Allocating a Forage Crop to Minimise Waste
25 October 2023
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Grazing forage crops with livestock, generally results in offering quality nutrition throughout the winter at a low cost, compared to housing animals. To ensure the forage crop is maximised it should be allocated appropriately to minimise waste such as trampling, while allowing for a balanced intake of protein and energy for the animals. This can be achieved through grazing animals behind an electric wire.
The electric wire or strips should be long and narrow, allowing for adequate feed space for the grazing animals to all feed at the same time e.g., 1 metre for cattle and 0.30m for sheep. The wire should be moved frequently, offering fresh feed which is ideally daily for cattle and up to every 3-4 days for sheep. A simple calculation can be done to work out how far to move the fence on a daily basis. We cover this further down.
Maximising Forage Crop Utilisation
To maximise the utilisation of the crop, it is essential to first understand its dry matter. There are book values available for all the various forage and brassica crops, however this yield will vary depending on the variety, agronomy and geography. For this reason, is would be advised to analyse the dry matter of the crop through a lab.
To calculate dry matter a small amount of equipment is required including, 1m square quadrat, if you don’t have one of these it may be measured electric fence posts, a bag, pair of shears or a knife, a set of scales and a note pad and a pen.
There are two methods to calculate dry matter,
- Leafy brassicas and broadcast root crops
- Root and beet crops in drills
For method 1 there are 4 simple steps as shown below,
- Place the quadrat in the field avoiding end riggs, etc.
- Cut 1 inch from the ground for leafy crops and lift all roots for root crops, clean the roots before placing in a bag
- Weigh the bag
- Calculate as below:
| Example | |
|---|---|
| Weight of the bag | 6kg fresh weight |
| Fresh weight per hectare (above x10,000) | 60,000kg fresh weight |
| Estimated or Actual dry matter (above x 11%) | 6,600kg dry matter |
| Tonnes of dry matter per hectare (above / 1,000) | 6.60 tonnes dry matter |
The method for root and beet crops is slightly different in that the rows width is measured to ensure a sample of 25m2 is measured e.g. if 50cm width then 5 metres is measured out. Bulbs are picked from either side of the measured row, and the leaf is cut from the bulb before putting these in bags for weighing seperately. This exercise is repeated five times over the field, and a total fresh weight of leaf and bulb is collected. The above calculation can then be repeated.
Calculate Daily Allocation
After calculating the yield of the crop, you can then calculate how far to move the fence or the daily allocation. Two examples are shown below, one with a 300kg steer, the other with a 70kg ewe. This calculation is adequate for forage and brassica crops, but not beet crops, these should be allocated differently.
| 300kg steer requiring 9kg DM/day | 70kg ewe requiring 1.4kg DM/day | ||
|---|---|---|---|
| A | Estimated total dry matter intake (using 3% bodyweight) | 9kg | 1.20kg |
| B | Crop inclusion of the diet (allowing 30% fibrous forage) | 70% | 70% |
| C | Daily requirement of forage crop (A x B) | 6.3 | 0.84 |
| D | Number of animals grazed | 50 | 300 |
| E | Daily requirement of forage crop (C x D) | 315kg DM | 252kg DM |
| F | *Estimated crop yield (DM/m2) (crop yield 10.5 tonnes @70% utilisation) – 1.05kg/m2 x 0.7) | 0.74 kg DM/m2 | 0.84 kg DM/m2 |
| G | Total Grazing Area Required/ Day (E/F) | 426 m2 of brassica | 300 m2 of brassica |
| H | Length of electric fence (feed face) | 200m | 150m |
| I | Width of fence moved per day (G/H) | 2.1 metres/day | 2.0 metres/day |
*Growing cattle will eat 3% dry matter of their body weight, ewes, will eat 2% of their body weight.
Animals should be transitioned gradually to forage crops, allowing the rumen to adapt to the change of nutrition. Animals should be introduced gradually on full stomachs, allowing only a few hours on the crop initially, before building up to full access over a period of time.
There should be a run back area for the livestock, allowing them to go off the crop and forage or to have a dry lying area. This may be a sacrifice area, rougher grazing or a neighbouring field. Livestock should be offered supplementary forage (hay/silage/grass) which should make up at least 30% of their daily intake.
Kirsten Williams, SAC Consulting, senior sheep and beef consultant
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