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Body Composition versus Nutritional and Other Factors
14 Body Composition versus Nutritional and Other Factors
I. INTRODUCTION The chemical composition of the whole empty body of an animal is due principally to species, heredity, environment, and nutrition. Changes in the concentration of fat, protein, and carbohydrates in the body reflect energy gain or loss. Change in body energy is utilized as a criterion of the energy value of feeds for maintenance, growth, and/or finishing livestock. Haecker (1920) concluded that the amount of water decreases and the amounts of ash and protein increase as the animals approach maturity, especially if finish ing does not intervene. Fat and water are variable, depending largely on the amount and kind of feed consumed, and together generally constitute 7 5 - 7 9 % of the whole empty body. It appears that the finishing process consists principally of replacing water by fat, or that the percentage body composition is markedly influenced by the deposition of large amounts of fat that contains very little water. Moulton et al. (1922) studied the fat-free composition of cattle ranging in development from early embryonic stages to maturity. The water content of the fat-free body decreased rapidly from the time of conception to birth, and then decreased less rapidly until a relatively constant concentration of water was reached at 5 - 1 0 months of age. Moulton (1923) introduced the concept of chemical maturity, which he defined as the age at which the concentrations of water, protein, and minerals in the fat-free tissues of the animal become prac tically constant. Different animals vary in their age of chemical maturity. That is, there is some decrease in the proportion of water and an increase in the propor tions of protein and ash as animals become older. Body weight changes are commonly utilized to indicate responses in many feeding experiments with livestock. In experiments of short duration, changes in rumen fill can result in appreciable errors. The use of body weight changes 275
276
14. Body Composition
assumes that weight gained or lost has the same composition irrespective or treatment. Such an assumption was early pointed out to be in error. By compar ing casein and urea as sources of dietary nitrogen for cattle, Watson et al. (1949) showed that although the animals fed urea diets gained only 70% as much weight as those fed casein, they gained 8 1 % as much energy. The total digestible nutrient (TDN) content or net energy (NE) values are commonly used criteria of the energy value of feed ingredients in the United States. It is recognized that the TDN of one feed does not necessarily produce a response of the same magnitude as an equal amount of TDN from another feed. This is especially true when comparing TDN values of concentrates and rough ages. Evaluating mixed feeds utilizing roughages for ruminants on a TDN basis is more complex than it is for nonruminants fed relatively roughage-free diets. Evaluation of feed on the basis of NE is less complex than it is for TDN in that a unit of NE in one feedstuff produces the same amount of a given response in a given animal as that produced by a unit of energy from entirely different types of feeds. NE values of feedstuffs and diets for maintenance and gain may be determined by metabolism and comparative slaughter feedlot trials. In such studies, the energy of whole empty animal bodies at the beginning and end of the feeding period is determined directly on tissues by calorimetry or indirectly by specific gravity (Lofgreen and Garrett, 1968; Garrett and Hinman, 1969). The specific gravity values are related to the fat and protein in tissues by chemical analysis. Empty bodies of cattle generally contain less than 0.5% carbohydrates (Trowbridge and Francis, 1910). Tissue carbohydrates are disregarded in dietary energy studies on feedlot cattle that involve sufficient time for considerable weight gains.
II. EFFECT OF DIET, BREED, AND SEX Blaxter (1962) concluded, from a biochemical appraisal of metabolic path ways involved in the deposition of protein and fat in cattle, that it seemed unlikely that one breed would be more energetically efficient than another. However, Garrett (1971) conducted comparative slaughter experiments with Holstein and Hereford cattle and compared the net efficiency of energy utiliza tion by the two breeds. The results indicated that Herefords were 12 and 20% more efficient than Holsteins in converting feed energy consumed above mainte nance to energy stored as protein and fat, respectively. The beef steers had gains that contained more fat, and consequently more energy, than corresponding gains by the dairy steers. The two breeds had equivalent gains of protein per unit of feed above maintenance. Nichols et al. (1964) compared Holstein bulls and steers for meat production from birth until slaughter at 800-1000 pounds. Bulls had slightly lower dressing
II. Effect of Diet, Breed, and Sex
277
percentages due to heavier hides and less fatty carcasses. Steers had higher marbling and more outside fat covering than bulls. Martin et al. (1978a) fed Holstein steers diets containing three levels of energy. The higher levels of dietary energy produced faster gains, more efficient conversion of dry matter to gain, greater deposition of fat, and higher carcass grade. Fortin et al. (1980a) studied the effects of energy intake, breed, and sex on muscle growth and distribution in Holstein and Angus bulls, steers, and heifers. The animals were fed energy at two levels, ad libitum and 6 0 - 7 0 % of ad libitum. In both breeds, irrespective of energy intake, sex had no influence on the growth rate of muscle in the thoracic and pelvic limbs relative to carcass side or total muscle. Neither breed nor energy intake altered the growth rate of muscle in the three joints relative to carcass side or total muscle. Fortin et al. (1980b) deter mined the chemical composition of Angus and Holstein bulls, steers, and heifers fed at two energy levels and slaughtered at weights ranging from 