Energy is an important component and perhaps the most fundamental factor for swine diets. Energy is not a nutrient per se but is a property supplied primarily from carbohydrates and fat and, to a lesser extent, through the metabolism of protein. It is a term that crosses numerous disciplines. In our daily lives it most often references the power to place something in motion such as vehicles and production equipment as fuel energy. As a component of our diets as well as animal diets, its importance is not often reflected in the scientific attention it receives. There has been remarkable little data and study devoted to dietary energy in the pig when compared to other nutrients. The determination of energy values of feedstuffs for swine is a difficult and tedious task, perhaps directly accountable to the limited amount of knowledge and basic information common to amino acids, vitamins, and minerals.
Energy, when used as a feedstuff, can be expressed as calories or joules. The United States prefers calorie. In most of the world, joule is most commonly used. A calorie is the amount of energy required to raise one gram of water from 16.5 degrees Celsius (C) to 17.5 degrees C, and is equivalent to 4.185 joules. Both calories and joules are commonly expressed in multiples of 1,000 so that kilocalories (kcal equals 1,000 calories) or megacalorie (Mcal equals 1,000,000 calories) are expressed on the basis of a pound or kilogram (kg) of ingredient. Similarly, kilojoules and megajoules are expressed on the basis of a kilogram.
Utilization of the energy derived from an ingredient is determined and described by numerous systems. The North American swine nutrition community has traditionally measured the energy contributions of ingredients and feeds, as well as the pig’s requirement, in metabolizable energy (ME) units. The energy units are based on gross energy as determined by bomb calorimetry minus the energy losses from fecal, urinary excretion, and digestive fermentation.
In other parts of the world, the net energy (NE) system is most prominent. The NE system, of which Dr. Jean Noblet of France has the most extensively researched model, accounts for further losses of energy (heat increment) during metabolism. Fat is very efficiently digested and metabolized in the tissues, carbohydrates with medium efficiency, and both protein and the nutrients from fiber are used very inefficiently. The preference and advantages of the respective systems have been debated extensively. An ideal energy system must define both a quantifiable energy content in an ingredient or blend of ingredients as well as a corresponding quantifiable energy requirement by the pig at various growth stages and production expectations. A diagrammatic energy flow system adapted from Ewan, 2001, is shown in Table 1.(1)
Thus, the often-described controversy between ME and NE systems often does not involve theoretical issues as much as the values used to express feed ingredients on a global basis. It is important that the energy derived from a specific ingredient is based on an energy system as expressed by using the same energy system as used for the animal’s requirements.
Whenever energy is discussed, fat is a primary ingredient of focus. Fat is the most concentrated source of energy among all of the commonly available feed ingredients. It likewise provides numerous other ancillary benefits and positive attributes to animal diets in addition to its energy contribution. But considering that feed cost is the most important expense in pig production, and energy represents the greatest proportion of this cost, the energy density of the diet plays a most important role. As such it should receive a higher status in swine research priorities. A symposium on dietary energy density at the 2003 annual meeting of the American Society of Animal Science, sponsored by the Fats and Proteins Research Foundation and organized by Dr. Jim Pettigrew, faculty excellence professor, University of Illinois, validated that belief.
Fat as an Energy Source
Drs. Ron Moser and Jim Pettigrew, while both were members of the faculty at the University of Minnesota in 1991, conducted a literature search and summarized research on the effects of adding fat to finishing pig diets.(2) Most of these data were generated in university research herds. The results showed that adding fat reliably reduced feed intake, increased energy intake, and improved feed efficiency. In the majority of trials, growth rate was increased as was back fat thickness. A five percent increase in daily gain and a 10 percent decrease in feed required per unit of gain were demonstrated across all trials. A “rule of thumb” response of a one percent increase in daily gain and a two percent reduction in feed required for unit gain has been used in North America as expectations from fat additions to swine grow-finish diets. Expectations may exceed those referenced in the above summary when using alternative ingredients that are so common in other countries when compared to the corn-soybean meal formations of the United States and when fed to high lean gain potential pigs.
