Efficiency of Converting Nutrients and Cultural Energy in Various Feeding and Grazing Systems

by C. Wayne Cook

Highlight: Yearlong total confinement and partial confinement feeding were compared to conventional range grazing to determine the cultural and digestible energy expended to produce a kilocalorie of dressed-carcass meat from weaner calves and the protein consumed to produce a pound of red-meat protein. The range groups required the least amount of cultural energy to produce a kilocalorie of meat and the total confined groups required the most. The total confined system on a low level of nutrition, where calves were weaned early, converted digestible energy most efficiently but converted digestible protein least efficiently, whereas range groups converted digestible energy least efficiently and digestible protein most efficiently.

During the past 30 years more intensive cropping systems have enabled agriculture to double crop production; however, use of fossil fuel has increased 2.3 times for each increment of food produced. During the past few years, grain has been a surplus commodity and, as a result, has been considered cheap livestock feed. Feeding high grain rations has increased the cultural energy used in the production of meat compared to the use of range forage which is produced primarily from solar energy. The world no longer has surplus food to feed an ever-increasing population, and the expenditure of the finite fossil fuels for food production therefore becomes a grave concern.

Cultural energy is the energy included in fossil fuels or other sources of energy that supplements solar energy in the production of food. This energy comes from labor, transportation, and electricity to produce and process foods. The energy required to manufacture machinery, fertilizers, and pesticides that are used in agriculture is also considered energy that subsidizes solar energy in producing plant growth.

As a result of the concern for the increasing expenditure of cultural energy for food production, a study of six feeding and grazing systems of beef cattle was analyzed to determine the cultural and digestible energy expended to produce a kilocalorie of table meat from weaner calves. The study was carried out at the Eastern Colorado Experiment Station on short grass range areas.

Procedures

One hundred and sixty six mature Hereford cows were divided into six groups to test three management systems at the Eastern Colorado Range Research Center. These systems were:

1. Native Range: 15 acres of rangeland per animal unit for 12 months.
   
   • Thirty cows were rotated on three l50-acre pastures at 2-month intervals and supplemented with 1 lb alfalfa pellets per head per day from November 1 to May 1.
     
   • Same as above with cows receiving a winter supplement of 2 lb alfalfa pellets per day.
2. Semiconfinement: 10 acres of rangeland per animal unit for 7 months.
   
   • Thirty cows were rotated on three 100-acre pastures from May 1 to December 1 and fed in drylot from December 1 to May 1 with the nutrient intake regulated at 6 ½ lb TDN (total digestible nutrients per day.)
     
   • Same as above with the drylot nutrient intake regulated at 8½ lb TDN per day.
3. Total Confinement: drylot 12 months.
   
   • Twenty-three cows were maintained on 6 ½ lb TDN per day except for the period April 15 to July 15, when they received 14 lb TDN. Calves had access to creep feed until weaned at 90 days of age, after which they were bunk fed a growing ration until October 14.
     
   • Twenty-three cows were maintained on 8 ½ lb TDN per day from October 15 to April 15 and 14 lb TDN from April 16 to October 14. Calves were creep fed and weaned October 15.

Cows confined to the drylot were fed sorghum silage, alfalfa hay, grain, salt, and mineral. The calves of the cows receiving 8½ lb TDN per day were creep fed a grain mixture for approximately 60 days following birth and were then fed silage, hay, and grain with enough soybean oil meal added to maintain the crude protein level above 15%.

Cows in confinement were bred artificially during a 40-day period and those in partial confinement and on native range were artificially inseminated during a 30-day period. Bulls were put with all cows for an additional 20 to 30 days and left long enough to make a 60-day breeding season.

Calculating Cultural Energy in Feeds Used

All cultural energy charged to feeds used in the trials was calculated after the outline used by Pimental et al. and Heichel. The individual crops used as feed and the input of cultural energy is shown in Tables 1 and 2.

It has been estimated that most agriculture machinery has about 8,000 kcal of cultural energy invested per pound and can be depreciated over an average life of 5 to 8 years. It was calculated that a 7-ton tractor depreciates over a 6½ year period to the extent of about 17,300 megacalories per year. Farm pickups and trucks have been said to contain energy equivalent to 15,000 miles of gasoline or about 1,500 gallons of gasoline, which totals about (1,500 x 31,056) 46,584 megacalories. Maintenance alone is estimated to be about twice the depreciation expenditure of cultural energy for farm machinery. Thus for depreciation and maintenance of farm machinery in general it was calculated that 45 megacalories for each hour of usage was considered appropriate for the average piece of large farm machinery over a life span of 6.5 years.

