Monthly Grazing and Browse Management for Sheep and Goat

Monthly Grazing and Browse Management for Sheep and Goat

This is a timeless, indispensable resource that I put together a few years back for  NRCS and Gallahger Fence.

This calendar helps you to prioritize your  grazing and forage management tasks for sheep and goats.  With so many components within the wholistic management schedule, having all of this information in one place will help to ensure that your  key management tasks don’t take you by surprise or, even worst, get missed for another season.

Information on how to manage grazing within transition periods, stretch forage supplies, apply different seeding mixes to different situations, determine the best hay feeding strategy for your operation, and more can be found in this calendar.

Monthly Grazing Management for Cattle

Monthly Grazing Management for Cattle

This is a timeless, indispensable resource that I put together a few years back for  NRCS and Gallahger Fence.

This calendar helps you to prioritize your  grazing and forage management tasks for cattle.  With so many components within the wholistic management schedule, having all of this information in one place will help to ensure that your  key management tasks don’t take you by surprise or, even worst, get missed for another season.

Information on how to manage grazing within transition periods, stretch forage supplies, apply different seeding mixes to different situations, determine the best hay feeding strategy for your operation, and more can be found in this calendar.

Fencing for Serious Graziers

Fencing for Serious Graziers

Electric fencing offers two major advantages over other types of fencing. One is cost. The cost to install a four-strand, barbed-wire fence is about $5,000 per mile. The cost to install a typical, single-wire, electric fence is about $1,600 per mile. If necessary, additional wires can be added to an electric-fence for about 10 cents per foot. The other big advantage of electric fencing is its ease of construction, which improves forage management opportunities. Small pastures can greatly enhance harvest efficiency and increase the amount of forage produced from a grazing system because of the amount of rest that is introduced into the system.


To download the entire pdf click here Electric Fence

Water Points

Water Points

Water the most important nutrient! It’s the largest quantity requirement for beef and dairy cattle (e.g. 15 gal/day = 125 lb/day). Water is commonly the weakest link in grazing systems. Water placement impacts grazing (overgrazing and under utilization) and nutrient (manure and urine) distribution.  If you have excessive trailing is a sign of needing better water distribution.


Download the entire Water Points PDF here.

Timely Tips – June

Timely Tips – June

We are at the change of seasons.  A time to contemplate and plan for summer forage. Note in the graph above, as temperatures hit 80 degrees F. or higher cool season forage production decreases and warm seasons forages kick in high gear.  I encourage you to make warm season and drought management decisions prior to the end of the recommended seeding date for warm season forages, July 1.


  • Stockpile cool season forage into summer
  • Graze a field hard to release the seed bank for natural regeneration
  • Seed summer annuals
  • Seed summer perennials
  • Fertilization to improve warm season production

Stockpile cool season forage into summer. 

Although I think it is wise to carry some cool season growth into summer, the quality of it will be dependent on temperature and rainfall.  It may hold all summer but if it gets hot and dry it will just be some carbon to lay down and forage quality will be very poor.  Red clover and annual lespedeza will extend growth into summer.

Graze a field hard to release the seed bank for natural regeneration

It’s a lot like rolling the dice.  Unless you know the field well you may release some warm season species you don’t want. This technique works extremely well for release of bermudagrass, crabgrass and dallisgrass.  Other plants that are also likely to grow white clover (if it is cool and moist), ragweed, lambsquarter (both test like alfalfa but stock don’t always consume them), spiny amaranth (weed due to spines other amaranths are palatable and high quality), cocklebur (bad weed, big canopy, sometimes consumed), nimblewill (terrible grass weed that looks like bermudagrass, not readily grazed). Grazing 20% of the pastures low May –June is a decent strategy.

Seed summer annuals. 

Crabgrass, cowpeas and lablab are the only species that UT recommend planting as late as July 1.  Forage & Field Crop Seeding Guide For Tennessee

Crabgrass Improved Variety Options Crabgrass improved variety options:

Quick and Big and Red River.

Quick and Big is fast growth and Red River has a longer growing season.  You may want to seed a blend of the two, sometimes folks add annual lespedeza to the mix.

