The main reason for this is the breeding season.
If grass growth continues to be buoyant into May and June, grass management decisions over the next few weeks will determine whether we maximise a cow's intake on pasture, by maintaining grass quality or whether we limit intake and diet quality by allowing grass to become too strong.
Remember that high quality pasture contains a high proportion of green leaf and a small proportion of stem and dead matter, and this principle should be a key focus as we graze through the second rotation and head into the third.
The first step to managing your grass supply and quality is to know what your desired pre-grazing yields is.
Ideally, cows should be grazing between 1,200 and 1,300kgDM/ha in spring, although, depending on your stocking rate and management, this may vary from a minimum of 1,000kgDM/ha to a maximum of 1,600kgDM/ha.
The first step in determining your ideal pre-grazing cover is to calculate your demand per hectare.
This is simply the number of grazing cows or young stock multiplied by the intake of grass per head, which is then divided by the number of grazing hectares available (ie not closed for silage).
For example, 100 cows being fed 17kgDM grass per head (minus 1kg meal) have a daily demand of 1,700kgDM/ha. If this figure was over 30ha, the demand per hectare per day would be 57kgDM/ha/day.
In essence for a farm in this situation, grass growth would have to equal this figure for the average pasture cover to stay the same.
If grass growth was 67kgDM/ha, then theoretically the grass cover would increase by 70kgDM/ha over a seven day period and, if grass growth was 47kgDM/ha, the grass cover should have decreased by 70kgDM/ha over seven days.
Once you've calculated this figure, the next step is to multiply it by the desired rotation. At peak grass growth, rotations should not exceed 24 days and can be reduced to less than 20 days if you are a confident grass manager.
A rotation length of 21 days is often a safe bet and, if this was multiplied against a demand of 57kgDM/ha/day, this would require 1,197kgDM/ha to be available to feed your cows adequate quantity and quality.
The final step is to add on your desired residual, which should be ideally 0kg to no more than 150kgDM/ha in spring.
If we assume that paddocks have been grazed out well to a residual of 50kgDM/ha, this would then set a target pre-grazing cover of 1,247kgDM/ha.
If you ignore this 'trigger level' and end up grazing swards of closer to 1,500kgDM/ha, you will find that your actual rotation length will slow and more and more paddocks will present with heavy pre-grazing covers.
On top of this, heavier pre-grazing covers facilitate the grass plants' urge to send up a seed head and further reduce grass quality.
The calculated pre-grazing yield is an excellent and simple grazing tool and should trigger you into action to manage surplus grass and even potential grass deficits.
When your pre-grazing yield is exceeded, there are three management options to manage a grass surplus. These are:
1. Accumulate a surplus on a small area to be conserved as pit silage/bales (long term silage);
2. Surplus on a small area to be conserved immediately, often as bales (short term silage);
3. Remove a small area of pasture and reseed or sow a crop that can be eaten after the period of surplus.
All three options aim to prevent the immediate surplus manifesting into a surplus all over the farm and the overall loss of quality.
After finally getting the growth weather we need and prosper on, it would be a shame to compromise the cow at such a critical stage of her lactation.
So walk the farm, create a feed wedge with the pre-grazing yield target clearly marked and act on the information accordingly.
- Mary Kinston is a dairy consultant based in Co Kerry. Email: firstname.lastname@example.org