Key words: Hereford, Simmental, marbling, shear, palatability, growth performance, carcass

Transcription

1 Effects of breed and dietary energy content within breed on growth performance, carcass and chemical composition and beef quality in Hereford and Simmental steers I. B. Mandell 1, E. A. Gullett 2, J. W. Wilton 1, O. B. Allen 3, and R. A. Kemp 4 1 Department of Animal and Poultry Science, 2 Department of Food Science, and 3 Department of Mathematics and Statistics, University of Guelph, Guelph, Ontario, Canada N1G 2W1; and 4 Agriculture and Agri-Food Canada, Lethbridge Research Station, Lethbridge, Alberta, Canada T1J 4B1. Received 21 October 1997, accepted 18 June Mandell, I. B., Gullett, E. A., Wilton J. W., Allen, O. B. and Kemp, R. A Effects of breed and dietary energy content within breed on growth performance, carcass and chemical composition and beef quality in Hereford and Simmental steers. Can. J. Anim. Sci. 78: Forty-eight Hereford and 60 Simmental steers were used to evaluate breed differences as affected by dietary energy content on growth performance, carcass and chemical composition, and beef quality. Diets were based on corn silage, alfalfa haylage, whole corn, and SBM and were formulated to provide 2.52 to 2.81 Mcal kg 1 ME and 11.7 to 12.6% protein in the growing phase and 2.69 to 2.86 Mcal kg 1 ME and 9.7 to 10.4% protein in the finishing phase. Low- and high-energy diets were formulated for each breed with the high-energy diet for Hereford serving as the low-energy diet for Simmental. Steers were slaughtered after attaining 8 to 10 mm backfat determined by ultrasound. Higher energy diets increased (P < 0.09) average daily gain (ADG) and feed efficiency within both breeds. Hereford gained more rapidly (P = 0.074) and were more (P = 0.001) efficient in converting feed to gain than Simmental. High-energy diets decreased (P = 0.001) days on feed for both breeds and increased (P = 0.001) carcass weights for Simmental. Otherwise, carcass and chemical composition were generally unaffected by dietary energy content. Simmental were heavier (P = 0.001) and leaner (P = 0.001) than Hereford while marbling classification and intramuscular fat content were similar (P > 0.10) between breeds. While shear force decreased (P = 0.043) feeding the low-energy diet to Simmental, other shear and palatability attributes were unaffected by dietary energy content or breed. Altering dietary energy content for Hereford and Simmental influenced growth performance without affecting carcass and chemical composition and beef quality. Key words: Hereford, Simmental, marbling, shear, palatability, growth performance, carcass Mandell, I. B., Gullett, E. A., Wilton, J. W., Allen, O. B. et Kemp, R. A. Effets de la race et du contenu énergétique de l aliment sur les performances de croissance, sur la composition de carcasse et sur la composition chimique et sur la qualité de la viande de bouvillons Hereford et Simmental. Can. J. Anim. Sci. 78: Quarante-huit bouvillons Hereford et 60 Simmental ont été utilisés pour évaluer les différences raciales quant à l influence du contenu énergétique de l aliment sur les performances de croissance, sur la composition de carcasse et la composition chimique et sur la qualité de la viande. Les aliments étaient faits d ensilage de maïs, d ensilage de luzerne mi-fané, de maïs-grain entier et de tourteau de soja, formulés de façon à fournir de 2,52 à 2,81 Mcal kg 1 de EM et de 11,7 à 12,6 % de protéines dans la phase de croissance et de 2,69 à 2,86 Mcal kg 1 EM et de 9,7 à 10,4 % de protéine dans la phase de finition. Chaque race était exposée à un régime à haute et un à basse teneur énergétique, le régime à haute teneur utilisé pour les Hereford servant de régime à basse teneur pour les Simmental. Les bouvillons étaient abattus lorsque l épaisseur du gras de couverture, mesurée aux ultrasons, était de 8 à 10 mm. Dans chaque race, les aliments à fort contenu énergétique donnaient lieu à un accroissement (P < 0,09) du GMQ et de l efficacité alimentaire. Les Hereford grandissaient plus rapidement (P = 0,74) et valorisaient mieux (P = 0,01) leurs aliments que les Simmental. En outre, la durée de l engraissement était plus courte (P = 0,001) chez les deux races et les carcasses étaient plus lourdes (P = 0,001) chez les Simmental. Par ailleurs, la valeur énergétique n avait généralement que peu d effet sur la composition de la carcasse ni sur la composition chimique. Les bouvillons Simmental étaient plus lourds (P = 0,001) et plus maigres (P = 0,001) que les Hereford, avec des cotes de persillé et de teneur en graisse intramusculaire semblables (P > 0,10) pour les deux races. Alors que la force de cisaillement était plus basse (P = 0,043) chez les Simmental exposés au régime à basse valeur énergétique, le contenu énergétique n influait pas sur les autres paramètres de texture et d appétibilité de la viande quelle que soit la race. Mots clés: Hereford, Simmental, persillé, cisaillement, appétibilité, performances de croissance, carcasse 533 Abbreviations: ADG, average daily gain; DMI, dry matter intake; LMA, longissimus muscle area

