Pasture and grazing management made simple 4: how to develop a grazing plan

This article outlines how to develop a grazing plan.

Feed budgeting is a procedure for formally planning and evaluating pasture management. It is an aid to improve the efficiency of your grazing decisions. Planning feed use is equally as important with pastures as it is with stored feeding.

A feed budget is simply a numerical description or inventory of grazing management through time. It can be likened to financial budgeting except the feed available (supply) represents income and animal demand or intake represents expenditure. Just as financial management through time (cashflow budgeting) requires income and expenditure to be balanced, feed budgeting describes how pasture growth and animal feed requirements can be matched through time. If the feed supply exceeds demand a ‘surplus’ of pasture exists; if animal demand exceeds the feed supply a ‘deficit’ exists. Feed surpluses may be expensive because pasture is a perishable commodity that deteriorates through time unless it is utilized by livestock or is stored (e.g. as hay or silage). Similarly, pasture deficits may be costly because livestock production is reduced.

One of the purposes of feed budgeting is to identify the most effective method(s) for reducing the impact of pasture surpluses and deficits on farm profit, animal performance and pasture production. Feed budgets can be used for both short- and long-term planning to determine how pasture should be allocated to the different classes of livestock on the farm.

To explain how grazing plans are developed let’s assume a 2 acre paddock is to be grazed by a herd of 40 milking cows. The average live weight of the cows is 1300 lb and milk production per day is 60 lb. A dry matter intake of 42 lb is required, with about 15 lb provided by concentrate. All 27 lb of forage DM is to be provided by grazed pasture. The average pre-grazing herbage mass is assessed to be 3000 lb DM per acre (see Article 2). A post-grazing residual dry matter (RDM of 1500 lb DM per acre (i.e. lax grazing) is required to ensure the 27 lb DM intake per day is achieved. The calculations to determine how long the cows should spend in the paddock are as follows:

Herbage available/acre = (3000 – 1500)
  = 1500 lb DM/a
  or 3000 lb DM in the 2 acres
Grazing duration = 3000 lb DM/ (40 cows x 27 lb DM/day)
  = 2.8 days.

This feed budget, or grazing plan, shows that the cows can be expected to get their forage requirements from this paddock almost three full days. The final day would need to be assessed after day 2. This may indicate that only a half day between mlkings would be possible because of loss of pasture through trampling if conditions have been wet, incorrect critical assessment of pasture mass or greater than expected cow intake.

By completing a similar calculation for each paddock the rest period between grazings or rotation length can be estimated as shown in Table 2 (see Article 7 for more detail about grazing rotations). For simplicity only three paddocks are assumed in the example. Let’s say that these were scored for herbage mass by eye assessment on April 30 and that the net herbage accumulation rate is expected to be 50lb DM/d during May. Paddocks can be grazed for half or full days.

Table 2 Feed budget calculation to determine the number of grazing days available and the rest period between grazings. A 1500lb DM/a post-grazing or residual herbage mass is assumed.

Pdk # Area (acres) Herbage (lb DM/a) Grazing Days Dates Expected herbage (lb DM/a)
1 2 3000a 3.0b 5/1 – 5/3c 2250e
2 5 2900 7.0 5/4 – 5/10 1900
3 6 2400 8.0d 5/11 – 5/18 1500

a Herbage mass present when pastures were scored on April 30.

b Grazing days are calculated as shown in text sample.

 c The calendar dates when each paddock is expected to be grazed.

d The number of grazing days including regrowth (10 days x 50 lb DM/d = 500 lb DM/acre) before paddock 3 is due to be grazed. A total of 2900 lb DM/a (2400 + 500 lb DMK/a) should be present for grazing on May 11.

e The amount of herbage that is expected in each paddock after the last paddock (3) has been grazed. In this case about 15 days will elapse before paddock 1 is to be grazed again (15 days x 50 lb DM/ha/d = 750 lb DM/a regrowth; to be added to the 1500 lb DM/a residual after grazing).

Notice that the calculations include herbage growth that is expected to occur prior to each paddock being grazed. For example, paddock 3 is not due to be grazed for 10 days. The 500lb DM (10 days x 50lb DM/ac expected) that should grow before grazing needs to be included in the calculation of grazing days. The feed budget shows a 15 day rest between grazings of paddock 1 should be possible (i.e. 7 and 8 days respectively in paddocks 2 and 3). This rest period does not allow sufficient herbage to regrow to maintain the rotation (e.g. paddock 1 with 2250 lb DM/acre will only provide grazing for 1 full day on May 19). This reflects the high stocking rate (13 acres for 40 cows or 3 cows/acre). Clearly changes to grazing management are required to prevent overgrazing and reduce milk production, especially as herbage growth rates normally decline in the summer. Increasing supplements, reducing the number of animals grazing, increasing the pasture area, or reducing the time spent grazing are some options available to increase the rest period.

These examples show how feed budgeting by paddock can be used to plan grazing. Notice also how the feed budgets highlight the importance of information such as stocking rate, the amount of pasture available for grazing and pasture growth rates. He calculations involved in feed budgeting are straight-forward and can easily be done with a calculator. Some of your time is required (maybe 1 hour per week) to get the information and complete the calculations, but you will find that this more objective approach to grazing management will help to reduce risk and will increase your awareness of how much pasture the cows are eating.

Author

Warren Parker

Warren Parker
8 articles

Chief Executive of Manaaki Whenua/Landcare Research, NZ

Former Chief Operating Officer—Science at AgResearch, NZ

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