in the diet, there will often be a drop in milk yield. In young calves, if there is a deficiency or lack of calcium in the diet, poor skeletal development and growth rates may be seen.  

Phosphorus is the second most abundant mineral in the body with 80% found in the bones and teeth. Phosphorus is important for energy utilisation, metabolism, bone formation and maintenance, and it can affect feed efficiency. If a diet is deficient in phosphorus, the following symptoms may present themselves, reduced appetite, reduced milk yield, infertility, and pica. Clinical phosphorus deficiency tends to occur in high yielding dairy cows whereas it is less likely to be seen in beef cattle due to their lower requirements for phosphorus in the diet. Deficiency signs in beef cattle tend to present themselves as poor production, with low intakes resulting in poor growth rates. The calcium to phosphorus ratio is important to consider to reduce the risk of deficiency, the target ratio is between 1.5:1 and 2:1. Phosphorus deficiencies tend to be more common when cattle are grazing or forage fed rather than cows fed a total mixed ration.  

Magnesium – 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. Magnesium has many relationships with other minerals which can impact how much of it is absorbed and can result in a deficiency for the animal - high calcium may lower magnesium absorption whereas high phosphorus reduces magnesium availability. A key relationship is between magnesium and potassium as increased levels of potassium lower magnesium absorption by locking it up. Grass staggers (magnesium deficiency), is typically seen in the spring when the concentration of magnesium in the grass is low but the grass is growing rapidly, and potassium levels are high. Staggers can occur when cattle are housed if the silage is high in potassium which locks up the magnesium meaning it won’t be readily available for uptake.  

Trace elements for cattle 

Trace elements are required in small quantities in cattle diets, as seen in Table 1, these trace elements 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 element 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 trace elements are deficient in the diet.  

Table 1 Trace Element Requirements. Source Teagasc 

The lower end of the range is for routine use and the higher levels are advised for stock at risk of severe deficiency. If you need advice on supplementation, please speak to your nutritionist or vet.  

Copper is mainly stored in the liver where it remains until it is re-directed to the cells which require it. Copper is involved in over 300 key enzymes in the body and its function includes energy utilisation, immune system function, fertility, wool, and hair production. Therefore, copper is critical for growth in youngstock and fertility in heifers and cows. Molybdenum, sulphur, and iron are antagonists of copper which can impact absorption and utilisation of copper by the body. Copper deficiency tends to present itself as reduced fertility in cows and poor growth rates in calves and youngstock. Copper needs to be managed carefully to avoid toxicity which is when there is a significant build up in the liver. 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.  

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. Calves that are born alive may be hairless and weak with a high incidence of death shortly after birth. Clinical signs of iodine deficiency in growing and adult cattle are less likely to be seen, however you may see effects on reproduction like irregular cycles, low conception rates and retained placentas. 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 so supplementation is required.  

Selenium is vital for growth of the animal through their muscle development and important for supporting immune system function. Selenium plays a key role in fertility; in cows it is related to egg production and egg quality whilst in bulls it is related to sperm quality. If selenium levels are too low, cows may have early embryonic deaths and for bulls there may be more cows that are barren. Other signs of selenium deficiency include white muscle disease, retained placentas and low immunity to diseases.   

Mineral testing and diagnostics 

Prior to supplementing, it is important to take some time to determine whether mineral supplementation is required or not. Mineral testing can be completed on forage and grass samples to determine the quantity of minerals available for the animal to uptake through their diet. Having accurate information about the minerals in the forage or grass can ensure that the ration is formulated to meet the requirements of the cattle.  

Determining whether the animal has a deficiency or toxicity can be done through blood sampling or liver testing for copper. Normally testing will involve taking samples from a select number within each group with the results being used to determine what supplementation, if any, is required.  

Supplementation methods 

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 that are available such as buckets, boluses, drenches, mineralised concentrates or powdered minerals - each method can provide a consistent supply of minerals to your cattle.  

• Buckets can be used for supplementation of minerals, however there is a reliance on each animal utilising the bucket every day which is not guaranteed so there could be an inconsistent 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 a duration of time.
• Drenches may be an option if the cattle are being weighed or handled on a regular basis to allow the drench to be administered regularly, which can be as often as 4 to 6 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.  

 If you want to review your mineral supplementation plan, speak to your vet or nutritionist to discuss your options to determine the correct amount of minerals required by your cattle throughout their production cycle. When you are reviewing your mineral supplementation plan, it is important to note down all types of supplementation methods you are currently using on farm to ensure there is not an over-supply of minerals.  

 Author: Dr Cara Campbell 

SAC consulting