The seeding rate of crabgrass is 3 to 5 lb/ac.  If you add annual lespedeza 8 to 10 lb/ac.  Crabgrass is a reseeding annual that responds to disturbance at least once a year.  Cowpeas, high quality drought tolerant legume which makes a good smother crop if you have an undesirable weed you are trying to control.  Even though it is a little late for millet you may want to add 10-20 lb/ac. of pearl or browntop millet with the cowpeas.  Lablab is typically grown for wildlife food plots but is good forage for ruminants too best used in a mix.


Seed summer perennials

Bermudagrass is the only plant UT recommends planting as late as July 1.  I usually just recommend bermudagrass on areas that are planned for heavy use areas or where nutrients are going to be high.  Bermudagrass has some issues, stem maggot (it kills the primary stem tip reducing production) which most spray an insecticide for control, grazing could be used to reduce impacts also bermudagrass does best where nutrients are high.  There are several improved bermudagrass varieties: Cheyenne II (highest producing seeded type); Laredo (Allied seed variety, blend of Mohawk , KF-194, & Rancher; Wrangler (most cold tolerant).  You can also establish bermudagrass with clippings using Vaughn’s No. 1 which is typically thought of as the Cadillac of bermudagrasses for our area. Bermudagrass can produce high tonnage, be used hard and overseeded with clovers and winter annuals the second year after establishment.

Another warm season grass option although it is too late to seed now is native warm season grass (NWSG) it’s best sown when seed are exposed to a couple of cold chills (vernalization). Now is the time to start planning for it.  I like NWSG sown on lower fertility soils so weed competition is less. On low production you are not giving up much production while the natives are establishing for a couple of years. Usually herbicides are used to establish NWSG however an option to establish it without herbicides would be to terminate existing vegetation with tillage plant a summer annual leaving most of the biomass on the soil surface then no-tilling in cereal rye.  Dormant planting NWSG in December – April into cereal rye.  Rolling down the cereal rye in early April for weed control.  Natives will emerge through the residue in the spring.

Fertilization to improve warm season production

Applying nutrients to grass May – July increases warm season production.  Nitrogen has the biggest impact on forage production, nitrogen also increases protein content in the grass.  Typically no more than 60 lb of nitrogen is recommended in one application and typically applications should be scheduled 30 or more days apart. I personally don’t like over 45 lb of nitrogen in one application because if it turns off dry, high rates of nitrogen can cause forage to accumulate nitrates.

Grazing Annual Cover Crops

Grazing Annual Cover Crops

“Can we graze cover crops?”  The answer is yes, with an “it depends” attached.  It depends on soil conditions, the growth stage of the cover cro,; the reason you planted cover crops, and whether you’re involved in a conservation plan or program that requires other criteria.  Annual cover crops can be utilized quite well by grazing livestock, and they can also be part of a cropping system that can enhance the soil resource, but if grazed then it has to be managed correctly.

The nutritional values of most cover crops will meet the needs of most grazing livestock.  The ability to utilize annuals with grazing livestock allows longer rests periods for pastures, and also the ability to grow more forage, and graze longer reducing the amount of fed feed. Utilizing livestock on a cropland field can also be advantageous for increasing biological activity because of all the added flora of the rumen.  The majority of the nutrients that run through a ruminant animal are placed right back onto the ground from where they came.  The grazing of slightly more mature material mixed with a lower carbon to nitrogen (C:N) ratio species can help increase soil organic matter and get the nutrients in a more available form for the next crop.

These reasons can be positive as long as the primary purpose of the cover crop is not compromised.  Grazing must not cause any additional compaction problems, erosion, and/or rutting, and there must be adequate live plant material left behind.  This live plant residual is needed for adequate growth for the primary purpose(s) of the cover crop such as adequate cover for erosion control, winter survival, and adequate leaf area available for termination; sufficient root growth to reduce compaction and recycle nutrients; etc.

Dry or frozen soils are the ideal conditions to graze cover crops.  The livestock should not be grazing the cover crop under wet soil conditions unless a large amount (>2 tons/acre) of mature vegetation is present.  These larger amounts are normally only accomplished from a summer planting.  The key here is to not increase compaction…at all…nor to cause pugging that will cause erosion or hinder no-till planting of the cash crop next spring.

The cover crops also need adequate growth available before any grazing is initiated.  The start grazing height will vary some according to the species, but generally you want a minimum of eight (8) inches of growth for most species and rarely do you want to graze it down any lower than four (4) inches.  Maintaining adequate live plant residual is critical in keeping the plant growing and serving the intended primary purpose.

