Autumn is a great time to check the mineral status of your herd. Copper (Cu) is an interesting mineral, it is stored in the liver and is released in the blood stream when it is required. There is a seasonal component to copper levels in the liver, with autumn having the highest and spring having the lowest levels.
Some symptoms of copper deficiency are poor growth or weight loss, low milk production and poor reproductive performance. A blood sample is not very effective at identifying a copper deficiency but a liver sample is.
This week's post is a short summary on copper supplementation and liver biopsies in dairy cows.
Key Points
Both copper deficiency and copper toxicity can can be a risk in New Zealand.
To monitor herd copper status, at least 10 to 12 liver biopsy samples should be taken, which is best done in autumn.
Discuss with your vet the best option for testing copper (and other) deficiencies in your herd.
Franklin vets have a few posts on diagnosing copper deficiency. They liken copper storage in the liver and blood to a tank with a pipe at the bottom. The liver being the tank and the blood being the pipe. The job of the liver is to release copper into the bloodstream to maintain a normal level of copper.
It is only when the liver stores are extremely low, that the blood level of copper would be low (the tank is nearly empty so cannot keep the pipe full). In this case both a liver test and a blood test would indicate (correctly) that copper supplementation is necessary.
In situations with near low liver storage of copper the blood level would look normal, when in fact the cow's "tank" of copper is nearly empty, so supplementation is required. A blood test alone in this case would not identify copper deficiency, whereas a liver sample would.
Another situation that could happen is the liver or "tank" is nearly full but the blood level would look normal. In this instance, supplementation of copper could lead to copper toxicity. Again a blood test may not identify this correctly but a liver sample would.
Generally speaking, copper deficiency is more common in NZ than copper toxicity is, but cases of toxicity do occur.
How many cows need to be liver sampled?
This study was investigating how many cows needed to be sampled to get a good indication of the whole herd's copper status. For logistical (and financial) reasons, we can't sample the whole milking herd to know the exact copper status of the herd. So we need to pick a smaller group of the herd to sample. But how many cows do we need?
A liver biopsy result between 45 to 95 micro mol/kg fresh weight of liver is within the marginal range. Which is the biopsy result we would start to be concerned about. In autumn, the desired copper level is higher than 300 micro mol/kg fresh weight to ensure that cows do not fall into the marginal range before calving.
This study looked at liver samples taken from 18 herds in the Manawatu region to identify how many cows need to be sampled in order to get a precise measurement of the herd average and to ensure the herd is above the 300 micro mol/kg fresh weight to indicate they are not copper deficient.
The minimum sample size identified in this study was 12 samples per herd, this number is much higher than what has traditionally been done (4-5 cows). The reason for this is that there can be considerable differences in copper levels within a herd, therefore collecting samples from a slightly larger number of cows can help the vets get a better estimate of the whole herd's copper status. A previous study recommended 10 to 12 samples are required, which the authors of this study agreed with.
How is a liver biopsy collected?
A liver biopsy is collected by your vet. Cows are held in a head bail and the sampling site is numbed before a needle is inserted into the liver to take the biopsy sample. Have a chat with your vet if you want to learn more about it.
Case Study
Copper toxicity was diagnosed in a herd in the Waikato following an investigation into the deaths of six cattle from a herd of 250 dry cows.
The farmer initially thought this herd had problems with copper deficiency and was supplementing multiple sources of copper over a long period. In fact the herd was identified as having copper toxicity instead. Unfortunately, this is an example of how important monitoring copper levels is, perhaps the herd did have a copper deficiency one year, so did in fact need supplementation. After a few years without checking liver copper levels, the supplementation was unnecessary and sadly causing more harm than good.
This case study also identified a poor relationship between liver and blood copper levels which again reinforces the importance of collecting liver samples and not blood samples to assess the copper status of the herd.
I had a quick google of what some vet practices have to say on copper deficiency/toxicity and found this awesome list of key messages from Anexa:
Don’t risk your animals becoming low in copper and suffering production losses.
Don’t waste your money on unnecessary supplementation if you don’t need it.
Don’t supplement copper blindly and risk toxicity.
What I can gather from these studies and vet resources, is that it makes sense to get a sample 10-12 cows of the herd liver biopsied in autumn for copper levels each year to make decisions on if your herd needs to be supplemented for copper over winter. This should avoid both deficiencies and toxicities from occurring. It also doesn't make financial sense to be throwing mineral supplements at cows if they don't need them!
Furthermore, in cases when some of the herd are grazing on different farms, or areas of the same farm, there can be big differences in copper status. For example, grazing R1 and R2 heifers off-farm or on a separate section of the home farm. Maybe the main milking herd has adequate copper levels but the heifers are deficient? It pays to check just to make sure!
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Full Papers:
Case study - Johnston, H., Beasley, L. & MacPherson, N. Copper toxicity in a New Zealand dairy herd. Irish Veterinary Journal 67, 20 (2014). https://doi.org/10.1186/2046-0481-67-20
Other links
Tokoroa and Districts Veterinary services - https://www.tokvets.nz/production-animals/tokoroa-vets-mineral-supplementation/
Franklin vets - https://franklinvets.co.nz/2020/05/19/copper-testing/