Energy

ENERGY - A Critical World Resource

-by C. Wayne Cook

Introduction

The ecologists of the world must view the energy requirement of the human population with more realism. There are indeed social and economic factors that emerge as more important to sustaining a homosapian ecosystem than preservation of natural biological systems in a pristine condition with man as an outsider.

Animal life on the earth may soon become a term for meat with other considerations assuming a minor role. Human population numbers of the world continue to soar and food production continues to lag behind. Wildlife populations throughout the world are giving way to livestock grazing for meat, milk and clothing. This will continue as long as human population numbers continue to increase and sustenance becomes the primary consideration. Wildlife populations on the earth are estimated to be only a tenth of the numbers (biomass) compared to only 50 years ago. There are no longer empty continents or unsettled frontiers and our land resources must be used at maximum biological efficiency to provide food to nurture the human population at a level of acceptable standards.

It costs more than twice the energy in feed to produce a pound of fat than it does a pound lean in all species and classes of animals. Therefore, we are concerned with just enough fat distribution to make the meat palatable for human consumption. Fat cover or accumulation in the body cavities is a waste of food energy since in the market place it is dressed out or cut away and sold as waste products but which is still charged to the consumer of edible meat cuts as a result of poor distribution and so called "finish." This cannot be tolerated in future beef production because of the competition for grain concentrates for direct human consumption throughout the world. Therefore, feeding and marketing of meat products for the future must consider a lower grade of finish and a better distribution of lean and fat in the dressed carcass.

Many studies have shown that the greater the fat to lean material laid down as body gain increases the cost because it requires 2.25 times more energy to produce a pound of fat compared to a pound of lean meat. In addition much of this fat is laid down as fatty covering or as an accumulation of reserves in the body cavities all of which are considered cut away dressing or byproducts to lean meat production. In a report by Pecot in an Agricultural Research Service Report it was noted that even the trimming of fat from the carcass before sales amounted to 16 percent removal for the choice grades but only 3 percent removal for the good grades. This does not consider the loss of body cavity fat that was also cut away as inedible material. Yearling steers fed to high good grade produced 64 percent total retailable yield of meat compared to only 51 percent for average or medium choice grade of finish. The consumer must pay for this so called "finish" which is , to a large degree, a waste of energy conversion.

The average percentage of fat for dressed carcasses of prime, choice and good grades are 41, 35 and 28 percent respectively as shown by Agricultural Research Service Report (1-965). Thus the energy cost of producing gain because of the fat to lean ratio is increased by at least 15 percent for each higher grade of finish.

Data from Neumann and Snapp shows that yearling steers in feed lots show a marked trend in increased cost for each 100 pounds gain during a 160 to 200 day full-feed toward finishing as follows (Table 1). Table 1 shows intake of energy and total cost per each 100 lbs gain during custom feed lot fattening. This shows that the higher the finish the greater the cost because of inefficient use of energy intake. The practical question that arises; is it feasible to feed beyond low choice or even high good grades because of the extravagant use of high priced feeds that can be used directly by humans rather than converted to excessive animal finish? This all seems to indicate that the consuming public will be forced to purchase the high good grade or the low choice grade simply because we cannot continue to be extravagant users of cereal energy for the production of cut away fat material. A concentrated effort to improve fat distribution on animals during the early feeding program through a selective breeding program could improve the meat quality immensely.

Native rangeland forage is a natural renewable resource that avails itself each year to be processed into rich protein food by the use of grazing animals on our native biological systems. This renewable resource represents a tremendous wealth of food energy that is converted from the solar energy at minimum cost. When we consider that all life on the earth is directly or indirectly dependent upon plant life and that only one third of the earth's surface is land, and furthermore that about 50 percent of this land area is rangeland and has no alternate productive value, it behooves man to consider efficient use of the total food potential of range herbage. At the present time our world surpluses of food are almost completely exhausted and man must depend upon the potential plant life in our present ecosystems to feed our ever increasing population. Our total energy needs are now an international problem because of our needs to export food in exchange for fossil fuels. It has been proposed that all energy sources for food and fuel of the earth be identified with each country and subsequently be placed on computer programs for allocation over time to meet the needs of our ever increasing world population.