Dr. Mike Tokach and his colleagues at Kansas State University have more recently defined the effects of added fat on contemporary finishing pigs in commercial environments. Two important characteristics of these experiments differ from the studies reviewed earlier. First, they were done with modern pigs, genetically leaner, and with lower feed intake. These characteristics make it more likely that the pigs will respond to the increased energy intake with increased growth rate. Additionally, these high lean pigs are less likely to become fatter. Second, the experiments were conducted in a commercial environment where voluntary feed intake and growth rates are usually less than in the less stressful environments of research farms. The lower feed intake provides for a favorable response to added dietary fat to be more consistent and even of higher magnitude. A lower heat increment of fat metabolism can be an advantage in warm environments where feed intake is further compromised.
The Kansas State data was summarized for 25 experiments over the last 10 years.(3) The more recent data supported the hypothesis that the modern pig does respond more consistently and in greater magnitude to higher density diets. The Kansas State data verified the improved feed efficiency that has in the past been associated with dietary fat additions. These data were extrapolated into a very consistent favorable economic response as well. An economic assessment model used an extra 4.76 kg (10.47 pounds) at market with 11.9 kg (26.18 pounds) less feed to illustrate the effect of improved weight gain upon modern swine facilities. If added energy improves average weight gain, the value of the extra gain must be included in the economic evaluation. Using current costs, an 8.5-pound increase in market weight would return a 90-cent margin over feed costs per pig marketed. The margin can improve if the weight helps move pigs into a packer’s optimal weight range grid that discounts for light weights. In today’s production systems of all in-all out, pigs must meet a days-to-market schedule or be discounted for light carcasses.
Improved feed utilization possesses ancillary cost benefits not often considered in economic models. The feed manufactured through a given mill is reduced. Similarly, the required number of feed deliveries to the swine facility is reduced. The actual reduction in feed production and pelleting costs, the increased longevity of mill equipment, and the control of dust also benefit economics and the environment.
The Net Energy System
Dr. Jean Noblet has provided data that compares the relative energy density of several feedstuffs using the energy systems of digestible energy (DE), ME, and NE.(4) In evaluating those of corn, soybean meal, and ani-mal fat (fat not characterized), the rel-ative values were as listed in Table 2.
Another rather standard “rule of thumb” is that the energy derived from fat is approximately 2.35 times that of corn. The Table 2 data indicates that when using an NE system, the energy level from animal fat is actually 2.7 times that of corn. Soybean meal is significantly degraded in energy content basis the NE system. Animal fat is reported to provide 3.7 times the energy per unit as compared to soybean meal when using the NE system where as 2.26 times based on either the digestible or metabolizable systems. These discrepancies become extremely important in many parts of the world that use a more diverse feedstuff menu than is common to the United States. It becomes significant to U.S. formulations in that there are so many interactions and variables between amino acid nutrition, protein accretion, dietary energy density, and energy intake. Most nutritionists are agreed that energy density should be the first factor decided upon in diet formulations. Secondly, amino acid requirements should be expressed as a ratio to energy, except perhaps during specific phases. But what energy system best defines those requirements is still in debate.
Recent data summarized by Dr. Roger Campbell confirm the impressive response achieved by adding fat to increase dietary energy density.(5) Dr. Campbell also discussed an observation that even though adding fat to the diet during the early stage of growth improves performance at that time, it may reduce feed intake and growth subsequently. In his observations, withdrawal of dietary fat at any stage of production reduced performance when compared to feeding programs without dietary fat at any stage. The traditional usage of fat is to include higher levels in the early growth stages and reduced levels as the pig progresses to market weight. It is known that the young pig has a lower digestibility of fat, which improves as the pig grows and matures. These observations need exploration but the elimination or perhaps even lowering fat levels in the finishing phase may be contra-indicated. It is becoming much clearer that increasing the energy density above that in a corn-soy diet improves growth performance and profitability of finishing pigs. This is especially evident in modern genotypic pigs raised in commercial production. Fat is the only practical ingredient to accomplish such.