121 to 706 kg. The accretion rate of fat was not affected by sex, but accretion rates of protein and ash were more rapid in Holsteins than in Angus cattle in the high-energy dietary groups. Angus bulls had a faster accretion of fat than Holstein bulls. Fortin et al. (1981) concluded from composition studies with Angus steers, bulls, and heifers that the growth rate of fat relative to carcass side was greater in a high-energy than in a low-energy dietary group, whereas with corresponding sex groups of Holsteins, the growth rate of fat was not altered by the level of energy intake. The breed (Angus versus Holstein) generally did not influence the growth rate of muscle and bone plus tendon. A number of studies have demonstrated that bulls gain more rapidly and convert feed to lean meat more efficiently with less fat than steers (Cahill, 1964; Prescott and Lamming, 1964; Field, 1971). Bulls generally produce meat with less marbling, coarser texture, darker color, and less tenderness, depending on their age. However, organoleptic studies with young bull meat indicate a high level of palatability. Arthaud et al. (1977) compared carcasses of bulls and steers fed at two levels of energy and slaughtered at 12, 15, 18, and 24 months of age for composition and taste panel evaluation. Bulls made faster gains on less feed per unit of gain and had less fat in the carcass than steers at all ages. Bulls exhibited a slight but consistent tendency toward more maturity than steers of the same age. Quality grades and taste panel scores of meat were generally higher for steers than for bulls, but the differences were small. Taste panel scores for bulls were acceptable. Jesse et al. (1976a-c) determined the empty body and carcass protein, fat, water, and ash of Hereford steers slaughtered at 227, 341, 454, and 545 kg body weight. The diets consisted of the following ratios of corn to corn silage (dry basis): 30 : 70, 50 : 50, 70 : 30, and 80 : 20. The composition of the empty body and the carcass gain by comparative slaughter were not affected by the diet. The greatest increase in fat occurred after the cattle reached 341 kg, and the
278
14. Body Composition
percentages of empty body and carcass gains from 454 and 545 kg were 63.4 and 68.3%, respectively. Aberle et al. (1981) studied the effect of the following dietary treatments of steer calves: (1) high-energy diet for 210 days, (2) low-energy diet for 77 days, followed by high-energy diet for 140 days, (3) low-energy diet for 153 days, followed by high-energy diet for 70 days, and (4) low-energy diet for 230 days. The low-energy diet was intended to give gains of 0.68 kg/day. The steers were slaughtered at the same age. Those fed the low-energy diet for longer periods had less carcass fat, smaller ribeye areas, and lower-quality grades than steers fed the high-energy diet for longer periods. Longissimus muscle from steers fed the lowenergy diet had lower collagen solubility than muscle from those fed the highenergy diet for 70 days or more. It was concluded that the growth rate of cattle before slaughter affects meat palatability, particularly tenderness, and that the growth rate may be a more important determinant of tenderness than the length of time cattle are fed high-energy diets. Rouquette and Carpenter (1981) observed the carcass characteristics of wean ling calves grazed at three levels of forage availability to an average age of 259 days. The grazing areas supported 6.27, 4.52, and 2.72 cow-calf units/hectare and calf weaning weights of 236, 2 5 1 , and 289 kg, respectively. Carcasses of calves that grazed the high-forage availability area were fatter than those of calves that grazed the lowest available pasture area (5.08 versus 1.27 mm over the longissimus muscle), and their longissimus muscle areas were more than 18% larger. Steer carcasses showed greater average daily gains and larger long issimus muscle areas than heifer carcasses, but heifer carcasses had more fat thickness over the longissimus muscle and more kidney, pelvic, and heart fat. Martin et al. (1978b) fed varying levels of crude protein to bulls in the weight range of 220-410 kg and found that near-maximal weight gains were obtained by feeding a continuous level of 11.1% crude protein. However, bulls fed diets containing 13.3 or 15.5% crude protein gained significantly faster during the first 56 days of the 168-day feedlot trial. During the last 84 days, the bulls fed the 11.1% crude protein diet appeared to compensate, so that the total gain did not differ among the three protein dietary groups. Lemenager et al. (1981) studied the effects of four dietary protein levels (9.6, 10.7, 12.5, and 13.9%) on Angus bulls provided early and late in 140-day feedlot trials. Bulls fed the 12.5 and 13.9% crude protein diets did not differ in gains, but both groups gained more rapidly than those fed the lower protein levels. Broadbent et al. (1976) reported that Angus steers had carcasses with more fat, less bone, and a higher lean : bone ratio than Ayrshire or British Friesian steers. Carcass data on the crosses of the three purebreds fell midway between their parent values and did not differ significantly. The investigators concluded that their data refuted the hypothesis that crossbred cattle produced carcasses with higher muscle : bone ratios. Lindsay and Davies (1981) fed Friesian steers
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III. Realimentation of Cull Cows