Livestock should not be left in any one area for a very long period.  Ideally, livestock should be moved or allocated new forage every 1-2 days.  Larger allotments can be utilized, but expect slightly less efficiency.  Livestock can remove vegetation very fast; keep a keen eye on the cover crops to make sure they are not overgrazed.  The cover crop should be checked every day, whether moving the livestock or not.

The best utilization and control is achieved by strip grazing annual cover crops.  Strip grazing is allocating out a set amount of forage that you know will meet the needs of the livestock for a set time frame and still maintain the required live plant residual after removing the livestock.  This can be achieved with reels of poly-wire and step-in posts.  Generally you will want three sets (reel and sufficient posts) for the front fence, the back fence, and the fence of the next move.

If grazing highly digestible forages add some roughage to slow the passage through their rumen enabling them to absorb nutrients.  The best solution is to not select only highly digestible, high nitrogen forages for a cover crop when they may be grazed.  These highly digestible forages move quite quickly through the livestock’s digestive system when grazed alone.  Planting a mix of forages that will provide both fiber and protein in balance is ideal.  An example could be mixing a warm season annual grass with a brassica in late summer to be grazed later that fall or early winter after the warm season grass has dried off.  Grazing cover crops in the early reproductive stage is the best way to slow the rate of passage through the animal.  You can also feed some hay or soyhulls to slow down the rate of passage.

Water should be provided to the grazing livestock and moved on a regular basis to keep them from spending too much time in any one area.  Portable tanks and water lines are a good way to do this.  Having hydrants or quick couplers located along one side of the field will allow multiple connecting sites.

It is rare to have good soil conditions for grazing throughout the entire fall, winter, and early spring.  Generally, do not leave livestock on the field all winter long.  They should be moved off the site if soil conditions dictate the need to prevent degradation, even if there is available forage still present.  Have a plan to move the livestock off of the field during wet periods, such as moving them to a perennial pasture or sacrifice lot, until ground conditions are okay to continue grazing.  Do not feed the livestock any feed or hay out on the cropland field to prevent excessive gathering and trampling.  Overused sites will become compacted!

Summer idle ground could also be planted to an annual cover crop mix, then grazed either during the growing period, or stockpiled for fall or winter use.

A cover crop mix to consider for grazing and soil health is:

Species                               Pounds/AC       

               Cereal Rye                         40

               Wheat                                 26

               Crimson Clover                 4

               Turnips                               1

               Radish                                 2


The rate of wheat could be increased to as much as 100 lb/ac.  If you are real adventurous you can add a couple of pounds of buckwheat and one pound of sunflowers. The buckwheat and sunflowers will freeze out at first frost.  Perennials properly managed build soil better and more cost effectively than annuals it is typically only recommended to seed annuals in fields with less than 50% desirable stand of cool season perennials like tall fescue because money spent on fertilizer instead of seed would yield more return.  The best pasture to drill cool season annuals in is warm season pastures like bermudagrass, crabgrass, dallisgrass and johnsongrass pastures.

Managing Pastures for Horses and Mud

Managing Pastures for Horses and Mud

Living in mud creates an unhealthy environment for a horse. Mud harbors bacteria and fungal organisms which cause diseases such as abscesses, scratches, rain scald, and thrush. Mud is also a breeding ground for insects, especially filth flies. Insects are annoying at best and at worse carry diseases, bite, and can cause allergic reactions.  If horses are fed on muddy ground they can ingest dirt or sand particles with hay. This can lead to sand colic, a very serious digestive disorder. Standing in mud can lower body temperature, causing unthriftyness and even hypothermia. In summer the temperature on unvegetated soil can be 9 degrees F hotter than vegetated land. Mud also creates a slick, unsafe footing which can cause slips and injuries for both horses and humans. Due to the weight of horses, their habits, and the closeness of grazing, paddocks can easily be overgrazed and when soils are saturated, vegetation is easily mudded out.


The first step in reducing mud (organic matter and water) is management of surface runoff from roofs, roads and the watershed in general. Locate structures and facilities on well drained areas away from drainage ways and sensitive areas.  Locate facilities (barns, shade, water, feed areas, etc) so runoff doesn’t directly enter any water bodies (ponds, streams, intermittent streams, wetlands, sinkholes, depression areas, well heads, etc.).  Typically guttering, dips in road, grassed waterways, and diversions, will address most runoff problems.  Tile drainage can be used for saturated soils if the area is not a “wetland”.


