Grazed grass is the cheapest source of feed for milk production in Northern Ireland. Optimising the proportion and quality of grazed grass in the cow’s diet will have a significant effect on profitability. Increasing the number of days grazing is one of the most important factors in increasing the proportion of grazed grass in the diet.
There are several factors involved in optimising grazing efficiency and increasing the number of days at grass, ranging from the nutrient status and management of the soil, the grass varieties grown, the structure of the farming system such as calving pattern, the grazing infrastructure of roads and water troughs and the grazing management at the shoulders of the grazing season (early spring and late autumn). One of the most important factors in optimising grazing is grass budgeting.
Grass budgeting is the process of balancing grass growth and the grass intake demand of the grazing livestock. The basic ingredients of successful grass budgeting are;
- Grass Measuring
- Grass Allocation
- React and Adjust
- Grass Measuring
You can’t manage what you don’t measure and this is especially true for grass. Grass can be a very difficult crop to manage given its seasonal growth curve, which leads to large fluctuations in the amount and the quality of grass grown over the course of the grazing season. Grass measuring should be carried out on a weekly basis throughout the grazing season and ideally every 5 days during peak growth through May, June and July.
The measuring of the grass can be carried out by several methods including the rising plate meter and cutting and weighing. Grass measurement at CAFRE is carried out weekly with a rising plate meter.
The Rising Plate Meter
The rising plate meter is a simple tool which calculates the sward mass in kilograms (kg) of dry matter (DM) per hectare (kg DM/ha) from the compressed sward height measured in centimetres (cm). When the plate is lowered onto the sward the distance from the ground to where the plate rests on top of the sward is measured. Newer digital plate meters calculate the sward cover automatically, based on a predetermined equation within the digital device. To calculate the sward height using a manual plate meter, the final plate reading should be subtracted from the initial plate reading and be divided by the number of measurements taken.
Several variations of equations can be used to calculate sward cover from sward height, depending on the different stages of the growing season. The following equation was developed at the Agri-Food and Biosciences Institute (AFBI) for use throughout the grazing season;
Compressed Sward height (cm) x 248 + 608 = Sward Cover in kg DM/ha
Sward height = 9.5cm
9.5 x 248 + 608 = 2,964 kg DM/ha
30 to 40 measurements should be taken per paddock in a ‘W’ or ‘X’ pattern to give a strong representative assessment.
Cut and Weigh
Cut and weigh is the most robust method of measurement per sample, however unless several sites per paddock are cut and weighed it may be a less representative value for the entire paddock.
- Place a quadrat (0.5m x 0.5m) in a representative area in the paddock
- If the grass is wet comb the grass to remove excess water
- Cut the grass inside the quadrat to ground level
- Gather all of the grass cut into a bag and weigh it (subtracting the weight of the empty bag)
- Calculate the DM yield in the paddock using the following equation;
- The grass dry matter % (DM%) used in the equation and can range from 14% – 23% dependent on the stage of the season and the weather conditions. In a mix of rain showers and sunshine, grass DM% is typically 16%.
Weight of grass (kg) x grass DM% x 40,000 = kg DM/ha in the paddock
Weight of grass = 450 grams (g) (or 0.450 kg)
Grass DM% = 16% (or 0.16)
40,000 (there are 40,000 quadrats in a hectare)
= 0.45 x 0.16 x 40,000 = 2,880 kg DM/ha
2. Grass Allocation
Once the sward covers on each of the paddocks or fields have been calculated, it is necessary to calculate how much grass is available for grazing on the paddock. The ideal pre grazing cover is 2,900 – 3,000 kg DM/ha. The ideal post grazing cover is 1,500 Kg DM/ha (4cm), however such tight grazing may hinder the performance of higher yielding Holstein cows and a post grazing residual of 1700 to 1800 kg DM/ha may be more attainable.
Grass Available = (Pre grazing cover /kg DM – Post grazing cover /kg DM) x grazing area/ha
|Example: (3,000 kg DM/ha – 1,700 kg DM/ha) x 1.8 ha = 2,340 kg DM|
It is important to accurately quantify the grass demand, which is the amount of grass which the group of livestock require for grazing each day. Individual animal intake will vary with several factors including the weight and size of the animal and if they are being fed meal or offered buffer feeding e.g. silage. At peak intake, under good grazing conditions, dairy cows can consume 16 – 18 kg DM/cow/day.
Once the individual animal demands have been established, multiply by the number of animals in the group to calculate the group demand. Dividing the amount of grass available in a paddock (kg DM), by the daily demand of the group of livestock (kg DM) will calculate how long the paddock will graze the group.
Grass available = 2,078 Kg DM
Group Demand = 1,385 Kg DM
= 2,078 / 1,385 = 1.5 days grazing = 36 hours
3. React and Adjust
Measuring the grass covers on the grazing platform is only useful if the correct management decisions are made as a result. Creating a grass wedge is a helpful management tool to help make weekly grazing decisions. A grass wedge is a simple bar chart of the grass covers in each paddock, ordering the paddocks from the highest to lowest pasture cover, creating ‘the grazing wedge’. It is an easy to follow visual display of the quantity of grass available across the grazing platform.
The paddocks which are to be grazed next will be easily identifiable from the grass wedge, as well as the amount of grass available in them. The grass wedge will also identify if there is a surplus or deficit of grass on the grazing platform.
There are several different scenarios in which management decisions need to be taken. The management decision taken should depend on the stage of the season, the weather and the individual farm that week.
Tools to help manage a deficit;
- Increase the grazing area by grazing silage areas if possible
- Reduce grazing demand by introducing or increase supplement feed (concentrate) or buffer feed additional fodder
- Reduce the number of grazing animals
- Increase the amount of fertiliser sown
Tools to help manage a surplus;
- Identify paddocks with heavier covers to cut out and conserve as baled silage
- Reduce the amount of concentrate feed being fed
- Increase the number of grazing animals
- If the surplus is prolonged, use the opportunity to reseed swards on the grazing platform if necessary
Various forms of grass budgeting software packages are available, which can be very helpful in making the most out of your grass measurement data. Through inputting grass covers and livestock details, a range of different reports can be generated at the click of a button. These features include the grass wedge, a grass budget, annual growth reports and spring and autumn rotation planners.
Please see attached pdf document ‘Using grass budgeting software’ for further information.
CAFRE have developed a number of decision support tools in partnership with AFBI. These tools can be accessed through DAERA Online Services.