Fattening heifers to heavy weights to enhance marbling: Efficiency of gain

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1 Fattening heifers to heavy weights to enhance marbling: Efficiency of gain P. L. Dubeski 1, J. L. Aalhus 1, S. D. M. Jones 2, A. K. W. Tong 1, and W. M. Robertson 1 1 Agriculture and Agri-Food Canada, Research Centre, 6000 C & E Trail, Lacombe, Alberta, Canada T4L 1W1; and 2 Agriculture and Agri-Food Canada, Research Centre, Lethbridge, Alberta, Canada T1J 4B1. Contribution no. 828 Received 22 April 1996, accepted 1 August Dubeski, P. L., Aalhus, J. L., Jones, S. D. M., Tong, A. K. W. and Robertson, W. M Fattening heifers to heavy weights to enhance marbling: efficiency of gain. Can. J. Anim. Sci. 77: Feedlot performance and carcass composition were measured in two studies to evaluate the use of common Canadian breeds and nutrition programs for production of highly marbled beef for the Japanese market. Weaned heifer calves (n = 221, initial weight 265 kg) of Angus, Hereford, and Hereford Angus (HA) breeding were slaughtered at 500, 590, and 680 kg in exp. 1. In exp. 2, yearling heifers (n = 216, initial weight 395 kg, same breeds as exp. 1 but including Holstein) were slaughtered at 590 and 680 kg. Cattle were randomly assigned to either a high plane of nutrition (HP) until slaughter or a moderate plane of nutrition to 500 kg (exp. 1) or 550 kg (exp. 2), followed by a high plane to slaughter (MHP). Mean days on feed, percent carcass fat, and percent intramuscular fat in longissimus muscle were 347 d, 38.6%, and 8.50% in exp. 1, and 281 d, 37.5%, and 7.87%, respectively, in exp. 2. In exp. 1, Herefords produced the most economical gains but the fattest carcasses (P < 0.05). In exp. 2, Holsteins had the most economical liveweight and lean carcass weight gains (P < 0.05). The cost of a percentage increase in intramuscular fat was lowest for Angus in exp. 1 (P = 0.05), similar for the breeds in exp. 2 (P = 0.29), and not affected by slaughter weight group. HP cattle gained liveweight, carcass, lean carcass, and intramuscular fat more economically than did MHP cattle (P ). The rate of deposition of intramuscular fat did not appear to increase with maturity. Feeding cattle to extreme slaughter weights using conventional feedlot diets produced extremely fat carcasses but did not produce highly marbled beef. Key words: Beef cattle, carcass, growth, intramuscular fat, marbling Dubeski, P. L., Aalhus, J. L., Jones, S. D. M., Tong, A. K. W. et Robertson, W. M Engraissement des génisses jusqu à un poids élevé pour favoriser la formation du persillé dans la viande : efficience du gain. Can. J. Anim. Sci. 77: A partir des performances en parc d engraissement et de la composition de la carcasse, nous avons évalué, dans le cadre de deux expériences, l aptitude des races bovines canadiennes communes et des programmes d alimentation pratiqués au pays, pour la production de boeuf fortement persillé destiné au marché japonais. Dans la première expérience, des génisses sevrées (n = 221, poids initial 265 kg) Angus, Hereford et Hereford Angus (HA) étaient abattues aux poids de 500, 590 et 680 kg. Dans l expérience 2, des génisses d un an (n = 216, poids initial 395 kg) des mêmes compositions génétiques que dans l expérience 1, plus la Holstein, étaient abattues aux poids de 590 et de 680 kg. Les animaux étaient affectés au hasard, soit à un régime nutritionnel riche (R) jusqu à l abattage ou d un régime modéré jusqu à 500 kg (exp. 1) ou à 550 kg (exp. 2) suivi d un régime riche jusqu à l abattage (MR). La durée d engraissement en jours, le pourcentage de gras de la carcasse et le pourcentage de gras intramusculaire dans le longissimus étaient, respectivement, de 347, 38,6 % et 8,50 % dans l expérience 1 et de 281, 37,5 % et 7,87 % dans l expérience 2. Dans l expérience 1, les Hereford produisaient les gains de poids les plus économiques, mais aussi les carcasses les plus grasses (P < 0,05). Dans l expérience 2, c est la Holstein qui affichait les gains de poids vif et les poids de maigre par carcasse les plus économiques (P < 0,05). Le coût d un accroissement d une unité de pourcentage des graisses intramusculaires était le plus bas pour les Angus dans l expérience 1 (P = 0,05). Dans l expérience 2, il n y avait pas de différence entre les races (P = 0,29). Ce coût n était pas lié au choix du poids à l abattage. Les animaux au régime riche manifestaient un gain plus rentable de poids vif, de poids de carcasse, de proportion de maigre par carcasse et de gras intramusculaire que ceux exposés au régime MR (P 0,0002). Le taux de dépôt de gras intramusculaire ne semble pas avoir augmenté avec le poids à l abattage. Le prolongement de l engraissement jusqu à des poids extrêmement élevés selon les formules d alimentation en parc pratiquées actuellement a donné des carcasses excessivement grasses, mais n a pas produit de viande plus persillée. Mots clés: Bovins à viande, carcasse, croissance, gras