barley-based diets with different levels of crude protein (formaldehyde-treated soybean meal) and slaughtered them at 365 or 465 kg liveweight. Steers fed 23.7 g nitrogen per kilogram of dry matter and slaughtered at 365 kg liveweight had more fat depth at the 12th rib than those fed 2 7 . 9 - 3 8 . 5 g nitrogen per kilogram of dry matter in their diets. Animals slaughtered at 465 kg liveweight were not affected by dietary nitrogen in regard to fat depth at the 12th rib. Chigaru and Topps (1981) observed the effects of reducing feed intake for winter-calving cows to the maintenance level for 6 weeks from week 10 of lactation. Changes in body water estimated by the dilution of tritiated water and deuterium oxide at the end of each feeding period were used to calculate changes in body composition. The weight losses during 'underfeeding" consisted main ly of fat, but some cows apparently mobilized relatively large amounts of pro tein. More fat was mobilized by heifers than by cows, and cows appeared to mobilize more protein than heifers. Only a few cows were able to achieve complete tissue repletions upon "refeeding." Loveday and Dikeman (1980) slaughtered steers of Angus x Hereford (AHX) reciprocal crossbreeding and Brown Swiss sired-steers out of AHX reciprocal crossbred dams at an energy efficiency and endpoint of either 9.0 Meal N E per kilogram of gain (EEP) or 11.5 Meal N E per kilogram of gain (EEP ). There were no differences in the chemical composition of adipose fat between EEP and E E P steers or in lipogenic enzyme activities of 6-phosphogluconate dehydro genase, glucose-6-phosphate dehydrogenase, or nicotinamide adenine dinucleotide phosphate (NADP)-isocitrate dehydrogenase. 4
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2
III. REALIMENTATION OF CULL COWS Beef cows grazing range pastures normally undergo cyclic loss and gain in weight due to seasonal variation in availability and quality of forage. Cows culled during poor grazing periods are generally quite thin, and the usefulness of their carcasses is limited. Such cows that have undergone malnutrition generally have higher than normal rates of gain when realimented, and compensatory gains are usually associated with better feed efficiency (Wilson and Osbourn, 1960). Short-term feeding of cull cows to obtain compensatory gain should increase their salvage weight and improve carcass quality. Swingle et al. (1979) conducted several trials with cull range cows to deter mine their level of performance during realimentation. Composition of carcass gains was estimated by comparative slaughter values before and after realimentation. Concentrates at various levels (80, 40, and 22%) were fed during realimen tation and the cows were slaughtered at different final body conditions. Across all trials, average carcass gain contained 5 1 % fat, 14% protein, and 35% moisture. The percentage of protein in most wholesale cuts decreased and that of
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fat increased in all wholesale cuts when culled cows were realimented (Wooten et al., 1979). Marchello et al. (1979) utilized data obtained on carcasses of realimented range cows to develop the following equations for predicting carcass protein or lipid from plate composition: Carcass protein, % = 18.59 - (0.008 x cold carcass weight) + (.029 x ribeye area) — (0.31 x % of kidney, pelvic, and heart fat) - (0.1 x % of plate bone) - (0.54 x % of plate lipid) + (0.189 x % of plate protein). R = 0.79. Carcass lipid, % = 2.2 + (0.022 x cold carcass weight) - (0.07 x ribeye area) + (0.492 x 12th rib fat thickness) + (0.639 x % of plate lipid). R = 0.97. 2
2
IV. DIETARY FATS It has been established that the major fatty acids of dietary fats will appear in the body fat stores of nonruminant animals (Channon et al., 1937; Bhalerao et al., 1961; Alsmeyer et al., 1955). Only small changes have been found in the body fat of ruminants fed normal additions of either a saturated or a highly unsaturated fat at a level of 4 - 8 % of the diet (Willey et al., 1952; Edwards et al., 1961; Erwin et al., 1963; Roberts and McKirdy, 1964). It has been suggested that dietary fat is deposited in the fat depot of ruminants as in nonruminants, provided the fatty acids are not subjected to the hydrogénation of microbes in the rumen (Ogilvie et al., 1961). Dry den and Marchello (1973) made a fatty acid analysis of subcutaneous and intramuscular fat at 10 locations in the carcass and four muscles of CharolaisHereford steers fed diets that contained various levels of safflower oil (0, 5, 10, and 15%) or 6% animal fat. In longissimus, triceps brachii, semimembranous, chuck intramuscular fat, pericardial, mesentary, kidney, brisket, and caudal tissues, safflower oil in the diet caused the depot fat to become more unsaturated than that of controls. Brisket fat was not affected by safflower oil. Intramuscular fat from steers fed diets supplemented with animal fat became more saturated, while the safflower oil caused the fatty acids of these tissues to become more unsaturated. Skelley et al. (1973) evaluated the effects of vitamin A, corn silage, and raw soybeans on the fatty acid composition of carcass depot fat in steers. Raw soybeans in the diets decreased the total amount of saturated fatty acids, but vitamin A and corn silage had no effect on them. Stearic acid accounted for a great deal of the saturated fatty acids, while oleic acid accounted for much of the unsaturated fatty acids. Fat thickness and yield grade had little relationship to the percentages of individual fatty acids.
VII. Predicting the Composition of Beef Carcasses
281
V. IMPLANTS Harris et al. (1979) implanted Hereford steers with 36 mg zeranol or 200 mg progesterone and 20 mg estradiol benzoate at the initiation of a feedlot trial and 87 days later. The steers were slaughtered when they reached choice live grade. The zeranol-implanted steers gained less than the progesterone-estradiol-im planted steers during the first 87 days and yielded carcasses with less external fat, more kidney fat, and higher marbling scores. Average daily gains were the same for the two implanted groups overall to the time of slaughter. Cross and Dinius (1978) compared steers fed 94% ground alfalfa hay- or dehydrated alfalfa mealcontaining diets, with and without Synovex S (progesterone plus estradiol) im plants, for 120 days. The implant decreased the amount of marbling of longissimus muscle and the U.S. Department of Agriculture (USDA) quality grade of carcasses but increased the ribeye area. The implant had no effect on fat thick ness. The type of alfalfa did not affect fat thickness or the percentage of kidney, pelvic, and heart fat or ribeye area. Pelleting of the diet reduced the amount of marbling.
