Trace Elements

Supplementing Trace Elements in Cows

By Alan Thatcher

Senior Veterinarian, Massey University

Certifying agencies generally require evidence of deficiency before allowing supplementation. The agencies are also not in favour of medicating water supplies but there is recognition that there may be no other practical option in some circumstances. If hay or silage is available, an alternative option is to dilute and use a watering can or a backpack sprayer on a rolled out bale. Note mg/kg = ppm (parts per million)

Copper (Cu)

Copper is a vital component of many enzyme systems. The first effect of deficiency is usually an impact on reproduction. In more extreme cases there is condition loss, diarrhoea if molybdenum is involved, and changes in coat colour. There are two mechanisms whereby animals may become deficient; either there is inadequate copper in the pasture or competing elements may prevent the absorption of copper by the cow. These competing elements include molybdenum (Mo), sulphur (S), iron (Fe) and zinc (Zn). Iron and zinc are only likely to be a problem under special circumstances. A cow will only ingest high amounts of iron if eating significant amounts of iron-rich soil, such as when grazing pasture very low, especially in winter. Water containing iron becomes unpalatable at concentrations far below that required to interfere with copper. Zinc only becomes significant if supplemented at high rates for an extended period of time during the Facial Eczema season. In both cases, pasture copper levels have to be marginal to low for these elements to affect levels in the cow. Molybdenum is the most important competing element. It combines with sulphur to form a thiomolybdate which is a potent inhibitor of copper absorption. Many farms have had Mo applied with fertiliser over the years (the objective was to assist N

fixation by clover) which is still present in the soil. Liming helps make Mo more available to plants so some organic farms may be particularly susceptible to excess pasture levels. There is also a seasonal effect with Mo levels highest in winter/early spring. Peat soils can have a very high Mo content.

If 60% or more of paddocks have spring pasture Mo levels of 2ppm or greater,

monitoring the copper status of the cows is important.

Testing:

Copper levels in cows decline during the winter and early spring. As long as they have sufficient stored in the liver to see them through, there will not be a problem. Reserves are normally replenished in summer but if the summer is particularly dry and zinc needs to be fed through the autumn, there may not be enough stored up by winter.

Direct measurement of liver copper in autumn is the gold standard as blood levels only tell you what is happening on the day and won’t start to drop until liver reserves are almost exhausted. Biopsies are an option but many prefer to arrange to have samples taken from cull cows at the works. You can do this through your vet – the

standard number is 4 cows, but if you suspect a problem, try to get at least 6 done. They may automatically analyse for Se and Co as well but unless you particularly want these done, save yourself some expense and ask for copper only. Blood testing can be useful in mid-spring (being mindful it’s only a snapshot) since the cows are likely to be lowest at this time. If they’re OK in September, they should be fine for the rest of the season.

Supplementation:

Copper sulphate (bluestone) in the water supply at the rate of 1 gram per cow per day is often enough to correct a simple pasture insufficiency. If the problem is due to high Mo levels, copper sulphate will probably not work. Copper chelate is available as a pasture spray and this seems to work well unless Mo levels are very high – it does have to be applied regularly however. Aim for a minimum pasture Cu:Mo ratio of 4:1 but note that care needs to be taken with pasture sprays – they tend to be quite potent. Conventional farmers get around the Mo problem with injections or capsules and these are probably the methods of choice should they ever be allowed. Some plants, notably chicory and plantain, accumulate copper to a degree and may help in a marginal situation. “Osflo” also contains useful amounts. Adding bluestone to fertiliser is probably not a good idea – it has the potential to upset soil organisms.

Selenium (Se)

Since NZ soils are almost universally deficient, this is the element that almost everyone will need to supplement. Se is a component of enzymes that function as antioxidants which in turn are important in milk fat synthesis and the immune system. Deficient animals will have reduced production, poor reproduction and be susceptible to disease. The highest demand by cows is in the first 4 months of lactation, gradually declining as the milk curve drops off.

Testing:

Se is the one element where there is a good correlation between soil, pasture and animal levels and there is little seasonal variation. However, plants do not actually need it and will not accumulate good levels unless forced to. Plant availability is relatively short-lived – Se additives to the soil tend to become unavailable or leach

within a few months or at most, a year. Basal (unsupplemented) pasture levels are typically around 0.02 – 0.03 ppm. Aim for 0.1 – 0.3 ppm on the milking platform. Cows can be liver tested at the same time as  copper or blood tested. The best time to blood sample is pre-calving (if there’s been no recent supplementation) or mid-spring as a check test. 4 cows is minimum but 6 is better. Little variation between individual cow values suggests levels are rising or stable – a wide variation suggests they are falling. Interpretation remains a little controversial

as to what is an ideal level in a dairy cow. The range classed as adequate on lab reports is fine for dry stock and will keep cows healthy with no reproductive issues but high producing cows will generally benefit from increasing levels. Thus serum Se of 150 (or 2.0 GPX) is the minimum but most vets recommend levels around 5 – 600 (equivalent to around 12 GPX) at least up until the end of mating.