itramusculaire, persillé Recent changes in the Japanese tariff laws have opened the Japanese beef market to Canadian beef products, and tariffs are expected to continue to decline over the next 15 yr. Most Canadian beef carcasses score poorly (1 3 on a scale of 1 5; 5 is most desirable) in Japanese quality grades, primarily because of inadequate intramuscular fat (marbling). Each increase in Japanese quality grade is worth approximately US$0.75 kg 1 carcass (Hayes 1990). Factors known to affect marbling include slaughter age, nutrition, sex and breed. The proportion of intramuscular fat 625 increases with age and particularly with time on a highenergy diet (Aalhus et al. 1992). Manipulating the grain:forage ratio in feedlot diets may influence marbling (Henrickson et al. 1965). Heifers begin to fatten at a lighter weight than steers and bulls (Berg and Butterfield 1976) but Abbreviations: ADG, average daily gain; BW, body weight; CP, crude protein; DE, dietary energy; HA, Hereford Angus or reciprocal cross; MGA, melengesterol acetate; MHP, moderate-high plane; NEg, net energy for gain

2 626 CANADIAN JOURNAL OF ANIMAL SCIENCE the rate of marbling deposition is similar in steers and heifers (Zinn et al. 1970). Breeds differ substantially in ability to deposit marbling (Koch et al. 1976, 1979, 1982). The purpose of the present experiments was to determine if breeds readily available in Canada and known for their genetic ability to deposit marbling could efficiently produce beef with extreme levels of marbling when raised under Canadian feedlot conditions beyond normal Canadian slaughter weights. Because of the relationship between age and marbling, two experiments were conducted, one with weaned calves and one with yearlings. Target slaughter weights ranged from 500 kg to 680 kg, the Japanese market endpoint. Heifers were fed in both studies because they mature earlier than steers. Two nutritional regimes were compared because the high-energy nutritional program is most common, whereas the MHP program is used to delay fattening of lightweight heifers to achieve heavier slaughter weights. The Angus, Hereford, and Holstein breeds and the Hereford Angus cross were selected because these breeds produce more marbling than the continental beef breeds (Knapp et al. 1989). The data are presented in a series of three papers. The current paper covers animal performance, carcass composition, and efficiency and costs of liveweight, carcases, lean, and intramuscular fat production. Canadian, Japanese and US carcass grades are discussed in the second paper, while the third paper focuses on the meat quality of cattle raised to heavier slaughter weights than required in North America (Dubeski et al. 1997a,b). MATERIALS AND METHODS The animals used in these experiments were raised and slaughtered in accordance with the principles and guidelines specified by the Canadian Council on Animal Care (1984). Experiment 1 Two hundred and twenty-one 6- to 8-mo-old weaned heifer calves (73 Angus, 73 Hereford and 75 HA) were purchased at cattle auctions. A representative group of 10 heifers from each breed were maintained on the low energy diet and slaughtered early in the trial (4 to 25 d on feed) to determine initial composition. The remaining animals were stratified by weight within breed and randomly assigned to either a high plane HP or MHP feeding regime and to one of 18 pens, such that both feeding regimes and all pens had a similar initial weight. The grain content of the diets was adjusted in order to produce maximal gains for the HP diet and the second phase of the MHP feeding regime, and to restrict gain during the moderate phase of the MHP program to 0.7 kg d 1. Between the start of the experiment and the time at which average treatment weight reached 500 kg, the MHP cattle were fed 35.2% grain [grain contained 92.0% steamrolled barley, 1.0% animal tallow, 1.5% molasses, and 5.5% supplement (supplement nutrient composition: 12.4% CP, 1.0% NPN, 3.4% fat, 0.13% sodium, 0.46% calcium, 0.35% total phosphorus, 0.57% potassium, 18.6 ppm Cu, 38.8 ppm Mn, 54.5 ppm Fe, ppm Co, 0.22 ppm I, 5500 IU vitamin A kg 1, 550 IU vitamin D kg 1, 2.2 IU vitamin E kg 1 )] and 64.8% barley silage, and the HP cattle were fed 81.6% grain and 18.4% silage (DM basis). The proportion of grain in the diet was increased for both MHP and HP when each group reached 500 kg. On a DM basis, the proportion of grain was 69.3% for MHP pens between 500 and 590 kg average liveweight, and 78.1% between 590 and 680 kg average liveweight. For the same weight ranges, the proportion of grain (DM) was 89.5 and 95.7%, respectively, for the HP cattle. Changes in the diet were accomplished by increasing the proportion of grain in the diet over a 14-d period. Pen feed intakes were recorded daily. Animals were weighed every 28 d. Diets did not contain an ionophore or MGA and cattle were not implanted. Experiment 2 Two hundred and sixteen yearling heifers (53 Angus, 53 Hereford, 55 