BIOLOGICAL EFFICIENCY FROM RANGELANDS THROUGH MANAGEMENT STRATEGIES

by C. Wayne Cook

SUMMARY

In a biological system both plants and animals are integral to serving man's needs; however, the full potential of the system is not generally known and is seldom reached with presently used management skills.

Plants differ in how efficiently they convert solar energy into biomass; animals differ in how efficiently they convert plant production into meat. Management techniques can enhance the production of plant communities through developed diversity and planned grazing systems. Similarly, animals respond remarkably to management practices that provide a nutrient balance that meets their physiological need.

The efficiencies of plant and animal populations in converting sunlight into forage and thence into animal biomass is an important aspect of evaluating the biological efficiency of rangeland ecosystems. Careful selection of range types, animal species, and management systems is crucial.

The biological efficiency of entire plant-animal systems is frequently judged on the basis of net monetary return to the overall management operations. But biological efficiency alone, without a cost-and-return evaluation, cannot ensure profitability. Performing a marginal cost analysis that evaluates each successive production increment throughout the management system is the only way to practically use biological efficiency.

All feeding (or production) levels contribute to biological efficiency and must be carefully evaluated in management decisions. That is, the output (weight gain and offspring production) of all animals must be evaluated, not just of breeding age animals. The biological efficiency of rangelands can be increased by 1) supplementing range forage with harvested forage crops, 2) multispecies grazing, and 3) increasing the animals' genetic potential for using range forages.

INTEGRATED USE OF RANGE AND CROP FORAGES

In the United States, rangelands alone are not generally suited to producing acceptable-grade meat from domestic animals. However, current studies are showing that range forage, when used along with permanently seeded pastures and grazing-crop forages, can produce acceptable meat. This method can be more economical and biologically efficient than conventional methods of feedlot fattening. This work showed that by using a system of grazing range along with seeded spring pastures of crested wheatgrass and sorghum forages in the late summer and fall (when range forage is mature and dry), acceptable beef could be produced without the use of grain.

As shown in table 1, animals given complementary forages (treatment 2) produced a higher grade of carcass than did animals grazing only range (treatment 1). However, the actual dollar cost and expenditure of mechanical energy for cultivation was higher for the complementary forages. From the standpoint of biological efficiency when calculated strictly on the basis of animal biomass produced per hectare of land, the complementary forage system was considerably more efficient. The range only produced 24 lb/acre (27 kg/ha) of retail meat and the complementary forages produced 37 lb/acre (42 kg/ha). This is a fair comparison because the forage sorghums and the seeded range were grown on comparable native rangeland that was plowed and seeded (which constitutes a manipulated ecosystem).

It can be seen in table 2 that biological efficiency, when calculated on the basis of energy used for cultivation expended per kilogram of retail meat produced and marginal costs per kilogram of retail meat produced, varies with each increment of the production cycle. The production of the calf before weaning is inefficient compared to production by a weaner calf. This is because the indirect conversion of plant metabolic energy to animal biomass by the calf before weaning is not as efficient as the direct conversion by growing animals. In addition, only 90% of the females produced a calf that lived until it was weaned. Therefore, barren animals are a burden for the surviving offspring. The most efficient animal appears to be the yearling steer, which only requires energy for growth and maintenance.

At 8 to 19 months a steer is considerably more efficient in converting plants to biomass than his dependence on milk when younger or while he was receiving concentrate feed in the feed-lots. This suggests that the range livestock producer should at least consider maintaining an all-age group, consisting of weaner calves, yearling steers, and heifers, to take advantage of the lower energy requirements of growing animals. Such a practice provides flexibility for coping with the year-to-year variation in forage production that is rather marked on most western rangelands. During the dry years weaners would be sold; perhaps no yearlings would be grazed. This would include even most replacement heifers if the drought were severe. However, during favorable years all weaner calves might be kept in the herd. This flexibility increases the biological efficiency of rangeland production over the long run.

The rather high efficiency of the 60-day feeding period (table 2) following grazing was due to the compensatory gains made as a result of shifting from grazing to feedlot rations. The extended feeding period from 60 to 90 days was inefficient when based upon weight of retail meat because of the large production of fat that was cut away or dressed away with the offal. Thus, over fattening animals is not an efficient use of land resources (grain). Over fattening would not necessarily be detected unless the data is analyzed by each period of the production cycle.

MULTISPECIES GRAZING

The use of rangelands by two or more animal species has long been known to increase the biological efficiency of these lands. First, the animal species differ in the plants they select; therefore, more than one species of animal will more uniformly use the total herbage production. Second, some animal species prefer rougher topography while others prefer more level terrain. Third, animal species differ in their efficiency of producing offspring (multiple births, precociousness, mortality, longevity, etc.).

