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GERALD F. COMBS Nutrition and Management Aspects of Nonruminant Animals Related to Reduction of Fat Content in Meat Many experiments have been conducted with the growing pig in an effort to increase the ratio of lean to fat in the carcass. Studies, usually de- signed for other purposes, also have shown that the body composition of broiler chickens, ducks, and turkeys may be modified. Some of the factors studied that may affect the body-fat content of nonruminant animals include genetic stock, age and weight marketed, sex, exercise, ambient temperature, and diet. Diet factors include energy level and source, protein level and quality, energy-protein balance, nutritional adequacy, restriction in amount of feed, and frequency of ingestion and physical form of the diet. This paper will not endeavor to treat the genetic aspects of this prob- lem, nor will it attempt a comprehensive review. Only selected papers that illustrate certain principles will be cited. AGE, BODY WEIGHT, AND SEX The first prerequisite for high lean-to-fat ratios in pig carcasses is the genetic potential. There are wide differences in the ratio of lean to fat between and within breeds or crossbred pigs reared under com- mercial conditions. Most nutritional treatments designed to reduce body fat (as energy restrictions) are likely to reduce body weight gain at the same time. Reid et al. (1968), who conducted studies in which various diets were fed to 714 male castrates and female pigs of nine breeds from 1 to 116
Nutrition and Management Aspects of Nonruminant Animals 117 923 days of age, found that 97.6% of the variation in body-fat content of pig carcasses is ascribable to variability in body weight. They ob- tained the linear equation y= 1.46761x-1.35758, where y=log,O weight (kg) of fat in empty body and x=log:O empty body weight (kg). These workers found that the concentrations of body water and fat were highly, though inversely, related, with a correlation coefficient of -0.990 in the pig. Their data suggest that only small changes in carcass fat can be achieved without adversely affecting growth rate. As growth proceeds in pigs beyond a certain weight, the impetus to deposit fat appears to exceed that for protein, and body fat increases in a curvilinear manner. Data of Richmond et al. (1970) illustrate these relationships (Figure 11. Marketing animals at lower body weights will result in some reduction in the fat content of meat. 200 So Cal z o Z 100 _ V 50 o Carcass / ~- fat Muscle Bone 0 so 150 200 250 llVE WEIGHT IN POUNDS FIGURE 1 Carcass, muscle, fat, and bone weight relative to live weight in pigs. (From Richmond et al., 1970)
118 GERALD F. COMBS In the chick, the carcass wafer: nitrogen ratio ranges from 26:1 at day-old to about 16: 1 at maturity, but this ratio is remarkably constant at any given age despite major differences in diet, body size, or per- centage of body fat. As in the pig, body fat varies inversely with body water. Although considerable deviation in body-fat content as a function of body weight has been achieved in poultry, a prediction equation, based on age, has been developed (Combs, 1968) for normally fed male broiler chickens, as follows: 9 = 0.094x + 59, where y = percentage of ether extract of empty carcass and x=age in days. Edwards et al. (1973) obtained similar data with broilers; the data showed rapid in- crease in percentage of carcass fat with age. Females consistently had a higher percentage of body fat than males, but the difference was espe- cially pronounced after the seventh week (Figure 2~. Reports by Teague et al. (1964), Martin (1969), and Newell and Bowland ( 1972) indicate that boars produce carcasses with more muscle and less fat than castrates. Gilts appear to be intermediate in carcass fat (Table 11. Marketing of boars instead of barrows offers promise as a way to reduce fat, if procedures can be devised to eliminate sexual odor. Studies involving late castration (Bratzler et al., 1954; Newell et al., 1973) and implantation of boars with diethylstil I 6 j 11 _ z Cat 9 _ o ~ 7 - /: Combs (1968) Y = 0.094x + 5.9 ~ x ~x Edwards (1973) x = Males ~ = Females 0 2 4 6 8 10 AGE OF BROI LERS, WKS FIGURE 2 Effect of age on fat content of broilers. (From Edwards et al., 1973 )
Nutrition and Management Aspects of Nonruminant Animals 119 TABLE 1 Effect of Sex on Performance and Carcass Composition of Pigs a Observation Boars GiltsBarrows Average daily gain ( kg ) 0.72 0.720.73 Feed/gain 3.01 b 3.31 c3.40 c Backfat (cm) 9.62b 10.79 c12.14 Loin eye (cm) 27.00 ~29.4oc25.80 D Carcass fat (%) 33.905 35.60 b C4l.40r a SOURCE: Newell and Bowland (1972). b,c,& Means with the same superscripts or no superscript are not significantly different at the 1% level. bestrol (Plimpton et al., 1967; Teague, et al., 1964; Newell and Bow- land, 1973) indicate that the intensity of taint can be markedly de- creased or eliminated. Early slaughter is another way to eliminate this problem. EXERCISE ( PIGS ) Studies with pigs by Mandigo et al. (1971) and Murray et al. (1974) reveal that forced exercise on the treadmill has little effect on carcass composition of pigs. These studies involved pigs ranging from 12 to 60 kg and various techniques of measurement. At the start of Murray's study, which involved 12-kg pigs, exercise