HA and 53 Holstein) were purchased at cattle sales. The beef and Holstein heifers were about 19 and 14 mo old, respectively. The procedures followed in this trial were identical to those for exp. 1, with the following exceptions. Animals were randomly assigned to one of 24 pens. MHP cattle were fed the low-energy diet until average pen weight reached 550 kg, and then the proportion of grain was increased. From initial weight to 590 kg, and 590 to 680 kg, the amount of grain in the diet averaged 37.2 and 81.9%, respectively, for MHP cattle, and 77.3 and 83.5%, respectively, for HP cattle (DM basis). Slaughter and Carcass Evaluation In exp. 1, cattle were slaughtered at average pen weights of 500, 590 and 680 kg, whereas in exp. 2, cattle were slaughtered at average pen weights of 590 and 680 kg. When a pen average reached the designated slaughter weight, a representative group of animals (three or four per pen) was chosen for slaughter such that average weight of animals slaughtered was similar to average weight of animals remaining in the pen. These animals were removed from their pens at 08:00 h on the day before slaughter, weighed, and then held without feed but with free access to water until 15:00 h (maintaining pen groups). The cattle were transported to the Meat Centre (5-min truck ride) for overnight lairage. A final liveweight was recorded and the animals were stunned by captive bolt, exsanguinated and dressed. Carcass weights did not include kidney and pelvic fat. Warm carcass side weights (and final trimmed carcass side weights) were recorded prior to chilling the carcasses at 1 C for 24 h. After 24 h, cold side weights were recorded to determine cooler shrink losses. Following grading (Japanese, US, and Canadian grades), the left carcass sides were dissected into primal cuts (round, butt, loin, flank, chuck, rib, brisket, shank, and plate). The primal cuts were then dissected into lean, bone (including connective tissue), intermuscular, subcutaneous, and body cavity fat (Rompala et al. 1984). Intramuscular fat concentration of the longissimus muscle was determined chemically using an ether solvent in a Soxtec apparatus. Statistical Analysis All data were analyzed using the GLM (General Linear Models) procedure of the SAS Institute, Inc. (1989). Animal

3 DUBESKI ET AL. EFFICIENCY OF STRATEGIES USED TO ENHANCE MARBLING IN BEEF 627 Table 1. Experiment 1. Effects of slaughter weight group, breed, and nutrition on animal performance (least squares means) Weight group Breed Nutrition 500 kg 590 kg 680 kg SEM Hereford Angus HA SEM MHP HP SEM Number of groups Initial livewt (kg) a 279.8b 283.0b Final livewt (kg) 493.6a 586.8b 661.4c a 582.4b 584.9b Intramuscular fat gain (%) z 5.37a 7.23b 8.26b ab 8.01b 5.93ab a 7.60b 0.36 Final intramuscular fat (%) z 6.92a 8.78b 9.81b a 9.79b 7.57a a 9.16b 0.36 Days fed 255a 351b 436c 4 370c 345a 327a 5 391b 304a 4 ADG (kg d 1 ) 0.789a 0.865b 0.859b b 0.803a 0.851b a 0.939b DM intake (kg) 2170a 3050b 3748c b 3044b 2830a b 2750a 39 Silage DM intake (kg) 1050a 1209b 1281c a 1209b 1159a b 474a 8 Grain DM intake (kg) 1120a 1835b 2460c b 1835b 1670a a 2276b 34 DE intake (Mcal) 6910a 9959b 12446c b 9960b 9218a NEg intake (Mcal) 2359a 3475b 4400c b 3479b 3209a a 3531b 51 z Intramuscular fat expressed as a percentage of longissimus muscle (wet weight basis). a c Weight group, breed, or nutrition means in the same row with different letters differ (P < 0.05). performance and efficiency data were tested using pen means, whereas slaughter data and carcass composition were tested using individual animal observations. All live animal performance data were summarized by pen, and by 28-d periods. Mean days on feed and feed consumption were calculated for each pen and slaughter weight combination, assuming that all animals within the pen in any given period consumed the same amount of feed. DE of the grain mix was estimated at Mcal kg 1 DM from ingredient tables [National Research Council (NRC) 1984], and DE of the silage was the average of laboratory estimates (2.25 Mcal kg 1 DM). NEg was estimated from the DE content of the complete diet (NRC 1984). For each breed in each experiment, body composition of the initial kill animals was regressed against liveweight. These regression equations were used to calculate initial composition of each animal slaughtered in the 500-kg, 590- kg and 680-kg weight groups based on its on-test weight. Because there was a poor relationship between intramuscular fat and liveweight for each breed in the initial kill, initial intramuscular fat concentration for each animal was estimated to be the breed mean. Carcass gain, lean carcass gain, and percentage change in intramuscular fat concentration of the longissimus muscle were calculated for each animal by difference from its predicted initial composition and averaged for each pen weight group combination. Mean feed efficiencies and average daily gains were then calculated for each slaughter weight group