Fat has the biological effect of slowing the passage rate of digesta in the digestive tract. Because of this effect, the digestibility of other nutrients is improved. This is referred to as the “extra caloric” effect of fat. This effect can offset the increased passage rate associated with higher fiber ingredients as well as provide energy compensation for their being lower in energy content. Thus, fat additions provides for a multitude of benefits in energy nutrition. Because of their lower heat increment and greater efficiency in utilization, animals fed diets where fat has been substituted for an equivalent metabolizable energy in the form of carbohydrate, a greater net energy will be achieved. The benefit of increasing the energy density above that provided in a corn-soy diet has been referenced. Conversely diluting the diet below the value of a corn-soybean meal diet with other energy sources consistently reduces the margin over feed and the net profit for the swine operation.(3) Thus, the addition of fat to lower energy ingredients are very often alternatives for maintaining pig meat production at lower costs. Ethanol by-product ingredients supplemented with amino acids and fat are only opportunistic examples. Dietary fiber has been suggested as an adjuvant to gastrointestinal health. More attention has been directed to fiber in swine nutrition as more controversy continues on the use of oral antibiotics in animal production. It is well known that dietary fiber provides little energy to growing pigs with little knowledge possessed for older swine. Any increase in fiber necessitates energy supplementation. There is a compelling need for data in numerous areas of energy nutrition to address these uncertainties.
Carcass Quality
The discussion of fat (energy) for enhanced pork production efficiency always includes their affect on carcass quality. As has been referenced, the pig of today has changed dramatically from that of the past. As the Moser-Pettigrew summary illustrated in 1991 and demonstrated by Stein and Easter 1996,(6) a rather consistent increase in back fat thickness was observed in addition to the average daily gain and gain/feed improvements. This can be illustrated in Table 3 by the summary of numerous trials for several growth and carcass characteristics.
This observation has been a concern for the use of fat in finishing swine diets. It has not been a concern with modern high lean genotypes. In fact, pork quality has been improved by adding rendered animal fats to finishing swine diets. The enhanced usage of “metabolic modifiers” and the expected use of conjugated linoleic acid (CLA) to further increase protein accretion has developed concerns for the production of carcasses with limited interstitial fat, reducing pork quality characteristics.
Added fat during the finishing period has the potential to alleviate those concerns. In an experiment conducted at Purdue University by Dr. Allan Schinckel and associates to determine the individual and combined effects of dietary fat (tallow or choice white grease), CLA and ractopamine (Paylean) on growth performance and carcass quality of a genetically lean population of gilts addressed this issue.(7) The results of this research demonstrate that feeding diets containing added fat to genetically lean gilts increases production efficiencies and pounds of pork produced. The addition of dietary fat to ractopamine-supplemented diets maximized carcass weight gain without affecting percentage lean in the carcass. The fat deposits of the pig are influenced by its dietary fatty acid intake and can be intentionally manipulated by adjustments to the diet. Certainly this is another area of needed research emphasis. The genetic potential for protein synthesis will continue to increase in swine but at perhaps a slower rate than the past decade. Compounds to partition nutrients will be used in swine rations with increasing frequency. Energy density of the diet to enhance production and carcass quality will receive increased attention and animal fats certainly have a role to play.
References:
1. Ewan, R.E. 2001. Swine Nutrition, Second Addition, CRC Press LLC: 85.
2. Moser, R.L., and Pettigrew, J.E. 1991. “Fat in Swine Nutrition.” Swine Nutrition. Butterworth-Heinemann, Stoneham, MA. Chapter 8.
3. Tokach, M., et. al. 2003. American Society Animal Science Annual Meeting “Energy Density of Pig Diets Seminar.” To be published in seminar proceedings.
4. Noblet, J. Journal of Animal Science Volume 81, Supplement: 155, Abstract #612.
5. Campbell, R. 2003. American Society Animal Science Annual Meeting “Energy Density of Pig Diets Seminar.” To be published in seminar proceedings.
6. Stein and Easter, R. 1996. Dietary Energy Concentration Affects Carcass Leanness in Finishing Hogs. University of Illinois, Swine Research Reports #41.
7. Schinckel, A. P. Evaluation of the Effects of Dietary Fat, CLA and Ractopamine on Growth Performance and Carcass Quality in Genet-ically Lean Gilts. FPRF Directors Digest #313.
Tech Topics - October 2003 Render