had no effect on feed intake, rate of gain, efficiency of feed utilization, or body composition, even though pigs were forced to walk more than 60 km in 9 weeks. Morrison et al. (1968) found that feed intake and growth rate were reduced when pigs were made to exercise by running or walking along a concrete alley, but the exercise had no significant effect on backfat thickness. It appears that the energy used for exercise in pigs is a relatively small part of the total energy intake. Exercise offers little promise of practical importance as a means of reducing body fat in meat. ENVIRONMENTAL TEMPERATURE Environmental studies with pigs raised in different ambient temperatures have yielded inconsistent results with respect to the effect on body fat. Seymour et al. (1964) found that dietary protein level and tempera- ture had a significant effect on the yield of lean cuts. Higher protein levels (20%, 17%, and 14%) resulted in more lean cuts, and the dif
120 GERALD F. COMBS ference was greater at an ambient temperature of 60° F than it was at ambient temperatures of 36° or 90° F. However, temperature had little effect on backfat when low protein levels (16%, 13%, and 10%) were fed, although more feed was required per unit of gain as the ambient temperature was lowered. Also, Hale (1971) observed that pigs raised in winter (mean temperature of 12-8° C) consumed more feed and had significantly thicker backfat than pigs raised in summer (mean temperature of 24-50° C). On the other hand, Bowland (1970) reviewed studies showing that pigs raised outdoors in winter in Edmonton, Canada, were leaner than others reared in confinement in heated barns. However, this effect is attributed to the reduced rate of gain. Any environmental influence that alters rate of growth can be expected to affect the lean-to-fat ratio, but this is likely to be accompa- nied by an increase in feed requirements per unit of weight. Studies conducted in controlled environments (Edwards et al., 1971b) showed, however, that slightly higher levels of body fat were obtained at 85° F than at 45° or 65° F when the diet contained added fat (Table 21. These results are in agreement with the work of Pope (1960), who found that increasing the ambient temperature from 75° to 90° F significantly increased body fat in broilers fed diets containing added fat and that reducing the temperature from 75° to 55° F reduced carcass fat content. Pope (1960) also found that inclusion of 5%-10% corn oil in a mash feed during the finishing period (5-7 weeks) increased the body- fat content of broiler chickens from 25% to 30% (dry basis). The in- clusion of 5%-10% corn oil in finishing diets of broilers kept in a 90° F constant-temperature room during the fifth to the eighth week of age permitted slightly more rapid increase in body-weight gain and a sig- nificant increase in body-fat content than was obtained on diets con- taining only 2% added fat. This increased growth rate was attributed to the reduced heat increment involved in the metabolism of a higher fat-containing diet. TABLE 2 Effect of Ambient Temperature and Diet on Body Fat in Broilers ~ ~0 ~ a Ration 45o F 65° F 85° F Low fat, high protein 5.9 6.5 5.8 Low fat, low protein 8.2 8.5 9.6 High fat, high protein 6.7 10.7 11.2 High fat, low protein 13.1 12.0 15.5 ~ SOURCE: Edwards et al. ( 197Ib) .
Nutrition and Management Aspects of Nonruminant Animals 121 Unless broiler feeds are pelleted, the inclusion of fat increases the energy density of mash feeds. Such diets permit greater intakes of energy and protein, even if proper energy-protein balance is maintained. When fat is added in place of a cereal component without adjustment in pro- tein level, the energy: protein ratio widens and the broiler consumes relatively more energy and deposits more body fat. This is illustrated by the results obtained by Edwards et al. (1973), who obtained in- creases in body-fat content in broilers at market age by adding four commercial fats to feeds without adjusting the protein content (Table 3 ~ . DIETARY FACTORS Any change in diet or diet management that minimizes overconsump- tion of energy in relation to needs (for maintenance, growth, activity, and temperature control) can be expected to result in less fat deposi- tion in the carcass of growing animals. Body composition for each strain, breed, or cross appears to have a genetically determined "norm" that prevails unless dietary or other stresses are imposed to modify it. Lean body mass seems to retain rather fixed proportions of protein and water at any given stage of development, with alterations in body composi- tion resulting primarily from dilution by the amount of obese tissue that is deposited. Reduction of energy intake then becomes the primary means of reducing the fat content of meat. Although energy intake may be achieved by limiting the amount of TABLE 3 Effect of Added Dietary Fat on Carcass Lipid in Broilers a Supplemental Fat ( % ) b Acid Age Cottonseed Cottonseed BeefPoultry (weeks) None Oil Soap Stock TallowFat Males 6 6.3 8.5 9.1 10.89.6 7 7.6 10.0 11.1 11.912.7 8 10.1 13.5 13.3 1 1.512.3 9 9.9 1 1.5 13.2 13.11 1.3 Females 6 8.5 10.6 10.4 1 1.61 1.0 7 9.3 1 1.2 12.2 12.512.9 8 1 1.8 14.1 14.8 14.815.3 9 11.8 13.8 14.0 20.211.3 a SOURCE: Edwards et al. ( 1973 ) . b 3.25% in starters; 5.25% in finishers.
