Magnesium in Ruminants

Magnesium in Ruminants

Biological availability (bio-availability) of magnesium is tested in vitro or in lab by observing the rate of solubility of magnesium compounds in rumen fluid or in a weak acid solution. This method is common and popular because they are less time consuming and much less costly than in vivo method which is extensive and longer process.
Absorption of magnesium in ruminants occurs throughout the digestive tract but primarily in the rumen and reticulum, provided the magnesium is readily soluble.

Common sources of magnesium are feed grade Mg-salts. As example: MgO, Mg(OH)2, MgSO4, Mgcl. Among them, first three are more bio-available.

Factors affect magnesium utilisation
There are many factors affecting the absorption of magnesium from the gut. The following factors need to be considered to ensure optimum utilisation of magnesium:

  • Imbalance of other minerals, such as Ca, P and K. Excess amount of these minerals may decrease Mg absorption.
  • Fat: Fat has tendency to bind with Mg, resulting formation of soap. Thus Mg availability is reduced.
  • Ionophore, such as monensin and lasalocid may increase Mg absorption.
  • Age: the younger the better to mobilise Mg
  • Particle size: particle size of Mg-salts is highly correlated with the solubility. The finer the particle, the higher the solubility.
    Particle size Fine Medium Coarse
    Solubility (mEq/l) 157.26 128.08 86.01
  • Calcination temperature of Mg: 800 °C- 1100 °C has higher Mg availability, less than 605 °C is worst and above 1300 °C has also negative effect on availability.
  • Palatability: magnesium sulphate and magnesium chloride are less palatable than magnesium oxide.

Excess magnesium
Excessive amount of magnesium can cause damage in rumen wall. As a result, diarrhoea, lethargy, reduced appetite may be observed.

It is recommended that dry cows should receive a diet containing 0.35% magnesium, and lactating cows 0.28% magnesium. Hence the old recommendation of 10 – 12 gm magnesium per cow per day is no longer appropriate. Other factors that increase magnesium requirements of cows during the winter/spring period are:

  • Low magnesium levels, high K levels, and/or high crude protein levels in spring pasture.
  • Cold wet weather in spring depressing grass growth and cow intakes.
  • High cow demand for magnesium over calving and early lactation.

Availability of Magnesium from Magnesium Oxide Particles of Differing Sizes and Surfaces. B. W. Jesse et al J Dairy Sci 64:197-205, 1981
Comparison of Four Magnesium Oxide Sources. Each Fed at Three Dietary Concentrations to Lactating Cows. David K. Beede et al 29 Florida Dairy Production Conference, Gainesville, April 14-16, 1992
Comparison of Methods to Determine Relative Bio-availability of Magnesium in Magnesium Oxides for Ruminants R. O. van Ravenswaay et al Journal of Dairy Science Vol. 72, No. 11, 1989
Magnesium – getting the right amount into your cows DairyNZ Spring Survival Guide 2011
Magnesium supplementation Farm Fact 3-1, DairyNZ, October 2009
Relative bio-availability of magnesium sources for ruminants as measured by urinary magnesium excretion R.O. van Ravenswaay et al Animal Feed Science and Technology Volume 39, Issues 1–2, 16 November 1992, Pages 13–26 26

Recent Articles


10th May 2022

Last week during the sponsors breakfast at the AARN conference in Melbourne we formally presented our latest product offering... Read More

Biostrong® starts your flock strong and maximises production

14th March 2022

Biostrong® Protect OFC • Maintains feed intake particularly under conditions of enhanced challenge • Supports poultry gut health and resilience to... Read More

Lipidol® Ultra Trial in Heifers – Robotic Dairy Australia

24th November 2021

Background: Digestion is a 2-step process. First, ingested feed materials are broken down into readily absorbable nutrients by digestive enzymes.... Read More

Stress Reduction in Pig Production

17th September 2021

Not only we human beings face stressful situations. Pigs also suffer from stress – be it from heat, from... Read More

Copper supplementation in grower / finisher production - Source, solubility and levels fed matter

04th May 2021

Trouw Nutrition researchers found that adding hydroxy chloride copper (IntelliBond®) to swine diets could help improve growth performance and... Read More

Protein efficiency in ruminants - not just a topic for the cow's performance

15th March 2021

Reduced eutrophication, Over-fertilization of the fields, High nitrate pollution of the waters – Nitrogen losses are a big issue. These... Read More

Say goodbye to the effects of cattle transport stress with RFCs

24th February 2021

Road trips are fun. They take us to new destinations to see exciting things. While we often find adventure... Read More

CELMANAX boosting cattle performance in the absence of antibiotics.

24th February 2021

As meat labelled with no antibiotics ever (NAE) becomes an increasing preference in many households, the animal industry is... Read More

Hydroxy trace minerals reduce effects necrotic enteritis

19th August 2020

Research finds that adding hydroxy trace minerals to feed can reduce mortality and improve performance comparable to an ionophore... Read More

Trace minerals: Even distribution is the key

19th August 2020

Formulating diets to meet the mineral requirements of production animals is critical to maximise health and production efficiency. The... Read More