UNDERSTANDING THE CRITICAL ROLE OF MINERAL SUPPLEMENTATION FOR THE TRANSITIONING DAIRY COW

Phosphorus

Phosphorus is vital for energy metabolism, bone mineralisation, and cellular function. Transitioning dairy cows require increased phosphorus intake to support fetal growth, lactation, and maintenance of metabolic processes. Phosphorus deficiency can lead to reduced milk production, poor reproductive performance, and skeletal abnormalities. Supplementation with phosphorus-rich feed or mineral supplements ensures adequate phosphorus levels, promoting overall cow health and productivity. Most farmers underestimate the need for phosphorous in high production dairy cattle and this can result in them seeing production losses, higher infertility, and even cases of clinical deficiency (crawler cows) in their herds.

Sodium

Sodium is essential for maintaining salt-water balance, acid-base equilibrium, nervous system function, and is the key element for saliva production. Saliva is essential in the primary breakdown of fibre – when the saliva is swallowed it then becomes the primary rumen buffer, ensuring rumen pH is held within its optimal range. 

During transition, dairy cows may experience increased sodium requirements due to changes in diet and metabolic demands. Sodium deficiency can lead to dehydration, reduced feed intake, and impaired rumen function. Supplementation with sodium chloride (salt) helps meet cows’ sodium needs, ensuring proper hydration, rumen function, and overall metabolic balance. Any salt deficiency, particularly during early lactation when rumen function requires large quantities of sodium, can exacerbate metabolic challenges and compromise cow health, productivity, and reproductive performance. 

Magnesium

Magnesium plays a critical role in muscle and nerve function, as well as energy metabolism. During transition, magnesium supplementation helps prevent grass staggers (hypomagnesemia), a potentially fatal condition characterised by muscle tremors and convulsions. 

Magnesium deficiency at any time of the season, but particularly during lactation, can have serious implications for animal health, reducing milk production, and making it harder to get the cow back in-calf. A lesser-known fact is that magnesium has a key function in the thyroid, where it activates the T4 hormone. Magnesium also stimulates the production and release of calcitonin, the hormone that stores calcium into the bone – this is very important during lactation when bone storage is critical.

Chloride

Most farmers would not consider chloride to be an important element. When the average person thinks of chloride, they are more likely to relate it to its more active and toxic by-product chlorine, that is commonly used in swimming pools. In reality, chloride is one of the most essential elements to all life, hence it is abundant in both soil and the foods soil produces.

At a very basic level, chloride is essential in the production of the gastric acids required in the stomachs of all mammals. While cattle are ruminants, they still have a primary stomach (called the abomasum), which requires copious amounts of hydrochloric acid as a key part of the digestive process.

At a slightly more complex level, chloride is absolutely essential in maintaining the correct acid-blood balance. Chloride is readily absorbed through the intestinal wall directly into the blood, making it the ideal mineral salt to incorporate into a negative DCAD pre-calving transition blend. Chloride is very well tolerated, excesses are easily excreted with little downstream risk, and it is 40% better absorbed than sulphur-based minerals in these blends. 

Sulphur

Sulphur is an essential nutrient required for normal growth and reproduction of bacteria in the rumen of cattle. Sulphur is essential for rumen microbial synthesis of certain amino acids (cysteine, cystine, and methionine), vitamins (thiamine and biotin), and other enzymes. The ideal level of sulphur in the diet is around 0.3%, but it is not uncommon for sulphur levels to exceed this. Excessive sulphur levels can lead to sulphur antagonism in the rumen and will interfere with vitamin B1 (thiamine). It also complexes with selenium and iodine, which can impact antioxidation as well as thyroid function.

Although sulphur is beneficial in a negative DCAD transition diet, levels should be kept within a tight range and calculated taking underlying dietary levels into consideration. Excessive levels of sulphur in the diet can cause some critical deficiencies.    

Trace elements 

In addition to macro minerals, adequate levels of trace elements are essential for the transitioning cow. These include:

• Copper: Copper is one of the elements that has a high requirement and is essential for health and performance in dairy cattle. Copper works as a powerful antioxidant within the cytoplasm of every cell and because it works at the cell level, form is all important. In order to guarantee high absorption, the copper should be chelated, meaning it is attached to an amino acid. Provided copper is administered in the correct chelated form, it will be successfully absorbed within the intestinal system. 

• Zinc: Like copper, zinc is important at a cellular level as it drives one of the most important antioxidant pathways. In its elemental (non-chelated) form, zinc is only partially absorbed and can be poorly translocated through the body. Given this, it is important for most applications that zinc be chelated in order to ensure good intestinal absorption. However, there is one possible exception to this rule – in situations where facial eczema is a risk, non-organic zinc is useful for saturating the liver cells and can give good liver protection from spore toxins. Zinc is essential for skin integrity, wound healing, and immune function. 

• Selenium: Selenium acts as an antioxidant, supporting immune function, reproductive health, and – most importantly – helps to drive energy by underpinning healthy liver and thyroid function. Selenium is of utmost importance to healthy liver function, enhancing production of the antioxidant glutathione peroxidase, which is key to liver cell regeneration. One of selenium’s lesser-known roles is in the production of thyroid hormones, sharing equal status with iodine when it comes to healthy thyroid hormone production. In ruminants, selenium availability can be hampered by a combination of factors:

• Selenium can be antagonised in the rumen by the same natural goitrogens that hamper iodine availability. These toxins are common in the clover portion of pasture, and in brassica crops commonly fed to cattle. 
• Selenium is also further degraded by free sulphurs in the diet. Rumen microbes will combine degraded sulphur thiols with selenium, forming a potentially toxic selenothiol production. It is very important that farmers identify high free sulphur in the diet and supplement selenium in forms that will ensure mineral-induced deficiencies of selenium are well covered.
• Unlike iodine, degraded forms of selenium can also have a potentially toxic effect at the cell level. Selenium that has been degraded with sulphur can cause increased cell death prior to secretion. Taking this into account, farmers may want to consider using an organically-bound, or rumen-protected form of selenium in situations where these issues are likely to occur. 

Consequences of inadequate mineral supplementation

Just as adequate mineral levels have a positive effect on health, production, and milk production, inadequate mineral supplementation will have the opposite effect. 

Common consequences include:

• Increased risk of metabolic disorders, such as milk fever and hypomagnesemia.
• Reduced milk yield and quality.
• Poor reproductive performance, including delayed conception and increased calving intervals.
• Compromised immune function, leading to higher susceptibility to diseases.

Correct mineral supplementation that takes into account environmental factors, potential antagonistic mineral reactions, and animal stress levels, will ensure adequate levels of the correct forms of mineral will be supplemented seasonally. Minerals play a pivotal role in setting up transitioning dairy cows for a successful and profitable season, as well as ensuring these same cows are well supported through lactation. By understanding the important roles macro minerals and trace elements play during this time, dairy farmers can support the metabolic processes and physiological functions critical for a successful transition.