VI. pH OF MUSCLE Sodium pyrophosphate injected antemortem into cattle increased the glycoly sis and lowered the initial pH of tissues (Howard and Lawrie, 1957). Huffman et al. (1969) injected four lots of mature sheep with pyrophosphate or hexametaphosphate antemortem and observed the muscle pH to be lower initially for the treated sheep than for the controls. No correlation was observed between tender ness of loin chops and muscle pH, but it was noted that the meat from animals fed a low-calcium : phosphorus diet was more tender than that from control sheep and that the initial pH of low-calcium : phosphorus-fed animals was lower than that of controls.
VII. PREDICTING THE COMPOSITION OF BEEF CARCASSES The most accurate method of determining carcass composition is by chemical analysis of the whole carcass. Obviously, this is time-consuming and expensive, and renders the carcass unsalable. Hankins and Howe (1946) reported that the chemical composition and separable physical components of the 9 - 1 0 - 1 1 t h rib cut of slaughter steers were highly related to the composition of the entire carcass, and developed equations for predicting carcass composition. Reid et al.
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14. Body Composition
(1955) summarized composition data on beef versus dairy cattle, males versus females, and age of bovines. Regression equations were given relating (1) the age of animal to the protein, ash, and water of the fat-free body and @) the water content of beef, dairy, male, and female animals to the fat content of the whole empty body when the body's water content was determined. The estimation of the chemical composition and energy content of whole animal bodies by Reid et al. (1955) utilized the system of Kraybill et al. (1952) in which the carcass fat was estimated from both the 9 - 1 0 - 1 1 t h rib cut using the prediction equation of Hopper (1944) and the body water content using the antipyrine method (Soberman et al., 1949). These relationships are generally regarded as crude estimates. Garrett and Hinman (1969) related the specific gravity of Hereford steer car casses to the water, fat, nitrogen, ash, and energy contents determined by chem ical analyses of whole empty bodies. The investigators concluded that the highly significant coefficients of correlation and the low standard errors indicate that carcass density is a good index of the carcass and empty body composition of steers. Carcass fat and offal fat had identical caloric values of 9.385 ± 0.08 kcal/g, and the dry fat-free organic matter (protein) of the carcass and empty body had caloric values of 5.532 and 5.539 kcal/g, respectively (Garrett and Hinman, 1969). Vance et al. (1971) observed that the chemical composition of meat sawdust, obtained by sawing wholesale cuts, was highly correlated with the composition of the carcass. Preston et al. (1974) evaluated steers of varying weights and degrees of fatness to determine the relationship between carcass specific gravity and carcass composition, and the effect of bone proportionality on this rela tionship. Bone proportionality (11.7-18.6% separable bone) did not alter the relationship between carcass specific gravity and carcass composition. Specific gravity of the carcass was highly correlated with carcass fat ( - 0 . 9 6 ) , protein (0.89), and water (0.94). Ledger et al. (1973) subdivided sides of beef carcasses into 11 cuts, which were then dissected into fat, muscle, and bone. They devel oped a table from which the carcass composition of the animal was read once the specific gravity of the 10th rib was determined. Mata-Hernandez et al. (1981) utilized feedlot steers varying in genetic back ground, feeding regimen, and management to evaluate specific gravity measure ments and USDA quality and yield grade factors as predictors of carcass chem ical composition. Steers were slaughtered when they reached 1 cm of fat thickness at the 12th rib or had been on feed for 220 days, in the case of those fed as calves, or 120 days, in the case of those fed as yearlings. Specific gravities of the left side quarters and standard wholesale cuts were determined after a 72-hr chill. The soft tissue was separated from bone and analyzed for fat, protein, and water. Prediction equations for composition from specific gravity and carcass traits as independent variables gave higher coefficients of determination than equations for specific gravity alone. The specific gravity of various wholesale
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VIII. Body Composition of Live Animals
cuts possessed predictive characteristics equivalent to those of the specific grav ity of the entire side. Jones et al. (1978) reviewed the literature on measurement of bovine carcass density and its relationship to fatness. They suggested that density measurement of carcasses would be more repeatable if they were determined in water on the killing chain prior to final washing and shrouding. The estimate of carcass fatness could then be included in the grading scheme.
