Management decisions that impact forage availability, such as forage species/cultivar to plant, fertilizer and weed control needs, along with herd genetics, are very important to the bottom line of any cattle farm.
However, stocking decisions are the most important and should be considered a management tool in meeting short-term and long-term production goals.
Stocking rates are optimally set to provide economic return while not causing pasture deterioration that ultimately leads to costly re-establishment of desirable forages.
Adjustments of stocking rates may also be necessary to compensate for dry weather patterns and seasonal slumps in forage growth.
Stocking rates should be set and adjusted based on a good knowledge of the forage species/cultivars being utilized (growth potential, distribution and quality), herd forage consumption and nutrient needs, soil characteristics (fertility, pH, drainage, etc.) and seasonal weather and rainfall patterns.
Stocking rate controls forage availability
Stocking rate is ideally expressed as bodyweight per acre or animal units (animal unit = 1,000-lb cow), and not strictly on animals per acre.
Dry matter consumption is dependent on bodyweight, with higher intakes by heavier animals making greater demands on forage supply.
Assuming a yearling calf daily consumes 2.5 percent of their bodyweight in dry matter, a 500-lb calf with an average daily weight gain of 2.0 lbs per day will consume approximately 1,100 lbs of dry matter over 90 days, whereas a 600-lb calf gaining 2.0 lbs per day consumes about 1,500 lbs of dry matter over the same period.
For lactating beef cows, 1,000-lb and 1,400-lb cows producing 20 lbs of milk at peak lactation consume approximately 2,200 and 2,700 lbs of dry matter, respectively, over the first three months of lactation.
Basing stocking rate on bodyweights is necessary for balancing forage intake with forage availability. For example, dry matter intake of cows in early lactation or the last three months of pregnancy will increase over those of dry cows.
These higher intakes can occur during periods of low forage growth (summer slump in pasture growth or drought patterns).
Bodyweight can be used to set stocking rates of cowr pastures, but it should also be understood that bodyweight per acre increases as suckling calf bodyweight increases over time.
Furthermore, forage consumption by suckling calves increases over time and places heavier demands on forage supply.
On the other hand, creep grazing or creep feeding of supplements are typically used to increase weaning weights, and they can reduce forage consumption and conserve the available forage.
Effect of stocking rate on animal performance
Stocking rate directly impacts stocker weight gain or bodyweight and condition of cows. Maximum average daily weight gain by stockers is achieved over a range of light stocking rates that results in forage intake being less than pasture growth (Figure 1).
The highest average daily weight gain is achieved with light stocking rates because cattle can selectively graze the highest-quality forage (primarily immature leaves and minimal stem tissue), but undergrazed pastures will accumulate forage grasses and therefore be wasted.
As forage availability decreases as the stocking rate is increased, forage intake will eventually exceed forage growth rate and cause average daily gain per animal to decline.
However, these reductions in average daily gain are compensated by generating greater weight gain per acre for all animals grazed.
These increases in weight gain per acre will occur until a stocking rate is reached where average daily gain is too low to generate higher weight gain on a per-acre basis, and net return declines.
Furthermore, pastures become excessively overgrazed. These effects of stocking rate on cattle performance and pasture health are influenced by soil fertilizer, pH and rainfall patterns.
In other words, a well-fertilized pasture with optimum soil pH and soil moisture will carry more cattle than one that is limited in soil fertility, pH or moisture.
Should stocking rates be set to maximize average daily gain per animal or to maximize total weight gain per acre on perennial grass or grass-clover pastures?
The answer is neither; stocking rates that maximize average daily gain per animal are typically too low to generate the gross return needed to pay input costs, and a stocking rate that maximizes weight gain per acre will eventually result in stand thinning and weed encroachment.
The optimum stocking rate is one that compromises between daily gain per animal and per acre. Rotational grazing should be used, particularly for those forages known to lack persistence with intensive grazing and in regions that typically have dry weather patterns during the growing season.
It is obvious that forage species differ considerably in quality, but their growth potential over ranges of stocking rates also vary (Figure 2).
Higher-quality forages (examples include orchardgrass, bromegrass, ryegrass, wheat and forage sorghum) generate high average daily gains, but weight gains will fall sharply as forage intake exceeds pasture growth.
With grass-clover pastures, the rate of decline in average daily gain with increased stocking rate can also sharply change as clovers are grazed out with heavy grazing intensities.
Productive forages that are moderate to low quality, such as bermudagrass and bahiagrass, tend to be more productive at heavier grazing intensities to generate weight gain.
Bodyweight changes with cow-calf pairs over a range of stocking rates are not as distinct as with stocker cattle.
Following calving, light stocking rates can generate weight gain and condition of cows, but heavier stocking could cause weight losses, which is related to the cow taking “weight off her back” to maintain milk production.
Suckling calves will, therefore, not be as sensitive to increases in stocking rate until forage reaches a low availability that severely limits milk production and forage intake by the calves.
Trends in weight gain over moderate to light stocking rates are similar between continuous and rotational grazing, but average daily gains with rotational grazing are generally higher with heavier stocking rates.
Furthermore, pasture stands under moderate to heavy stocking rates can be better maintained using rotational grazing systems.
Options in adjusting stocking rates during periods of low forage growth
Perennial cool-season grasses and clovers actively grow in the spring and early summer. There is a typical slump in growth during the middle to late summer, which is followed by an increase in pasture growth in the fall.
These forage growth patterns are strongly influenced by air temperature and rainfall patterns. Intensive cattle production requires that stocking rates be set and adjusted as growth patterns change throughout the season.
Cattlemen have a choice to either stock pastures heavy to utilize the active spring growth or stock pastures conservatively to not overgraze during the summer months.
An intensive grazing system will stock pastures to maximize utilization of spring growth, but adjust stocking rates as forage growth declines in the summer.
Aggressive culling of poor performers or selling heavier calves can be done to reduce stocking rates.
Supplementing with hay or alternative feed sources reduces forage intake needs to increase the number of cattle a pasture can carry.
This option becomes more feasible in the presence of drought patterns. Rotational grazing can maintain acceptable animal performance with maximum forage utilization and can extend forage growth and grazing into the early summer months.
A low-intensity system typically sets stocking rates conservatively to reduce the risk of pasture shortages in mid-summer.
Undergrazed spring growth becomes “rank” and low in quality but available for grazing in the summer as pasture growth declines.
Another option to utilize active spring growth is to purchase cull cows or stocker calves to increase stocking rates and maximize pasture utilization while adding value to these cattle prior to the summer slump in pasture growth.
References omitted due to space but are available upon request.
