As we near the end of August, growth rates are beginning to drop. Weekly grass measurement is needed to ensure the autumn budget is on target. The peak grass covers on farm should be achieved by balance day; the date when demand/ha matches growth, before growth rates drop below demand for the remainder of the year and we eat into the ‘grass bank’.
The Average Farm Cover (AFC) required by balance date is dictated by:
1. Stocking rate – A peak AFC of 1,200kg/ha; (for a spring calving farm) or a maximum cover/cow of 450kg. E.g. a farm stocked at 3.0LU/ha would build up to a peak AFC of 1,200kg, whereas a farm stocked at 2.0LU/ha would build up to a peak cover of 900kg/ha (450kg/cow). To increase cover above this would result in higher pre grazing covers, poor grass utilisation and suppressed regrowths, as well as curtailing milk production
2. Seasonal calving – autumn-calving herds do not build up the same level of grass cover on farm as high pre grazing covers (>1,700kg/ha) are not suitable for fresh calvers, primarily due to the lower dry matter intakes and energy content of autumn grass compared to spring grass. To ensure pre grazing covers do not exceed 1,700kg, we must target an AFC of 850-900kg/ha by mid-September, irrespective of stocking rate. The cows will be supplemented from early-mid October depending on AFC and fully housed by early November, contrasting a spring-calving herd that would try to stay at grass until mid-late November. This will enable the grazing platform to accumulate extra growth in November ahead of the heightened grass demand of next spring when all cows will be at peak intake at turnout, resulting in a high demand.
On farms where spring and autumn calving is practised, the target covers will be between the two above scenarios, dependent on the percentage of animals calving in autumn. Johnstown Castle research has shown that were a herd is partially autumn calving/predominantly spring calving, calving in October (instead of late August/September), allows for easier management, fresh calvers can be grazed by day for the first two weeks of lactation then housed by night.
Accumulating heavy grass covers in autumn must be done carefully and through using the autumn grass budget to help predict target weekly growth rates and AFC’s. Grazing residuals must be excellent to ensure high grass utilisation is achieved this autumn. If ordering fertiliser for blanket spreading the final rotation, a compound will be beneficial, allowing some replacement of p and k off-take throughout the year. Scanning cows must be done by early September to have reasonable accuracy in pregnancy status/due date in spring.
