Guidelines to determining rest period
Rest enables pastures to regrow and store energy reserves before the next grazing. The main predictors of rate of regrowth are temperature (maximum and minimum) and rainfall. As a rule, when pasture growth is slow (winter and dry periods), the rest period needs to be longer and when pasture growth is fast (spring) the rest periodcan be shorter, but generally not less than 20 days.
Post-grazing pasture phase and ground cover are the major drivers for predicting the rest (regrowth) period required before the pasture is ready for grazing again. Plan the grazing sequence of paddocks so that each paddock will be at the desired pasture quantity (kg green DM/ha) and quality (MJ ME/kg DM) at the start of grazing.
• When the planned start date is too early (eg insufficient regrowth), slow the rotation by adding extra paddocks to the planned sequence or provide supplementary feed.
• When the predicted start date is too late (eg excessive growth), speed up the rotation by removing paddocks from the planned sequence.
• Allocate any removed grazing units to other stock based on their grazing needs or plan for fodder conservation, reseeding or later use as dry standing feed.
By using a minimum pasture base of 1,000kg DM/ha and the following formula:
(Number of days in the month) x (Daily pasture growth rate kg DM/ha/day*) = Total monthly pasture growth (kg green DM/ha) for ungrazed pasture.
The number of days’ rest can be estimated for any month by calculating each monthly pasture growth (kg green DM/ha) and adding these monthly totals to achieve a target of say 2500kg green DM/ha at the start of grazing.
What to measure and when
When checking each grazed paddock, post-grazing pasture quantity (kg green DM/ha) and ground cover are the main indicators for predicting the rest (regrowth) period. Based on your measurements and observations aim to predict the start of grazing to within plus or minus two days of the actual start date.
The predicted rest period and planned start for the next grazing event can be delayed or advanced according to the:
• Monthly rate of pasture growth.
• Growing season (good, average or poor)
• Botanical composition of the pasture
• Measurement of the post-grazing herbage mass
• Resource management requirements to maintain a productive pasture base.
Observations begin after removal of stock. When the planned or predicted start of the next grazing event is about seven days away, check more frequently to begin grazing just before pasture energy content and growth starts to decline.
Commonly used grazing terms
Digestibility – A measure of the proportion of pasture or feed that, once consumed, can be utilised by the animal. Higher digestibility usually means higher animal production.
Dry matter (DM) – Plant material without water. Usually expressed as a percentage of total weight of feed.
Fat score– An objective score of the extent of fat cover in live animals.
Feed intake– Amount of feed eaten by an animal, measured in kilograms dry matter per day per head.
Feed on offer (FOO) – Kilograms of total dry matter per hectare (kg DM/ha). The total amount of aboveground, attached plant material.
Grazing unit – A set of paddocks that forms a distinct grazing management unit for one or more herds. It may be a planned rotation where planned movement of the herd(s) ends back at the start point, or it may be a planned sequence, which differs from a rotation in that it is open-ended within the planning timeframe.
kg DM/ha – Kilograms of total dry matter of pasture per hectare. Sometimes called feed on offer (FOO).
kg green DM/ha – Kilograms of dry matter of green pasture per hectare.
M/D – The content of metabolisable energy in feed dry matter. Units are MJ ME/kg DM.
Metabolisable energy – Energy from feed that can be used for animal production.
MJ ME/kg DM – Megajoules of metabolisable energy per kilogram of dry matter. A measure of the energy content of feed, directly related to feed digestibility.
Pasture availability (kg green DM/ha) – Kilograms of total green pasture per hectare. Sometimes called feed on offer (FOO).
Pasture allowance (PA) (kg DM/day/head) – The estimated maximum food intake plus an allowance for trampling and fouling. Allowance is also the pasture available divided by the number of stock.
Pasture growth rate (PGR) (kg DM/ha/day) – The daily growth in kilograms of green dry matter of pasture per hectare.
Pasture quality (MJ ME/kg DM) – Megajoules of metabolisable energy per kilogram of dry matter. A measure of the energy content of feed, directly related to feed digestibility. (It can be calculated as 0.15 x dry matter digestibility % or 0.16 x organic matter digestibility %.)
Plant phenology –The growth stage a plant has reached in its maturation process. This term can be non-specific regarding observable measurements such as plants in phase I, II and III, or specific and measurable by terms such as number of live leaves per grass tiller, or the nature of lower clover leaves (alive or dead).
Plant senescence – The point at which ageing of a plant results in growth stopping in the plant or part of the plant. At this stage energy accumulation ceases, and net utilisable energy starts to drop in the plant or plant part.
Stocking density (head/ha) – The number of stock per hectare on a grazing area or unit at any one time (usually used to describe the number of stock per unit area in a high-density grazing situation).
Stocking rate (DSE/ha) – The number of stock on a paddock or a whole farm (usually used to describe the long-term stocking rate, at least on an annual basis).
Tactical grazing – The practice of using a range of grazing methods through a single year or series of years, to meet different animal and pasture objectives at different times. This is now recognised as the best grazing method.