in each pen based on the shrunk liveweight at slaughter. The efficiency of intramuscular fat deposition was always based on the chemically determined intramuscular fat concentration, not a subjective marbling score. Production costs were calculated for each weight group in each pen using a commercial software program (Alberta Agriculture, Food and Rural Development 1993). Beef ration was priced at $124 t 1 (87.5% DM) and barley silage at $38.58 t 1 (35% DM). Interest was estimated at 9% and all other production costs including shipping, bedding, yardage, processing, treatment, and mortality were typical costs for feedlots in Alberta (weaned heifers: purchase price $95 cwt 1, processing cost $5 calf 1, death loss 2%, 25% of calves require medical treatment at an average cost of $10 calf 1. Yearling heifers: purchase price $80 cwt 1, processing cost $3, death loss 1%, 10% require medical treatment at an average cost of $10. All cattle: commission $1 cwt 1, trucking $1 cwt 1, bedding $0.05 d 1, yardage $0.15 d 1 ). All data were analyzed using a model containing slaughter weight group, breed, plane of nutrition, and their interactions. Linear contrasts with one degree of freedom were used for means separation (P < 0.05). RESULTS AND DISCUSSION Feedlot Performance Liveweights, days on feed, ADG, and feed intakes are summarized by slaughter weight group, breed and nutrition treatment in Tables 1 and 2. Weights in these tables are farm weights; final shrunk weight treatment means are provided in Tables 3 and 4. The cattle in these two experiments were fed to higher slaughter weights than is usual for these breeds. Most feedlot steers and heifers marketed in Canada are fed until they reach 5 to 12 mm subcutaneous fat at the 12th rib. Based on regression of actual subcutaneous fat depth on liveweight, the weaned heifers in exp. 1 would have attained a backfat depth of 4 mm (the minimum backfat to qualify for the A grade) at 350 kg liveweight, and the yearling heifers in exp. 2 had equivalent backfat at 400 kg. As slaughter weight increased, the heifers in these experiments became excessively fat with up to 35 mm backfat and Canadian yield grades deteriorated (Dubeski et al. 1997a). However, health of the animals was not compromised by their excessive fatness and the prolonged period of feeding. Cattle were slaughtered when mean pen weight, not individual animal weight, reached the target weight, resulting in a large variation in final liveweight within each slaughter weight group. In exp. 1, final liveweight ranged between and kg (mean ± 35.6 kg) for the 500 kg slaughter weight group, to kg (mean ± 52.7 kg) for the 590 kg group, and to kg (mean ± 43.7 kg) for the 680 kg slaughter weight group. The weight group nutrition interaction was significant (P < ) for ADG in both experiments. Because the

4 628 CANADIAN JOURNAL OF ANIMAL SCIENCE Table 2. Experiment 2. Effects of slaughter weight group, breed, and nutrition on animal performance (least squares means) Weight group Breed Nutrition 590 kg 680 kg SEM Hereford Angus HA Holstein SEM MHP HP SEM Number of groups Initial live wt (kg) b 416.1b 413.1b 336.9a Final live wt (kg) 598.4a 677.6b Intramuscular fat gain (%) z 4.50a 6.74b Final intramuscular fat (%) z 6.75a 9.00b a 8.94c 8.36bc 7.55ab Days fed 239a 323b 4 264a 283b 266a 313c 6 319b 243a 4 ADG (kg d 1 ) 0.758a 0.805b b 0.708a 0.761b 0.881c a 0.879b DM intake (kg) 2470a 3301b a 2828a 2687a 3343b b 2662a 60 Silage DM intake (kg) 1058a 1180b a 1148b 1038a 1249c b 576a 19 Grain DM intake (kg) 1412a 2121b a 1679a 1649a 2094b a 2087b 46 DE intake (Mcal) 8004a 10934b a 9227a 8820a 11017b NEg intake (Mcal) 2777a 3860b a 3219a 3092a 3873b z Intramuscular fat expressed as a percentage of longissimus muscle (wet weight basis). a cweight group, breed, or nutrition means in the same row with different letters differ (P < 0.05). Table 3. Experiment 1. Effects of slaughter weight group, breed, and nutrition on animal, carcass and tissue weights (least squares means) Weight group Breed Nutrition Root 500 kg 590 kg 680 kg Hereford Angus H A MHP HP MSE Number of animals z 57(53) 67(66) 67(65) 63(57) 63(62) 65(65) 97(93) 94(91) Live plant wt. (kg) 468a 564b 638c Warm carcass wt (kg) 276a 342b 394c Dressing ratio (g kg 1 plant wt) 591a 606b 616c 600a 611b 603a 601d 608e h cooler shrink (g kg 1 ) Carcass composition, (g kg 1 cold carcass wt) Carcass muscle 515.0c 484.6b 471.7a 478.9a 493.5b 498.9b 505.9b 474.9a Carcass bone 136.8c 120.6b 112.5a 121.1a 122.0a 126.8b 126.6b 120.0a 8.71 Carcass total fat 348.3a 394.7b 415.8c 400.0b 384.5a 374.3a 367.4a 405.1b Subcutaneous fat 125.2a 156.2b 172.0c 164.9b 143.2a 145.3a 142.7a 159.6b Intermuscular fat 194.9a 209.4b 214.6c 206.8b 212.0b 200.0a 197.1a 215.5b Body cavity fat a 30.0b 3.68 Other fat depots (g kg 1 plant wt) Kidney fat 20.4a 23.0b 23.0b d 22.7e 3.28 Omental fat 25.7a 31.3b 33.3c 31.2b 29.7a 29.4a 27.8a 32.3b 3.53 Mesenteric fat 17.7a 22.6b 26.8c d 22.3e 3.78 z Number in