Dairy notes May 2009
Heat detection
With a slippage in calving pattern being a significant feature in many dairy herds this past year, there are going to be more cows than usual to serve after turn-out. For herds using AI, a heat detection aid such as tail painting should prove very useful.
Apply a 10 cm wide strip of paint along the tail head to all cows not confirmed in calf. Check the cows at milking time – a rubbed stripe is likely to indicate heat activity. Update the heat records to identify cows which are not cycling.
Tail painting and record keeping will also prove useful where a bull is being used. Rubbed tail paint will help you identify cows which have been served, allowing you to record a service date - aiding future decisions on drying off date and dry cow antibiotic use. The records will also let you identify early if there is a bull fertility problem.
Changing paint colour after a cow has been served will help to identify non-cycling cows needing veterinary attention.
Wilting
The positive impact of feeding high dry matter silage on cow intake and performance was evident on many units last winter - hopefully the weather will again favour wilting. To achieve a target dry matter of 25 percent consider:
- Assessing dry matter (DM) before mowing. If grass is wet when walked, the DM is about 15 percent. If your boots are dry the DM is about 20 percent
- A crop cut at 20 percent DM will reach target in 24 hours if left in single swathes in dry weather.
- In ideal wilting weather a crop will reach target within 8 hours if spread out
- Even in good wilting conditions, crops cut damp will need to be spread if the target DM is to be achieved within 24 hours.
- Avoid overwilting which can produce unstable silage. If ensiling is delayed, rowing up swathes reduces wilting rate.
Fertiliser for Second Cut
Silage making will soon be in full swing so now is the time to decide which fertilisers to purchase for second cut. Soil fertility and availability of slurry will have the major influence on this choice.
Do you have recent soil analysis results for the silage fields? Make use of this information to plan cost effective use of slurry and fertilisers. 100kg nitrogen (N)/hectare (80 units/acre) is the normal recommendation for second cut, but phosphate (P) and potash (K) recommendations vary according to soil reserves. The P & K requirements for soils at various indices are given in Table 1.
Table 1 – P & K Recommendations for Second Cut
| Soil Index | 0 | 1 | 2 | 3 | >3 |
|---|---|---|---|---|---|
| P kg/ha | 25 | 25 | 25 | 0 | 0 |
| K kg/ha | 120 | 100 | 75 | 40 | 0 |
The table indicates the total P & K requirements for the second cut. Allowance has to be made for the N, P & K content of any slurry applied before deciding what fertiliser needs to be applied. For example, a field with a soil analysis of P index 2 and K index 1 requires 100 kg N: 25 kg P: 100kg K/hectares (80 units N: 20 units P: 80 units K/acre).
If 22,500 litres of cow slurry/hectare (2,000gallon/acre) are applied by spread plate, the nutrients available for grass growth will be 13.5 kg N: 27 kg P: 72 kg K /hectare. While the P in the slurry will meet the crops P requirements, an additional 86 kg N and 28 kg K will have to be applied as fertiliser. 7.0 bags/hectare (2.8 bags/acre) of a high N: high K compound such as 25.0.13 could be used, with a small surplus of potash being applied. If the slurry is applied using trailing shoe allowance can be made for the more efficient use being made of the slurry nitrogen. With 10 kg more N available from 22,500 litres of slurry, fertiliser use could be cut to 6.2 bags/ hectare (2.5 bags/ acre).
If no slurry is available for application, then the option would be to apply 7.5 bags/hectare (3 bags/acre) of a high potash compounds such as 24.6.12 with additional potash applied as a separate dressing of muirate of potash (60 percent K) at a rate of 1.25 bags/hectare (0.5 bags/acre).
Sulphur deficiency is now quite common in second and third cut silages so ensure the fertiliser used for these later cuts contains sulphur.
Take advantage of the trailing shoe system to reduce fertiliser nitrogen use