22 GERALD F. COMBS feed provided or feeding time, nutritional modifications are usually more complex and interdependent in their effects on body composition. Nevertheless, the dietary factors that have the greatest effect on energy intake, and thus carcass composition, are energy concentration of the diet, protein level of the diet, and, especially, the ratio of energy to protein. EN ERGY : P ROT EI N RAT IO Chickens Fraps (1943), in studies designed to measure productive energy values of feed ingredients, observed increases in body-fat content of growing chicks when fats were substituted for cornmeal in a standard ration. Substitution of casein, cottonseed meal, or other protein feedstuR pro- duced chickens of lower fat content. Hill and Dansky (1954) reduced the carcass fat as much as 40% in 40 36 m 6 32 X a 28 I LO in 6 ~ 24 C' 20 16 _ i/ i 1 ' 1 1 1 1 1 1 5 ~45 ~ 55 60 65 70 Dl ETARY PROD. ENERGY/PROTEI N RATIO FIGURE 3 Effect of energy: protein ratio on body fat of chicks. (From Donald- son et al., 1956) / / / · / . / / - · / ,~ . /
Nutrition and Management Aspects of Nonruminant Animals 123 broilers by feeding diets containing high levels of oat hulls, which lowered the energy concentration. They concluded that feed consump- tion was determined primarily by the energy level of the ration. Donaldson et al. (1956) observed that as the ratio of energy to pro- tein in the ration was widened, broiler chickens consumed more energy and deposited more fat and less water in their carcasses (Figure 3~. A highly significant positive correlation (~0.951) was obtained be- tween the caloric: protein ratios (kilocalories of productive energy per pound divided by percentage of protein) and percentage of carcass fat (wet basis); and a highly significant negative correlation ~-0.914) was obtained between the calorie:protein ratio and percentage of body water. The fat deposited in the carcass was in excess of the water dis- placed when diets containing caloric: protein ratios wider than 50:1 were fed. Edwards et al. (1971a) plotted the body-fat data of Fraps (1943) against the calorie:protein ratio to test the concept proposed by Donald- son et al. (1958~. Linear functions fitted to both sets of data were not significantly different with regard to slopes on intercepts. They also found that the data of Hill and Dansky (1954) showed a similar rela- tionship when body fat was plotted as a function of the caloric: protein ratio. These are important findings. Although different caloric: protein ratios were achieved in these studies by widely different dietary manipu- lations, the body-fat content was still highly correlated with the ratio of energy to protein in the diet. E N E ROY : P ROT KIN RAT IO Ducks Scott et al. (1959) obtained marked differences in body-fat content of White Pekin ducks by alterations in the energy: protein ratio of the diet, thus providing further support for the belief that the ratio of energy to protein is more important than either the energy or protein level per se in determining feed intake and body fat (Donaldson et al., 1956~. Ducks fed diets ranging in metabolizable-energy content from 1,325 to 816 kcal per pound with similar protein levels (15.8%-16.4% ~ exhibited lower carcass fat (oven-ready basis) as the energy: protein ratio was narrowed (Table 4~. Similar results were obtained with diets in which the protein level had been increased from 16.3% to 28.9%. In energy level, these diets were comparable. As a result of feeding these higher protein diets, carcass fat was reduced from 32.7% to 24.2% (Table 5~. In another experiment, both energy and protein levels were
124 GERALD F. COMBS TABLE 4 Effect of Varying Dietary Energy on Fat Content of Pekin Ducks a ME per Pound of Diet Carcass Fat (kcal)b ME: Protein Ratio b (DO) 1,325 81 32.7 1,197 73 3 1.2 1,070 66 29.8 946 59 30.0 816 52 26.3 a SOURCE: Scott et al. (1959) . b Value refers to Kcal of metabolizable energy per pound of diet-percent protein. changed through equally wide ranges in such a way as to maintain comparable energy: protein ratios. No differences in carcass fat were obtained. In more recent studies, Dean (1967) reduced the body fat of ducks at market weight by only 1.4% by increasing the protein in isocalonc diets (without change in amino acid pattern) from 18~o to 24%. Dean pointed out that the duckling grossly overconsumes dietary energy during the latter part of its growing penod. He questioned the economic feasibility of materially reducing the carcass fat by diet changes without some form of feed restriction. CALORIE: PROTEIN RATIO Turkeys Studies with Maryland White turkey poults (Donaldson et al., 1956) involving the inclusion of 3%, 10.5%, or 18% corn oil in the diet to TABLE 5 Effect of Varying Protein Level on Fat Content of Pekin Ducks a Dietary Protein (% ) ME: Protein Ratio b Carcass Fat ( % ) 16.3 85 32.7 18.4 74 29.8 20.5 65 29.0 22.6 58 26.6 24.7 52 25.7 26.8 47 25.1 28.9 43 24.2 a SOURCE: Scott e' al. (1959). Value refers to Kcal of metabolizable energy per pound of diet percent protein.
Nutrition and Management Aspects of Nonruminant Animals 125 achieve three energy levels, with five protein levels at each energy level, revealed differences in carcass fat. As with chickens, widening the ratio of energy to protein increased voluntary energy intake and reduced pro- tein intake per unit of gain, with a resulting increase in carcass fat. However, dietary fat level per se had a much greater effect on body fat of poults than it had on broilers. This effect-added fat in increasing body-fat stores in poults cannot be explained in terms of energy- protein balance alone. It may be due in part to the increased energy density of the mash feed. In this connection, metabolizable calories from starch and calories from corn oil, when pair-fed to chicks at graded levels to supply up to one half of the dietary energy of chicks, were found to be equally effec- tive in promoting growth and body-fat deposition at normal ambient temperatures (Combs, 19571. ENERGY INTAKE AND NITROGEN RETENTION Most of the studies with poultry that show highly significant relation- ships between the energy: protein ratio and body-fat content have dealt primarily with normal to low protein levels. When the protein level is reduced below that required for a given energy level, chickens increase their voluntary energy consumption and deposit more body fat. This overconsumption of energy, which occurs when feeds containing low protein levels are fed, has been demonstrated with a wide variety of diets (Combs, 1957; Robel, 1957; Combs, 1964; Thomas and Combs, 1967; Potter, 19681. In several studies designed to develop appropriate equations for predicting amino acid