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or concentrates
Meat Science 57 (2001) 379±386
www.elsevier.com/locate/meatsci
The eating quality of meat of steers fed grass and/or concentrates P. French a,b, E. G. O'Riordan a, F. J. Monahan b, P. J. Carey b, M. T. Mooney c, D. J. Troy c, A. P. Moloney a,c,* a Teagasc, Grange Research Centre, Dunsany, Co. Meath, Ireland Faculty of Agriculture, University College Dublin, Bel®eld, Dublin 4, Ireland c Teagasc, The National Food Centre, Dunsinea, Castleknock, Dublin 15, Ireland b
Received 7 March 2000; received in revised form 26 August 2000; accepted 2 September 2000
Abstract The objective was to determine, relative to animals expressing their full potential for carcass growth, the impact on meat quality of increasing carcass growth of grazing steers by supplementing with concentrates or by increasing grass supply. Sixty-six continental (Limousin and Charolais) crossbred steers (567 kg) were assigned to one of six diets: (1) 18 kg grass dry matter (DM); (2) 18 kg grass DM grass and 2.5 kg concentrate; (3) 18 kg grass DM and 5 kg concentrate; (4) 6 kg grass DM and 5 kg concentrate; (5) 12 kg grass DM and 2.5 kg concentrate; or (6) concentrates daily. Animals were slaughtered after an average of 95 days. Samples of the M. longissmus dorsi (LD) were collected at the 8±9th rib interface and subjected to sensory analysis and to other assessments of quality following 2, 7, or 14 days aging. Carcass weight gain averaged 360, 631, 727, 617, 551 and 809 g/day for treatments 1 to 6, respectively. There was no dierence between diets for colour, Warner±Bratzler shear force (WBSF) or any sensory attribute of the LD. WBSF was negatively correlated with (P<0.05) carcass growth rate (ÿ0.31) but only a small proportion of the variation in meat quality between animals could be attributed to diet pre-slaughter or carcass fatness. It is concluded that high carcass growth can be achieved on a grass-based diet without a deleterious eect on meat quality. # 2001 Elsevier Science Ltd. All rights reserved. Keywords: Grass; Concentrates; Meat quality
1. Introduction Feed costs are a major proportion of total variable costs in most beef systems and eciently managed grazed grass can be the cheapest feedstu in temperate climates (O'Riordan & O'Kiely, 1996). The value of beef from grass-®nished cattle is often discounted compared with concentrate-fed beef because of perceived dierences in tenderness (Chrystall, 1994), colour (Baardseth, Skrede, Naes, Thomassen, Iversen, & Kaaber, 1988), juiciness (Hutchings & Illford, 1988) and ¯avour (Melton, 1990). There is evidence, particularly from North American beef production systems, that concentrate-fed animals produce more tender and better-¯avored meat than forage-fed animals (Larick et al., 1987; Medeiros, Field, Menkhaus, & Russell, 1987). However, in many of these experiments, dietary eects were confounded by dierences in animal age, pre-slaughter growth rate or * Corresponding author. Fax: +353-46-26154. E-mail address: [email protected] (A.P. Moloney).
carcass weight/fatness at slaughter (e.g. Bowling, Smith, Carpenter, Dutson, & Oliver, 1977; Harrison, Smith, Allen, Hunt, Kastner, & Kropf, 1978) factors that in¯uence meat quality, in particular tenderness and ¯avour (Spanier, McMillian, & Miller, 1990). French et al. (2000a) showed that when steers had a similar mean rate of carcass growth, pre-slaughter diet per se (autumn grazed grass, concentrates or grass silage) did not aect the sensory perception of meat quality. In that study, the rate of carcass growth was restricted to that of animals fed unsupplemented grass and was less than the genetic potential of the animals used. To maximise pro®tability, the growth potential of the animals should be achieved with maximum inclusion of grazed grass but without an impairment of sensory quality. We hypothesised that inclusion of grass in high-energy ®nishing diets for beef cattle would have little eect on meat quality. The objective of this study therefore, was to measure the quality of meat from cattle ®nished on grass alone, on concentrates oered ad libitum (expressing full genetic potential for growth) or on various combinations of both.