parentheses is the number of carcasses dissected to provide carcass composition. a cweight group, breed, or nutrition means in the same row with different letters are significantly different (P 0.001). d,enutrition means in the same row with different letters are significantly different (P < 0.05). ADG of the MHP cattle was restricted until 500 or 550 kg, overall ADG of MHP cattle improved as slaughter weight increased. In exp. 1, ADG was lower for the MHP treatment at 500 kg compared with the MHP treatment at 590 or 680 kg (P < ), and similarly, in exp. 2, ADG was lower for MHP treatment at 590 compared with 680 kg (P < ). However, ADG did not differ between the slaughter weight groups for HP pens in either experiment (P 0.17). In exp. 1, ADG for cattle fed to 500, 590, and 680 kg was 0.647, 0.769, and kg d 1, respectively, for MHP pens, and 0.931, 0.962, and kg d 1, respectively, for HP pens (SE kg d 1 ). In exp. 2, mean ADG was and kg d 1 for MHP pens slaughtered at 590 and 680 kg, respectively, and and kg d 1 for HP pens slaughtered at 590 and 680 kg (SE kg d 1 ). Mean days on feed to reach 500, 590, and 680 kg in exp. 1 were 301, 398, and 474 d, respectively, for MHP pens, and 209, 303, and 399 d, respectively, for HP pens (SE 6.5 d). In exp. 2, MHP and HP pens took 279 d and 199 d, respectively, to reach 590 kg, and 359 and 288 d, respectively, to reach 680 kg (SE 6.0 d). As expected, MHP pens also consumed more total DM and silage DM, and less grain DM, than HP pens. However, mean DE and NEg intakes were not affected by nutrition treatment. ADG became more variable as days on feed increased (data not shown). ADG was found to peak at 180 to 210 d on feed for weaned Hereford heifers, and then gradually decline (Zinn et al. 1970). In both experiments, ADG of some heifers (except Holsteins in exp. 2) declined to close to 0 kg d 1 before slaughter. Although cattle in Japan are slaughtered at liveweights up to 680 kg, our target slaughter weights appeared to exceed the genetic capabilities of some British breed heifers. In exp. 1, Herefords were lighter initially than Angus and HA, and required more time to reach slaughter weights compared with Angus and HA (Table 1). In both experi-

5 DUBESKI ET AL. EFFICIENCY OF STRATEGIES USED TO ENHANCE MARBLING IN BEEF 629 Table 4. Experiment 2. Effects of slaughter weight group, breed, and nutrition on animal, carcass and tissue weights (least squares means) Weight group Breed Nutrition Root 590 kg 680 kg Hereford Angus H A Holstein MHP HP MSE Number of animals z 84(70) 93(80) 45(37) 43(38) 45(39) 44(36) 90(79) 87(71) Live shrunk plant wt (kg) 572a 652b Warm carcass wt (kg) 341a 394b 374b 381b 376b 339a Dressing ratio (g kg 1 plant wt) 596a 605b 611b 622c 613b 555a h cooler shrink (g kg 1 ) b 10.8a 2.29 Carcass composition (g kg 1 cold carcass wt) Carcass muscle 516.6a 481.2b 488.0b 497.8b 465.6a 544.4d 504.2e 493.7f Carcass bone 131.9a 120.3b 120.7b 113.3a 115.4a 155.1c 127.7e 124.6f 8.18 Carcass total fat 351.5a 398.4b 391.3b 388.9b 419.0c 300.5a 368.1e 381.8f Subcutaneous fat 129.0a 157.1b 164.4c 148.0b 174.6d 85.1a Intermuscular fat 193.6a 211.8b 200.4b 210.8c 215.2c 184.4a 199.8e 205.7f Body cavity fat a 30.1bc 29.2b 30.9c 28.1a 30.2b 3.36 Other fat depots (g kg 1 live plant wt) Kidney fat 24.6a 26.7b 21.9a 24.7b 23.6ab 32.5c 24.4a 27.0b 3.74 Omental fat 32.9a 37.6b 30.3a 33.1b 31.7ab 46.0c 33.3a 37.3b 4.83 Mesenteric fat 27.3a 30.4b 23.2a 28.9b 27.3b 35.9c 26.9a 30.8b 4.75 z Number in parentheses is the number of carcasses dissected to provide carcass composition. a-dweight group, breed or nutrition means in the same row with different letters are significantly different (P 0.001). e,f Nutrition means in the same row with different letters are significantly different (P < 0.05). ments, Herefords and HA had higher ADG than Angus (P 0.002). Both Angus and Herefords consumed more DM and energy than did HA in exp. 1. In exp. 2, Holsteins were lighter in weight initially, required more time on feed and ate more feed than did the other breeds. Daily feed intake of Holsteins was 5.9% higher than the average for the beef breeds. At the same body weight, mean DM intake of Holstein steers was 8 to 15% greater than mean DM intake of beef steers (Owens et al. 1985; Hicks et al. 1990). The maintenance requirement of Holsteins is about 7% greater than for beef breeds, and has been attributed to the higher proportion of visceral organs and associated higher rate of protein turnover (Truscott et al. 1983a). The overall mean for marbling was 8.50% in exp. 1, compared with 7.87% in exp. 2. Both intramuscular fat concentration and gain in intramuscular fat increased with slaughter weight group (P ) in both experiments (Tables 1 and 2). Based on days fed (Table 1), intramuscular fat increased by 0.021, 0.020, and 0.019% d 1 for the 500-, 590-, and 680- kg weight groups, respectively, in exp. 1. Similarly, in exp. 2, marbling increased by 0.019% d 1 and 0.021% d 1 for the 590 and 680 