requirements of chicks on the basis of growth rate, body size, and body composition, groups of chicks were fed ad libitum isocaloric diets containing widely different levels of the same protein mixture-Combs, 19641. At each protein level, other groups of chicks were pair-fed to provide identical protein but reduced energy intakes. The effects of varying the energy and protein intakes in one of these studies is given in Figure 4. The efficiency of nitrogen retention was increased from 49.9~o to 56.4% as protein level was lowered by one half in the diet of chicks fed ad libitum because of the sparing effect of the extra energy consumed. When energy intake was restricted at any given protein intake, the body-fat content was reduced accordingly, growth was impaired, and the efficiency of retention of di- etary protein was progressively louvered. P. R. Crowley and G. F. Combs (unpublished) have analyzed the data from one experiment of Robel (1957) and quantitated the sparing effect of energy on protein. They found that 17.5 metabolizable kilocalories from nonprotein sources resulted in the same amount of protein retention in the carcass as did
26 24 _ 22 _ Cal ~ 18 X CC I UJ CD Cal at 14 10 6 ./ / ~ 1 1 1 1 1 it's/ - GERALD F. COMBS ·' s.1 30 60 90 120 150 METAB. KCAL CONSUMED/BIRD (17-28 DAYS) FIGURE 4 Effect of protein and energy intakes on body-fat content of broiler chicks. (From Combs, 1964) 1 g of protein in the diet, or that 1 g of dietary protein was equal to about 4.4 g of carbohydrate, or 2 g of fat. Summers et al. (1965) reported that carcass fat of chicks was in- creased in a linear manner as the protein level of their diet was reduced in a factorially arranged experiment involving four levels of energy and five levels of protein. They also observed (Summers et al., 1964) that the retention of dietary nitrogen by chicks was improved when the energy: protein ratio was widened by increasing the energy level of the diet (Tables 6 and 7~. To summarize: As the protein level is lowered, energy content is increased or the energy: protein ratio is widened, carcass fat content is increased, and the percentage of dietary nitrogen and dietary energy retained in the carcass is increased. AMINO ACID DEFICIENCY The effect of a specific amino acid deficiency on voluntary appetite and body composition is different from that of a low-protein diet (or a wide energy: protein ratio). While both of these retard growth, chicks fed a diet with a normal protein level but deficient in a single amino acid fail to show any overconsumption of energy or an increase in percent of
Nutrition and Management Aspects of Nonruminant Animals 127 TABLE 6 Effect of Dietary Energy and Protein Level on Carcass Fat in Chicks Dietary Protein (% ) ME per Gram 10 14 18 22 26 All Levels of Diet (kcal)b Carcass Fat (Dry Basis) (% ) 2.50 28.3 25.6 21.6 19.3 18.2 22.6 2.78 31.9 29.0 25.4 22.3 20.5 25.8 3.05 33.2 31.4 27.6 24.7 23.0 27.9 3.33 33.9 32.3 26.4 21.0 19.7 26.7 Average 31.8 29.6 25.2 21.8 20.3 a SOURCE: Summers et al. ( 1965 ) . ~ ME = metabolizable energY. body fat. This has been observed repeatedly in chick studies with diets deficient in methionine and lysine at the University of Maryland. Shank (1969) did find that energy intake and carcass fat of chicks were increased very slightly as lysine was lowered just below the optimal level, but further reduction in lysine resulted in a slightly lower body-fat content as the deficiency became more severe. These results are in marked contrast to the effect of low-protein diets. Diets that have been "imbalanced" by the addition of one or several amino acids also may depress feed consumption and lower carcass fat of chicks (Khalil et al., 1968). Overconsumption of energy and increases in the carcass fat have been observed with pigs fed cottonseed meal and sunflower meal due to TABLE 7 Effect of Dietary Energy and Protein Level on Nitrogen Retention in Chicks a Dietary Protein (% ) G M^E~per ram 10 14 18 22 26 All Levels of Diet (kcal)b Nitrogen Retention (Jo) 2.50 54 55 46 44 36 47 2.78 54 56 49 48 41 49.6 3.05 54 57 52 49 47 51.8 3.33 53 58 55 51 47 52.8 Average 53.8 56.5 50.5 48 42.8 a SOURCE: Summers et al. (1964). b ME = metabolizable energY.
28 GERALD F. COMBS the suboptimal levels of lysine (H. C. McCampbell, personal com- munication). Just how protein level, amino acid deficiencies, and imbalances exert their effect on appetite is not known, but the increased amount of free energy produced from metabolism of protein would be expected to reduce feed intake. Brobeck (1948) pointed out the intimate cor- relation between body temperature and food intake and suggested that heat acts on the sensitive neurons of the rostral hypothalmus and the preoptic area of the brain or directly upon neurons of the "appetite center." HIGH PROTEIN LEVELS In view of the effect of protein level per se on voluntary energy intake and body composition as described above, a series of studies was con- ducted at the University of Maryland with growing broilers to determine whether increasing the protein above that needed for optimal growth would further reduce the feed required per unit of gain and body-fat content (Combs, 19651. This was tested in both starter and finisher feeds. Protein levels were increased in broiler starters from 21% to 27.5% by increasing the dietary protein level, while maintaining the same level of the first limiting amino decides) or by increasing the level of the limiting amino asides) and total dietary protein proportionately. The results obtained in four experiments during the first 4/ weeks are summarized in Figure 5. Increasing the protein level in broiler finishers from 20% to 24% also resulted in about 4% less feed energy per unit of gain from 4/ to 8 weeks of age and produced broilers with about 1~/~% less body fat. Later studies revealed that differences in body composition at 4~/2 weeks would disappear by 8 weeks unless the excess protein stress was continued during the finishing period. Dean (1967) made a study in which carcass fat in ducks was reduced by diet. He found that much of the early reduction was overcome by the time the ducks reached market age. Khalil et al. (1968) prefed chicks a low-protein diet for 8 days to produce obese chicks (24.1% body fat) and fed others restricted amounts of a high-protein diet to produce low-fat chicks (1.8% ). When these chicks, of the same size and age but differing greatly in body-fat content, were allowed to eat ad libitum a complete, balanced diet, little differences in body-fat content remained ~ 1 0.3 % versus 1 3 .6 % ~ after only 9 days. This illustrates the chick's ability to adapt and provides an explanation for compensatory growth effects.