Actual gasoline (gallons used) was estimated on a per hour or per acre basis and charged as cultural energy at the rate of 31,056 kilocalories per gallon, whereas diesel fuel was charged at the rate of 34,783 kilocalories per gallon.

Transportation has been calculated in various ways, but in the present study, transportation off the farm by commercial trucks and to and from the field were combined and charged at 4 kcal/lb/mile. Pimental et al. suggests that 15 kcal/lb of product will cover transportation to and from the field and to the source of sale. Slesser states that a truck can move goods 500 miles for 131 kcal/lb. This calculates to be about 3.82 kcal/lb/mile. Pimental et al. estimates transportation of corn yield in New York to be about 70,000 kcal/acre or about 4 kcal/lb/mile when sold locally or used near the source. This counts gasoline, labor for the driver, and depreciation of the energy content of the machine. In this study much of the produce was actually used at the source of production.

The cultural energy used in irrigation varies considerably, depending upon the type of irrigation. If pump wells are used, the cultural energy is estimated to be about triple that required for stream or ditch irrigation by gravity feed. Slesser states that irrigation for some cereal crop production in the drier areas may be as high as 20,000 megacalories per acre. Pimental states that for corn farming where irrigation is used the average input in cultural energy for supplementary water is about 905.6 megacalories per acre. In many areas of the east where corn is raised, only small amounts of irrigation water are used, but in the west substantial quantities of supplemental water are required for corn production. Since irrigation of corn used in this study came from gravity-fed water out of the South Platte river and additional labor, machinery, and gasoline are included in separate categories, an average of only 34 Mcal per acre for irrigation of corn was used. This would be the cultural energy charged against reservoir, channel, and ditch construction.

An average active man requires from 2,500 to 3,000 kilocalories per day, and for hard labor about 5,000 kilocalories. In the present study it was estimated that the average farm hand works 8 hours per day and requires at least 4,000 kilocalories. It was further estimated that for every kilocalorie of food consumed 5 kilocalories of cultural energy were required to produce, process, and transport it for consumption. Actually, from 7 to 10 kilocalories of fossil fuel are required to produce 1 kilocalorie of table food, but some of the food is raised on the ranch. Therefore, about 2,500 kcal (4,000 kcal X 5 / 8) of cultural energy are required per man-hour of labor on the farm or ranch.

The literature and correspondence with chemical companies suggest that most pesticides require about 11,000 kilocalories per pound in their manufacture, transport, and application in common agriculture usage for the control of insects and weeds. If the application of the herbicide required 4,000 kilocalories per acre, 2 pounds of pesticide could be applied for 18,000 kilocalories per acre.

Results

Cow Weights
Cows in confinement that were wintered on 6½ lb TDN (Total Digestible Nutrients) lost approximately 4% more body weight from December to May than those fed 8½ lb TDN. Compensatory gains were more rapid during May and June for the cattle wintered at the low nutrition level regardless of whether they went to grass or were left in drylot and fed 14 lb TDN until after breeding.

Weaning Weights
The heaviest weaning weight of calves, 460 lb, came from the drylot cows that received 8 ½ lb TDN per day. This group was followed by the total confinement group fed 6½ lb TDN whose calves were early-weaned and weighed 417 lb. Both range groups weaned calves weighing 414 lb and the partial confinement group that received the higher nutrition levels produced weaner calves weighing 411 lb (Table 3). The total confinement cows wintered on 8½ lb TDN had a 97.4% calf crop at weaning, thus producing 448 lb per breeding cow. The early-weaned calves from the confinement cows receiving 6½ TDN during the winter had a 94.5% calf crop, with an adjusted average weaning weight per cow of 394 lb.

Cultural Energy for Range Livestock
The cultural energy for range cows was calculated according to the best estimates of management on the experimental ranch in eastern Colorado. The operation was based upon a 250-cow unit where cows are left on the open range yearlong and receive only a supplement during the winter from December 1 to May 1 (Table 4). Just prior to and during the early part of the breeding season, both range groups were fed a concentrate supplement for 2 to 3 weeks at the rate of 2 lb per day. The cultural energy used in producing feeds and transportation was calculated according to the source of the feed and for the labor and transportation to obtain and feed it, as presented in Table 1. The range cattle required 2.48 and 2.61 Mcal of cultural energy per pound of calf weaned for the cows wintered on l and 2 lb of supplement, respectively.

