‘On/off’ grazing good for cows and grass health

By KEVIN O’SULLIVAN, TEAGASC ADVISOR GRASS is the cheapest foodstuff and the most fundamental way of lowering costs of production on dairy farms is to target a longer grazing season with higher grass utilisation.

In spring ground and weather conditions can prove difficult and thereby reduce opportunities for grazing.

Early spring grazing improves the overall grass growth capacity of a farm but where pastures are badly damaged due to poaching in wet conditions regrowth rates will be reduced. The level of reduction will vary depending on the level of damage incurred but can be between 30-50% reduction for the second grazing rotation.

However good management strategies coupled with good grazing infrastructure can safely increase the number of grazings achieved in early spring and prevent poaching damage to pastures.

The technique known as ‘on/ off grazing’ has a important role to play on all dairy farms. This is an approach whereby cows graze for a limited period (2-4 hours) after each milking.

The aim of on/off grazing is to strike the balance between feeding cows adequately while at grass and minimising the levels of pasture damage. This strategy should be implemented during periods of wet weather/ poor ground conditions to increase the number of days at grass. Turning out cows with an enthusiastic appetite (ie hungry) for grass is also critically important to the success of this strategy as the cows need to concentrate on grazing and nothing else. Cows tend to do most damage to swards when they are not grazing intensively by wandering around. Cows can become restless and move around particularly during poor overhead conditions.

Dairy cows have two main grazing bouts during the day. The first and main grazing bout occurs early in the morning typically after morning milking.

The second grazing bout occurs later in the evening after milking. Previous studies have shown that dairy cows have a natural inclination to graze after a period of fasting. This helps explain why cows have grazing bouts after both milkings. The aim behind the concept of on/off grazing is to take advantage of the cow’s own natural instinct to graze after each milking when given access to grass.

Research indicates that on/ off grazing results in similar milk solids and bodyweight in dairy cows as that of cows that had full access to pasture.

Cows generally adapt to the on/off grazing system after about two days. For practical reasons, the evening milking should be carried out earlier in the evening (eg 3pm) so cows that are on an on/off grazing regime are brought in at 7-8pm in the evening.

Farmers should select the most appropriate paddocks and back fence the cows to prevent damage. Avoid vulnerable paddocks and paddocks with poor access. Paddocks with lower covers are more suitable for on/off grazing and an increased residual height of grass is acceptable in order to prevent damage to the sward.