Improving Animal Health and Production by Increasing the Trace Element Content of Forage
Trace elements, as the name implies, are required in very small quantities by both plants and animals, and concentrations are measured in parts per million (ppm) or mg per kg. The trace elements discussed in this article, copper, cobalt, selenium, zinc and iodine are those necessary for livestock health and production, and they can be solely supplied by grass and clover.
Copper
Probably the most complicated and controversial of the trace elements under consideration is copper. Copper deficiency in cattle is characterised by a lightening in the coat to a rusty colour due to inadequate melanin synthesis. But not all cattle carrying such a coat are suffering from copper deficiency since breeding also has an influence. (See the Grassland section of the website for deficiency symptoms).
Anaemia leading to stunted and unthrifty growth, together with scouring, often accompanies the coat colour change. In the lactating animal, milk production and quality suffer, and a breeding animal shows a weak oestrus making heat detection more difficult, often leading to a reduced conception rate.
Cobolt
Cobalt plays a key role in both energy and protein metabolism and a deficiency means that the suffering animals, usually weaned lambs, are unable to benefit from the grass and clover they consume. A condition known as pining results in a progressive loss of appetite, anaemia, poor growth and in severe cases actual weight loss.
Selenium
Selenium deficiency influences muscle growth and in young animals the condition of white muscle disease or muscular dystrophy results in the muscle being drained of colour. This leads to a very stiff walk in affected animals. In cattle after calving, due to reduced muscle power in the uterus, there is an increased incidence of retained placenta. Antibody response is also weakened when challenged by an infection such as pneumonia, mastitis or worm burden.
Zinc
Although zinc is required by very many enzyme systems involved in carbohydrate, protein and lipid metabolism a deficiency has an effect on the exterior of the animal. The skin develops dry, crusty, scaly patches with hair loss and in sheep the fleece quality is sub-standard. Both cattle and sheep develop feet problems because of poor hoof strength and lameness. Fertility in the male may also be depressed because of a reduction in sperm production.
Iodine
The classical sign of iodine deficiency is an enlarged thyroid gland known as goitre, which develops as the body tries to compensate for a low iodine supply by increasing the size of the dependent gland. Because of a reduced metabolic rate, milk production, growth rate and reproductive activity, due to an irregular oestrus, all suffer. A greater number of stillborn or weak calves and lambs are born and after giving birth, cows have a greater tendency to retain their placentas.
Forage as a Trace Element Supply
Now that we have established how utterly fundamental trace elements are to livestock health and production, how can we make sure that every grazing animal receives an adequate supply? One method which has gained increasing acceptance in the UK and Ireland is to treat the grass itself with a granular mix of the trace elements coated on salt crystals. Only one application is required each year, usually in the spring, to last for the complete grazing season. This technique has several advantages over other methods. Each animal benefits every day and indeed with each mouthful of treated grass while grazing, rather than expecting it to select from a free-access source. Labour-saving, stress-free and yet demonstrably efficient are adjectives which have been used by farmers to describe pasture treatment with trace elements. Of course the New Zealanders, who are very knowledgeable about grassland management, and the Finns have applied selenium to their soils successfully for many years. When you think about it, what could be more natural than making use of growing grass to carry the necessary added trace elements into livestock.
Author: Tom Blair, UK
Published: April 2001