SUCKLER cows are a category of stock that get very little compound ration and therefore get little opportunity to be fed supplementary minerals.
There are seven ' major' minerals and 15 'minor' or trace minerals that are regarded as essential for good animal health and performance. A deficiency of one or more of any of these minerals can have major effects on performance and therefore the correction of deficiencies can give a big return for relatively small expenditure. Normally grass and good quality silage are reasonably well balanced for the major minerals but deficiencies of trace minerals, mainly copper, iodine and selenium are common in Irish pastures.
The most important major minerals that can be deficient are calcium, phosphorous, magnesium and sodium. Cows on a diet of poor hay or straw should get some supplementation of the major elements. Diets containing high levels of cereals are deficient in calcium and those containing high levels of pulps and molasses are deficient in phosphorous while having adequate to excess calcium. Excess calcium combined with low magnesium in the diet precalving can result in milk fever immediately after calving. Most compound rations contain a blend of cereals/cereal by-products and pulps/molasses, which tend to balance the major elements.
The most common trace element deficiencies in cattle on forage are copper, iodine, selenium and cobalt. Some of the clinical signs of deficiencies in copper, iodine and selenium are common such as retained afterbirths, abortions, stillbirths, deaths in young calves as well as lowered immunity to disease such as scours, pneumonia and mastitis. Getting a definitive diagnosis of trace mineral deficiencies can be tedious and sometimes difficult. For example, where a blood test may show deficient levels, there may be no clinical signs and supplementation with the trace element is unlikely to give a response if production performance is satisfactory. A response to treatment is most likely where the following conditions apply; (i) herd health and performance is below normal; (ii) some clinical signs indicate a deficiency; (iii) laboratory tests on blood or feed show deficiencies; (iv) supplementation shows a definite improvement in health or performance. The initial step is to check out obvious causes of poor performance such as inadequate nutrition, parasites, other diseases and poor environmental conditions.
For cows in late pregnancy the three most important trace minerals are copper, iodine and selenium. Adequate copper supply in the diet improves immunity status of the newborn calf resulting in better resistance to scours and pneumonia which is the greatest threat to calves in the first month of life. Iodine is stored in the thyroid gland and deficiencies result in enlarged thyroids in the newborn calves. Calves with a deficiency look normal at birth but have lowered immunity and could have a high death rate in severe cases.
Therefore, suckler cows in the last 4 - 6 weeks of pregnancy should be fed about 100g per day of a pre-calver mineral/vitamin mix. The most effective way to do this is to spread the allowance once or twice per day on the silage. High quality mineral licks may also be used but the intake is more variable as is water medication.