VIII. BODY COMPOSITION OF LIVE ANIMALS There is interest in the use of objective procedures to determine the body composition of live animals. Among such methods are the sonoray utilized by Hedrick et al. (1962), electronic meat measuring equipment (Domermuth et al., 1973), and K (Lohman et al., 1966; Frahm etal, 1971). Clark et al. (1976) evaluated the body composition of steers ranging in weight from 183 to 574 kg from K measured in a whole body counter. After the animals were monitored for K , they were slaughtered and tissues were ana lyzed. Independent variables, liveweight and carcass weight, live and carcass K , and carcass specific gravity were used to predict the dependent variables, carcass or empty body fat, nitrogen, gross energy, and water. The R values between K and nitrogen, fat, gross energy, and water were lower than when specific gravity was compared to these dependent variables. When K and liveweight were used to predict the nitrogen, fat, gross energy, and water of the carcass, R values of 0.87, 0.87, 0.84, and 0.84, respectively, were obtained. 4 0
4 0
4 0
4 0
2
4 0
4 0
2
I. INTRODUCTION The chemical composition of the whole empty body of an animal is due principally to species, heredity, environment, and nutrition. Changes in the concentration of fat, protein, and carbohydrates in the body reflect energy gain or loss. Change in body energy is utilized as a criterion of the energy value of feeds for maintenance, growth, and/or finishing livestock. Haecker (1920) concluded that the amount of water decreases and the amounts of ash and protein increase as the animals approach maturity, especially if finish ing does not intervene. Fat and water are variable, depending largely on the amount and kind of feed consumed, and together generally constitute 7 5 - 7 9 % of the whole empty body. It appears that the finishing process consists principally of replacing water by fat, or that the percentage body composition is markedly influenced by the deposition of large amounts of fat that contains very little water. Moulton et al. (1922) studied the fat-free composition of cattle ranging in development from early embryonic stages to maturity. The water content of the fat-free body decreased rapidly from the time of conception to birth, and then decreased less rapidly until a relatively constant concentration of water was reached at 5 - 1 0 months of age. Moulton (1923) introduced the concept of chemical maturity, which he defined as the age at which the concentrations of water, protein, and minerals in the fat-free tissues of the animal become prac tically constant. Different animals vary in their age of chemical maturity. That is, there is some decrease in the proportion of water and an increase in the propor tions of protein and ash as animals become older. Body weight changes are commonly utilized to indicate responses in many feeding experiments with livestock. In experiments of short duration, changes in rumen fill can result in appreciable errors. The use of body weight changes 275
276
14. Body Composition
assumes that weight gained or lost has the same composition irrespective or treatment. Such an assumption was early pointed out to be in error. By compar ing casein and urea as sources of dietary nitrogen for cattle, Watson et al. (1949) showed that although the animals fed urea diets gained only 70% as much weight as those fed casein, they gained 8 1 % as much energy. The total digestible nutrient (TDN) content or net energy (NE) values are commonly used criteria of the energy value of feed ingredients in the United States. It is recognized that the TDN of one feed does not necessarily produce a response of the same magnitude as an equal amount of TDN from another feed. This is especially true when comparing TDN values of concentrates and rough ages. Evaluating mixed feeds utilizing roughages for ruminants on a TDN basis is more complex than it is for nonruminants fed relatively roughage-free diets. Evaluation of feed on the basis of NE is less complex than it is for TDN in that a unit of NE in one feedstuff produces the same amount of a given response in a given animal as that produced by a unit of energy from entirely different types of feeds. NE values of feedstuffs and diets for maintenance and gain may be determined by metabolism and comparative slaughter feedlot trials. In such studies, the energy of whole empty animal bodies at the beginning and end of the feeding period is determined directly on tissues by calorimetry or indirectly by specific gravity (Lofgreen and Garrett, 1968; Garrett and Hinman, 1969). The specific gravity values are related to the fat and protein in tissues by chemical analysis. Empty bodies of cattle generally contain less than 0.5% carbohydrates (Trowbridge and Francis, 1910). Tissue carbohydrates are disregarded in dietary energy studies on feedlot cattle that involve sufficient time for considerable weight gains.
II. EFFECT OF DIET, BREED, AND SEX Blaxter (1962) concluded, from a biochemical appraisal of metabolic path ways involved in the deposition of protein and fat in cattle, that it seemed unlikely that one breed would be more energetically efficient than another. However, Garrett (1971) conducted comparative slaughter experiments with Holstein and Hereford cattle and compared the net efficiency of energy utiliza tion by the two breeds. The results indicated that Herefords were 12 and 20% more efficient than Holsteins in converting feed energy consumed above mainte nance to energy stored as protein and fat, respectively. The beef steers had gains that contained more fat, and consequently more energy, than corresponding gains by the dairy steers. The two breeds had equivalent gains of protein per unit of feed above maintenance. Nichols et al. (1964) compared Holstein bulls and steers for meat production from birth until slaughter at 800-1000 pounds. Bulls had slightly lower dressing
II. Effect of Diet, Breed, and Sex
277
