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The first essential of the DairyCo 3-Step Sward Management System involves walking pastures on a regular basis to assess the amount of field cover available.
Field cover is the total supply of pasture DM available for grazing and expressed in kilograms of dry matter per hectare measured by a plate meter.
Pasture walking needs to be a weekly activity from around early February until early December. At periods of peak growth it is advisable to assess pastures more frequently as the condition of swards can change very rapidly.
Assessing Swards Visually
Assessments must be made of both sward height and density. Density is important because swards with a high proportion of clover and a large number of grass tillers may contain a much greater amount of herbage than open ryegrass-only swards of a similar height.
Estimating field cover can be difficult when swards are grazed unevenly as a result of poaching, spoilage and/or contamination with urine and faeces, but with measurement an overall cover can be assigned to the field.
The height of pasture growth relative to a Wellington boot can provide a useful practical reference point - a 1500 kg DM/ha field cover roughly equates to heel height while ankle height grass represents a cover of around 2000 kg DM/ha. These are just guidance, and it must be remembered that measurement with a plate meter or using the 3 leaf method will give you the more accurate information you will need to achieve maximum utilisation.
Assessing all fields available for grazing allows them to be ranked in order of cover (from highest to lowest) to determine the order in which they are grazed. Sward cover assessments can also be used throughout the season to determine the best time to start and finish each grazing.
Target field cover for the start of grazing (Pre-Graze Point): 2600 - 3000 kg DM/ha
Target field cover for the removal of stock (Residual): 1500 kg DM/ha
The key target is achieving the residual of 1500 kg DM/ha as this maintains good regrowth and quality in the next grazing round, so the easier it is for cows to graze to 1500kg DM/ha the better. So for cows that are not aggressive grazers, such as cows receiving supplementation (buffer), it may be better to enter these cows at a lower cover of, say, 2600 kg DM/ha which will enable them to achieve the required residual. This is as opposed to the aggressive grazing animals of a solely grass based system which should be able to graze from 3000 kg DM/ha to 1500 kg DM/ha relatively easily.