Principles Of Rotational Grazing

(Also referred to as Prescribed Grazing Management or Management Intensive Grazing)

The goal of rotational grazing management is to allow plants to continually produce large volumes of high quality leaf material by setting (1) frequency, (2) intensity and timing, and (3) duration of grazing.

Frequency of Grazing

The period of time a pasture is allowed to recover between successive grazings is referred to as the rest period. The rest period (plus residency time, see below) sets the frequency with which a pasture is grazed. Rest periods should vary over the growing season to allow plants to achieve their maximum rates of growth without becoming so tall and rank that quality is reduced and intake losses occur (see Fig. 8). Note that maximum growth rate occurs at a greater height with tall grasses (orchardgrass) than short grasses (perennial ryegrass, bluegrass).

During the spring, orchardgrass and tall fescue pastures of coastal BC and the PNW produce 100-125 kg/ha (90-110 lb/ac) of dry matter per day. In a 15 - 20 day growth period, the forage height will reach 20 - 25 cm (8 - 10 in) and contain between 1200 and 2000 kg/ha (1100 - 1800 lb/ac) of dry matter available for grazing above a 5 cm (2 in) residual stubble height. During the summer and early fall, growth rates slow to 50 - 70% of those in the spring so a longer rest period (25 - 30 days) is required to accumulate a similar amount of forage. Long rest periods occasionally expose forages to the risk of leaf diseases such as as scald (late spring and summer), stripe rust and powdery mildew (late summer and fall).

Table 4. Comparision of 'Management Intensive Grazing' to 'Traditional Grazing' techniques.
Characteristic Managment Intensive
Grazing
Traditional Rotational
Grazing
Stocking Density * Up to 200 cows/ha
(80 cows/ac)
5 - 20 cows/ha
2-8 cows/ac)
Stocking duration 12-24 hours 1-2 weeks
Rotation length 10-20 days 30 days +

Intensity and Timing of Grazing

The degree to which pasture herbage is grazed down during a grazing event is referred to as the intensity of grazing. The greater the intensity of grazing, the greater the rate of forage utilization, and the greater the harvest efficiency. In practice, grazing intensities are evaluated by comparing pre-grazing and post-grazing forage heights.

When establishing grazing heights, the most important factors include (1) type of pasture plants, (2) time of year, and (3) production objectives of the livestock enterprise.

Pastures consisting of tall grasses (timothy, orchardgrass, tall fescue, reed canarygrass) and legumes (red, ladino and alsike clover, etc.) should be grazed from an initial forage height of 20 - 25 cm (8 - 10 in) down to a residual stubble height of 5 - 6 cm (2 - 2.5 in). This results in 70 - 80% apparent forage utilization. However, the time of year must also be taken into consideration.

Fig 11. The duration that livestock are allowed to access a paddock or field is called the residency period.

On wet soil conditions, where punching or poaching (excessive trampling) of the pasture could be a problem, it is best to let the forage accumulate to a greater height prior to grazing and then to leave a larger proportion of the forage in the pasture after grazing. Keep in mind that grazing cattle may uproot tall grasses on wet soils. Orchardgrass is probably more susceptible to being uprooted than tall fescue or perennial ryegrass. Although this method will help protect the soil and the stand, it does reduce harvesting efficiency, and will require that the pasture be clipped once the soil dries out.

Grazing heights may also need to be adjusted during hot dry weather. Some producers say that it is best to leave more residual forage in the pasture to shield the soil from the sun in order to prevent excessive soil temperatures and encourage good root growth. A large proportion of roots are near the soil surface and leaving some forage canopy protects the roots from overheating and drying out.

Fig 12. Cattle graze selectively; they consume the best forage first and leave the rest for last.

Choice of grazing height has a different effect on productivity per animal and productivity per unit of land area. As the proportion of herbage utilization increases, production as measured on an individual animal basis decreases. This is because the longer and more closely livestock graze a pasture, the amount and quality of forage available for grazing declines. As a result, there is a reduction in dry matter intake per animal and in individual animal performance.

In contrast, increasing the amount of forage utilization increases production per unit area. Even though production per animal is lower, a greater number of animals may be supported, and as a result, a greater amount of the forage produced is converted into livestock product. Paradoxically, if too much of the available forage is utilized, not only is there a reduction in production per animal, there is also a reduction in the amount of production per area.