Supplementation:

Se “Chip” is the only certified prill-type product. Applying it in the autumn will maximise levels in the cows in early spring. However, levels can drop off as spring progresses, hence it’s always a good idea to do a check blood test around mid-September. Injections are allowed but they only work for a short time (a month or so). Se as sodium selenate can be added to the water supply either daily or 3 times a week. The objective is to provide an extra 3 – 5mg per cow per day. Be careful if working with concentrated Se selenate, it can be quite toxic. Chelates are available as a pasture spray. The latter work well but again be careful to follow recommendations – they are quite potent. Don’t forget the run-off. Although dry stock requirements are not as high as for lactating cows, significant amounts of hay or silage cut from the run-off and fed to the herd will affect cows’ overall Se intake.

Cobalt (Co)

For much of NZ, Co is not an issue. However farms on central North Island pumice country and areas of the Waikato and Bay of Plenty where ash showers or floods have resulted in deposits from Tarawera or Taupo may need some attention. Levels in pasture show a marked seasonal variation, lowest in late spring/early summer. Co

is a component of vitamin B12 which is synthesised by bacteria in the rumen then stored in the liver and can be drawn on in times of shortage. It is essential for energy metabolism and deficiency primarily results in loss of appetite. Two circumstances can aggravate a marginal situation; parasitism in young calves interferes with B12 absorption and sudden liver damage (such as with eczema) results in massive release of B12 into the bloodstream. This is excreted in the urine leaving the cow with somewhat depleted liver reserves.

Testing:

Animal testing is carried out by analysing for B12. Diagnosis, particularly in a marginal situation, is not easy in cattle. Unless levels are very low, blood testing yields little useful information. The gold standard is measuring liver reserves but this needs to be done in October/November, not a time when many culls are going for slaughter. Due to their invasive nature, biopsies are not popular and the necessity to use local anaesthetic means milk needs to be withheld for a week from biopsied cows. Pasture analysis is probably the best practical option. There can be quite a variation within and between paddocks so a wide range of samples need to be taken to get an accurate picture. Samples can be pooled to save costs if you are primarily doing this for Co. Adequate levels are 0.08 - 0.1 ppm. Note clovers typically have around twice the concentration of Co as rye grass so sampling needs to reflect the proportion of various grass species.

Supplementation:

B12 injections are allowed. Although uptake by plants is poor, cobalt sulphate added to fertiliser (at the rate of 1/3 kg/Ha/year or 1.4 kg/Ha every 3 years) is a common choice in the Taupo area. It is fairly expensive however. There is some indication that after 10 years of application, you can take a 3 or 4 year break.

Iodine (I)

Iodine is essential for proper function of the thyroid gland which produces a number of hormones controlling various aspects of energy metabolism. The classic sign of iodine deficiency is goitre although this is only likely to be extreme enough to be visible in young lambs. However, inadequate intake will affect cows (as usual, the first sign may be poor reproductive performance) and the viability of new-born calves.

If you have an abnormal number of calves born weak or dead, always check for iodine (and BVD…).

NZ soils are often deficient, especially inland areas, but even coastal zones can be affected after prolonged heavy rainfall especially if associated with weak on-shore winds. Some brassica crops (although not turnips or swedes) can produce substances called goitrogens which interfere with uptake of iodine by the thyroid.

Testing:

Unfortunately, blood testing animals may be expensive and, like B12, unrewarding. Traditionally the thyroid hormones have been analysed but in cattle a more accurate test may be for organic iodine. The pasture iodine test is also quite expensive, adding about 50% on to the cost of a standard mineral analysis. There is both a seasonal (highest in winter) and species variation (highest in ryegrass, reasonably high in clover and very low in grasses such as Brown Top and Poa). Testing suspect dead new-born calves involves dissecting out the thyroid gland and weighing it.

Supplementation:

In most cases, if an iodine teat spray is used, cows absorb enough through the skin. The problem may come in winter or with young animals. If feeding kale-type crops, beware of goitrogens. Stock Iodine is allowed. It can be added to water at the rate of 40ml/100 cows per day or sprayed on supplement