kg weight groups. Our results did not support the common belief that the rate of intramuscular fat deposition increases as fattening progresses. Intramuscular fat and intramuscular fat gain were affected by breed in exp. 1, whereas only intramuscular fat was affected by breed (P = 0.002) in exp. 2. Nutrition treatment had more effect on intramuscular fat deposition in calves compared with yearlings. Intramuscular fat and intramuscular fat gain were higher for HP cattle compared to MHP cattle in exp. 1 (9.16 and 7.60% vs. 7.85% and 6.30%, respectively, P = 0.015), but did not differ for nutrition treatments in exp. 2. Carcass Dissection Data Angus cattle had a significantly higher dressing ratio than Herefords or HA in both experiments (Tables 3 and 4). The dressing ratio for Holsteins in exp. 2 averaged almost 10% lower than the dressing ratio for the beef yearlings (555 vs. 615 g kg 1, P < ). The dressing ratio of Holsteins is usually about 5% lower than for beef breeds at equivalent liveweights (Jones et al. 1985; Mies et al. 1992). Weight group and breed did not affect 24 h cooler shrink, but shrink was lower for HP than MHP in exp. 2 (10.8 vs g kg 1, P = ). CARCASS COMPOSITION AND NON-CARCASS FAT DEPOTS. Weights of carcass muscle, bone, fat and fat depots are reported in Tables 3 and 4. The HP treatment had the same effect as an increase in slaughter weight; both increased total carcass fat, subcutaneous fat, intermuscular fat, and the dissectible non-carcass fat depots (kidney and pelvic fat, omental fat, and mesenteric fat) with minor exceptions. Kidney and pelvic fat was similar for the 590- and 680-kg weight groups in exp. 1, although higher than for the 500-kg weight group. HP cattle tended to have more subcutaneous fat than MHP cattle in exp. 2 (145.9 vs g kg 1, P = 0.08). In both experiments, body cavity fat was not affected by weight group but was greater for HP than MHP carcasses (P ). The fat concentration of gain increases with the rate of gain (Smith et al. 1977; Sully and Morgan 1982), thus carcass composition can be manipulated by changing the diet to alter rate of gain. For example, feedlot managers often feed a lower energy diet to small-framed calves, particularly heifers, until they reach a liveweight of 270 to 320 kg, to delay fattening and increase carcass weight. In the current experiments, the moderate energy phase of the MHP pro-

6 630 CANADIAN JOURNAL OF ANIMAL SCIENCE Table 5. Experiment 1.Effects of slaughter weight group, breed and nutrition on efficiency of production (least squares means) Weight group Breed Nutrition treatment Production efficiency 500 kg 590 kg 680 kg SEM Hereford Angus HA SEM MHP HP SEM Number of pens DM/liveweight gain (kg kg 1 ) 11.23b 10.22a 10.12a a 11.25c 10.40b b 9.76a 0.13 DM/carcass gain (kg kg 1 ) 15.91b 14.75a 14.59a b 13.80a 0.17 DM/lean carcass gain (kg kg 1 ) a 30.62b 30.25b b 27.39a 0.34 DM/intramuscular fat gain (kg % 1 ) ab 404a 516b b 385a 24 DE/liveweight gain (Mcal kg 1 ) 35.7b 33.4a 33.6a a 36.6b 33.7a DE/carcass gain (Mcal kg 1 ) b 48.2a 0.6 DE/lean carcass gain (Mcal kg 1 ) a 99.6b 98.0ab DE/intramuscular fat gain (Mcal % 1 ) ab 1311a 1664b b 1347a 15 NEg/liveweight gain (Mcal kg 1 ) a 12.7b 11.7a a 12.5b 0.2 NEg/carcass gain (Mcal kg 1 ) a 17.7b 0.2 NEg/lean carcass gain (Mcal kg 1 ) 33.0a 33.7ab 34.8b a 35.1b 0.4 NEg/intramuscular fat gain (Mcal % 1 ) ab 455a 574b Total cost kg 1 liveweight gain $2.15b $1.91a $1.91a $0.03 $1.85a $2.15c $1.97b $0.03 $2.08b $1.91a $0.03 Total cost kg 1 carcass gain $3.04b $2.76a $2.75a $0.04 $2.75a $2.94b $2.87ab $0.04 $3.01b $2.69a $0.04 Total cost kg 1 lean carcass gain $5.82b $5.52a $5.60ab $0.08 $5.38a $5.84b $5.75b $0.08 $5.96b $5.34a $0.07 Total cost/% intramuscular fat gain $85.15 $82.77 $93.81 $5.80 $87.55ab $76.75a $97.43b $5.80 $99.61b $74.88a $4.74 a cweight group, breed, or nutrition means with different letters in the same row are different (P 0.05). gram was fed much longer and to higher weights than would occur in commercial practice, in an attempt to sustain effects of energy restriction on carcass composition when cattle were fed to heavier slaughter weights than normal. The effects of nutrition on carcass composition were more pronounced when heifers were started on feed as weaned calves rather than as yearlings. Averaged across slaughter weight groups, HP carcasses had 3.77% more fat than MHP carcasses in exp. 1 (Table 3), but only 1.37% more fat in exp. 2 (Table 4). Yearlings were less responsive to nutrition than calves for several reasons. Yearlings were as lean as calves (20.0 vs. 19.9% carcass fat) but 135 kg heavier initially. They had previously undergone a period of reduced gains on pasture or during backgrounding, equivalent to a moderate phase of nutrition. Furthermore, MHP yearlings grew faster than HP yearlings at the same weight after adaptation to the HP diet (0.85 vs kg d 1 ), negating effects of the earlier feed restriction by depositing more fat. In comparison, MHP