2 534 CANADIAN JOURNAL OF ANIMAL SCIENCE The effect of dietary energy content on beef quality has been evaluated with several studies in the past (Arthaud et al. 1977; Prior et al. 1977; Dikeman et al. 1986). Angus or Angus-cross cattle were evaluated in all three studies while Prior et al. (1977) evaluated large type cattle by including 3/4 or greater Charolais and Chianina crossbreds. This latter study fed the large type cattle such that their finish exceeded the maximum requirement for the current Canadian yield grade 1 finish while palatability attributes were not directly compared between small and large cattle types. In all three studies, the authors concluded that palatability attributes were generally unaffected by dietary energy content. Diversity in the ability to fatten between British and Continental breeds of cattle has long been recognized, with Gregory et al. (1994a) recently reporting that on an age-constant basis, British breeds had fat depths of 12 mm backfat vs. 4 to 5 mm in their Continental breed counterparts. Ration formulation for commercial beef cattle production will be influenced by the specific breed type being fed. Breed differences in the ability to fatten will result in large breed differences in days to market when cattle are fed to a common compositional endpoint (Prior et al. 1977; Vanderwert et al. 1985). However, scientific studies often use common nutritional regimens across breeds to prevent confounding. This study was conducted to evaluate the effect of dietary energy content on within-breed differences while using one nutritional regimen to compare breeds diverse in their ability to fatten on growth performance, carcass and chemical composition, and beef quality in Hereford and Simmental steers. MATERIALS AND METHODS One hundred and twenty-six steer calves were purchased from producers in central and Southwestern Ontario who could provide cattle with the following requirements : 1) purebred Hereford or at least 7/8 Simmental; 2) seven halfsibs per sire; and 3) male calves born between 1 February and 31 May. Steers from 8 Hereford and 10 Simmental sires were purchased with six half-sibs per sire starting the trial. The 108 head were randomly allotted to 18 pens with six head per pen. Steers were bedded on long straw in 4.92 m 8.31 m pens enclosed in a cold environment barn with access outdoors.all pens were equipped with Calan gates to enable accurate determination of dry matter intake for individual animals. Cattle were gradually adapted over 28 d to one of three growing rations (Table 1) in which three half-sibs per sire were fed either a low- or high-energy ration for 90 d. Cattle were then switched to a corresponding low- and high-energy finishing ration. All cattle were implanted with Synovex- S. Animals were fed daily with refusals weighed and removed on a weekly basis. Pens were checked thrice daily to detect and treat health problems. Steers were weighed every 28 d to assess total liveweight gain (kg) for the calculation of ADG. Feed intake data (kg) were summated every 7 d to determine DMI (kg) and feed efficiency (kg feed kg 1 gain). Cattle were fed until they attained 8 mm backfat determined by ultrasound according to the procedure of Perkins et al. (1992). All cattle were slaughtered at a commercial abattoir, which did not use electrical stimulation. Carcasses were individually tagged on the kill floor to enable identification in the grading cooler. Hot carcass weights were recorded prior to overnight spray chilling. The carcasses were then graded in the normal manner by Agriculture Canada meat graders using the criteria to determine carcass grade and lean yield effective 5 April Left primal ribs from each carcass were delivered to the University of Guelph Meat Wing for further processing. The interface between the 12th and 13th ribs was used to obtain the following carcass measurements: 1) subcutaneous fat (mm) at 1/4, 1/2 and 3/4 position over the longissimus; 2) grade fat (mm) or minimum fat in the last quadrant over the longissimus; and 3) longissimus muscle area (LMA, cm 2 ). The 9th 11th ribs were separated into muscle, bone, and subcutaneous, intermuscular and body cavity fat (Lunt et al. 1985) to determine yields of dissectible lean, fat and bone (g kg 1 rib weight). Post-separation of the three rib section, the longissimus muscle roast was vacuum packaged and stored at 2 C until 7 d post-mortem. Longissimus muscle from the 12th rib was treated analogously to the three-rib longissimus muscle roast. After aging the roasts and steaks were stored at 24 C. All epimysium was removed from the longissimus muscle steak from the 12th rib after thawing. The steak was then cut into cubes and freeze dried prior to grinding for chemical analyses. The dried sample was ground using a commercial coffee grinder. Water content was calculated from the difference in weight after freeze drying corrected for any