Vegetation: It is the nature of a horse to graze continuously and to graze close. Horses prefer grasses over other vegetation types. Good vegetation management begins with having an alternative place for horses off of the grass when the vegetation is vulnerable to damage. Vegetation should be grazed no closer than 3” for tall fescue and 2” for bermudagrass.  Start grazing when grass is 5” to 8” tall.  Begin grazing time gradually- too much pasture can cause serious problems.  Start grazing about an hour at a time and work up to several hours over a period of weeks. Ideally paddocks would be established in the turf grasses tall fescue and bermudagrass. Tall fescue has the longest growing season and bermudagrass is the most resilient. Generally these will be present in separate paddocks with 30% of the paddocks being bermudagrass.  Stockpile grass on some of the paddocks for use during dormant periods (drought or cold). When soils are saturated horses need to be off of the paddocks.  A stall can serve this purpose but most horse owners prefer to have horses outside for at least a couple of hours three or more times a week.


Heavy Use Area: A small heavy use area surfaced with rock (3/8” diameter or smaller) is recommended for exercise and protecting grass paddocks.  The recommended size of an exercise lot (heavy use area) depends on the horse’s nature, exercise, and age.  The size of the heavy use area can vary from 16’ x 16’ area to a long, narrow enclosure (20’ or 30’ wide by 100 feet) where the horse could actually trot or even gallop.    The exercise area could be used by multiple horses at different times.  The heavy use area would be best located central to all of the paddocks.  Typically it is best to have facilities such as water, mineral, shade, and feed separated for animal distribution.  In this case since the paddocks are small placing water and shade on the same heavy use area will keep the cost down and get maximum use from the heavy use area.


Fencing: Choose the safest fencing you can for your sacrifice area and paddocks. Horses are hard on fences however, they tend to respect electric fencing.  Best if perimeter fence of paddocks is equivalent to a 5 wire or more high tensile electric fence and interior fence is polytape.  White coated high tensile wire is more visible than high tensile wire.  Some owners report problems with high tensile wire cutting horses.  If polytape is slightly twisted it will shake less in the wind. The minimum recommended size for paddocks is 0.4 ac/horse (1.2 ac{0.4 x 3 paddocks}/horse).  A minimum of 2 gates should be installed so gates can be rested, reseeded, and etc. Locate gates for optimum use and flexibility in dividing up paddocks.  Grouping horses will reduce management and cost.



Alternative 1 (Horses provided full feed): In addition to the stall and heavy use area it’s recommended to have a minimum of two grassed paddocks.  0.4 ac/ paddock x 2 = 0.8 ac/ horse. Example: 5 horses = two 2ac paddocks 4 acres total needed in addition to stalls and heavy use area.  .


Alternative 2 (Horses provided 2/3 to full feed): If no stall is used a minimum of a heavy use area is needed with three paddocks.  0.4 ac/ paddocks x 3 = 1.2 ac/horse.  Example: 5 horses = three 2ac paddocks 6 acres total needed in addition to a heavy use area.


Alternative 3: No stall or heavy use area (Approximately one ton of hay would need to be fed per horse): If no stall or heavy use area is used to control horse access to paddocks a minimum of 3 paddocks are needed with a minimum of 0.8 to 1.0 acres/paddock, = 2.5 to 3.0 acres/horse.  Rotate horses to maintain vegetation on the paddocks and allow fields to rest and recover after grazing.  Example: 5 horses = three 5ac paddocks.  Total acres needed = 15acres.


Healthier pastures mean more pasture productivity, healthier horses, and a cleaner environment.


“Horses for clean water”

Cowboy Math – Acres per Paddock

Cowboy Math – Acres per Paddock

This table assumes 5 inches of growth at turn in and good to excellent forage weighing 300 pounds per acre inch.  Livestock numbers are based on 1,000-pound animals with a calf up to 300 pounds.  Consumption rate is based on an average of 2.6 percent of body weight consumed per day throughout the year. Paddock size is an estimate that is best kept within 30% of recommended size.  Recommended paddock size is based on the assumed production information in the table.