Cultural Energy for Confinement Feeding
An estimated 90 man hours; 105 machine hours involving one 2-ton truck, grinder, mixer, and a tractor loader to clean lots; and 525 gallons of gasoline per month were required to feed 250 head of cattle in confinement. The calculated cultural energy in labor and machinery to feed 250 brood cows in confinement for 30 days was 21,255 megacalories or about 85 megacalories per cow month. In like fashion, an additional 34 megacalories per month of cultural energy in labor and machinery were required to creep feed the calf.

The cows in total confinement required 7.26 and 7.53 Mcal of cultural energy per pound of calf weaned for the 6.5 and 8.5 lb TDN feed level, respectively; and the semiconfined cows produced a pound of weaner calf at an expenditure of 3.98 and 4.53 Mcal of cultural energy for the low and high level of feeding, respectively.

Comparison of Six Feeding Systems
Animal production for each of the six feeding systems was compared on the basis of a 250-cow operation. The production year was divided into four seasons depending on phase of animal production and availability of range forage: October 16 to April 17, April 18 to June 17, June 18 to
August 17 and August 18 to October 15.

The average calving date was April 17, the end of the first season. The live weight of calves produced at this time was calculated as the average birth weight (70 lb) times the number of cows (250 head) times the percent calf crop (Table 5). During the remaining seasons, live weight depended on daily gain and death loss that occurred in the separate systems.

Since the weaner calves weighed from 410 to 460 lb, a dressing percentage of 57.9% was used and the fat content was assumed to be 11.2% and the protein was assumed to be 16.6%. Energy in body fat was calculated as having 9.4 kcal per gram and body protein as having 5.7 kcal per gram.

Digestible Energy/Energy of Meat Produced
A comparison of the various systems of management showed that digestible energy in the feed or forage converted to energy in meat of weaner calves was most efficient for the low nutrient level of total confinement (Table 5). This is believed a result of weaning the calves after 90 days of age and feeding them a growing ration. The two range groups produced the lowest return of food energy in dressed calf meat per unit of digestible energy consumed largely because some of the energy was utilized in foraging. In addition the range forage during various periods of the spring and summer while the plants were growing furnished excessive amounts of digestible energy for lactating cows and growing calves, and thus was not used efficiently.

A high protein supplement at the lower level fortified with Vitamin A would have been a better method of supplying nutrient requirements during the winter, which would have used more effectively the digestible energy in the dormant range forage compared to alfalfa.

Digestible Protein/Meat Protein Produced
The two range groups produced more edible protein meat from weaner calves per unit of digestible protein consumed than did other management systems. As can be noted in Table 5, confined groups where calves were weaned early or creep fed were the least efficient systems with respect to protein conversion. This suggests that early weaned calves convert digestible energy effectively but protein rather poorly. In the partially confined groups, it appears that the lower feeding level during winter showed a greater rate of protein conversion than the higher level of feeding.

Cultural Energy/Energy of Meat Produced
As would be expected, the yearlong range grazing system with a winter supplement required considerably less cultural energy than did other systems (Table 5). Range livestock production when sold as weaner calves produced about 1 kcal of dressed-carcass meat for each 5 kcal of cultural energy expended in supplemental feed, machinery, gasoline, and labor for a 250-cow ranching enterprise. Partial confinement, where cows were corralled and fed for 5 months during the winter and grazed on the range during spring and summer, produced a kilocalorie of dressed-carcass meat from weaner calves for an approximate cost of 8 to 9 kcal of cultural energy. Total confinement required about 15 kcal of cultural energy for each kilocalorie of dressed meat or about three times as much cultural energy to produce a kilocalorie of edible meat from weaner calf production compared to range calf production.

Optimizing Feeding Systems
The results from the six feeding systems were used to determine the most efficient hypothetical combination of systems under four different criteria as selected by a computer program (Table 5). The first criterion was to maximize feed energy conversion, described as the ratio of digestible energy going into the animals to gross energy from the dressed carcass. The most efficient combination of systems was a low level of feeding in total confinement during the winter, a high level of feeding in total confinement during the spring and summer, and finally grazing the native range from August 18 until October 15. Under such a system, 39 kcal of digestible energy are needed for each kilocalorie of red meat produced. This is only slightly better than the total confinement system with 6½ lb TDN fed daily.

