Minerals and other supplements

Minerals and vitamin supplements

Most fresh and conserved forages offered to ruminants contain adequate levels minerals and vitamins to sustain production. However, in some cases total diet concentrations of minerals may be low (e.g. Ca in fodder beet) or concentrations of antagonising minerals may reduce mineral bioavailability to the animal (e.g. high Mo and S reducing Cu). Additionally, there is wide variation between farms when it comes to the mineral content of a forage produced. Because of this, farmers should ensure that their forages are analysed for mineral content so that appropriate mineral supplementation rates are followed.

Dairy animals can receive minerals from a variety of sources including forages, concentrates, free access minerals, boluses, water, drenches and veterinary products. When calculating out the total daily supply of minerals to the animal it is important that all these sources are taken into account. Having one person with oversight of the mineral nutrition on the farm helps reduce the risk of leaving one or more sources out of the calculation but ultimately it is the farmer who has responsibility for the dietary concentrations.

In a study of mineral use on British dairy farms, researchers at Harper Adams University found that minerals were generally over supplemented to dairy cows. The work, highlighted that Cu in particular was being over supplemented on the assumption that antagonists were high in the forage. However, many farmers did not analyse their forages for mineral content and when the researchers examined the forage they found no correlation between high dietary Cu and high levels of Mo, S and Fe.

Perhaps the most important thing to remember with mineral supplementation is that the animal’s requirements will vary depending on their growth stage or lactation stage, whilst dietary supply will very much depend on the basal forage composition. Consideration must be given to both the supply and requirement side of the equation when deciding on an appropriate mineral supplementation level.

Amino acids supplements

Under normal feeding conditions, a well balanced supply of microbial and feed protein will provide sufficient amounts of amino acids (AA) for milk production. Microbial protein in particular is well balanced in terms of amino acid profile and is sufficient to meet the requirements of approximately 1kg of milk protein/day. However for protein yields greater than this, the contribution of feed protein to AA flow becomes more important and imbalance may become an issue for essential AA. Lysine and methionine were initially thought to be the most limiting AA for milk production and these forms are most commonly supplemented to dairy cows. However, more recent studies are questioning whether these AA are in fact limiting milk production with some research suggesting the histidine or leucine may be limiting in grass silage based diets.

An AHDB funded review of protein nutrition concluded that farmers who supplement with either lysine or methionine should be aware that a response in milk production is only likely where intake and supply of other AA do not become limiting.

Fat supplements

Fats are an energy dense feed containing approximately twice the metabolishable energy of barley. However, it is important that fat supplements are fed in a form that limits their activity in the rumen. This is because fats impair the ability of rumen microbes to digest fibre reducing the amount of fermentable energy available to the animal. To overcome this issue, fats can be chemically treated to reduce their activity in the rumen. They then pass into the abomasum where the chemical treatment is dissociated from the fats allowing them to be efficiently digested in the duodenum (proximal part of the small intestine). The value of fat supplements in the diet depends on the response of the animal in terms of milk production and the cost of including the fat. Additionally, there is growing concern over the long term sustainability of fat sources. 

Yeasts supplements 

There are many feed supplements on the market that contain either live or dead yeast cells. A meta-analysis review of live yeast supplementation by researchers in France reported that the product increases pH and VFA concentrations whilst reducing lactate concentrations. However the relative changes were small and could have been influenced by intake, NDF content of the diet or concentrate content of the total diet. The inclusion of yeast in the diet of dairy animals should be made on the basis of a return on investment through improved milk production. 

Rumen buffers

These feed supplements are designed to resist a decline in rumen pH that occurs when feed is fermented in the rumen. Under normal feeding conditions, where adequate physically effective fibre is included in the diet there is probably a reduced requirement for rumen buffers. Where changes are to be made to the diet (eg concentrate inclusion rate) then this should be done gradually to avoid digestive upsets and lowering rumen pH. If there is a necessity to have high concentrate levels in the diet, then there may be a role for rumen buffers but it is also important that the animal's ability to buffer the rumen is also encouraged through provision of adequate fibre.