calves adapted to the HP diet grew at the same rate as HP cattle at the same weight. Breed affected most carcass components and fat depots. Among the British breeds, in each experiment the breed with the most rapid growth rate (Herefords in exp. 1, HA in exp. 2) produced the fattest carcasses. Holstein carcasses contained significantly more lean and bone, and less total fat, especially subcutaneous fat, compared with the British breeds. Holsteins also had less intermuscular fat, but more body cavity, kidney, omental and mesenteric fat than the other breeds as previously observed (Truscott et al. 1983b). Efficiency of Production An interaction between slaughter weight group and nutrition affected most measurements of efficiency or cost of liveweight, carcass, and lean carcass gain because MHP cattle produced more rapid, more efficient gains after they were transferred to the high grain diet (Tables 5 and 6). For example, in exp. 1, MHP cattle slaughtered at an average pen weight of 500 kg consumed more DM per kilogram liveweight gain then MHP cattle slaughtered at 590 or 680 kg (12.32 vs and 10.63, SEM 0.22, P < ). In exp. 2, MHP cattle slaughtered at 590 kg required ± 0.38 kg DM kg 1 liveweight gain compared with only ± 0.38 kg DM kg 1 gain for those killed at 680 kg (P < 0.001). Differences in DM, DE, or NEg required per kilogram gain of liveweight, carcass weight, or lean carcass weight were not detected as slaughter weight increased for the HP cattle. In exp. 1, the costs of a unit gain (live, carcass, or lean weight) was lower for MHP cattle killed at 590 and 680 kg than at 500 kg, but the cost of gain for HP cattle was not affected by weight group (P < 0.05). In exp. 2, the cost of live, carcass, or lean weight gain was about 20% higher for MHP cattle slaughtered at 590 kg than for 680 kg MHP cattle or the HP cattle (P < 0.001). Differences in ADG, feed consumption, dressing ratio, and carcass composition among breeds affected the economics of production. The breed with the highest ADG (Hereford in exp. 1, Holstein in exp. 2) produced the cheapest liveweight gain. In exp. 1, Herefords had the most economical carcass and lean carcass gains. In exp. 2, cost of carcass gain was similar for the British breeds and Holsteins (P = 0.14) because the lower dressing ratio of Holsteins countered their more efficient liveweight gains. The cost per unit of lean carcass gain was least for Holsteins due to their extreme leanness, highest for Angus, and intermediate for HA and Herefords (P = 0.02). The HP nutrition program was more economical than the MHP program per unit of liveweight, carcass, lean carcass, or intramuscular fat gain due to cheaper energy from grain, more rapid gains, and associated lower interest, bedding, and yardage costs. In both experiments, HP cattle required less DM per unit of liveweight, carcass, lean carcass, or

7 DUBESKI ET AL. EFFICIENCY OF STRATEGIES USED TO ENHANCE MARBLING IN BEEF 631 Table 6. Experiment 2. Effects of slaughter weight group, breed, and nutrition treatment on efficiency of production (least squares means) Weight group Breed Nutrition treatment Production efficiency 590 kg 680 kg SEM Hereford Angus HA Holstein SEM MHP HP SEM Number of pens DM/liveweight gain (kg kg 1 ) 14.18b 12.87a b 14.57b 13.61b 12.36a b 12.58a 0.27 DM/carcass gain (kg kg 1 ) b 16.28a 0.39 DM/lean carcass gain (kg kg 1 ) b 36.62a 0.84 DM/intramuscular fat gain (kg % 1 ) ab 491a 515ab 657b b 499a 39 DE/liveweight gain (Mcal kg 1 ) 45.9b 42.7a ab 47.5b 44.6b 40.7a DE/carcass gain (Mcal kg 1 ) DE/lean carcass gain (Mcal kg 1 ) DE/intramuscular fat gain (Mcal % 1 ) ab 1600a 1686ab 2150b NEg/liveweight gain (Mcal kg 1 ) ab 16.6b 15.6ab 14.3a NEg/carcass gain (Mcal kg 1 ) NEg/lean carcass gain (Mcal kg 1 ) NEg/intramuscular fat gain (Mcal % 1 ) ab 557a 590ab 633b Total cost kg 1 liveweight gain $2.67b $2.43a $0.04 $2.58b $2.77c $2.60bc $2.24a $0.06 $2.68b $2.42a $0.04 Total cost kg 1 carcass gain $3.38 $3.23 $0.06 $3.22 $3.42 $3.25 $3.31 $0.08 $3.49b $3.12a $0.06 Total cost kg 1 lean carcass gain $7.65b $7.25a $0.13 $7.75bc $7.83c $7.23ab $7.00a $0.19 $7.87b $7.03a $0.13 Total cost/% intramuscular fat gain $ $94.99 $6.85 $ $93.16 $98.03 $ $9.68 $ $95.30 $6.85 a-c Slaughter weight group, breed or nutrition means with different letters in the same row are different (P 0.05). intramuscular fat gain compared with MHP cattle. Most studies have shown that feed:gain is superior for HP diets compared with MHP diets (Oltjen 1971; Lancaster et al. 1973) but differences in efficiency of energy use for lean carcass growth or intramuscular fat deposition are not well defined. The efficiency of intramuscular fat deposition was not affected by weight group (Tables 5 and 6), or by an interaction between weight group and nutrition. However, the NEg required per unit of intramuscular fat gain tended to increase with weight group in exp. 1 (P = 0.07). The efficiency of intramuscular fat deposition was affected by breed