Nutrition and Management Aspects of Nonruminant Animals 129 104 100 y Z `~, 96 A: of LU ~no U] O~ ` ~Protein and Limiting Amino Acids - __ Raised in Balance 9= 0.549x + 64.1 / ~ _ y = 0.639x + 58 Protein Raised but Limiting Amino Acids not Raised Above 100% of Estimated Requirement 1 1 1 70 66 62 58 54 52 METABOLIZABLE C/P RATIO FIGURE 5 Effect of caloric: protein ratio on energy efficiency and feed conver- sion. (From Combs, 1965) ENERGY AND PROTEIN LEVELS ( PIGS ) Dietary energy and protein levels have been varied in a large number of studies as a means of influencing energy intake and fattening in pigs. Feed consumption has been restricted by using bulky, low-energy rations, limiting feeding time, and reducing the quantity of ration fed. The effect of energy restriction has been studied with the pregnant sow and piglets as well as with growing and finishing pigs. Early Nutrition Investigators appear to agree that bodY-fat content of market pigs can- not be influenced appreciably by nutritional man~pulahon ot the diet or the sow. Composition studies of newborn- pigs of widely different genetic and environmental origin (reviewed by Topel, 1971) revealed little variation in composition. Lowering the energy level of the sow's diet appears to have little practical importance in changing the composition _ ^, , ~ _ _ ~ ~ ~ . .~ ~ , . ~ ~ ~ ,~ ~ ~ . ~ ~ of her offspring; the sow electively buyers them trom nutritional ~n- adequacies. Moreover, most effects of nutritional deficiencies on pre- natal growth and fetal composition would be accompanied by impaired growth and development and, in severe cases, by death and resorption of the embryo.
130 GERALD F. COMBS Ever since the classic studies of McMeekan (1940), showing that the carcass composition of the pig changes considerably as it grows heavier and older, efforts have been made to influence the relative body- fat content by nutritional means. Early nutrition may affect body compo- sition at weaning, but it is likely to have little effect on body-fat content at market weight. Birth weights of pigs are influenced by many factors, including nutri- tion. If pigs heavy at birth are fed properly, they normally grow faster and are heavier at 8 weeks than pigs lighter at birth. Bowland (1965) fed starting rations varying in protein and changed the rates of gain to 9 or 10 weeks (23-kg body weight) but found that these effects on early growth were lost and that no differences in carcass characteristics re- ma~ned at 90-kg body weight. Wyllie et al. (1969) also observed considerable differences in body composition of pigs fed diets containing 10%, 17%, 24%, or 31% protein to approximately 24 kg body weight (Table 8~. Pierce and Bowland (1972) obtained differences in gain with dietary protein levels from 14% to 20% during the starting period but noted a compensatory feed-conversion effect during later stages of growth and no difference in carcass quality at market weight. Topel (1971) reviewed studies in which pigs were fed diets con- tain~ng different protein levels, with high- and low-energy levels, dunug the weanling period. Subsequently, they were fed normal finishing ra- tions to body weights of 90 and 110 kg. No significant differences in carcass composition remained at slaughter weight. It would appear, therefore, that reduction in energy intake of pigs from birth to body weights of 23 kg has no practical influence on body composition at market weights if similar growing-finishing rations are fed later. Rather, it is suggested that pigs be fed so as to reach body weights of 23 kg as soon as possible if most efficient growth is to be achieved. Special care should be given to the nutritional adequacy of TABLE 8 Protein Level and Body Composition of Pigs (23.9 kg) a Starter Protein Level (% ) Carcass Composition 10 17 24 31 Ether extract (% ) 27.5 20.3 13.8 12.1 Protein (%) 13.0 14.8 16.0 16.5 Water (%) 55.5 60.9 65.8 67.4 Ash (%) 2.9 2.9 3.0 2.8 a SOURCE: Wyllie et al. (1969).
Nutrition and Management Aspects of Nonruminant Animals 131 the diet with respect to amino acids, vitamins, and minerals during this period. Finishing Period A large number of studies indicate that to affect carcass fat, dietary modifications or changes in feeding practices must be imposed during the finishing period or after the pig reaches a body weight of about 60 kg. It is likely that the principles of nutritional management that apply to poultry also apply to pigs, but most of the genetic types of pigs used in the United States for meat production are likely to deposit large amounts of fat in their carcasses unless energy intake is restricted. Genetic types that will respond to differences in diets (higher protein level) appear to be a prerequisite to progress along these lines. Davey and Morgan (1969) demonstrated a significant interaction be- tween line and diet. Carcasses from pigs selected for low fat content had significantly more lean at market weight than did those selected for high fat content. At the same time, pigs from the low-fat line produced significantly more lean when fed a 20% versus a 12% protein diet, and the high-fat line failed to respond (Figure 6~. Ad Lean fat 20 I ~ 15 In 10 5 HIGH LOW FAT FAT 20% PROTE I N HIGH LOW FAT FAT 12% PROTEIN FIGURE 6 Average weight of physically separated carcass lean and fat of high and low-fat pigs fed 12% or 20% protein diets. (From Davey and Morgan, 1969)
132 GERALD F. COMBS Perhaps this explains part of the lack of agreement among researchers who have attempted to modify carcass fat by increasing the protein level. Several workers have obtained little effect from higher protein levels (12%-18% ~ on carcass fat: lean ratios (Hudman and Peo, 1960; Clawson, et al., 1962; Meade et al., 1966; Newell and Bowland, 1972~. Others have reported significant increases in muscle deposition from feeding more protein (Robinson and Lewis, 1964; Holme et al., 1965; Lee et al., 1967~. Less deposition of intramuscular fat or marbling has been observed when higher protein diets are fed during the finishing period. Pigs with greater genetic potential for lean carcasses can be ex- pected to respond to higher levels of dietary protein. Among the many studies involving the energy level of pigs' finishing rations is that of Hale ( 1971 ), in which ground corncobs were added to dilute the energy and tallow was added to increase it (Table 9~. Backfat increased as the energy level increased, and the proportion of lean cuts and loin-eye area tended to decrease. As one would expect, average daily gain decreased with the lower energy diets, but the net amount of lean cuts was greater. Baird et al. (in press) found that pigs fed high- and low-energy finishing rations had significantly less backfat and greater percentages of lean cuts. When the energy content was diluted by the addition of fiber (cottonseed hulls), a similar improvement in carcass quality resulted (Table 10~. But when fat was added to the high-fiber diet to restore its energy, carcass quality was no longer affected. Hence, dietary fiber per se was not exerting any effect on fatness in finishing pigs. Feed Restrictions Skitsko and Bowland (1970) also fed two levels of dietary energy to pigs sired by Durocs, Hampshires, and Yorkshires and found that the TABLE 9 Effect of Dietary Energy Level on Fatness in Pigs a Diet supplement 25~o 8% 4~o 8% ObservationCobs Cobs Basal Tallow Tallow Average daily gain (lb)1.63 1.83 2.05 2.03 2.09 Feed/gain3.88 3.72 3.07 2.85 2.59 Average backfat thickness (in.)1.16 1.33 1.39 1.52 1.55 Loin-eye area (sq in.)3.81 3.57 3.52 3.27 3.30 Lean cuts (lb)81.80 80.00 77.60 76.50 76.10 a SOURCE: Hale ( 1971 ) .
