The Science of a Drench Slurry Preparation Using Vetmag
Vetmag Ultrafine is a nutritional supplement in New Zealand for the prevention of Hypomagnesaemia (grass tetany) in sheep and cattle. One commonly employed method of administration, particularly for dry cattle, is orally via drenching.
Reaction and reactivity with water: Vetmag is a high quality and very reactive form of magnesia (MgO) and like all magnesia will react with water to form magnesium hydroxide (Mg(OH)2.
The reaction known as hydration is as follows: MgO + H20 = Mg(OH)2
Subsequently soluble magnesium ions are released and made available to the animal being treated according to the following reaction: Mg(OH)2 <--> (Mg2+) + 2 (OH)-
It can be seen by simple reactions that it is necessary for MgO to be in hydrated form as Mg(OH)2 before it can be absorbed into the animals blood system.
Hydration may occur before administration, in the case of a drench; or within the animal, where MgO powder is consumed directly, such as for pasture dusting.
The rate and degree of hydration within the animal cannot be easily predicted or controlled and it is possible that unhydrated magnesia, particularly when low reactivity products are used, may pass through the animal and offering little or no remedial benefit.
The use of a pre-hydrated drench administration is therefore recommended and ensures remedial benefits over other forms of administration.
The method of administration, rate of hydration and therefore reactivity of MgO used are clearly important factors in determining the bio-availability of magnesia product (refer to Bioaval summary).
Pre-hydrated drench preparation:
Weigh out a minimum of 1kg of Vetmag for every 3 litres of water (one 25 kg bag will require 75 litres of water). It is preferable to use warm or tepid water (30 - 40C) to kick-start the hydration reaction.
Stir and continue stirring until even consistency and mark the level of liquid on the side of the mixing vessel. While Vetmag will settle if left to stand, it is easily re-suspended and it is therefore recommended that continuous agitation be employed during drench preparation and administration to ensure uniform dosing.
Heat will be generated and continue until the hydration reaction is complete. Due to the high reactivity of Vetmag, the rate of heat generation is usually greater than the rate of heat loss through the walls of the container or as steam and can be sufficient for the mixture to boil.
Do not be alarmed of the mixture appears to react vigorously or boils - this is a sign of a good quality, reactive product.
Rapid heat generation is quite normal for high grade, reactive magnesia products such as Vetmag. It may be that this has not been previously observed with other lower quality or lower reactivity magnesia products.
Note: Boiling may be avoided by using cool water for mixing and/or adding the material slowly and/or using metal mixing vessels to dissipate heat generated.
Allow sufficient time for the drench slurry mixture to cool prior to drenching. If steam was generated during hydration, check and add water if necessary to the original liquid level mark on the mixing vessel.
Maintain agitation of the mixture throughout the drenching where possible. Where continuous mechanical agitation is used ensure the device is set to reach the bottom of the drench container.
Add any compatible drenches such as bloat remedies to the cooled drench slurry.
Calibrate drenching equipment to deliver the required or recommended dosage.
Footnote: The heat of hydration for Magnesia (MgO) is 8.9 kcal/Mol. I.e. 8900 calories of heat are released for every 40 grams of MgO. This means that 1kg of MgO can raise the temperature of 3kg of water (3 litres) theoretically by 74oC. In practise the temperature rises much less due to heat losses through the vessel as water vapour or steam. Using a metal mixing vessel will more readily allow heat dissipation.
June 1996
© Copyright - freely available for reprint as long as attribution is made to Independent Veterinary Supplies Ltd (NZ) as source of material.
® Vetmag is a registered trademark to, and is manufactured by, Queensland Magnesia Pty Ltd, Australia.