Rather phenomenal changes with respect to producing food products will involve our present day land use alternatives. For instance, shall we produce 30 bushels of wheat per acre or graze the herbage growth and obtain 150 pounds of beef or plant a sorghum and produce even more beef per acre? Will it be economical to use our precious water for irrigation to produce 700 pounds of beef per acre or use the water to support industry or a housing development?

We can presume that scientists will continue to increase the biological efficiency of ecosystems by planting improved species, controlling pests, using fertilizers, breeding more efficient plants and animals, and using better overall management techniques. It is still apparent however, that range forage throughout the world represents a tremendous potential of energy and should receive the attention it deserves. According to a recent study (Table 2) if we convert usable range forage by a ewe-lamb operation during spring and summer every 12 pounds of ingested air-dry forage produces a pound of lamb; with a cow-calf operation about 16.3 pounds of usable air-dry forage produces a pound of weaner calf and by using yearling steers during only the growing season about 10 pounds of usable air-dry range forage can produce a pound of beef.

Research to date suggests that the range forage will be used at maximum to produce the young offspring by means of either a cow-calf or a ewe-lamb operation and croplands will be used more extensively to produce forage for fattening but the finishing process may be done by simply supplementing the grazed forage and then only to the finished grade of high good. According to Thomas input of energy from fossil fuels to produce food in cultivated or agronomic ecosystems amounts to about 10,000 calories for each 3,000 calories of edible material from crops by conversion of the sun's energy. If this is true then man should maximize the use of the natural renewable range forage because of the reduced energy cost to process it into meat or cereal for man.

Some scientists feel that increased acreage of irrigated lands will solve our future nutritional problems but water is becoming more valuable for use in industry and households. It is estimated that industrial, municipal, domestic, and power requirements of 1971 will triple by the year 2002. Thus the use of water for agriculture will indeed become very competitive. Increasing demands for water will be an important part of the energy crisis, and may emerge as a limiting factor in nutrition requirements for man throughout the world.

A primary consideration in the function of an ecosystem is the efficiency of conversion of solar energy to plant material by the primary producers. This is the first step in evaluating efficiency of turnover of energy by the various trophic levels and the efficiency of energy export from the ecosystem from year to year.

The conversion of solar energy through photosynthesis by plants is governed largely by light, water and nutrients. On rangeland ecosystems there is usually unlimited sunlight but the leaf area index is far from complete coverage of the surface area. Therefore, there is little correlation between primary productivity and incident solar radiation. Plant life may be dormant many months of the year because of low temperatures and limited soil nutrients and moisture reduced photosynthetic activity. Even at best, less than 2 percent of the total solar energy is converted to chemical energy. However, energy conversion and transfer among different trophic levels in the range ecosystem is an important principle that can serve as a guide to management activities for efficient use of all cycling nutrients in the system.

Duncan proposed a model for predicting or evaluating efficiency of solar energy conversion by foliage by considering the following canopy architecture: leaf area, leaf angle, leaf position, reflectivity, transmissivity, brightness of sun, and position of the sun. It does not appear that the model would optimize energy conversion in range ecosystems unless it included other limiting factors such as soil nutrients and moisture either of which could be more important than the leaf characteristics.

Since the functions of the ecosystem actually start with the process of plant photosynthesis, it is important to understand this physiological phenomenon. Age of leaves are important in the effectiveness of conversion of energy from sunlight. As would be expected, the more mature leaves are less efficient than the younger ones. Life forms and species of plants differ in the effectiveness of their chlorophyll-bearing tissue in converting radiant energy to chemical energy.

Defoliation by animals, infestation by parasitic insects that suck the life-giving saps from the plants, and diseases that cause malfunction of the plant tissue all decrease the efficiency of food manufactured by plants.

The herbivore population is generally proportional to food produced or food available for consumption. In any event, the entire consumer population is directly or indirectly related to the ability of the plant population to furnish adequate food. Animal population dynamics, of course, depend on more than food supply since diseases, catastrophe or social behavior may also be regulatory.