Farmers must find a compromise between maximizing production per animal and per land area that suits the production objectives of their livestock enterprise. Because grazing heights are the primary controlling factor in the efficiency of pasture production and utilization, they can be extremely useful in guiding the compromise. For optimum animal performance, the previously recommended residual forage heights would be increased by perhaps 50%. For maximum production per land area, residual forage heights should be reduced by perhaps 25%. Managing grazing heights is a skill gained with grazing experience.

Duration of Grazing

The duration that livestock are allowed access to a paddock or field is called the residency period. Residency periods are based on balancing the total amount of forage required by the livestock with the amount of forage in the pasture so that an appropriate amount of forage utilization is achieved. Note that for continuous grazing, residency time is season-long.

The principle of rotational grazing is that residency periods should be long enough to allow the stock to harvest the forage, but not so long that damage to plant growth occurs from uncontrolled defoliation. Residency periods should also ensure that livestock performance is not reduced below acceptable limits, and that forage is not wasted through increased trampling and fouling with manure and urine. When forage supply is in balance with demand, selecting a shorter residency period will provide a higher and more consistent quality of forage, and increase forage consumption by grazing animals (improved harvest efficiency).

Animals graze selectively, they consume the highest quality forage first and leave the rest for last. Unfortunately, what is left is subjected to increased amounts of trampling and fouling with manure and urine. As a result, the longer the grazing animals reside in a paddock, the greater selection they will exercise. Extending residency periods for too long not only reduces the amount of forage actually harvested, it can also negatively influence animal performance.

In order to maintain high and consistent levels of milk production, lactating dairy cows should be given fresh paddocks every milking or every other milking (Table 5). Other classes of livestock can meet their minimum nutritional requirements with longer residency periods (including season-long occupancy - called continuous grazing) provided the total forage supply is adequate, and wasting forage is not a concern. However, where maximizing forage production and harvest efficiency are indicated as primary concerns, residency periods should not exceed seven days.

Manure Lagoon liquid is applied with irrigation water. Blended 1:6 with irrigation water. Have flush barn with solid/liquid separator. Cattle will graze right under the gun. Solids applied on silage/hay field. Apply 3.5 million L (900,000 US gal) of manure over entire acreage. 2 applications. Use Nova meter when applying to know nutrient content. In general, 150,000 L (40,000 US gal) contains 20kg (50 LB) of ammonium-nitrogen. Irrigate with lagoon water on pastures 3 times during growing season: late February, mid-June, August. Solid manure goes on neighbour's land.
Lime Very important. Lime is used to supply calcium more than to adjust pH. Yes, over 100 tons/year applied on farm. Yes. pH values have been ammended with lime. Over the last 8 years have raised pH from 5 to 5.6 Yes, lime is applied at 600-1200 kg/ha (500 to 1000 LB/ac) every 2nd year.
Pasture harvesting On first crop, will harvest some pastures for silage when grass gets ahead. Will make silage out of lowland pastures for 1st crop. Upland pastures only clipped if growth exceeds consumption. Will harvest pastures as silage when grass gets ahead. Close-off field sections of 4-8 ha (10-20 ac) and harvest as silage or hay. Generally, no more than once a year. Usually set aside 6 ha (15 ac) for silage. The key is harvesting early.
Fencing Main paddocks have a permanent single-strand electric fence. Secondary paddocks are larger, about 4 ha (10 ac) and subdivided as necessary with temporary electric fence. Permanent electric fence around larger paddocks, up to 12 ha (30 ac), subdivided with temporary electric fense. Use 'tumblewheel' fences in front of herd, and ploy wire reel in back of grazing herd. Perimeter fencing is a combination of high tensile wire and barbed wire. Permanent electric fence around large paddocks, 4-6 ha (10-15 ac), subdivided with temporary electric fence.
Weed management (see Chapter 5) Not a big deal - clip thistles. We let the cows do it. Spot-spray thistles. Clip weeds once during the season. In the more acid soils, buttercup can be a concern. Most weeds, except for bull thistle, are palatable and nutritious. Cows will eat Canadian thistle if mowed and prickles are facing away.
Main advice Attitude. Attitude - make up your own mind what you're going to do and do it! Farms ask me about switch to grazing to save their operations. If they are heavily capitalized (buildings and equipment), a switch to grazing can't save them. Intensive grazing can provide more satisifying management option for many farmers. Intensive grazing managment takes about an 80% time commitment in labor (just like confined operations), but you're outside more with your herd and that makes it worthwhile. The cows are working for their feed, instead of the farmer. Need to be flexible in all your