The pasture surplus dream
The big issue to focus on in this early stage of the season is to continue to seek to achieve ad-lib feeding of the milking herd - that is to say, the cows are being allowed to eat as much as they can so that they have a chance to reach their peak milk production potential.
Given the extremely difficult season to date, it is hard to imagine leaving post grazing pasture residuals slightly higher than the normal 1500kg DM per ha but this is the best sign that milking cows are ad-lib feeding. Hopefully we find ourselves in this situation by the start of September!
However, by the start of October pasture quality should become the focus and the post grazing residual pasture levels need to be back on the target of 1500kg DM per ha (25% of the paddock with some clumping left and a tiller height of three to four centimeter between the clumps).
If the pasture base becomes stalky, then feed quality will decrease leading to a fall in the herd's milk production in late spring and early summer, even though there appears to be plenty of pasture available to graze. A rapid fall from peak production is usually an indication that there has been poor pasture control leading up to this stage of the season. In fact, many trials have demonstrated that production is affected right through the summer period if target post-grazing residuals are not achieved through a period of spring surplus.
Crucial to this aspect of pasture management is the early recognition of a developing pasture surplus and a plan to deal with it. Failure to react quickly will lead to a deterioration in the pasture sward as well as a reducing ability to convert any surplus into quality silage. Proof of the difficulty in getting this right are the surveys that show that more than 70% of the silage made in New Zealand is of poor quality and will not meet the needs of a lactating dairy cow.
When is there a surplus and how big is it? The three-leaf principle can be used as the basis for this assessment by firstly establishing the speed for the rotation which in turn determines the area that can be grazed by the herd each day. If this area will provide more pasture than the cows are capable of grazing to the target 1500kg DM per ha residual, then the area allocated for grazing can be reduced. The balance of the area is then surplus that can accumulated and harvested as grass silage.
If quality silage is the goal, aim for a maximum period of closure of five to six weeks from the last grazing as from this point on, the protein and energy levels will be steadily falling. The golden rule is that if it is not suitable to feed to a milking cow before conservation, then it will certainly not be suitable after conservation!