Rotation Frequency




Grazing Efficiency
































































Acres/     = (Animal Wt.) X (Intake Rate in % Body Weight) X (Animal No.) X (Days on Paddock) Paddock                        (Inches) X (Pounds per Acre Inch) X (% Grazing Efficiency)

Example 1

Where should I locate water in a 16-acre or smaller field?  Given: 50-head cow herd weighing 1,000 pounds, turn cattle in field at 5” height on good forage, rotation is seven days.

Answer:  The best location for water would be in the middle of a fence line, because for a seven-day rotation, 12-acre paddocks are recommended.  If all fields are of similar size, water could be placed in every other fence line provided that travel distance to water is less than 800’ (water point’s 1,600’ apart3).

Grazing Efficiency2


Number of Paddocks

Approximate Days

on Each Paddock

Grazing Efficiency Includes

Maintaining Minimum Stubble



40% or less

or (80% over-grazed, low yield)

4 to 6 paddocks

7 to 9 days

40 to 55%

8 to 10 paddocks

4 days

55 to 65%

24 to 45 paddocks

1 day or less

70 to 80%



70 to 80%

Grazing Efficiency2


Number of Paddocks

Approximate Days

on Each Paddock

Grazing Efficiency Includes

Maintaining Minimum Stubble

Continuous ——-

40% or less

or (80% over-grazed, low yield)

4 to 6 paddocks 7 to 9 days 40 to 55%
8 to 10 paddocks 4 days 55 to 65%
24 to 45 paddocks 1 day or less 70 to 80%
Hay ——- 70 to 80%

3 Recommended Travel Distance to Water

Lactating Dairy


Herds water as a group if travel distance is over 800’ or lead cow travels over hill or leaves shade for water.

Beef Cows, Stockers, Horses, Sheep, or Goats


1000’ flat land

Reasons for Rotational Grazing

Reasons for Rotational Grazing


  • Calmer livestock– having control of animals is a huge part of overall management.
  • Reduced hay fed– a 12 paddock system vs. continuous resulted in 31% less hay fed
  • Carrying capacity is increased– typically moving from a monthly rotation to a weekly rotation will increase carrying capacity by 20 to 30%
  • Increased gain per acre– rotating animals in a 12 paddock system vs. continuous grazing resulted in a 37% increase in pounds of calf per acre
  • Temperature reduction– vegetation compared to bare soil reduces temperature by ~ 8 degrees in summer
  • Improved Wildlife Habitat– Varying the height of forage and diverse forage systems improve food and cover for wildlife. Biologist like plant diversity and plant diversity comes from soil disturbance and rest for plant recovery.  In a grazing system wildlife are always the first grazers which provides the best nutrition.


  • Better persistence of forages– particularly of forages sensitive to continuous grazing. In general woody plants that goats prefer require a longer rest period (~45 days).
  • More weeds are consumed- some weeds are high quality
  • More uniform grazing, Improved utilization- Continuous grazing typically only utilizes approximately 30- 40% of standing forage whereas rotating approximately twice a week (rotate based on forage height) improves utilization to 60 – 70%.
  • Excess pasture growth harvested as hay- improves utilization even more
  • Higher production– Typically due to increased stubble height, more leaf area, and more moisture conservation production can be increased by 20% over continuous close grazing.
  • Better management– with proper fencing forages with different management needs are fenced facilitating improved management such as overseeding and treading in seed.



  • Reduced Runoff- Improved vegetative cover has 3 times less runoff than overgrazed pasture
  • Improved filtering of water– Increasing stubble height improves filtering of runoff.
  • Better distribution of dung and urine– improving the environment through proper placement.
  • Improved water quality– with proper fencing animals spend less time loafing in water areas and drink from selected and protected watering points. Bacteria, concentration of nutrients and soil erosion are all reduced when practicing rotational grazing.
  • Streambanks are more stable– Livestock enter streams less frequently (i.e. 5 paddocks system- animals are in one paddock only 20% of the time that’s a reduction of 80%). Treading followed by rest increases plant diversity – resting allows vegetation to establish or recover.  Grazing provides better plant diversity than total exclusion which long term results in only woody vegetation.
  • Soil loss- Overgrazed pasture can have soil loss of 9 tons relative to 1 ton for well managed pasture.


Pasture to Silvopasture

Silvopasture Plan

Goal: Managing timber and grass to the advantage of both.


