Trace Element Requirements for dairy cows

This article is limited to Copper, Cobalt, Selenium and Iodine. These have been well studied in New Zealand and world-wide so we can make recommendations with confidence. Other elements probably play important roles as well, but we either don’t know enough, or requirements are so small that they are easily filled by what’s in the average diets.

Over the years I have adopted a KISS system of managing trace element nutrition of dairy cows. It revolves around animal tissue testing and adjusting supplementation, such that deficiencies in principle never happen.

The mineral chain of events is something like this: parent rock Þð soils Þð plants Þð animals, with interactions and absorption coefficients occurring in many places along the chain. These interactions may prevent minerals from passing from one media into the other, e.g. a high soil test of Copper doesn’t always translate in a high animal Copper level if a high Sulphur/Molybdenum level exists. Because these interactions can be quite unpredictable, I prefer to test the “end user”; the animal.

This article is limited to Copper, Cobalt, Selenium and Iodine. These have been well studied in New Zealand and world-wide so we can make recommendations with confidence. Other elements probably play important roles as well, but we either don’t know enough, or requirements are so small that they are easily filled by what’s in the average diets

My preferred testing strategy:

	Autumn (May/June)	Spring (Sept/Oct)
Liver copper (4-6)	+	-
Serum Fx (=copper) (6-10)	-	+
Serum Selenium (6-10)	+	+
Serum B12 (4-6)	+	+
SerumT4 ((4-6))	(+)	(+)

1. Sample no’s depend on herd size; the larger the herd, the more samples.
2. Fx measures Copper in serum.
3. Serum Selenium preferred over GSH-Px. The latter is a Se containing enzyme, indicating available Se 2 months prior to test date.
4. B12 is used to measure Cobalt
5. T4 is used to measure Iodine
6. Don’t forget to test young stock as well, often overlooked.

Autumn testing before allows you to ensure the animals have sufficient reserves to come through the winter without deficiencies; winter is the low-intake/high demand period for most of the trace elements. A Spring test before mating starts covers that critical period.
If a test result indicates inadequate levels, firstly the animals’ reserves need to be filled up, as well as a strategy put in place to maintain normal levels thereafter. Once the blood/liver levels fall within the normal ranges, there is no benefit to be expected from lifting levels any higher.

The Elements.

Copper.

Copper deficiency is quite common. High soil Molybdenum and Sulphur, to a lesser extent Iron high levels reduce copper availability, even if Copper level itself is high (secondary deficiency). Zinc (supplementation) also reduces copper availability. There are areas in NZ with low Copper soil levels (primary deficiency).
Copper plays an important role in many enzymatic processes in the body. It is involved in nerve function, bone growth, immune system, as an antioxidant and many more.

Copper is stored in the animals’ liver, from where it is released as required. Copper intakes reduce over winter, so measuring liver levels in Autumn (pref. by biopsy, alternatively through the works) is a good way to ensure supplies are adequate before the critical period. Spring test can be done through (cheaper) blood tests.

Deficiency symptoms: diarrhoea, low production, ill thrift, bone fractures, low fertility etc. In theory Copper can be toxic to cows, but at sensible rates this is not a problem. The one exception could be the use of Copper injections during Facial Eczema challenge (Also, (FE) liver damage often leads to false high readings of blood copper and cobalt).

Selenium.

Selenium deficiency is widespread in NZ. Selenium plays an important role in the immune system, and acts as an anti-oxidant in tandem with vit E. There are indications that high Sulphur and Iron levels may interfere with Se availability.
Deficiency symptoms: ill thrift, diarrhoea, low milk production, low conception rates, white muscle disease. Selenium is toxic to animals at 5-10 times recommended daily intakes (signs: diarrhoea, tissue haemorrhage, oedema)

Cobalt.

Cobalt deficiency is found in certain areas of NZ, the NI Central Plateau being a well- known (but not the only!) one. It is incorporated in two enzymes active in Energy and Protein metabolism. A deficiency will lead to animals starving, even while the supply of ME/DM is adequate! Sheep are much more susceptible to Co deficiency, in this way they can act as indicator animals for cows. High soil temperatures/dry soil conditions make soil Co less mobile, so summer is the critical period for Cobalt. Not very toxic: 100-200 times normal dose results in deaths.

Iodine.

Iodine deficiency does not seem to be a widespread problem in NZ dairy cattle. There are reports on goitre and related problems in sheep and goats in the literature. Supplementation trials with cows have not given conclusive results. The most likely problem-scenario is where a large proportion of the diet consists of Brassica’s: Glucosinolates and thiocyanates found especially in Kale and Rape can severely reduce Iodine uptake (even more so when in flower). Not very toxic: growth depression from 30-50 times normal daily intake.

Daily requirements for Cows.

The following table (N. Grace) gives the estimated dietary trace element concentrations required for lactating cows. These figures need to be interpreted with care because of said interactions between minerals. Meaning that even if the intakes in the table are met, interactions could still result in unsatisfactory levels in the animal.

Element	Mg/kg DM req’d.	Total mg req’d. (@ 15 kg intake)
Copper	8-10	120-150(-250)
Cobalt	0.06	0.9
Selenium	0.04	0.6
Iodine	0.5	7.5

Supplementation.

There are many mineral products on the market, varying in route of administration, dosing interval, efficacy and price. My personal approach is to choose a low cost/high efficacy product, with preferably low labour requirements for administration. Often this means soluble products through an in-line or floating dispenser. However, each situation is different, for instance, where cows drink out of water races, dosing with an inline dispenser is not possible, or where extremely high Mo and S levels inhibit Cu absorption, Cu-injectables will give much better results etc. Therefore I can’t give you a one size fits all recommendation.

Application of trace minerals with fertilizers is a possibility. But I don’t generally recommend it because it means stepping back a few places on the mineral chain of events, increasing the likelihood of interactions and low absorption rates. Only if soil levels become limiting for pasture production, application directly to soils is a useful tool.

Plant requirements/Animal requirements.

The following table comes out of Use of Trace Elements in New Zealand Pastoral Farming (NZ Fert. Manufacturers’ Research Ass. publication).

Adequate pasture levels for pasture growth	Essential for plants	Essential for animals	Adequate pasture levels for animals
14 ppm	Boron
7 ppm	Copper	Copper	10 ppm
		Cobalt	0.06 ppm
		Selenium	0.03 ppm
		Iodine	0.25 ppm
49 ppm	Iron	Iron	?
24 ppm	Manganese	Manganese	?
0.10 ppm	Molybdenum	Molybdenum	?
15 ppm	Zinc	Zinc	?

Much of the information in this article comes from Managing Trace Element Deficiencies by Neville Grace, AgResearch, and Use of Trace Elements in New Zealand Pastoral Farming, Fert.Research (DRC). Both excellent booklets if you wish to read a little more than this short article can contain.

Helwi Tacoma
Dairy Consultant/Director
Intelact Nutrition