residual moisture from oven drying at 100 C. Determination of chemical fat was conducted using method A (Association of Official Analytical Chemists 1990) for ether extraction of fat. Collagen solubility was determined using the procedure of Hill (1966) while collagen content was calculated by multiplying hydroxyproline content by a conversion factor of 7.25 (Bergmann and Loxley 1963). Longissimus muscle roasts from 104 head were used to evaluate palatability attributes of beef. An eight-member trained taste panel was used to evaluate palatability attributes using CSA (Computerized Sensory Analysis Version 4.2, Compusense Inc., Guelph, Ontario) software. Palatability attributes included: 1. Softness the force required to compress the sample between the molar teeth; 2. Tenderness the force to chew, measured after three chews excluding the first bite; 3. Initial juiciness amount of moisture released by the sample after five chews; 4. Beef flavour the amount of full meaty flavour present after eight chews; 5. Juiciness the amount of saliva absorbed during the mastication process; 6. Time spent chewing time taken to chew the sample completely for swallowing. An unstructured line scale with verbal anchors based on quantitative descriptive analysis (Stone and Sidel 1985) was used in which the left anchor, 0, represented scoring of either very firm (softness), very tough (tenderness), very dry

3 MANDELL ET AL. BREED AND DIET DIFFERENCES ON BEEF QUALITY 535 Table 1. Ingredient and projected chemical composition of rations fed to steers Ration Low energy High energy (Hereford) High energy (Hereford) Low energy (Simmental) z (Simmental) Growing rations (% of DM) Ingredient Corn silage Alfalfa haylage Whole corn Soybean meal Mineral-vitamin premix y Estimated analysis DM ME (Mcal kg 1 ) NE m (Mcal kg 1 ) NE g (Mcal kg 1 ) Crude protein Finishing rations Corn silage Alfalfa haylage 12.6 Whole corn Soybean meal Mineral-vitamin premix y Estimated analysis DM ME (Mcal kg 1 ) NE m (Mcal kg 1 ) NE g (Mcal kg 1 ) Crude protein z High-energy ration for Hereford same as low-energy ration for Simmental. y Mineral-vitamin premix contains limestone, trace-mineralized salt, rumensin, potassium sulfate and a vitamin premix. (initial juiciness), very weak (beef flavour), very dry (juiciness), and very short (time to chew) while the right anchor, 10, represented scoring of either very soft (softness), very tender (tenderness), very juicy (juiciness), very intense (beef flavour), very juicy (juiciness), and very long (time spent chewing). The taste panel was trained and conducted according to procedures outlined by Mandell et al. (1997). Roasts were prepared for the taste panel by tempering for approximately 44 h at 0 4 C to reach an internal temperature of 2 5 C at time of cooking. Roasts were cooked at 177 C in an electric oven to an internal endpoint temperature of 68 C determined by a type K flexible high temperature probe located in the centre of the roast. Roasts were weighed pre- and post-cooking and cooked in previously weighed pans to determine total cooking losses. Warner-Bratzler shear measurements were conducted on cooked beef which had stood at room temperature for approximately 3 h after removal from the oven. Three to four cores,15 mm diameter by 2 cm, were removed parallel to the long axis of the muscle fibres. Shear measurements were made on each core using the MC300 NENE with Warner-Bratzler Shear Head (NENE Instrument Ltd., Wellingborogh, UK) recording peak shear force. Cores had been placed in the head with fibres running horizontally and then sheared across the fibres. Statistical Analyses Growth performance, carcass, chemical composition, and palatability data were analyzed using a mixed linear model (Henderson 1984). Three rations were formulated across the two breeds to provide low- and high-energy diets, with four diet-breed treatments including low-energy/hereford, lowenergy/simmental, high-energy/hereford, and high-energy/simmental. The initial model included diet-breed combination, covariates, all interactions of the foregoing, and sire nested within breed. Sire effect was regarded as random, but all other effects (except residual error) were fixed. The model was fit using PROC MIXED (SAS Institute, Inc. 1996) estimating the sire variance component using a restricted maximum-likelihood (REML) method. Covariates that were included in the analysis of growth performance, carcass, chemical composition, and palatability traits are presented in Table 2. Terms not significant at a probability of 0.05 were removed sequentially from the initial model to yield a final model for inference. Where the final model included covariates, adjusted means for predicted diet-breed combinations were not evaluated at a common value (e.g. the overall mean) of the covariates. Instead, partially adjusted means were used (Urquhart 1982; Allen et al. 1998), which consisted of the covariate mean specific to each diet-breed combination. Contrasts were then designed to compare: 1) low- vs. highenergy rations fed to Hereford (within Hereford); 2) low- vs. high-energy rations fed to Simmental (within Simmental); and 3) high-energy/hereford vs. low-energy/simmental (between breeds). This experiment was conducted following the animal utilization protocol approved by the University of Guelph