Nutrition and Management Aspects of Nonruminant Animals 133 TABLE 10 Effect of Fiber, Protein, and Energy Levels in Diets for Finishing Pigs a Fiber Level Protein Level Energy Level ObservationLow HighLowHigh LowHigh Average daily gain (kg)0.69 0.690.680.70 0.600.70 Feed/gain3.28 3.353.223.41 3.593.04 Backfat (cm)3.45 3.613.583.48 3.433.63 Longissimus (cm)30.60 31.6030.9031.40 32.1030.10 Loin (%)16.30 16.0016.0016.30 16.4015.90 Ham (%)21.80 21.4021.5021.60 21.9021.30 Lean cuts (% )55.40 54.7054.9055.20 55.6054.60 a SOURCE: Baird et al. (in press). carcass lean: fat ratio was closely associated with energy intake. The pigs were allowed to feed for two 1-fur periods each day. Pigs fed the high- and low-energy diets ate similar amounts of feed, but those re- stricted consumed less energy and deposited less carcass fat. Average daily gain was also reduced. Bowland (1970) reported that when the same low-energy diet was fed to pigs permitted to self-feed, they were able to eat more total feed and showed less difference in performance. How restriction of corn-base finishing diets affect carcass composition has been studied by Greer et al. (19651. Their results (Table 11) show that reduction of percentage of fat in the longissimus muscle, reduction in backfat, and increase in lean cuts were achieved by restricting diets. However, to appreciably decrease carcass fat, it appears that the energy restriction must be severe enough to markedly reduce gain in body weight. A further study involving full and restricted feeding of finishing pigs on pasture and drylot showed that restriction of feed to 80% of "full- fed" controls increased carcass leanness of market pigs kept in drylot but TABLE 11 Effect of Restriction of Corn-Base Diets on Carcass Fat in Pigs at 92 Kga Feedintake (kg/day) 3.15 2.44 1.80 Average daily gain (kg) 0.77 0.61 0.45 Feed/gain 4.09 4.00 4.00 Backfat (cm) 3.78 3.40 3.28 Ham and loin (% ) 35.90 38.00 39.40 Fat in longissimus (5to of dry matter) 20.70 14.30 11.40 a SOURCE: Greer et al. (1965).
134 GERALD F. COMBS not that of pigs on pasture (Baird et al., 1971). Increasing the energy level of the limited-fed, diet-reduced carcass leanness and increasing the protein content tended to increase leanness (Table 12~. According to Bowland (1970), pelleted rations usually permit greater feed consumption and thus result in fatter carcasses. This tends also to be true for poultry, even though feed consumption may also be influ- enced by other factors. Limited feeding in pigs also lowers the amounts of oleic acid and linoleic acid in proportion to stearic and palmitic acids in the backfat as compared with ad libitunz feeding (Topel, 1971~. Since feed restriction almost always results in less total gain in body weight as carcass fat is reduced, it is clear that improved methods of marketing are needed that will place more value on proportion of lean cuts and less on total weight. Accordingly, Lind and Berg (1973) studied the effects of three levels of feeding and three slaughter weights on the absolute yield of tissues, dressing percentages, and the yield of closely trimmed boneless retail cuts (CTBR). The left sides of the carcasses were dissected into muscle fat and bone, and the right sides were processed into closely trimmed boneless retail cuts, fat trim, and TABLE 12 Effect of Limited Feeding of Pigs to 93 Kg on Drylot and Pasture ~ 80% Full- 80% Full Fed with Fed with 80% Equal Equal ObservationsFull-Fed Full-Fed Protein Energy Drylot Daily gain (kg)0.71 0.62 0.67 0.72 Backfat (in.)3.56 3.20 3.18 3.68 Longissimus muscle (cm)31.20 31.40 31.40 29.60 Lean cuts (%)52.70 55.00 54.60 52.40 ME/kg gain (Mcal)511.70 10.60 10.30 11.90 Pasture Daily gain (kg)0.71 0.62 0.67 0.72 Backfat (in.)3.53 3.61 3.45 3.91 Longissimus muscle (cm)30.40 30.30 33.00 32.30 Lean cuts (% )53.90 53.40 53.70 53.60 ME/kg gain (Mcal)b13.00 11.90 11.10 12.30 a SOURCE: Baird e' a!. ( 1971 ) . b ME = metabolizable energy; Mcal .-megacalories.