Biological efficiency of range ecosystems should at least be calculated on the basis of exportable material from the system on a sustained-yield basis over time. This requires that a sufficient number of young be retained in the system to replace the old that are removed from the herd or die. Barren animals require food but yield no exportable offspring; therefore, the productive animals support the nonproducers. When calculated on this basis, it was found that cattle were 28% as efficient as sheep and sheep were 88% efficient as rabbits. Rabbits produce multiple offspring, and sheep produce a large percentage of twins. Both rabbits and lambs develop at a more rapid rate than cattle and are dependent upon milk for a much shorter period, both of which traits lead to increased efficiency.

In order to accurately evaluate the biological efficiency of grazing animals on rangelands, both natality and mortality must be known. These are affected by management. The state of nutritional balance with respect to physiological performance in the reproductive cycle is of great importance. The number of offspring that can be exported from the range ecosystem on a sustained basis depends upon conception, the number of individuals born, and the number weaned and ultimately exported.

In the more favorable environments of the western range it is possible to obtain a 120% to 130% lamb crop and a 90% to 95% calf crop at weaning. However, in more arid or harsh environments of the West it may be uneconomical to try to obtain more than a 100% lamb crop and a 90% calf crop at weaning. Such things as drought, heavy grazing, or perennially poor range conditions are vital factors affecting nutrient intake and, consequently, the fecundity and reproductive capacity of large herbivores grazing native ranges.

It is generally known that young females (replacements) have difficulty conceiving and, perhaps, have higher mortality among their young between birth and weaning. This is a result of less milk production and less intense mothering traits. In a review of this topic by Van Dyne it was reported that 15% of the 1-year-old caribou females bred; whereas 90% of the 3-year-old females bred. For Rocky Mountain elk it was reported that about 2% of the yearlings and about 73% to 95% of the 2-year-olds carried a fetus.

All large herbivores have a productive period that is termed their peak years. These peak years affect the biological efficiency of the animal/plant-production systems. For example, the peak production ages of range ewes are 3 to 5 years, and of range cattle are 4 to 8 years. This is because at these ages the females 1) give birth to more and larger offspring and 2) have higher milk production and stronger mothering instincts. Replacement range lambs placed in the breeding herd at 18 months generally will not produce more than 45% to 65% lamb crop, and the lambs will weigh 18 lb to 20 lb less than the other lambs at weaning time. Likewise, replacement calves at approximately 1 year, unless fed well after weaning, will not breed consistently. If they do conceive, they may have difficulty calving and produce calves that weigh 40 lb to 48 lb less at weaning than do calves from cows in their peak years of production.

The complementary or competitive effects of grazing between large herbivores can be calculated objectively only on ranges grazed in common or on comparable ranges grazed separately during comparable seasons. Otherwise, preference for various species or forage classes are not good approximations when averaged over many studies from many areas for a particular animal species. However, it is possible to group animal species into grazers that generally select 50% or more grass, such as horses, elk, cattle, and bison, and browsers that select 50% or more shrubs, such as sheep, goats, deer, and moose. The degree of overlap in the diet, of course, depends upon the species or forage classes available and the seasons grazed by the respective animal species.

It is generally acknowledged that wildlife offers great promise for increasing the biological efficiency of rangelands. On the African savanna and brushland a higher biomass was obtained when mixed populations of wild animals were used rather than a single species. In most of Africa a mixed population of wild ungulates efficiently use most of the herbage; domestic livestock used only a small part of it. In South Africa wild game animals furnish almost twice the amount of meat as did domestic animals.

The African savanna and brushlands produces more from mixed animal populations than from cattle alone because the wild population is better equipped to use the semiarid environment. Wild animals in addition to their special adaptation to the environment possess a resistance to endemic disease. The eland is important as an adaptable wild animal for prospective meat production in Africa .

The Saiga antelope in Russia contributes 6,000 metric tons of meat. In the Ukraine, elands are important for milk and meat. In Togoland the population consumes approximately equal amounts of meat from wild animals and domestic animals; 0.25 oz (7.2 g) of wild meat per person compared to 0.22 oz (6.2 g) of meat from domestic animals. In Ghana it was reported in 1966 that 15,015 tons (13,650 metric tons) of domestic animals including poultry were consumed compared to 26,667 tons (24,243 metric tons) of wild meat. It is estimated that domestic cattle in Africa are 20% to 30% less efficient in producing protein than are wild animals.

