The alkathene circle should be placed in representative areas of the crop (the more variability in the crop the more samples required) and everything within that circle should be cut, placed in the bag and weighed to give the fresh weight.
From these weights an average fresh weight can be calculated and this is then multiplied by 10,000 to convert from kg/m2 to kg/ha.
For example 86kg/m2 x 10,000 = 86,000kg of fresh weight/ha.
The next step is to get the drymatter percentage of the crop and this can be done by either sending a sample away to be tested or by using the kitchen microwave.
To measure drymatter, weigh out exactly 100g from one of the samples – digital scales are best to ensure accuracy.
Cut the sample into short lengths and microwave for five minutes (alongside half a glass of water to avoid setting alight) and re-weigh.
Repeat until the weight stops changing and this end weight will be the DM%.
So a 100g sample that weighs 14g post microwaving indicates a crop of 14%DM.
To determine yield multiply the fresh weigh by the percentage of DM.
In this example 86,000 x 0.14 (14%) = 12,040kg DM/ha.
The next step is to calculate the break size.
Knowing the yield of the crop – in this case 12,040kg DM/ha, the number of animals (100 for example) and the kg/DM/animal/day requirement it is possible to work out the width of the break. This is where the calculator is needed.
Divide the drymatter yield of the crop by 10,000 which, in this example, equals 1.2kg/DM/m2 (12,040 kg DM/ha divided by 10,000)
To determine the area required per animal divide the required allocation by the crop yield eg 7.5kg/DM by 1.2 DM/m2 = 6.25m2/animal.
So 100 animals multiplied by 6.25m2 =625m2 break. Divide this by the length of the face to get the width of the break. For example, 625m2 divided by 150m gives a 4.2m break width.
In calculating stock requirements it is important to take likely utilisation into account along with any supplementary feed such as hay, straw and balage.
While information is available on intake, as a rule of thumb 2% of bodyweight equals maintenance, so a 270kg bull requires 5.4kg DM/day for maintenance.
