How and why to rectify trace element deficiencies in heifers
© Tim Scrivener Stillbirths can be an economic and a welfare issue for dairy farmers – with losses in heifers often caused by trace element deficiencies.
Farmers Weekly spoke to James Husband, vet and head of livestock development at Map of Ag, to find out how farmers can best diagnose and rectify suspected deficiencies.
See also: How to work out your flock’s trace element requirements
Which element deficiencies can be a causal factor in stillbirths?
When faced with a high stillborn percentage, animals may be suffering from selenium and/or iodine deficiency.
Selenium is a key trace element that can affect the skeletal and cardiac system, as well as respiratory muscles, meaning the congenital form of a deficiency is often seen as perinatal (from pregnancy up to one year old) mortality.
Selenium is important for immune function, and some studies have shown that low maternal selenium status pre-calving has led to calves failing to show proper responses to vaccinations, too.
In milking cows, these issues are quite rare as this group is normally very well supplemented during lactation.
However, the same level of supplementation is not generally the case with heifers – which are often at pasture for long periods of time – and therefore greater stillborn rates can be seen.
Iodine deficiencies may also be seen alongside selenium deficiency, as selenium is part of a critical enzyme that converts the storage form of iodine, thyroxine, into its active form, T3.
What is the best way to diagnose a suspected deficiency?
Blood testing is usually the best method – although it is also possible to do a liver biopsy for selenium status, but this is much more invasive.
The most common blood test to estimate selenium status measures the concentration of a selenium-containing enzyme called glutathione peroxidase.
Submission of stillborn calves for post-mortem examination is very useful if iodine is the suspected cause. The thyroid gland of these calves will be enlarged and will have distinctive microscopic changes.
In both heifers and milking cows, the optimum time to sample is about two months prior to calving. This allows sufficient time to supplement stock before calving if a deficiency is detected.
You can also use milk samples to get an indication of trace mineral and phosphorus levels. This is done largely in the Netherlands, but is not commercially viable in the UK yet.
If a deficiency is found, what is the best way to rectify the issue?
For many farmers, a bolus is an easy, convenient solution if animals are remaining at pasture for long periods.
Boluses can be selected to target specific deficiencies and last a minimum of a few months, meaning heifers can go out to graze without the need for any further supplementation.
If this is not an option, then supplementation through the diet can help.
Depending on the quality of the grass or forage, feeding something such as a rearer nut or a suitably mineralised cake will usually contain enough selenium to rebalance a deficiency.
When thinking about mineral levels in feed, it is important to get forage analysed.
Grass silage can be extremely variable, and maize silage is not high in minerals in general, so it is worth having an analysis done to ensure you are supplementing correctly.
There are also deficiency hotspots in the UK – such as the Somerset Levels, where high molybdenum levels and high pH soils limit copper availability – so if you are in those areas, it is even more important to get analyses done.
That said, it is important not to assume you need supplementation, as issues can arise from over-supplementation, too – further justifying the importance of forage analysis and blood testing in cattle.
There are also injections available, some of which are depot – slow-release – injections, and others with a much shorter duration of action.
A potential advantage of injections is that they bypass potential “lock-up” issues in the rumen.
You can also do an input assessment. This involves adding together the amount of estimated selenium in grazing grass to the concentrate fed to give a rough indicator of the total amount of selenium in food sources.
However, most farms will require supplementation of some type, as there is not enough in grass alone if grazing is anything other than for relatively short periods.
AHDB case study: Tom Bletcher
Flintshire dairy farmer Tom Bletcher has reduced his stillborn rate from 8% to 2% in replacement heifers after diagnosing trace element deficiencies through blood testing.
Tom Bletcher © The Bletchers
The 400-head herd was selected for AHDB’s Herd Advance project in 2019. The first part of this involved looking at herd health and priority target areas within the business.
Stillbirths within heifers were highlighted as a key issue on-farm, with an average of 8% a month, and a high of 20% in the worst month.
According to Mr Bletcher, this was having an impact financially and was limiting the availability of replacement heifers – with some losses from animals with the highest genetic merit.
As a result, he sought the help of Farming Connect’s Animal Health Clinic which saw the vet take blood samples from in-calf heifers.
Test results showed that the heifers were suffering from multiple trace element deficiencies, but predominantly selenium.
The farm set about rectifying this by giving in-calf heifers a bolus at turnout and providing them with sufficient trace elements until they calved.
As a rule, heifers under 500kg are given one bolus, and those over 500kg are given two. Mr Bletcher says this has had a major impact on the herd with stillborn levels dropping to an average of 2% over 12 months.
Farm facts
Argoed Hall Farm, Mold, Flintshire
- 400-cow, year-round calving herd
- Managed by Tom Bletcher and his father, Roger
- Breeding own heifer replacements
- Investing in high genetic merit animals/sexed semen
- One of 500 farms selected to be part of AHDB’s HerdAdvance project
Source: AHDB Dairy