percentages due to heavier hides and less fatty carcasses. Steers had higher marbling and more outside fat covering than bulls. Martin et al. (1978a) fed Holstein steers diets containing three levels of energy. The higher levels of dietary energy produced faster gains, more efficient conversion of dry matter to gain, greater deposition of fat, and higher carcass grade. Fortin et al. (1980a) studied the effects of energy intake, breed, and sex on muscle growth and distribution in Holstein and Angus bulls, steers, and heifers. The animals were fed energy at two levels, ad libitum and 6 0 - 7 0 % of ad libitum. In both breeds, irrespective of energy intake, sex had no influence on the growth rate of muscle in the thoracic and pelvic limbs relative to carcass side or total muscle. Neither breed nor energy intake altered the growth rate of muscle in the three joints relative to carcass side or total muscle. Fortin et al. (1980b) deter mined the chemical composition of Angus and Holstein bulls, steers, and heifers fed at two energy levels and slaughtered at weights ranging from 121 to 706 kg. The accretion rate of fat was not affected by sex, but accretion rates of protein and ash were more rapid in Holsteins than in Angus cattle in the high-energy dietary groups. Angus bulls had a faster accretion of fat than Holstein bulls. Fortin et al. (1981) concluded from composition studies with Angus steers, bulls, and heifers that the growth rate of fat relative to carcass side was greater in a high-energy than in a low-energy dietary group, whereas with corresponding sex groups of Holsteins, the growth rate of fat was not altered by the level of energy intake. The breed (Angus versus Holstein) generally did not influence the growth rate of muscle and bone plus tendon. A number of studies have demonstrated that bulls gain more rapidly and convert feed to lean meat more efficiently with less fat than steers (Cahill, 1964; Prescott and Lamming, 1964; Field, 1971). Bulls generally produce meat with less marbling, coarser texture, darker color, and less tenderness, depending on their age. However, organoleptic studies with young bull meat indicate a high level of palatability. Arthaud et al. (1977) compared carcasses of bulls and steers fed at two levels of energy and slaughtered at 12, 15, 18, and 24 months of age for composition and taste panel evaluation. Bulls made faster gains on less feed per unit of gain and had less fat in the carcass than steers at all ages. Bulls exhibited a slight but consistent tendency toward more maturity than steers of the same age. Quality grades and taste panel scores of meat were generally higher for steers than for bulls, but the differences were small. Taste panel scores for bulls were acceptable. Jesse et al. (1976a-c) determined the empty body and carcass protein, fat, water, and ash of Hereford steers slaughtered at 227, 341, 454, and 545 kg body weight. The diets consisted of the following ratios of corn to corn silage (dry basis): 30 : 70, 50 : 50, 70 : 30, and 80 : 20. The composition of the empty body and the carcass gain by comparative slaughter were not affected by the diet. The greatest increase in fat occurred after the cattle reached 341 kg, and the
278
14. Body Composition
percentages of empty body and carcass gains from 454 and 545 kg were 63.4 and 68.3%, respectively. Aberle et al. (1981) studied the effect of the following dietary treatments of steer calves: (1) high-energy diet for 210 days, (2) low-energy diet for 77 days, followed by high-energy diet for 140 days, (3) low-energy diet for 153 days, followed by high-energy diet for 70 days, and (4) low-energy diet for 230 days. The low-energy diet was intended to give gains of 0.68 kg/day. The steers were slaughtered at the same age. Those fed the low-energy diet for longer periods had less carcass fat, smaller ribeye areas, and lower-quality grades than steers fed the high-energy diet for longer periods. Longissimus muscle from steers fed the lowenergy diet had lower collagen solubility than muscle from those fed the highenergy diet for 70 days or more. It was concluded that the growth rate of cattle before slaughter affects meat palatability, particularly tenderness, and that the growth rate may be a more important determinant of tenderness than the length of time cattle are fed high-energy diets. Rouquette and Carpenter (1981) observed the carcass characteristics of wean ling calves grazed at three levels of forage availability to an average age of 259 days. The grazing areas supported 6.27, 4.52, and 2.72 cow-calf units/hectare and calf weaning weights of 236, 2 5 1 , and 289 kg, respectively. Carcasses of calves that grazed the high-forage availability area were fatter than those of calves that grazed the lowest available pasture area (5.08 versus 1.27 mm over the longissimus muscle), and their longissimus muscle areas were more than 18% larger. Steer carcasses showed greater average daily gains and larger long issimus muscle areas than heifer carcasses, but heifer carcasses had more fat thickness over the longissimus muscle and more kidney, pelvic, and heart fat. Martin et al. (1978b) fed varying levels of crude protein to bulls in the weight range of 220-410 kg and found that near-maximal weight gains were obtained by feeding a continuous level of 11.1% crude protein. However, bulls fed diets containing 13.3 or 15.5% crude protein gained significantly faster during the first 56 days of the 168-day feedlot trial. During the last 84 days, the bulls fed the 11.1% crude protein diet appeared to compensate, so that the total gain did not differ among the three protein dietary groups. Lemenager et al. (1981) studied the effects of four dietary protein levels (9.6, 10.7, 12.5, and 13.9%) on Angus bulls provided early and late in 140-day feedlot trials. Bulls fed the 12.5 and 13.9% crude protein diets did not differ in gains, but both groups gained more rapidly than those fed the lower protein levels. Broadbent et al. (1976) reported that Angus steers had carcasses with more fat, less bone, and a higher lean : bone ratio than Ayrshire or British Friesian steers. Carcass data on the crosses of the three purebreds fell midway between their parent values and did not differ significantly. The investigators concluded that their data refuted the hypothesis that crossbred cattle produced carcasses with higher muscle : bone ratios. Lindsay and Davies (1981) fed Friesian steers
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III. Realimentation of Cull Cows
