Cattle are beginning to reappear in fields after their winter sojourn indoors.

Many farmers consider grass to be a cheap food for their livestock, but nothing could be further from the truth when the high capital value of land is taken into account - so it's important to graze it as efficiently as possible.

Managing pasture properly is one of the biggest challenges facing livestock farmers in the summer. Grass that is allowed to grow too long and form seed heads is fibrous and less nutritious - but overgrazing is just as bad and leads to ill-thriven animals through a shortage of food and a build-up of parasites, as well as weakening more productive grasses.

There is an old saying that "sheep should never hear the church bells twice in the same field". In other words, because sheep are selective grazers and prefer to nibble short, sweet grass leaves and clover, they thrive best when they are moved to fresh pasture every week.

Cattle on the other hand aren't so selective and will eat coarser grass but, like sheep, still do best on leafy pasture. Many exploit the different preferences of cattle and sheep by grazing them together - allowing the sheep to nibble the tastier, sweet grasses while the cattle eat the coarser ones.

Continuous grazing is a one-pasture system in which livestock have unrestricted access to the pasture area throughout the grazing season. It is a simple system to implement and manage with minimal capital investment and movement of animals.

However, continuous grazing usually results in poorer forage quality and quantity. Pastures are often grazed unevenly by livestock, as the animals overgraze the plants they like and shun the ones they don't. That has led farmers to develop controlled grazing systems.

Simple rotational grazing is a pasture system in which more than one pasture area is used and livestock are moved to different areas during the grazing season. Pastures need rest periods to recover from grazing and allow plants to re-grow. The longer a pasture rests, the less infected it will be with stomach worms.

Simple rotational grazing usually increases forage yields and quality allowing increased stocking rates and better weed control. On the other hand, fencing costs are likely to be higher than with continuous grazing, and there may also be a need to invest in more water troughs.

Intensive grazing systems like strip grazing and paddock grazing are often the most efficient, but involve a lot more management and investment. Strip grazing involves giving livestock a fresh allocation of pasture each day, and controlling the animals by means of an electric fence that is moved daily. It has the drawback that if the field is too big, the animals start to graze re-growth.

Paddock grazing overcomes that problem by moving animals every two to seven days to a new paddock. The great advantage of strip-grazing or paddocks is that any surplus grass can be made into silage at an optimum stage, rather than be allowed to become fibrous.

The trick with paddock grazing is to know how much dry matter (DM) is available, so it is essential to have a method of measuring the quantity of grass per hectare and its DM. Some are now measuring the grass in every paddock each week with an ATV-trailed grass meter. The information gathered is downloaded to a PC which uses a specialist programme to quantify the DM available on the farm. That gives the farmer a detailed understanding of the daily growth rate of his grass, allowing him to budget the herd or flock's feed going forward and the optimum time to move the animals on to the next paddock.

Different farmers have different criteria, but many farmers will move their livestock into a paddock when it has around 2500kg of DM per hectare and move them out when there is between 1200 and 1500kg left.

Some farmers don't allow their cattle out-of-doors to graze and practice a system called zero grazing, where grass is cut every day and carted to the sheds. That's more common elsewhere in Europe, although quite a few Scottish dairy farmers now keep their herds indoors all the time and feed them a TMR (total mixed ration). That's where grass is made into high-quality silage and mixed with other ingredients into a TMR that has the same nutritional value every day of the year.

It's all about making the most of grass.