4 536 CANADIAN JOURNAL OF ANIMAL SCIENCE Table 2. Covariates used in model building of experimental data z Trait(s) Days on feed, age at slaughter Growth performance (average daily gain, dry matter intake, feed efficiency) in growing phase Growth performance (average daily gain, dry matter intake, feed efficiency) in finishing phase Growth performance (average daily gain, dry matter intake, feed efficiency) overall (from start to finish) Grade fat Hot carcass weight, longissimus muscle area, lean yield, fat yield, bone yield, intramuscular fat content, sarcomere length Total cooking losses Total collagen, soluble collagen Warner-Bratzler shear, taste panel softness, tenderness, chewiness Taste panel initial juiciness, flavour, juiciness z Model-building process described in Materials and Methods. Animal Care Committee according to the guidelines of the Canadian Council on Animal Care. RESULTS AND DISCUSSION Two steers died during trial. Age at start of the trial did not differ (P > 0.10) between breeds with Hereford aged 234 ± 29 d vs. 230 ± 29 d for Simmental in contrast to heavier (P < 0.05) weights at start of trial for Simmental (275 ± 47 kg) vs. Hereford (242 ± 46 kg). Grade fat was included as a covariate in model building of all traits and remained in the final model for the following traits: feed efficiency during the finishing phase, yields of lean, fat, and bone, intramuscular fat content, sarcomere length, and taste panel chewiness. Contrasts were not affected when the covariate grade fat was evaluated at the targeted endpoint value of 8 mm across all diet-breed combinations or when partially adjusted means for grade fat were used, i.e. at grade fat values specific to each diet-breed combination. Increasing the energy content of the diet improved (P = 0.100) ADG, DMI (kg d 1 ) and feed efficiency in the growing phase for both breeds (Table 3). The large within breed difference in ADG for Hereford in the growing phase is probably due to corresponding differences (P = 0.001) in DMI with gut fill likely restricting intake in Hereford fed the high silage diet. Hironaka and Kozub (1991) reported gains of 0.91 kg d 1 in Hereford fed a 2.49 Mcal kg 1 ME diet as compared to 0.97 kg d 1 gains from the 2.52 Mcal kg 1 ME diet fed to Hereford in the present trial. In contrast, Prior et Grade fat (mm) Age at start of trial (days); weight at start of trial (kg) Age at start of trial (days); weight at start of trial (kg); days on feed; grade fat (mm) Age at start of trial (days); weight at start of trial (kg); days on feed; grade fat (mm) Age at slaughter (days) Age at slaughter (days); grade fat (mm) Age at slaughter (days); grade fat (mm); intramuscular fat content (g kg 1 ) Age at slaughter (days); grade fat (mm); intramuscular fat content (g kg 1 ); sarcomere length (µm) Age at slaughter (days); grade fat (mm); intramuscular fat content (g kg 1 ); sarcomere length (µm); total collagen (mg g 1 ); soluble collagen (g kg 1 ); grade fat intramuscular fat content Age at slaughter (days); grade fat (mm); intramuscular fat content (g kg 1 ); total cooking losses (g kg 1 ); grade fat intramuscular fat content al. (1977) only found 0.12 kg d 1 difference in ADG in Angus Hereford steers fed a 2.91 or 3.06 Mcal kg 1 ME diets. In the National Research Council (1996) nutrient requirements for beef cattle, energy requirements for another medium frame breed, Angus, included 5.55 Mcal d 1 for NE m and 3.68 and 5.74 Mcal d 1 for NE g to gain respectively 1.0 and 1.5 kg d 1 ADG. Based on the estimated values for NE m and NE g found in Table 1, lower ADGs by Hereford fed the low-energy diet were due to lower DMI, which restricted NE g versus Hereford fed the high-energy diet. Diet differences in ADG between Simmental are supported by findings with Charolais and Chianina crossbreds (Prior et al. 1977) fed 2.91 or 3.06 Mcal kg 1 ME diets, but are contrary to similar ADGs in large frame steers fed 3.05 or 2.88 Mcal kg 1 ME diets (Rompala et al. 1984). Hereford consumed more (P = 0.002) DM (g per BW basis) than Simmental in the growing phase. Improved (P < 0.10) feed conversion by feeding higher energy diets in all phases of production are supported by findings with Charolais steers (Rompala et al. 1984). In contrast ME content of the diet did not affect feed efficiency in British and Continental cattle (Prior et al. 1977). Diet effects on ADG were also found for Hereford in the finishing phase and Simmental overall with greater (P < 0.07) gains from feeding the high- vs. low-energy diets. Large differences in DMI within Hereford in the growing phase are probably responsible for increased (P < 0.001) ADG overall for Hereford consuming the high- vs. lowenergy diet.