Nutrition and Management Aspects of Nonruminant Animals 135 bone. The results show that the differences in dressing percentages could be attributed to fat content (Figure 71. As the slaughter weights increased, the percentage of muscle and bone decreased and the per- centage of fat increased. As the level of feeding was reduced from ad libitum to 4% and 3.5% of body weight, the percentage and total amount of muscle, or CTBR, cuts increased and percentage and amount of body fat decreased. The investigators concluded that the actual muscle in the carcass is closely related to the amount of CTBR cuts, and they found a good correlation between the closely trimmed, boneless ham or loin and the carcass muscle. Seventy-two animals of both sexes from two breeds were used in this work. PERIODICITY OF EATING Carcass data from pigs fed ad libitum (Allee et al., 1972) revealed higher body-fat content than data from pigs fed meals (Table 13~. Similarly, Friend and Cunningham ( 1964, 1967) and O'Hea and Leveille (1969) found that pigs fed a single meal daily deposited less body fat than pigs fed the same amount of feed over five meals (Table 14~. These results suggest that a hyperlipogenic state can be produced in the pig by restricting the feeding time. Leveille ( 1970) observed that rats trained to consume their food in a limited amount of time (meal-fed) underwent a gastric and intestinal hypertrophy. He also noted an enhanced rate of glucose absorption and an increased capacity to convert carbohydrate to fat. This hyperlipo- genesis is accompanied by an increase in the levels of several enzymes involved in lipid synthesis. Ingestion of meals also appears to induce an increased rate of lipid synthesis in the chicken (reveille, 1966~. Similarly, the digestive tract of the pig partly adapts by enlargement of the stomach and small intestine; thus, more food is consumed ~ a TABLE 13 Effect of Meal Frequency on Fatness in Pigs a Nibbler Meal-Fed (2h/24h) Days on test 60.00 60.00 Live weight (kg) 61.50 59.10 Backfat thickness (cm) 2.826 2.36 Perirenal fat (g/kg body weight) 9.40 7.90 Four lean cuts ( % ) 56.76 58.02 a SOURCE: Allee et al. ( 1972) . b p = < 0.05.
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Nutrition and Management Aspects of Nonruminant Animals 137 TABLE 14 Frequency of Feeding and Carcass Composition in Pair- Fed Pigs a Once Daily Five Times Daily Carcass gain (kg) 31.59 33.95 Carcass gain/day (kg) 0.37 0.35 Carcass fat (% ) 30.03 31.81 Backfat (mm) 51.82 56.89 Longissimus (cm) 27.81 28.00 a SOURCE: Friend and Cunningham ( 1964) . short time. Pigs fed only 2 h every other day were unable to consume as much food as ad libitum controls but gained almost as much weight (Allee et al., 19721. This reduced total energy intake appears to be partly responsible for the reduced level of carcass fat. Meal-fed pigs appear to be less active and to use their energy more efficiently, possibly because of the lower body-fat content. Restricting pigs to about 2 h of feeding per day during the finishing period may be one way to reduce carcass fat without a significant reduction in body-weight gain under practical conditions. SUMMARY Possible ways of reducing carcass fat in nonruminant animals are listed. Whether any of these are economical or practical will depend on other considerations. Use appropriate genetic stock. Unless the breed, cross, or strain used has the genetic potential for a high lean: fat ratio, most dietary manipula- tions are likely to have little effect on carcass fat. Market animals at lower body weights. Despite economic considera- tions, slaughter of nonruminant animals at lower body weights is per- haps the surest way to reduce carcass fat because the amount of carcass fat and body weight are highly and positively correlated for any given genetic stock. Feed nutritionally adequate, balanced rations. Provide at least mini- mal levels of all nutrients required for rapid growth of muscular tissues. This includes vitamins and minerals, as well as essential amino acids. Marginally low levels of the first limiting amino acid or mineral should be avoided because suboptimal or marginally deficient levels of certain of these may cause a relative overconsumption of dietary energy and increased deposition of body fat. For example, pigs fed a diet marginally
138 GERALD F. COMBS low in lysine would be expected to eat more feed per unit of weight gain and deposit more body fat. Maintain suitably narrow energy:protein ratios. When the level of protein is reduced below that considered optimal for growth and feed efficiency, the chicken, duck, turkey, and pig overconsume energy in relation to these needs and greatly increase the amount of carcass fat deposited. When the protein level is increased above the level usually considered optimal, the body-fat content of broilers is further reduced slightly. This is true even though the level of the first limiting amino acid~s) may not be increased. Accordingly, low protein levels should be avoided, and higher levels of dietary protein during the finishing period can be expected to minimize the carcass-fat content in relation to the genetic potential of the animal. The effects of higher levels of protein fed during early growth on body-fat content are generally lost if the high-protein stress on appetite is not continued throughout the finishing period. Reduce intake of dietary energy during finishing period. This can be done by reducing the energy concentration per unit volume of feed, restricting the amount of time animals are allowed to eat, and limiting the amount of diet fed. High-energy feeds, especially when pelleted, usually permit greater energy intake and hence more fat deposition in the carcass than do bulky, low-energy, mash feeds. Limiting the amount - - - -c' of eating time appears to hold promise tor pigs; a 2-h feeding period each day reduced feed consumption and carcass fat to some extent, compared with controls fed ad libitum, without adversely affecting body-weight gain. Reduce taint of boar meat. Marketing of boars instead of barrows would reduce carcass fat. Early marketing, late castration, and use of estrogen-active substances are ways of reducing the taint of boar meat. REFERENCES Allee, G. L., D. R. Romsos, G. A. Leveille, and D. H. Baker. 