IBC2000-8 Production

Grazing Bison:  Theories and Realities

John Grinde, DVM
Blindman River Feeding and Bull Testing Station
Bluffton, AB,  Canada

The following article was originally presented at the International Bison Conference in Edmonton, Alberta in August 2000.  The conference covered a wide array of bison topics including production, marketing, genetics, history and much more.  This article has been reprinted with the permission of the IBC2000 Chairman.

Introduction

With respect to pasture management, there are four main questions that require our attention: 1) where did we come from?, 2) where are we now?, 3) where are we going?, and 4) how do we get there?  The grasslands in North America evolved over millennia as sustainable ecosystems.  Key characteristics of the factors that contributed to this evolution are evident in Charlie Russell’s sketch.  Before the white man came, there was 1) multiple species grazing, 2) the predominate grazing animal (bison) was migratory, 3) there was a high stock density, and 4) predators were present.

Man has replaced this natural grazing over the last century by what we refer to as ‘traditional grazing management’.  Comparing traditional grazing management with the pre-white man natural grazing we find: 1) a single species of animal, which is non migratory, or fenced in, 2) low stock density, and 3) no predators. 

Where are you now?

Grassland managers must address the following questions:1) how long do you expect to graze this land each year?, 2) does it yield to expectations?,  3) are the plant  species present desirable?, 4) does it need to be torn up and renewed?, and 5) is the management plan truly sustainable?  In essence, can we do better?

Alan Savory and Stan Parsons have shaken the traditional grazing paradigm (Slide 1).  Their new paradigm came from their basic question - can  we manage grass to mimic the grazing process of wild herds and thus benefit our grasslands? Thus the concept of rotational grazing was introduced.

Geography and climate contribute to what Savory calls the brittleness scale. The distribution of moisture throughout the year and how quickly dead vegetation breaks down are important indicators of brittleness.          

Succession is the natural progression of an environment from a simple state to a more complex state. Cycles that affect this process are:

1)   The Water Cycle: does rainfall run off or is it retained and used by plants?

2)    The Mineral Cycle: are nutrients such as carbon and nitrogen cycling in our soil.  Examples are root penetration and surface litter.

3)    The Energy Cycle: is all sunlight captured by plant photosynthesis or does it strike bare ground? What are our fossil fuel inputs?    

4)    Community Dynamics: plant and animal communities change constantly and over time complex communities that are quite stable develop.

Management is the manipulation of these cycles to achieve desirable change.     

Where do you want to be?

Do you have personal goals?  Is land ownership one of them?  How can you manage land without goals? As a grassland manager is important to clearly identify your goals, therefore, write out a landscape description.  Do you want trees?  A monoculture of annuals? single species grasslands?  where do wildlife and birds fit into your plan?  Do you want to machine harvest crops?  Do you want to lengthen the grazing season?  Again, is what you are planning sustainable?

How do you get there?

As with any goal, progress is made by 1) being knowledgeable, 2) planning, 3) monitoring progress towards the goal, and  4) re-planning as required.  Included in your notes is a grazing chart on which the pastures are listed down the left side and calendar days across the top. I plan in pencil and record actual grazing with ink. This page then becomes a record of grass production.      

Monitoring -what do we measure? Monitor the re-growth of severely grazed plants of desirable species. They should be in a reproductive stage before  the next graze. Growth rates vary and thus, rest periods should also vary.  Monitor pasture transects by measuring i) percentage of bare ground, ii) litter cover, and iii) species diversity.  If monitoring does not show progress towards the goal, adjust then  re-plan. 

Grazing Principles

Grazing principles include: 1) animal impact, 2) stock density, 3) duration of grazing - avoid grazing re-growth, and 4) rest - the period of time between grazings. Use of these principles allows us to manipulate succession and work towards our goals.

1.      Stock Density is expressed as the number of animals per acre per day.  What do we achieve by controlling the stock density? We achieve, i) non selective grazing, ii) trampling of old plant material, and iii) scattering of litter and animal waste .  In Slide 2 there are 400 head on 2 acres.  They were moved twice, therefore, stock density of 100 hd/acre/day.  The cattle in this field were gaining 2.5 lbs per day.  This stock rate is similar that depicted in the Charley Russell sketch referred to earlier (not shown). At very high stock densities the effects are similar to animal impact.

Note: this stock density is easily achieved with poly-wire fence and beef cattle, but is more difficult with bison. The single polytape works well for beef cattle but I have not had good results for long with bison (300 head/4 acres – 1 polytape fence) and I have lots of mangled posts, reels and polytape to confirm my opinion.

2.      Animal Impact is the non selective trampling of excited animals (Slide 3).  While bison do this naturally, it is difficult to do with cattle.  What does it achieve?, i) breaks soil capping and litter layer allowing seed germination, ii) discourages woody species from encroaching, and iii) it improves water, mineral and energy cycles.

3.      Rest is simply ensuring that the plant is not regrazed until it has recovered from the impact of grazing.  Slide 4 shows total rest for 7 years in a non-brittle environment.  What is the effect of rest? - regeneration of woody species as succession moves to climax and an increase in wildflowers, which require long rest periods to regenerate. Slide 5 shows a pasture grazed at low stock density by both beef cows and bison cows (100 cows /30 acres).  Rest was determined by monitoring and varies from 50 to 100 days.  Recruitment of new brush occurred when grazing with beef cattle but grazing the same area with bison reversed this encroachment because bison are more destructive to trees.  The pasture Slide 6 is similar to the previous one except that stock densities have been much higher for 10 years (30-50 head/acre/day).  Succession has been pushed back to grassland.

4.      Duration of Grazing:  The next sequence of slides illustrates lengthening the grazing period into spring and fall (Slide 7-12). These bison yearlings were on grass since early April and off supplemental feed early in May as new growth started.  Note the density and impact from the bison feeling threatened by my presence (Slide 7).  This pasture was spring grazed (Slide 8) and is seen in Slide 7 with bison on it.  There are 120 bison on 10 acres for 9 days (Slide 9) . Stock density is 12 head/acre/day.  Note the variation in grazing severity (Slide 10). Higher stock density would help here.  The extremely grazed plants are not overgrazed because regrowth was not grazed.  Thus, root mass is not depleted.  The extremely grazed plants are the ones that should be monitored for regrowth as they will take longer to reach a reproductive stage than will less severely grazed plants.  Slide 9 shows the same pasture after a 55 day rest period.  Note that most plants are in a reproductive state and grazing will not damage them.  Nutritious forage can be carried into late fall and early winter and then be rationed out for grazing (Slide 11).  Pasture grazed in early September can be left to allow for regrowth.  Once growth has stopped for the year (Slide 12), it can be grazed without damaging the plant root mass. However, in my grass management program, fall grazed pasture will not be grazed until reproductive next summer.  Orchardgrass, which stores it reserves in a crown above ground, is an exception.  It will not tolerate close grazing, especially late in the season.  Pastures with heavy regrowth will be used for winter grazing.

Conclusion

Wherever you live, there will be advantages and disadvantages with respect to forage production, grazing season, costs etc. Your challenge is to utilize these advantages  to reach your goals in the competitive world of agriculture.  Planned grazing can reduce costs, improve carrying capacity, and be sustainable over the long term.  We are fortunate to live in a beautiful place with ample precipitation. Our disadvantage is it can comes as a white solid during any month of the year.  Welcome to Alberta and thank you.