5 MANDELL ET AL. BREED AND DIET DIFFERENCES ON BEEF QUALITY 537 Table 3. Breed differences and effects of dietary energy content (ME basis) on within-breed differences for growth performance in Hereford and Simmental steers z Breed Hereford Simmental Probability of larger F-ratio for contrasts w Covariates in final Low High Low High Within Within Hereford vs. Item model y,x energy energy energy energy SE Hereford Simmental Simmental Growing phase (days 0 to 90) Average daily gain (kg d 1 ) AGE** Dry matter intake (kg d 1 ) WT** Dry matter intake (g BW 0.75 ) WT(d-b)*; WT WT(d-b) Feed efficiency (kg feed WT(d-b)*; kg gain 1 ) WT WT(d-b)* Finishing phase (days 91 to slaughter) Average daily gain (kg d 1 ) AGE*; AGE AGE* Dry matter intake (kg d 1 ) WT**; AGE**; DOF**; DOF DOF** Dry matter intake (g BW 0.75 ) AGE**; DOF**; DOF DOF** Feed efficiency (kg feed WT**; AGE**; kg gain 1 ) AGE AGE**; DOF(d-b)**; DOF DOF(d-b)**; FAT(D-b)*; FAT FAT* Overall (day 0 to slaughter) Average daily gain (kg d 1 ) DOF** Dry matter intake (kg d 1 ) WT**; DOF** Dry matter intake (g BW 0.75 ) AGE*; DOF** Feed efficiency (kg feed WT**; DOF(d-b)** kg gain 1 ) Days on feed N/A Age at slaughter (d) N/A z Cattle were fed either a low- or high-energy ration formulated on a within-breed basis. The low-energy ration for Herefords included a 2.52 Mcal kg 1 ME diet during a 90-d growing phase followed by a 2.69 Mcal kg 1 ME diet until cattle achieved their targetted slaughter endpoint. The high-energy ration for Herefords also served as the low-energy ration for Simmentals and included a 2.69 Mcal kg 1 ME diet during a 90-d growing phase followed by a 2.81 Mcal kg 1 ME diet until cattle achieved their targetted slaughter endpoint. The high-energy ration for Simmentals included a 2.81 Mcal kg 1 ME diet during a 90- d growing phase followed by a 2.86 Mcal kg 1 ME diet until cattle achieved their targetted slaughter endpoint. y Covariates in final model after model building (described in Table 2) include: AGE = age at start of test (d); WT = weight (kg) at start of test; DOF = days on feed; FAT = mm grade fat; N/A = not applicable as no covariates remaining in final model. Covariates followed by (d-b) indicate the covariate nested within diet-breed combination. x Probability of significance for covariates in final model are indicated by either (P < 0.10), * (P < 0.05) or ** (P < 0.01). w Where the final model includes covariates, comparisons of diet-breed combinations were evaluated at covariate means specific to each diet-breed combination. Hereford outgained (P< 0.08) Simmental overall and during the finishing phase possibly due to use of backfat finish for slaughter endpoint. Simmental on the low-energy diet averaged 279 d on feed which differed (P < 0.001) from the 212 d on feed needed for Hereford. Since Hereford have lower maintenance energy requirements than Simmental (Ferrell and Jenkins 1985), the latter may gain less due to longer time on feed and lower efficiency for maintenance and gain than Hereford. These results are contrary to previous studies involving these breeds (Gregory et al. 1994a,b) where Simmental outgained Hereford after constant time on feed. However, Vanderwert et al. (1985) found another medium frame breed, Angus, to outgain a large frame breed, Limousin, when fed to a common backfat endpoint. Differences in source of sires between breeds may be responsible for breed differences in ADG. Simmental sires were primarily herd sires with six half-sibs per sire obtained primarily from one producer each. In contrast, Hereford calves were generally obtained from AI sires and thus several producers from across the province were needed to supply the calves. The use of AI sires for Hereford incorporates genetics which have in most cases been selected for growth in contrast to herd sires which may or may not have been performance tested. Five of the eight Hereford sires used in the trial had EPDs for yearling weight ranging from 81 to 105 lb (Canadian Hereford Association 1997). Breed differences (P = 0.001) in feed conversion overall and during the finishing phase may be due to slow rates of fattening in Simmental which increased days on feed to the backfat endpoint. Ferrell and Jenkins (1985) found greater utilization of