barley-based diets with different levels of crude protein (formaldehyde-treated soybean meal) and slaughtered them at 365 or 465 kg liveweight. Steers fed 23.7 g nitrogen per kilogram of dry matter and slaughtered at 365 kg liveweight had more fat depth at the 12th rib than those fed 2 7 . 9 - 3 8 . 5 g nitrogen per kilogram of dry matter in their diets. Animals slaughtered at 465 kg liveweight were not affected by dietary nitrogen in regard to fat depth at the 12th rib. Chigaru and Topps (1981) observed the effects of reducing feed intake for winter-calving cows to the maintenance level for 6 weeks from week 10 of lactation. Changes in body water estimated by the dilution of tritiated water and deuterium oxide at the end of each feeding period were used to calculate changes in body composition. The weight losses during 'underfeeding" consisted main ly of fat, but some cows apparently mobilized relatively large amounts of pro tein. More fat was mobilized by heifers than by cows, and cows appeared to mobilize more protein than heifers. Only a few cows were able to achieve complete tissue repletions upon "refeeding." Loveday and Dikeman (1980) slaughtered steers of Angus x Hereford (AHX) reciprocal crossbreeding and Brown Swiss sired-steers out of AHX reciprocal crossbred dams at an energy efficiency and endpoint of either 9.0 Meal N E per kilogram of gain (EEP) or 11.5 Meal N E per kilogram of gain (EEP ). There were no differences in the chemical composition of adipose fat between EEP and E E P steers or in lipogenic enzyme activities of 6-phosphogluconate dehydro genase, glucose-6-phosphate dehydrogenase, or nicotinamide adenine dinucleotide phosphate (NADP)-isocitrate dehydrogenase. 4
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III. REALIMENTATION OF CULL COWS Beef cows grazing range pastures normally undergo cyclic loss and gain in weight due to seasonal variation in availability and quality of forage. Cows culled during poor grazing periods are generally quite thin, and the usefulness of their carcasses is limited. Such cows that have undergone malnutrition generally have higher than normal rates of gain when realimented, and compensatory gains are usually associated with better feed efficiency (Wilson and Osbourn, 1960). Short-term feeding of cull cows to obtain compensatory gain should increase their salvage weight and improve carcass quality. Swingle et al. (1979) conducted several trials with cull range cows to deter mine their level of performance during realimentation. Composition of carcass gains was estimated by comparative slaughter values before and after realimentation. Concentrates at various levels (80, 40, and 22%) were fed during realimen tation and the cows were slaughtered at different final body conditions. Across all trials, average carcass gain contained 5 1 % fat, 14% protein, and 35% moisture. The percentage of protein in most wholesale cuts decreased and that of
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14. Body Composition
fat increased in all wholesale cuts when culled cows were realimented (Wooten et al., 1979). Marchello et al. (1979) utilized data obtained on carcasses of realimented range cows to develop the following equations for predicting carcass protein or lipid from plate composition: Carcass protein, % = 18.59 - (0.008 x cold carcass weight) + (.029 x ribeye area) — (0.31 x % of kidney, pelvic, and heart fat) - (0.1 x % of plate bone) - (0.54 x % of plate lipid) + (0.189 x % of plate protein). R = 0.79. Carcass lipid, % = 2.2 + (0.022 x cold carcass weight) - (0.07 x ribeye area) + (0.492 x 12th rib fat thickness) + (0.639 x % of plate lipid). R = 0.97. 2
2
IV. DIETARY FATS It has been established that the major fatty acids of dietary fats will appear in the body fat stores of nonruminant animals (Channon et al., 1937; Bhalerao et al., 1961; Alsmeyer et al., 1955). Only small changes have been found in the body fat of ruminants fed normal additions of either a saturated or a highly unsaturated fat at a level of 4 - 8 % of the diet (Willey et al., 1952; Edwards et al., 1961; Erwin et al., 1963; Roberts and McKirdy, 1964). It has been suggested that dietary fat is deposited in the fat depot of ruminants as in nonruminants, provided the fatty acids are not subjected to the hydrogénation of microbes in the rumen (Ogilvie et al., 1961). Dry den and Marchello (1973) made a fatty acid analysis of subcutaneous and intramuscular fat at 10 locations in the carcass and four muscles of CharolaisHereford steers fed diets that contained various levels of safflower oil (0, 5, 10, and 15%) or 6% animal fat. In longissimus, triceps brachii, semimembranous, chuck intramuscular fat, pericardial, mesentary, kidney, brisket, and caudal tissues, safflower oil in the diet caused the depot fat to become more unsaturated than that of controls. Brisket fat was not affected by safflower oil. Intramuscular fat from steers fed diets supplemented with animal fat became more saturated, while the safflower oil caused the fatty acids of these tissues to become more unsaturated. Skelley et al. (1973) evaluated the effects of vitamin A, corn silage, and raw soybeans on the fatty acid composition of carcass depot fat in steers. Raw soybeans in the diets decreased the total amount of saturated fatty acids, but vitamin A and corn silage had no effect on them. Stearic acid accounted for a great deal of the saturated fatty acids, while oleic acid accounted for much of the unsaturated fatty acids. Fat thickness and yield grade had little relationship to the percentages of individual fatty acids.
VII. Predicting the Composition of Beef Carcasses
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V. IMPLANTS Harris et al. (1979) implanted Hereford steers with 36 mg zeranol or 200 mg progesterone and 20 mg estradiol benzoate at the initiation of a feedlot trial and 87 days later. The steers were slaughtered when they reached choice live grade. The zeranol-implanted steers gained less than the progesterone-estradiol-im planted steers during the first 87 days and yielded carcasses with less external fat, more kidney fat, and higher marbling scores. Average daily gains were the same for the two implanted groups overall to the time of slaughter. Cross and Dinius (1978) compared steers fed 94% ground alfalfa hay- or dehydrated alfalfa mealcontaining diets, with and without Synovex S (progesterone plus estradiol) im plants, for 120 days. The implant decreased the amount of marbling of longissimus muscle and the U.S. Department of Agriculture (USDA) quality grade of carcasses but increased the ribeye area. The implant had no effect on fat thick ness. The type of alfalfa did not affect fat thickness or the percentage of kidney, pelvic, and heart fat or ribeye area. Pelleting of the diet reduced the amount of marbling.