Wildlife does, indeed, furnish large quantities of protein for Africa south of the Sahara. Rhodesia's production of protein per hectare from rangelands was about equal for wild animals and domestic animals. Game ranching is on the increase in East, Central, and southern Africa . When the diets and reproductive efficiency of each animal species are known, it is possible to determine the proper mix of animals for the greatest biological efficiency for a particular range area.

COMMON-USE STUDIES
In the mountainous ranges of Utah, Cook found that sheep and cattle grazed in common used 20% more of the usable forage than did either species singly. In southern Colorado it was discovered that goats and cattle used mountain-brush range with only a 5% overlap in their diets. Therefore, since available forage was about one-half grass and one-half shrubs, common use by cattle and goats produced almost twice the stocking capacity compared to single use by either species. In the shortgrass plains of northern Colorado it was found that a variety of grazing animals including cattle, bison, sheep, and antelope preferred forbs. The optimal grazing allocation of forage based upon animal size, plant species consumed, and topographic features used was 67% cattle, 20% bison, 12% sheep, and 1% antelope.

In Utah on foothill ranges it was found that grazing by livestock at the proper intensity during the spring increased the quantity of browse species available for big game the following winter . In a study on the Red Desert of Wyomingit was found that seasonal diet overlap was highest among horses, cattle, and elk, while sheep and antelope competed among themselves but did not compete to a high degree with cattle, horses, or elk (Olsen and Hansen, 1977).

Data from common-use studies that I conducted during 1963 and 1964 on medium-elevation foothill rangelands in northern Utah showed these ranges to be highly productive for early summer grazing when used by cattle and sheep. There was approximately 3.4 times more grass than forbs and 2.2 times more grass than the total of forbs and browse (table 3). Since cattle prefer grass and sheep prefer forbs and browse, the range was more suitable for cattle when other factors were equal. When used singly by cattle, they consumed 498 lb/acre (566.4 kg/ha) of air-dried matter, and when grazed singly by sheep they consumed 340 lb/acre (386.3 kg/ha). In this study the grasses were used to about 50% by cattle and forbs were used to about 50% by sheep. However, when the two types of animals were grazed in common at comparable intensities of use, they consumed 615 lb/acre (699.3 kg/ha) (table 3). It is therefore concluded that the range has a greater biological efficiency when grazed in common than when grazed singly by either cattle or sheep. The biological efficiency increased by 45% when shifted from sheep grazing to common use but increased by only 19% when shifted from cattle grazing to common use.

If the comparison of table 3 is made on the basis of, for example, gain in animal weight (lambs or calves), the biological efficiency for the area is greater for sheep than cattle. Sheep grazing produced an average of 27.4 lb/acre (31.15 kg/ha) or exportable lamb weight compared to only 21.5 lb/acre (24.47 kg/ha) of exportable calf weight. However, if yearling steers are grazed singly, the biological efficiency is 43.9 lb/acre (49.84 kg/ha).

When grazing cattle (cows, calves) and sheep (ewes, lambs) in common, the yield was 35.9 lb/acre (40.84 kg/ha), which was an increase in biological efficiency over sheep alone of 31% and over cattle alone of 67%. When grazing sheep (ewes, lambs) and steers in common, the biological efficiency was increased by 91% compared to sheep grazing singly and by 19% compared to steers grazed singly.

Daily consumption and gain were taken from animals grazing comparable ranges during early summer. These animals were grazed in a herd on mountain range, whereas the common-use studies were made in rather small enclosures with areas ranging from 3.75 acres to 10 acres (1.5 ha to 4 ha).

CONCLUSIONS
The biological efficiency of range ecosystems can be evaluated in many ways, but perhaps the best is as material that can be exported from the system on a sustained basis. This can be expressed as produce per unit of rangeland, produce per hundredweight of females maintained, or net return per unit of salable product. The biological efficiency of rangeland ecosystems can be increased by many methods of manipulating biological systems, but it may not prove profitable in a practical sense. Biological efficiency may be misleading unless each production activity is analyzed separately to determine where efficiency is gained or lost. For example, providing seeded range or crop forages to grazing animals during different phases of the production cycles may change the output of salable products.

Management systems strive to increase the biological efficiency of rangelands through maintaining proper diversity of plants along with a proper mix of animals. Generally, a mix of herbivores on a diverse rangeland ecosystem increases biological efficiency because of more uniform use of the plant biomass compared to use by only one animal species.

Plants that effectively convert solar energy to organic matter are palatable and nutritious and need to be considered in the overall grazing plan. In like fashion, animals that are suited to the plant communities and terrain should be selected for increased efficiency. Animals (herbivores) that produce multiple offspring that grow rapidly and depend on their mothers' milk for a comparatively short period of time are said to be highly efficient.