6 538 CANADIAN JOURNAL OF ANIMAL SCIENCE Table 4. Breed differences and effects of dietary energy content (ME basis) on within-breed differences for carcass and chemical composition in Hereford and Simmental steers z Breed Hereford Simmental Probability of larger F-ratio for contrasts w Covariates in final Low High Low High Within Within Hereford vs. Item model y,x energy energy energy energy SE Hereford Simmental Simmental Hot carcass weight (kg) AGE(d-b)** AGE* AGE* Grade fat (mm) AGE(d-b)**, AGE AGE* Longissimus muscle area (cm 2 ) AGE** Lean yield (g kg 1 ) v FAT**; FAT FAT** Fat yield (g kg 1 ) v FAT**; FAT FAT** Bone yield (g kg 1 ) v FAT** Agriculture Canada lean yield u Agriculture Canada marbling classification t Sarcomere length (µm) FAT(d-b)** Intramuscular fat (g kg 1 ) AGE**; FAT** Total collagen (g kg 1 ) IMFAT**; IMFAT IMFAT* Soluble collagen (g kg 1 ) N/A Total cooking losses (g kg 1 ) N/A z Cattle were fed either a low- or high-energy ration formulated on a within-breed basis. The low-energy ration for Herefords included a 2.52 Mcal kg 1 ME diet during a 90-d growing phase followed by a 2.69 Mcal kg 1 ME diet until cattle achieved their targetted slaughter endpoint. The high-energy ration for Herefords also served as the low-energy ration for Simmentals and included a 2.69 Mcal kg 1 ME diet during a 90-d growing phase followed by a 2.81 Mcal kg 1 ME diet until cattle achieved their targetted slaughter endpoint. The high-energy ration for Simmentals included a 2.81 Mcal kg 1 ME diet during a 90- d growing phase followed by a 2.86 Mcal kg 1 ME diet until cattle achieved their targetted slaughter endpoint. y Covariates in final model after model building (described in Table 2) include: AGE = age at start of test (d); FAT = mm grade fat; IMFAT = intramuscular fat (g kg 1 ), N/A = not applicable as no covariates remaining in final model. Covariates followed by (d-b) indicate the covariate nested within diet-breed combination. x Probability of significance for covariates in final model are indicated by either (P < 0.10), * (P < 0.05) or ** (P < 0.01). w Where the final model includes covariates, comparisons of diet-breed combinations were evaluated at covariate means specific to each diet-breed combination. v Yield data (lean, fat, bone) based on grams dissected lean, fat, bone in the 9th 11th rib per 1000 g weight of 9th 11th rib. u Agriculture Canada lean yield as predicted by federal graders using ruler. t Agriculture Canada marbling score based on devoid (B carcasses), trace, slight, and small marbling. Data recorded for ANOVA with assignments of 0 for devoid marbling, 1 for trace marbling, 2 for slight marbling and 3 for small marbling. ME for maintenance and gain by Hereford relative to Simmental while gain efficiency in Hereford exceeded Simmental when cattle were evaluated at endpoints based on marbling score or percentage longissimus muscle fat (Gregory et al. 1994b). Increasing the energy content of the diet decreased (P < 0.01) days on feed and thus age at slaughter. Hereford needed less (P = 0.001) time on feed than Simmental in attaining the backfat endpoint. This was expected given previous studies (Cross et al. 1984a; Gregory et al. 1994a) which found backfat to be 11 to 12 mm in Hereford and 4 to 6 mm in Simmental when slaughtered after constant time on feed at approximately 15 mo of age. Similar (P = 0.787) carcass weights in Hereford across diets (Table 4) agree with Tatum et al. (1988) for medium frame cattle, but is in contrast to differences in carcass weight between diets found with Angus (Arthaud et al. 1977; Burson et al. 1980). Heavier (P = 0.001) carcass weights in Simmental fed the low-energy diet are due to increased time on feed needed by the late-maturing Continental breed to attain a constant backfat endpoint and is consistent with a similar trend found with Charolais- steers (Rompala et al. 1984). Heavier (P = 0.001) carcasses in Simmental vs. Hereford are consistent with breed differences found with Hereford and Simmental slaughtered on a constant age basis (Cross et al. 1984a; Gregory et al. 1994a) or with early and late fattening cattle slaughtered at constant finish (Jones et al. 1984). The experiment was designed such that grade fat should have been constant across all treatments. Operator problems encountered in evaluating ultrasound images for determining cattle for slaughter are responsible for the between-breed difference (P < 0.01) in grade fat. Longissimus muscle area was not affected by dietary energy content agreeing with previous studies (Burson et al. 1980; Rompala et al. 1984; Crouse et al. 1985). Breed differences (Table 4) in LMA are similar to previous findings (Cross et al. 1984a; Gregory et al. 1994a). Most carcass traits (grade fat, LMA, yields of lean, fat, and bone) were similar (P > 0.200) within breeds agreeing with previous work (Prior et al. 1977; Rompala et al. 1984a; Tatum et al. 1988). Breed differences (P = 0.001) in lean and fat yield in the present study are consistent with the work of Gregory et al. (1994a). However, non-significant breed differences in