VI. pH OF MUSCLE Sodium pyrophosphate injected antemortem into cattle increased the glycoly sis and lowered the initial pH of tissues (Howard and Lawrie, 1957). Huffman et al. (1969) injected four lots of mature sheep with pyrophosphate or hexametaphosphate antemortem and observed the muscle pH to be lower initially for the treated sheep than for the controls. No correlation was observed between tender ness of loin chops and muscle pH, but it was noted that the meat from animals fed a low-calcium : phosphorus diet was more tender than that from control sheep and that the initial pH of low-calcium : phosphorus-fed animals was lower than that of controls.
VII. PREDICTING THE COMPOSITION OF BEEF CARCASSES The most accurate method of determining carcass composition is by chemical analysis of the whole carcass. Obviously, this is time-consuming and expensive, and renders the carcass unsalable. Hankins and Howe (1946) reported that the chemical composition and separable physical components of the 9 - 1 0 - 1 1 t h rib cut of slaughter steers were highly related to the composition of the entire carcass, and developed equations for predicting carcass composition. Reid et al.
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14. Body Composition
(1955) summarized composition data on beef versus dairy cattle, males versus females, and age of bovines. Regression equations were given relating (1) the age of animal to the protein, ash, and water of the fat-free body and @) the water content of beef, dairy, male, and female animals to the fat content of the whole empty body when the body's water content was determined. The estimation of the chemical composition and energy content of whole animal bodies by Reid et al. (1955) utilized the system of Kraybill et al. (1952) in which the carcass fat was estimated from both the 9 - 1 0 - 1 1 t h rib cut using the prediction equation of Hopper (1944) and the body water content using the antipyrine method (Soberman et al., 1949). These relationships are generally regarded as crude estimates. Garrett and Hinman (1969) related the specific gravity of Hereford steer car casses to the water, fat, nitrogen, ash, and energy contents determined by chem ical analyses of whole empty bodies. The investigators concluded that the highly significant coefficients of correlation and the low standard errors indicate that carcass density is a good index of the carcass and empty body composition of steers. Carcass fat and offal fat had identical caloric values of 9.385 ± 0.08 kcal/g, and the dry fat-free organic matter (protein) of the carcass and empty body had caloric values of 5.532 and 5.539 kcal/g, respectively (Garrett and Hinman, 1969). Vance et al. (1971) observed that the chemical composition of meat sawdust, obtained by sawing wholesale cuts, was highly correlated with the composition of the carcass. Preston et al. (1974) evaluated steers of varying weights and degrees of fatness to determine the relationship between carcass specific gravity and carcass composition, and the effect of bone proportionality on this rela tionship. Bone proportionality (11.7-18.6% separable bone) did not alter the relationship between carcass specific gravity and carcass composition. Specific gravity of the carcass was highly correlated with carcass fat ( - 0 . 9 6 ) , protein (0.89), and water (0.94). Ledger et al. (1973) subdivided sides of beef carcasses into 11 cuts, which were then dissected into fat, muscle, and bone. They devel oped a table from which the carcass composition of the animal was read once the specific gravity of the 10th rib was determined. Mata-Hernandez et al. (1981) utilized feedlot steers varying in genetic back ground, feeding regimen, and management to evaluate specific gravity measure ments and USDA quality and yield grade factors as predictors of carcass chem ical composition. Steers were slaughtered when they reached 1 cm of fat thickness at the 12th rib or had been on feed for 220 days, in the case of those fed as calves, or 120 days, in the case of those fed as yearlings. Specific gravities of the left side quarters and standard wholesale cuts were determined after a 72-hr chill. The soft tissue was separated from bone and analyzed for fat, protein, and water. Prediction equations for composition from specific gravity and carcass traits as independent variables gave higher coefficients of determination than equations for specific gravity alone. The specific gravity of various wholesale
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VIII. Body Composition of Live Animals
cuts possessed predictive characteristics equivalent to those of the specific grav ity of the entire side. Jones et al. (1978) reviewed the literature on measurement of bovine carcass density and its relationship to fatness. They suggested that density measurement of carcasses would be more repeatable if they were determined in water on the killing chain prior to final washing and shrouding. The estimate of carcass fatness could then be included in the grading scheme.
VIII. BODY COMPOSITION OF LIVE ANIMALS There is interest in the use of objective procedures to determine the body composition of live animals. Among such methods are the sonoray utilized by Hedrick et al. (1962), electronic meat measuring equipment (Domermuth et al., 1973), and K (Lohman et al., 1966; Frahm etal, 1971). Clark et al. (1976) evaluated the body composition of steers ranging in weight from 183 to 574 kg from K measured in a whole body counter. After the animals were monitored for K , they were slaughtered and tissues were ana lyzed. Independent variables, liveweight and carcass weight, live and carcass K , and carcass specific gravity were used to predict the dependent variables, carcass or empty body fat, nitrogen, gross energy, and water. The R values between K and nitrogen, fat, gross energy, and water were lower than when specific gravity was compared to these dependent variables. When K and liveweight were used to predict the nitrogen, fat, gross energy, and water of the carcass, R values of 0.87, 0.87, 0.84, and 0.84, respectively, were obtained. 4 0
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