Animax – Scottish Farmer March 2018 Dairy Special

What are the effects of trace element deficiencies on cow fertility?

We talk to Dr Elizabeth Berry BVSc, PhD, MRCVS about the vital role of trace elements on the fertility of dairy cows.

There are many different approaches to dairy herd nutrition, many of which are determined by individual variables on each farm. However, there are key aspects that apply to every herd when it comes to maximising herd performance.

Every dairy farmer relies on good nutrition and herd fertility to support pregnancy on an annual basis, produce a good healthy calf, and, an abundance of milk.

“Fertility issues can be complex and multi-factorial, however, to ensure good fertility, energy and protein must first be considered," says Animax veterinary director, Dr Elizabeth Berry, BVSc, PhD, MRCVS.

"A good indication of how much energy the cow is being provided with would be body condition scoring. However, you don’t want to wait until cows are losing condition to address this – it’s much more effective, for animal welfare, performance and financial returns, to prevent issues.

"All areas of nutrition must be looked at – from forages, straights, and trace elements – everything from the field, loader bucket and shovel to the teaspoon," she said.

With the wide range of geological soil types found in Scotland, Dr Berry said that this mean that trace element deficiencies can occur – influenced by local farming practices such as fertilisers, liming or crop type. Yet, trace elements are sometimes overlooked, which can be extremely detrimental to the herd performance.

Trace elements are essential for cell metabolism and many other body functions, including energy production, growth, reproduction and the nervous system – so have a major impact on animal performance.

She added: “A deficiency in trace elements will result in a variety of subtle symptoms that are often not noticed until the deficiency is rectified. Copper, cobalt, selenium, manganese, zinc and iron are all involved in essential enzyme reactions and these have an influence on fertility. Iodine is essential for the production of the hormone thyroxine, which determines cell metabolism.

“Cows may not be cycling or may have reduced heat related behaviour due to poor body condition, anemia or uterine infections, all of which can arise due to trace element deficiencies. Cows are also likely to have a greater requirement for certain trace elements at crucial times, such as calving."

According to the vet, copper is often the first trace element to be considered in fertility issues, with copper deficiency arising either due to a primary lack of copper in the diet or due to a tie up of copper by antagonists, molybdenum, sulphur and iron, or a combination of both of these. Excess copper is toxic and the amount added to the diet is controlled to prevent this. A high yielding dairy cow fed to yield can easily consume more copper in her diet than is ideal, hence a discussion with a vet is advised if copper supplementation is being considered.

“Cobalt is involved in crucial enzymes for energy production and in the prevention of anaemia," said Dr Berry. "Cows utilise rumen bacteria, to turn cobalt that is in their diet, into B12, which is then absorbed into the blood and turned into cobalt enzymes. There is evidence that in cobalt deficient cows, conception rates are reduced, while deficient cows treated with cobalt showed stronger oestrous.

“Iodine deficiency has been widely recognised, as a cause of hypothyroidism– also commonly known as an underactive thyroid. However, recently certain feeds have been identified as goitrogenic-feeds that can affect thyroid function by inhibiting synthesis of thyroid hormones, such as kale, rape, brassicas and white clover. Dairy farmers looking into extending their cropping varieties on farm need to be aware of this."

She added, that selenium, like copper, can also be toxic in excess. Selenium plays a vital role in areas such as uterine function and reducing retained cleansings. Selenium is also required by the thyroid gland, both for the uptake of iodine and the incorporation of iodine into thyroxine – illustrating the complex and yet vital nature of this trace element.

“There are usually predisposing factors which can result in disorders, due to other trace elements. Rations low in manganese, can result in depressed conception rates. Reproductive failure in the female and poor sperm function in the male, can be the result of zinc deficiency. Forages are rich in iron so deficiency is very rare," said Dr Berry.

While body condition scoring can be used to indicate how much energy is being supplied in the diet, it is harder and more expensive to try to quantify trace element status.

Some tests are inaccurate, impractical, or require careful interpretation. Copper status, for example, should be measured in liver samples however this is not practical, while blood copper levels can be inaccurate.

“In addition, the levels of trace elements can vary throughout the year as a result of weather conditions or rapid grass growth – basically, quick growth dilutes the trace elements," she said. "Spring grass can be high in sulphur, while soil and forage type along with interactions with other trace elements, can change the balance. This shows the difficulty in identifying the true status of trace elements in forage throughout the year.

Providing access to reliable sources of trace elements for cows at pasture can be challenging, particularly regarding copper. Traditionally, trace elements can be added to mineral licks, water supplementation or in a total ration formulation. Some minerals are unpalatable in water and mineral licks can attract wildlife and possible disease risks. Drenches do provide this option but must be repeated frequently as they usually do not last longer than a few weeks, while frequent handling of the cow, can be difficult from a practical aspect.

Instead, Dr Berry encouraged the use of a slow release, leaching bolus as a practical and reliable way of giving dairy cows trace elements. It gives a consistent supplementation of the essential trace elements to each individual animal.

Work carried out by Teagasc in Ireland, demonstrated how effective this could be in terms of productivity. Check with your vet, particularly with regards to supplementing copper.

"I believe boluses that include cobalt, selenium, iodine and possibly copper, at drying off and conception, will pay dividends and give the animal the optimal amount of the key trace elements needed to maintain fertility,” she concluded.