Efficiency of solar energy conversion within the ecosystem has received much attention. This appears of paramount importance because of the transfer of solar energy for sustenance of all life in the ecosystem. The existence of the ecosystem itself is dependent upon this phenomenon.
The herbivore population represents the first major turnover in the use of fixed photochemical energy in plants. This involves plant X animal and animal X animal interactions. The first interaction is obvious since it concerns animal response from consuming plants and plant response from being defoliated by animals. In this case, the stability of plant cover and animal response to consumption of the primary producers is a measure of efficiency of energy turnover.

In evaluating consumer response, it is necessary to consider more than gross energy content of the ingested forage. For instance, according to Cook and Stoddart maximum digestible energy (TDN x 2000) per unit area was produced by plants that were harvested only after they completed their annual growth cycle but maximum digestible protein was produced when the plants were harvested sometime during mid-growth and again at the end of the growing season. Livestock responses on grassland ranges were satisfactory only when phosphorus and digestible protein were adequate. This was true even though digestible energy was more than adequate.

It would seem that the biological efficiency of the range ecosystem could be based upon (1) the amount of photochemical energy or nutrients produced per unit of land surface area and (2) the amount of this material that is transported from the ecosystem in eatable produce, services, or wealth. The amount of solar energy converted to chemical energy or nutrients, and then to the consumers serves as a measure of efficiency of the ecosystem provided limiting factors are corrected through manipulation consistent with all uses to be made of the area and with reasonable cost and return relations.

It is generally acknowledged that as energy passes down the food chain from producer to consumer the efficiency of use of solar energy diminishes. In each case, however, management can increase the efficiency of energy utilization in the transfer from one trophic level to another.

The total gross energy produced by plants has already been identified as a measure of efficiency of the primary producers but the transfer of this energy to the consumers would, to a large degree, depend upon the chemical form of the energy furnishing constituents. For instance, many native browse and forb species produce rather high quantities of resins, waxes and essential oils that represent chemical energy. However, these forms are not available to the consumers. In studies by Cook it was found that grass species produced approximately 2050 kcal of gross energy per pound of dry matter during early growth and browse species produced about 2322 kcal. The browse plants however yielded only 1205 kcal of metabolizable energy for animal use compared to 1324 kcal of metabolizable energy per pound of dry matter in grasses. Later in the season when plants were mature, the grasses contained 1859 kcal and browse contained 1922 kcal of gross energy per pound of dry matter. The grasses netted 42.9 percent usable energy but the browse netted only 33.4 percent usable energy.

Thus, it is demonstrated that a nutritionally balanced diet can materially increase the efficiency of energy turnover in the ecosystem. This would be true of all animal life in the ecosystem.

Supplements not only furnish the deficient nutrients in the diet, but in many cases, they enhance the value of the range forage by increasing daily intake and digestibility of ingested range forage. In trials by Cook and Harris, protein supplements consisting of cottonseed meal or soybean meal increased digestibility of protein and cellulose in the range forage on desert ranges used during the winter. Intake of digestible protein and metabolizable energy from the range forage was increased by the protein supplements fed to range sheep at either 0.5 or 0.33 pounds per day. Cottonseed meal supplements in most cases increased daily intake of range forage. Energy supplements consisting of barley or corn reduced the digestibility of protein and cellulose in the range forage and in some cases, decreased daily intake of range forage.

Proper supplements fed to sheep on winter range during gestation have given as much as a 15 percent increase in lamb crop, 8 pounds more lamb per ewe, and a pound more wool per animal. Replacement heifers, when supplemented on the winter range, gained 20 pounds more than the controls and supplemented cows weaned 23 pounds more calf than unsupplemented cows.

Thus, it is shown that a protein supplement, when supplied to grazing animals on dormant desert ranges, actually increases the efficiency of energy turnover in the ecosystem even though protein may not be deficient in the forage.

It is generally acknowledged that sheep are slightly more effective in converting energy into gain and milk than cattle. There is however, a rather marked difference in the efficiency of energy conversion from range forage into gain of young weaned lambs and growing steers compared to gain from lambs and calves receiving milk during lactation. About 40 percent more gross energy is required per pound gain in sucking calves compared to steers.