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A guide to great grazing

Cow grazing

A guide to great grazing

Bernard Stack, InTouch feeding specialist, Alltech Ireland

With an unexpected delayed start to grazing this season, spring rotation planners had to be abandoned on many farms. The target of grazing 30% of the platform by the end of February did not happen on even the driest of farms. As a result, cows ended up being housed for longer, which has reduced the number of days at grass by 15 to 20. This loss means that most farms will lose a rotation this year.

Instead of starting the second rotation on April 1, most farms will aim to begin the second rotation by April 15. As a result, second-rotation grass becomes lush and leafy, making it an extremely powerful feed for cows. Second-rotation grass as a feed is the ideal driver of milk output, but not necessarily milk solids. During this time of the year, the grass is high in energy and protein but lacks fibre. Cows eating 17 kg DM of grass testing 12 ME have the potential to produce 22 litres, with enough protein at 25% content to support 42 litres potentially. The cows cannot absorb all this excess protein. As a result, the majority is converted to urea (which has an energy cost) and excreted.

In order to get the most out of second-rotation grass, the cow’s rumen needs to be at a stable/average pH (6.0). By slowing down the rate of grass digestion, cows will benefit from this feed fermenting in the rumen for a longer period. Using a parlour feed that has high fibre content and contains a live yeast, such as Yea-Sacc®, will help to maintain a stable rumen while grazing second-rotation grass. A healthy rumen with adequate fibre levels will lend itself to decent levels of butterfat and protein. It also helps negate the effects of the oil content of grass, which can negatively impact on butterfat.

Cows will be coming into peak lactation at this point, so they must not lose body condition around breeding time. High volumes of milk but low solids highlight that a cow is putting all her efforts into pushing out litres at the expense of body condition. Beating the drop in milk solids while cows are coming into peak lactation with breeding really makes April a key month in the cow’s calendar.

The four rules of better grazing:

  1. Residuals

Grazing to residuals of 4–5cm is a must when restoring the quality of swards after spring’s slow start. This point must not be overlooked, as less than favourable grazing conditions mean that grass from the first rotation will not have been properly grazed out in many paddocks.

  1. Protect grass regrowth

So as not to undo the great work of the cows in achieving residuals of 4 cm, it is vital to understand the important part regrowth plays in the entire system. Regrowth can occur 6–7 hours after a paddock is grazed out. If cows are in a paddock for too long and begin to nibble at regrowth, the shear point at which grass grows drops. Reducing this growth point means it will take grass longer to re-establish itself post-grazing.

Power in numbers is the phrase that comes to mind when discussing grass-regrowth protection. Moving through a paddock as quickly as possible will help to protect the paddocks regrowth. A 36-hour grazing infrastructure is vital, and having the correct paddock size for the number of cows grazing is a key calculation here. A herd of 100 cows will need a 1.9-ha or 4.8-acre paddock.

Paddock shape also plays a crucial role in protecting grass regrowth. A square paddock will encourage the group to graze as a mob. Try to avoid long, narrow paddocks, as the cows will have to track back over the regrowth when entering and exiting the paddock for milking.

  1. Rotation length

Growth rate will dictate the rotation length, and this is the first thing to adjust when making decisions based on the weekly grass wedge. The optimum rotation length is based on the week’s daily growth rate. The table below outlines target rotation lengths with growth rates. The higher the growth rate, the shorter the rotation length needs to be. By hitting the right balance, the grass should reach the three-leaf stage, which is ideal for cows to get the best out of this feed.


Growth rate kg DM/ha/Day

Target rotation length in days










  1. Pre-grazing cover

Targeting ideal pre-grazing covers of between 1,400–1,500 kg DM/ha from the second rotation onwards will lead to entering grass at the three-leaf stage. A cover of 1,400–1,500 kg DM/ha is the equivalent of 8–9 cm of grass. Entering covers that are too high (above 1,500 kg DM/ha) should possibly be skipped in the rotation and taken out as surplus bales. Methods to avoid grass from going ‘too strong’ in front of cows include increasing the demand on the grazing platform. Be careful not to push demand growth rates higher than 70 kg DM/ha/day, or you may find yourself short. Introducing extra stock onto the grazing platform can increase the demand for grass and, as a result, can control the covers that the cows are going into.

By following these grazing rules this season, you will be in a better position to manage the feed in front of the herd. By understanding not only the quantity of grass going into cows but the quality, it is possible to get the most out of this feed without compromising on milk solids. Meeting the cows’ nutritional demands through understanding how grass works in the animal will allow for better management of a feed that makes up to 90% of the diet this season.