27 July 2001

Bridge mineral gap but be sure you get it right

By Hannah Velten

MINERAL deficiencies are a potential problem for stock during summer grazing because, on a national basis, grass and grass silage is 15-30% deficient in trace elements vital for livestock health and fertility.

With farm margins desperately low this summer and a shortage of cattle replacements this autumn, it is essential for stock to hold to service, said Rumencos Kelvin Ratcliffe.

Speaking to producers at a fertility clinic, held at Kent Wool Growers, Handcross, West Sussex, Mr Ratcliffe said that many cattle and sheep are put out to summer grass without extra minerals available. Although producers may not be aware of any deficiencies experienced by stock for several months, sudden ill thrift and reduced fertility could hit.

"Mineral supplementation is widely used to bridge the mineral gap caused by summer grazing, however, it must be accurately matched to the mineral status of forage. Inaccurate supplementation is a waste of money as stock may not get minerals they require and will excrete any excesses. Minerals, such as copper, can be toxic when over supplied and others will stop other minerals being absorbed by the animal."

The idea of the clinics is to increase awareness of the importance of accurate forage analysis. Information from a database of 5500 grass and grass silage samples analysed by independent laboratory, Thomson and Joseph, has been used to produce five regional mineral status charts.

During the fertility clinics, producers can identify the major mineral deficiencies in their area for dairy or suckler cows and breeding heifers (see table).

David Thornton, Rumencos marketing manager, believes forage mineral levels have generally reduced due to several factors. "Modern varieties of ryegrass are so fast growing there is less time for roots to absorb minerals and because they are less deep-rooted, they do not pick up the full range of minerals available in soil.

"Liming of land has also increased levels of molybdenum in grass, which locks up other minerals. The progressive elimination of mineral-rich weeds and reduced use of organic manures and basic slag has also added to the mineral status problem."

There are obvious regional differences in mineral status, with the south-west revealing most deficiencies. Mr Thornton believes this is due to heavy grazing of land without mineral replacement, underlying rock type and high rainfall which leaches minerals.

"But by looking solely at regional mineral status, producers could be mislead as mineral status is extremely localised and changes each year," he warns.

Mr Ratcliffe points to areas around Gatwick and Heathrow airports which are heavily affected by sulphur deposits locking up absorption of copper. This trace element is vital for release of ovulation hormones and also influences milk yields and appetite. "Accurate mineral analysis comes down to postcode, rather than region," he added.

Mineral status will also change each year. Mark Littmoden, a cattle and sheep producer from Offham, East Sussex found this to his cost. He is having to supplement copper in diets for the first time. His pedigree Poll Dorset ewes failed to show signs of heat at tupping time this spring and, as a result, his lambing season will now be seven weeks behind. Last autumns lamb crop have also suffered from swayback and retarded growth and beef cattle are showing the signs of copper deficiency, with orange tinges in their coats.

Mr Littmoden believes the reduction in copper levels is due to last autumns wet weather combined with the wet spring washing trace elements out of the soil.

However, vet consultant Tony Andrews believes this summers grass growth also contributed to the problem. "During hot weather, grass growth slows and tends to burn, so stock eat less and they can also ingest soil containing iron, limiting copper absorption. After rain there is a growth spurt, but minerals are diluted in the grass."

Dr Andrews warns against supplementing copper for sheep routinely as it is toxic, so blood tests or liver tests are needed to confirm there is a deficiency. He also points out that cobalt and selenium deficiencies are common during summer, causing ill-thrift and white muscle disease, respectively.

However, ill-thrift does not always indicate a mineral problem, he warns. "First look at the worming strategy, then if they are getting enough to eat and finally blood-tests, taken when stock are on their grass diet without any mineral supplementation."

Although Dr Andrews is keen that mineral deficiencies are identified through blood test, Mr Thornton believes forage analysis helps pinpoint deficiencies on a particular farm. Fertility clinics will continue thoughout July and August across the country.

Producers can contact Rumenco with their postcode and receive a local mineral status (01283-511211, fax 01283-511013. &#42

MINERAL DEFICIENCIES

&#8226 Will reduce fertility.

&#8226 Regional and postcode variation.

&#8226 Accurate supplementation needed.

Regional mineral deficiencies


South-west Mg Mn Co Cu Zn I Se

Midlands and south Mg Mn Co Cu Zn Se

North Ca Mg Cu Zn Se

Scotland Ca Mg Cu Zn Se

Wales Mg Cu Zn Se

Key: Mg=magnesium, Mn=manganese, Co=cobalt, Cu=copper, Zn=zinc, Se=selenium, Ca=calcium, I=Iodine