1972. Metabolic adaptation induced by meal-eating in the pig. J. Nutr. 102:1115-1122. Baird, D. M., H. C. McCampbell, and J. R. Allison. 1971. Limited-fed diets equal in total protein and energy to full-fed diets for pigs in drylot and pasture. J. Anim. Sci. 33:39~393. Baird, D. M., H. C. McCampbell, and J. R. Allison. In press. The effect of levels of crude fiber, protein and bulk in diets for finishing hogs. J. Anim. Sci. Bowland, J. P. 1965. Relation of early gain to performance of growing and finish- ing pigs. Feedstuffs 37 :25. Bowland, J. P. 1970. Some factors influencing carcass leanness in swine. Feedstuffs 42:28. Bratz;ler, L. J., R. P. Soule, Jr., E. P. Reineke, and P. Paul. 1954. The effect of
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Nutrition and Management Aspects of Nonruminant Animals 141 Newell, J. A., L. H. Tucker, G. C. Stinson, and J. P. Bowland. 1973. Influence of late castration and diethylstilbestrol implantation on performance of boars and on incidence of boar taint. Can. J. Anim. Scat. 53:205-210. O'Hea, E. K., and G. A. Leveille. 1969. Influence of feeding frequency on lipo- genesis and enzymatic activity of adipose tissue and on the performance of pigs. J. Anim. Sci. 28:336. Pierce, A. B., and J. P. Bowland. 1972. Protein and amino acid levels and sequence in swine diets: effects on gain, feed conversion, and carcass characteristics. Can. J. Anim. Sci. 52:531-541. Plimpton, R. F., Jr., V. R. Cahill, H. S. Teague, A. P. Grifo, Jr., and L. E. Kunkle. 1967. Periodic measurements of growth and carcass development fol- lowingdiethylstilbestrol implantation of boars. J. Anim. Sci. 26:1319-1324. Pope,' D. L. 1960. Pages 48-53 in Nutrition and Environmental Temperature Studies with Broilers, 1960 Maryland Nutrition Conference for Feed Manu- facturers, March 17-18, 1960. Univ. of Maryland, College Park. Potter, J. H. 1968. The methionine requirement of the growing chick. M.S. Thesis. Univ. of Maryland, College Park. Reid, J. T., A. Bensadoun, L. S. Bull, J. H. Burton, P. A. Gleeson, I. K. Han, Y. D. Joo, D. E. Johnson, W. R. McManus, O. L. Paladines, J. W. Stroud, H. F. Tyrrell, B. D. H. VanNiekerk, G. H. Wellington, and J. D. Wood. 1968. Pages 18-37 in Changes in Body Composition and Meat Characteristics Ac- companying Growth of Animals, 1968 Cornell Nutrition Conference for Feed Manufacturers. Cornell Univ., Ithaca, N.Y. Richmond, R. J., R. T. Berg, and B. R. Wilson. 1970. Pages 8-11 in Lean, Fat and Bone Growth in Swine as Influenced by Breed, Sex, Ration and Slaughter Weight, 49th Annual Feeders' Day, Report, The University of Alberta, 1970. Robel, E. J. 1957. Protein requirement of chicks for maintenance of nitrogen bal- ance and growth. M.S. Thesis. The University of Maryland, College Park. Robinson, D. W., and D. Lewis. 1964. Protein and energy nutrition of the bacon pig. II. The effect of varying the energy and protein levels in the diets of 'finishing' pigs. J. Agric. Sci. 63:185-190. Scott, M. L., F. W. Hill, E. H. Parsons, Jr., J. H. Bruckner, and E. Dougherty. III. 1959. Studies on duck nutrition. 7. Effect of dietary energy: protein rela- tionships upon growth, feed utilization and carcass composition in market ducklings. Poult. Sci. 38:497-507. Seymour, E. W., V. C. Speer, V. W. Hays, D. W. Mangold, and T. E. Hazen. 1964. Effects of dietary protein level and environmental temperature on per- formance and carcass quality of growing-finishing swine. J. Anim. Sci. 23: 375-379. Shank, F. R. 1969. Studies on the available methionine requirement of laying hens and the available lysine requirement of chicks. Ph.D. Thesis. The University of Maryland, College Park. Skitsko, P. J., and J. P. Bowland. 1970. Performance of gilts and barrows from three breeding groups marketed at three liveweights when offered diets contain- ing two levels of digestible energy for a limited period per day. Can. J. Anim. Sci. 50:161-170. Summers, J. D., S. J. Slinger, I. R. Sibbald, and W. F. Pepper. 1964. Influence of protein and energy on growth and protein utilization in the growing chicken. J. Nutr. 82:463~68.
42 GERALD F. COMBS Summers, J. D., S. J. Slinger, and G. C. Ashton. 1965. The effect of dietary energy and protein on carcass composition with a note on a method for estimating car- cass composition. Poult. Sci. 44:501-509. Teague, H. S., R. P. Plimpton, Jr., V. R. Cahill, A. P. Grifo, and L. E. Kunkle. 1964. Influence of diethylstilbestrol implantation on growth and carcass char- acteristics of boars. J. Anim. Sci. 23:332-338. Thomas, O. P., and G. F. Combs. 1967. Relationship between serum protein level and body composition in the chick. J. Nutr. 91 :468~72. Topel, D. G. 1971. Pages 13-25 in Effect of Nutrition on the Body Composition of Swine, 1971 Georgia Nutrition Conference for the Feed Industry, Febru- ary 17-19, 1971. Univ. of Georgia, Athens. Wyllie, D., V. C. Speer, R. C. Ewan, and V. W. Hays. 1969. Effects of starter pro- tein level on performance and body composition of pigs. J. Anim. Sci. 29: 433-438.