in exp. 1 only. In exp. 1, Angus cattle deposited intramuscular fat the most economically, whereas HA were least efficient and Herefords were intermediate. In exp. 2, the Angus was the most efficient and the Holstein the least efficient in depositing intramuscular fat, but these differences were not significant. Intramuscular fat deposition was more efficient and more economical for the HP treatment in exp. 1. Although the same trends were seen in exp. 2 as in exp. 1, treatment differences were not significant. In these experiments, costs of production could have been reduced by feeding an ionophore and MGA to improve feed efficiency, and by selection of an appropriate growth implant to maximize lean growth. Efficiency would be improved by basing nutrition programs and target slaughter weights on frame size. Furthermore, the greater variation in intramuscular fat concentrations observed in exp. 1 (2.6 to 34.5%) than in exp. 2 (3.4 to 17.8%) suggests that calves could be selected for prolonged feeding to enhance marbling if their intramuscular fat can be accurately measured in the live animal prior to reaching normal slaughter weights. Estimated costs for liveweight, carcass and lean carcass gain were lower for calves compared with yearlings due to their superior feed efficiency. Calves have been reported to consume 2.7 to 3.9 kg less feed per day compared with yearlings, resulting in an improvement in feed efficiency of 10 to 23% (Lewis et al. 1990; Hickok et al. 1992). The lower feed consumption in calves and similar rate of intramuscular fat deposition compared with yearlings suggest that it may be cheaper to produce intramuscular fat in calves than in yearlings. Averaged over slaughter weight groups and nutrition treatments, the cost of producing a 1% increase in intramuscular fat was $87.24 for calves, and $ for yearlings. Current feedlot management practices designed to maximize feed intake may be inefficient when cattle are fed for prolonged periods to enhance marbling. The gain in intramuscular fat achieved by feeding to high slaughter weights was less than expected for all breeds in these experiments. Most carcasses graded AAA or low Choice and the remainder graded AA or Select, except for a limited number that graded Prime (Dubeski et al. 1997a). Similar results were achieved when Cameron et al. (1993) fed Angus steers a high energy diet for an additional 125 to 209 d to slaughter weights up to 680 kg. Considering that most British breed cattle should grade AAA or Choice at slaughter weights of 450 to 550 kg, feeding high energy diets past normal slaughter weights was not an efficient method to enhance marbling. Results of the current study suggest that British breed heifers deposit intramuscular fat most efficiently and most economically earlier in life, particularly when fed HP diets. Similarly, Hereford steer calves fed from 218 to 400 kg produced the most intramuscular fat on HP or high-moderate planes of nutrition, and the least on moderate or MHP of nutrition (Henrickson et al. 1965). However, ad libitum feeding of high energy diets late in the feeding period is inefficient when cattle are fed for an extended period of time

8 632 CANADIAN JOURNAL OF ANIMAL SCIENCE and may not be necessary to maximize marbling. The most efficient strategies to produce extreme marbling may involve feeding diets which restrict either feed intake or dietary energy concentration particularly in the latter part of the extended period of feeding. Long-fed heifer calves have poor feed efficiencies in commercial feedlots, and may be the ideal cattle type and sex to benefit from limit feeding (Peters 1995). The Japanese can produce lean carcasses with highly marbled beef by first feeding a low-grain diet and then limiting gain to no more than 0.15 kg d 1 during the last 5 mo of feeding (Hayes 1990). When 8-mo-old Angus steers were program fed to gain only 0.9 kg d 1 from 8 mo to 26 mo of age, 80% graded Prime (Lunt et al. 1993), whereas marbling was inferior in Angus steers fed a high grain diet ad libitum to 25 mo (Cameron et al. 1993). CONCLUSIONS The production practices tested in these experiments failed to reliably produce adequate intramuscular fat for specialty markets in North America or overseas (Dubeski et al. 1997a,b). In order to produce for these markets, it would be necessary to develop management programs to achieve carcasses with intramuscular fat equivalent to the US Prime grade (8.56% intramuscular fat; Savell et al. 1986). Prolonged feeding using MHP or HP nutrition programs increased intramuscular fat only slightly, at a high cost, and resulted in extremely fat carcasses which would be discounted based on yield grade. ACKNOWLEDGEMENTS Financial support for this research, contributed by Maple Leaf Foods, formerly Canada Packers, ShurGain Division and the Alberta Agricultural Research Institute Matching Grants Program, is gratefully acknowledged. 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