7 MANDELL ET AL. BREED AND DIET DIFFERENCES ON BEEF QUALITY 539 Table 5. Breed of dietary energy content (ME basis) on within- and between-breed differences in shear force and palatability attributes for Hereford and Simmental steers z,y bone yield disagrees with past studies. Gregory et al. (1994a) found increased bone in Hereford relative to Simmental when slaughtered at constant times on feed, while Jones et al. (1984) found increased bone in small vs. large rotational steers when data were adjusted to a constant proportion of subcutaneous fat. Agriculture and Agri-Food Canada lean yield within breeds was similar (P > 0.10) while breed differences (P = 0.001) in Agriculture and Agri-Food Canada lean yield are supported by between-breed differences in grade fat, LMA, and lean yield from carcass dissection (Table 4). Agriculture and Agri-Food Canada marbling score was similar (P > 0.10) both within and between breeds and contrasts with previous work (Cross et al. 1984a; Gregory et al. 1994b) where marbling scores in Hereford exceeded Simmental when cattle were slaughtered at a constant age. Intramuscular fat content was similar (P > 0.10) across all treatments in contrast to breed differences found with Angus and Limousin cattle when slaughtered at a common backfat endpoint (Vanderwert et al. 1985). Shackleford et al. (1994) found greater concentrations of intramuscular fat in Hereford vs. Simmental when cattle were slaughtered on an age-constant basis. Breed differences in days on feed are probably responsible for the absence of breed differences in marbling and intramuscular fat content for the present study Breed Hereford Simmental Probability of larger F-ratio for contrasts v Covariates in final Low High Low High Within Within Hereford vs. Item model x,w energy energy energy energy SE Hereford Simmental Simmental Warner-Bratzler shear N/A force (cooked meat), N Softness AGE** Initial juiciness AGE(d-b) ; LOSS**; LOSS LOSS** Tenderness IMFAT**; SARC* Beef flavour AGE**; IMFAT(d-b)* Juiciness LOSS**; LOSS LOSS** Chewiness AGE ; FAT*; TCOL(d-b)*; TCOL TCOL(d-b) ; SOLCOL* z Cattle were fed either a low- or high-energy ration formulated on a within-breed basis. The low-energy ration for Herefords included a 2.52 Mcal kg 1 ME diet during a 90-d growing phase followed by a 2.69 Mcal kg 1 ME diet until cattle achieved their targetted slaughter endpoint. The high-energy ration for Herefords also served as the low-energy ration for Simmentals and included a 2.69 Mcal kg 1 ME diet during a 90-d growing phase followed by a 2.81 Mcal kg 1 ME diet until cattle achieved their targetted slaughter endpoint. The high-energy ration for Simmentals included a 2.81 Mcal kg 1 ME diet during a 90- d growing phase followed by a 2.86 Mcal kg 1 ME diet until cattle achieved their targetted slaughter endpoint. y Palatability attributes include: softness (0 = very firm to 10 = very soft) = the force required to compress a sample with the molar teeth; initial juiciness (0 = very dry to 10 = very juicy) = the amount of moisture released from the meat after five chews; beef flavour (0 = very weak to 10 = very strong) = the amount of full meaty flavour present after eight chews; tenderness (0 = very tough to 10 = very tender) = the force required to chew the sample using three additional chews after initial compression; juiciness ( 0 = very dry to 10 = very juicy) = the amount of saliva absorbed during the mastication process; rate of breakdown (0 = very slow to 10 = very rapid) = the rate at which the sample disintegrates during the mastication process in preparation for swallowing; chewiness ( 0 = very chewy to 10 = not chewy) = the force needed to chew the sample completely for swallowing. x Covariates in final model after model building (described in Table 2) include: AGE = age at start of test (d); FAT = mm grade fat; IMFAT = intramuscular fat (g kg 1 ), SOLCOL = soluble collagen content (g kg 1 ); N/A = not applicable as no covariates remaining in final model. Covariates followed by (d-b) indicate the covariate nested within diet-breed combination. w Probability of significance for covariates in final model are indicated by either (P < 0.10), * (P < 0.05) or ** (P < 0.01). v Where the final model includes covariates, comparisons of diet-breed combinations were evaluated at covariate means specific to each diet-breed combination. based on findings by Gregory et al. (1994b). In the present study, similar LM fat deposition was found between breeds when days on feed differed by approximately 35 d. In contrast, Gregory et al. (1994b) found that Simmental required 339 