A ewe, with her newborn lambs, following a winter in a shed is turned into a field of leafy spring grass. Ignoring the grass, first she nibbles a dandelion leaf, and next a dock. Why?
Cattle are introduced to an excellent new sward of grass and clover, yet they first go and clip the old grasses round the hedges. Why?
Cows are grazing lush paddocks, yet their first choice is the grass beneath the electric fence wires and this is grazed the barest of all. Why?
Why do some cattle lick the clay, munch at your jacket or even try to chew stones?
It is tempting to think that in each of these cases some internal signal is directing the animal to select plants or a material that will correct a dietary deficit. A lacking of trace elements springs to mind.
"Maybe, but not necessarily so," says Dr Phil Rogers, whose Teagasc career embraced the subject of trace elements and minerals in livestock.
"It may be the fibre that an animal seeks. Also cattle and sheep like variety in their diet and they may nibble at plants or materials out of curiosity."
But trace element deficiency was and is very much a fact in Irish livestock. As Dr Rogers outlines it: "You have the four majors -- calcium, phosphorous, magnesium and sodium; six traces -- copper, cobalt, zinc, iodine, zinc and manganese; plus the three vitamins -- A, D3 and E."
Crop growth, too, can be impacted by trace elements such as zinc, copper, cobalt and boron.
Trace element deficiency in livestock can result in poor thrive, poor fertility, higher mastitis, weak and dead calves, retained afterbirth and a general weakening of the immune system.
With the main dairy and beef cow breeding season about to start, correcting any trace element deficiency is a management issue for farmers. Where a deficiency exists, correcting this problem is extremely cost effective.
Many of the above nutrients can be recycled within the system once the initial deficiency is corrected. Exceptions are iodine and magnesium, and possibly cobalt.
Grasses and plants can vary widely in their trace element content depending on the soils beneath and interactions with other trace elements.
The table (pictured), compiled by Teagasc, shows a huge range in the soil levels of some trace elements.
Soils formed from the parent materials granite, sandstones and quartzites are low in cobalt, copper and zinc. In contrast, soils formed from basalt shale and dolerites are richer in these trace elements.
Peaty soils are extremely low in trace elements, especially copper, and this can be exacerbated by high molybdenum. Limestone contaminated with clay can be okay for trace elements but not so for pure limestone.
Couple this with the fact modern fertilisers contain less contaminants, which in the past may have carried trace elements.
Higher use of fertiliser and lime tends to exhaust supplies of trace elements. Modern higher yielding grasses and crops are more demanding on trace elements.
If you really want to trigger a trace element problem, reclaim and reseed and use high levels of fertiliser on marginal land. If you want to precipitate a copper deficiency, use excess sulphur fertiliser on a soil that is already low or marginal in copper.
Within grasses, the leaf carries less trace elements than stem. Slower growing grasses and weeds are generally higher in trace element content.
At this time of year lush, low dry matter, leafy grass passes through cattle quickly and emerges as a greenish black scour. This fast rate of passage results in poorer absorption of trace elements and magnesium. Hence the extra threat of grass tetany in cows and ewes grazing wet spring grass.
Adding a fibre such as hay or straw reduces the rate of passage of leafy grass. This gives more time for mineral and trace element absorption.
However, it is important to get the balance right. Throwing trace elements at livestock is not a panacea to cure all ills. Modern, fast growing, high sugar and leafy grasses may be deficient in trace elements but these grasses still put most money in the farmers' pockets.
At one stage Teagasc operated a laboratory at their centre in Grange which analysed cattle blood samples for trace element levels. This gave an excellent picture nationally but regretfully this lab has been closed. On copper, the lab showed that in the 1960s, 63pc of dairy herds were copper deficient. This was addressed mainly by supplementing dairy rations so much so that by the 1990s, only 2pc of dairy herds were copper deficient.
At that time the beef herds showed little improvement on copper levels. Iodine was deficient in 80pc of herds and is still likely to be the trace element in greatest deficit.
Cobalt deficiency is widespread in sheep, especially in lambs post weaning. But some vets in the midlands have also reported a cattle response to cobalt.
Supplementation of trace elements can be via self-feed licks in buckets, by inclusion in a ration, by injection, by rumen bolus.
Dr Rogers has a preference for oral supplementation either incorporated in the ration or via a bolus.
"It's the cheapest, surest and most effective," he says.
Recently in the Farming Independent, Laois suckler farmer Robin Talbot reported enough satisfaction in cow breeding performance from using a trace element bolus for him to repeat the exercise.