Light Management and Tree Planting:


Harvest salable timber or perform hack and squirt technique to remove low grade trees providing light for regeneration of trees and to grow grass.  Work with forester on designated trees to remove. NRCS can currently not recommend removal of trees by other methods due to potential impacts on bat habitat. The minimum light needed to grow cool season grass is 50% light to the ground with a minimum opening of 0.10 ac (66’x66’).  To grow warm season grass a minimum of 60% light (70’ x 70’) is needed to the ground.  The layout of trees can be scattered or in rows or a combination of the two.  Minimum trees per acre is 27 trees/ac (average spacing of 40’x40’) and the maximum to grow grass is 304 trees/ac (average spacing of 8’x 18’).  Thinning may be required in the future to improve tree growth and maintain productive grass. 

 Shade for Livestock:  

If shade is needed for livestock planting trees on the south and or west side of a paddock is desired, south fence line is best.  Unless it is a wide band of trees that will provide 63 square feet of shade or more per cow calf with access through the shade a line of trees will be needed on every fence line.  Another option is a cluster of trees planted or left so livestock have access to shade from multiple paddocks.  In this case ideally there would be a cluster of shade trees accessible from all paddocks.  The minimum size of this planting is 630 square foot per cow calf with the shade area used fifty percent or less of the time.

Livestock exclusion:

If trees are less than 15’ tall they will need to be protected from livestock for horned cattle it will likely be longer.  The typical browse height is 5 to 6’ so we want to protect the trees from browsing to 6’ or higher.  Set stocked livestock are more likely to rub on the trees and remove the bark girdling and killing them.  Livestock exclusion can be: a fence that restrains livestock away from the terminal bud and trunk, factors are height of the fence and distance from the tree (i.e. 42” electric fence and 24” inset of tree), a cage 18” diameter 6’ tall, 6’ diameter 5’ high or tubex or vexar 6’ tall secured with multiple post to prevent damage from livestock. Be observant watching for any potential damage to trees.  When trees are young they are particularly prone to browsing and being rubbed on.  Protection of the terminal bud is the main concern.  In wet conditions do not allow livestock to graze timber areas where soils are prone to compaction (e.g. Godwin soil type). Be aware of the danger of windfall to humans and livestock where trees have been killed by hack and squirt particularly in windy conditions.  Also be sure grazing restrictions are adhered to according to herbicide label or UT guidelines.

 Grazing Management:

 Practice rotational grazing for cool season forages allow forages to reach a minimum of 8” prior to grazing and graze down to 4” or taller. Allowing forages to reach the boot to early head stage is ideal for soil health and achieving the best balance of biomass for and forage quality. Livestock should not be allowed to denude land under trees, strive to maintain soil cover of both residual plants and dead residue. Rotation will be based on grass height, cover and impacts on trees and all vegetation however an approximate rotation will be 4 days or less on a paddock and a recovery time of 28 days or more. A recovery time of 45 days or more will be strived for. In the winter time a recovery time between grazing may be as long as 210 days.
Native warm season grasses (NWSG) will be 18” tall prior to grazing and not grazed lower than 8”. Manage for 12” height or taller prior to the first frost or November 1 whichever occurs first. After frost they can be grazed, it may improve production of NWSG to graze them low in March prior to green up. A managed prescribed fire can also improve production of NWSG, contact TWRA or TDF before burning. If vigor of native grasses is slower than expected allow them a longer regrowth period prior to grazing remove no more than half of the height when you do graze them.

 A graze plan (forage animal balance spreadsheet) will accompany this document.

Seeding Mixtures for silvopasture areas


Cool Season grass mix:



 Native Warm Season grass mix: 




 Locate mineral, supplementary feed and hay 30’ or further away from desirable trees.  Water for livestock will be placed high on the landscape and strategically located so the paddock can be further subdivided.  Strive for a travel distance for livestock to water being 800’ or less.  The pipeline can be burst proof high density poly pipe on top of the ground or buried 18” underground permanent water tanks can be installed but you are encouraged to use quick couplers with portable troughs. In general water is needed in every other fence line.


 Be observant and manage livestock to enhance the growth of trees and forage.  If trees are showing signs of decline reduce livestock access to the trees. Manage to keep adequate light to the ground to grow forage and respect minimum grazing heights.