vs. 200 d with Hereford to achieve longissimus fat content of 4.5%, similar to LM fat deposition in the present trial. Sarcomere length did not differ (P > 0.10) across or within breeds. Non-significant differences in these traits were expected given the nature of the diets fed and the finish achieved by steers. Total collagen content did not differ (P > 0.10) within breeds, which is supported by the absence of dietary energy influencing total collagen content in previous studies (Wu et al. 1981; Rompala and Jones 1984; Crouse et al. 1985; Dikeman et al. 1986). Simmental had lower (P = 0.061) amounts of total collagen than their Hereford counterparts, which contrasts with non-significant breed differences in total collagen comparing Hereford vs. Simmental (Cross et al. 1984b) and Angus vs. Limousin (Vanderwert et al. 1986). Greater (P < 0.084) concentrations of soluble collagen in cattle fed the higher energy diets agrees with past studies (Wu et al. 1981; Rompala and Jones 1984; Crouse et al. 1985). In contrast to total collagen, soluble collagen did not differ (P > 0.10) between breeds, disagreeing with the work of Cross et al. (1984b) where soluble collagen content of Simmental exceeded Hereford.

8 540 CANADIAN JOURNAL OF ANIMAL SCIENCE Dietary energy content did not affect Warner-Bratzler shear of cooked meat for Hereford. Lower (P= 0.043) shears were found for Simmental fed the low-energy diet relative to steers fed the high-energy diet. This is supported by Dikeman et al. (1986) where shears were lower in Angus bull calves fed a low-energy diet. In contrast, Crouse et al. (1985) did not find any effect of dietary energy content on shear force. The absence of a between-breed difference in shear is supported by Cross et al. (1984a) and Shackleford et al. (1994) in studies where cattle were slaughtered on a constant age basis. With the exception of juiciness, there were no differences in palatability attributes within breeds or between breeds (Table 5). Previous studies (Dolezal et al. 1982; Tatum et al. 1982; Smith et al. 1983) did not find any differences in juiciness, amount of connective tissue, myofibrillar and overall tenderness, flavour desirability, and overall desirability with the range of grade fat and intramuscular fat content (Table 4) found in the present study. Several studies (Prior et al. 1977; Burson et al. 1980; Dikeman et al. 1986; Miller et al. 1987) found no effect of dietary energy content on palatability attributes of beef. In contrast, Crouse et al. (1985) found Angus and Simmental cattle fed a high-energy diet to have lower taste panel scores for ease of fragmentation, amount of connective tissue, tenderness, and flavour intensity, but similar scores for juiciness to beef from cattle fed a low-energy diet. Cross et al. (1984a) found beef from Hereford bulls and steers to be similar in flavour, tenderness, ease of fragmentation, and amount of connective tissue versus beef from Simmental while Hereford beef was judged to be juicier than Simmental beef as is the case for this study. Others (Crouse et al. 1985; Gullett et al. 1985) have found no differences in palatability attributes between early and late fattening breed types. In conclusion, use of high-energy diets improved ADG and feed efficiency and decreased days on feed for both Hereford and Simmental. Dry matter intake increased with the high-energy diet for Hereford via incorporation of grain from 5 to 28% of the diet. Hereford outgained and were more efficient in converting feed to gain than Simmental. These breed differences were most likely due to using backfat as a slaughter endpoint with the early fattening Hereford, and the late fattening Simmental. Use of high-energy diets generally did not affect carcass and chemical composition or palatability attributes. This is important for both producers and consumers in that minimizing feed costs may not necessarily compromise beef quality for consumers. Breed differences in carcass composition were as expected due to the different fattening characteristics of the two breeds used. The absence of breed differences in intramuscular fat content, shear, and palatability attributes is most likely due to use of similar backfat endpoints for the two breeds. Feed costs in finishing the late fattening Simmental to a common backfat endpoint as the Hereford may not be profitable to the producer. Further research is warranted to evaluate breed differences in carcass and meat quality and determine genetic progress for improving the fattening characteristics of Continental breeds such as Simmental to decrease days to market. 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