The second criterion was to optimize the efficient use of cultural energy. This criterion was expressed as the ratio of cultural energy used to gross energy in the carcass. The most efficient system in terms of cultural energy expended was the use of range grazing from October 16 to April 17 with animals that received 1 lb of alfalfa supplement daily during the winter. The animals that had received the higher level of range supplement were selected as being most efficient in converting cultural energy to red meat during spring (April 18 to June 17). This efficiency in the use of cultural energy was followed by grazing from June 18 to August 17 animals that had been wintered on a high level of nutrition under confinement (8½ lb TDN). The fourth system for greatest efficiency in use of cultural energy consisted of grazing cows that had been wintered on the low level of nutrition (6½.1b TDN) and now had their calves by their side and grazing on the range with the yearlong range cattle. These systems by periods used the least amount of total cultural energy and required the lowest quantity of kilocalories of cultural energy (4.91) per kilocalorie of meat produced. This was only slightly better than the low lever of supplementing range cows, which required 4.97 kcal of cultural energy per kilocalorie of meat in the dressed carcass.

The third criterion was to maximize the use of digestible protein in the feed for the production of protein in the dressed carcass. The most efficient use of feed protein in the winter resulted from supplementing the range cattle with 1 lb of alfalfa. The second period, from April 18 to June 17, shows that the total confined cows on the low level of nutrition (6 ½ lb TDN) was selected by the computer. During this period, however, both total confined groups received 14 lb of total digestible nutrients. This selection is understandable because the high level of TDN for the group previously fed a low level of nutrition would make compensatory responses and therefore use digestible protein more efficiently.

During the summer and fall the selection of the management systems for greatest efficiency of protein utilization in the computerized theoretical feeding system was the same as for greatest efficiency in the use of digestible energy. It required 10 lb of digestible protein to produce 1 lb of edible protein in a weaner calf carcass by the most efficient management systems for utilization of feed protein. Again, this was only slightly more efficient than the two range groups.

The fourth criterion was to maximize red meat production. The high level of nutrients fed during the winter under confinement was selected by the computer. This was followed during the spring by the grazing animals that had the highest level of range supplements during the previous winter. The summer and fall management system for greatest red meat production was the high level of nutrient intake for total confinement, which was 14 lb TDN during these two periods prior to weaning. These management systems produced a maximum of 472 lb live weight per calf and a total of 114,916 lb live weaning weight for the 250 breeding cows.

The feeding systems selected by the computer and discussed are hypothetical. Actual experiments are needed to determine if the proposed systems actually are more efficient than those studied. In some cases the proposed "efficient" systems differed only slightly in the selected criteria from the systems studied.

Summary

Six feeding and grazing systems were analyzed to determine the cultural and digestible energy expended to produce a kilocalorie of table meat from weaner calves and the digestible protein consumed to produce a pound of red-meat protein. Two groups were run on open range year long, with one group receiving 1 lb and the other receiving 2 lb of winter supplement per day. Two group were run on open range for 7 months during spring and summer but confined during fall and winter with a low and high level of confined feeding. The third system involved two groups which were fed in total confinement: group one received 6 ½ lb TDN/day yearlong except from April 16 to July 18, when they received 14 lb TDN, after which the calves were weaned and fed a growing ration; the other group received 8 ½ TDN/day from October 15 to April 15 and 14 lb/day from April 16 to October 14.

Digestible energy was converted most efficiently by the cows receiving the low level of nutrients in total confinement, because the cows were weaned 90 days of age and fed a growing ration. The range groups were least efficient in converting digestible energy into gross energy in meat of weaner calves, because digestible energy was excessive in the spring and early summer range forage and therefore wasted.

The yearlong range groups required the least amount of cultural energy to produce a kilocalorie of table meat and the total confinement groups required the most. The semiconfinement groups required almost twice as much cultural energy and the total confinement groups required three times as much cultural energy to produce a kilocalorie of dressed carcass meat compared to the range grazing system.

Digestible protein utilized to produce a pound of protein in red meat was highest in the lower feeding level of total confinement where calves were weaned early and fed a growing ration and most efficient in the lower level of supplementation for the range groups.

A computer program selected the various seasonal feeding systems for optimization of conversion of digestible energy, cultural energy, and total protein in the feed for hypothetical feeding procedures. Also, a hypothetical management system was selected from the six feeding systems studied for the maximization of total production of carcass meat.