0309-1740/01/$ - see front matter # 2001 Elsevier Science Ltd. All rights reserved. PII: S0309-1740(00)00115-7
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2. Materials and methods 2.1. Experimental design and animal management From a larger study concerned with strategies for beef production from autumn grass (French, O'Riordan, O'Kiely, Carey, & Moloney, 2000b), six treatment groups were chosen for assessment of meat composition and eating quality. The six groups (11 continental [Limousin and Charolais] crossbred steers per group: initial body weight 567 [S.D.=34.1] kg) were oered, per animal daily, (1) 18 kg grass dry matter (DM), (2) 18 kg grass DM and 2.5 kg concentrate, (3) 18 kg grass DM and 5 kg concentrate, (4) 6 kg grass DM and 5 kg concentrate, (5) 12 kg grass DM and 2.5 kg concentrate or (6) concentrates ad-libitum+1 kg straw. Animals were blocked on descending bodyweight into blocks of 6 and within block assigned at random to treatment. Groups 1 to 5 inclusive, rotationally grazed a predominantly perennial ryegrass pasture. Daily grass allowances were achieved by varying the size of the grazing area. Animals were oered a fresh allowance daily and did not have access to the previous days allowance. Pre-grazing grass mass was estimated by cutting four strips (each 1.25 m; 4 cm stubble height) three times weekly from the areas to be grazed by each group. Grass intake was estimated using the n-alkane technique of Mayes, Lamb, and Colgrove (1986) as modi®ed by Dillon and Stakelum (1988). Thus, animals were dosed with gelatine capsules containing 500 mg dotriacontane and faeces samples collected twice daily. A pelleted concentrate, which was a mixture of ground barley (0.29), unmolassed beet pulp (0.29), maize gluten (0.29), soya-bean meal (0.05), molasses (0.05) and mineral/vitamin mix (0.03), was oered individually to all animals receiving supplementary concentrates. The appropriate animals were restrained individually in a purpose built mobile feeder in the ®eld and oered 2.5 kg concentrates per head at 08:00h, before being allocated a fresh daily grass allowance. Animals remained restrained until the concentrates were consumed (approximately 20 min). Animals receiving 5 kg concentrates daily were restrained and oered a further 2.5 kg concentrates at 16:00h. Animals oered concentrates and straw were accommodated in a slatted ¯oor shed and oered their diets individually through electronically controlled gates. The average duration of the feeding period was 95 days from 22 August. 2.2. Post-slaughter carcass measurements and sampling Animals from the four heaviest blocks were slaughtered after 89 days, from the next four blocks after 95 days and from the remaining three blocks after 101 days. On the day of slaughter, animals were weighed, mixed during loading onto one truck, transported 120
km to a commercial slaughter facility and slaughtered at random within 6 h of removal from Grange Research Centre. After slaughter, cold carcass weight (hot carcass weight0.98) was recorded. Carcass weight gain was estimated as the dierence between ®nal carcass weight and 55% of initial liveweight The carcasses were classi®ed for fat score (1=leanest and 5=fattest) using the EU Beef Carcass Classi®cation Scheme. The weight of kidney and channel fat (KCF) on each carcass was also recorded and expressed as a proportion of carcass weight. The pH of the M. longissimus dorsi (LD) was measured at hourly intervals for 8 h and at 24 h and 48 h post-mortem by making a scalpel incision at the 5th/6th rib and inserting a glass electrode (Model EC2010-11, Amargruss Electrodes Ltd., Castlebar, Co. Mayo, Ireland) attached to a portable pH meter (Model no. 250 A, Orion Research Inc., Boston, USA) approximately 2.5 cm into the muscle. During each of the second and third slaughter times, the temperature of the LD muscle was measured in 3 randomly chosen carcasses/treatment. Temperature probes were inserted approximately 6 cm into the LD muscle immediately anterior to the 9th rib and temperature was recorded at 15 min intervals up to 24 h post-mortem using a data logger (Grant Squirrel Series 1250). The sides were cold-boned at 24 h post-mortem. Samples of LD were vacuum packed (SuperVac GK-166T) and aged at 4 C for 2, 7 or 14 days post-mortem. Steaks, 2.5 cm thick, were cut after 2 days for compositional analysis and after 2, 7 and 14 d post-mortem, for sensory analysis and Warner±Bratzler shear force (WBSF) measurements. These were vacuum packed and frozen at ÿ30 C for subsequent analysis. 2.3. Measurements on fresh meat Steaks (2.5 cm thick) were cut at 14 days post-mortem for colour measurements according to the procedure of Strange, Benedict, Gugger, Metzger, and Swift (1974). Freshly cut samples were wrapped in an oxygen permeable PVC wrap and allowed to bloom at 4 C for 3 h. The Hunter `l', `a' and `b' value of each sample was then measured using a Hunter lab Ultra Scan XE colorimeter with Universal Software Version 2.2.2 (Hunter Associates Laboratory, Inc., 11491 Sunset Hills Road, Reston, Virginia, USA). Steaks (2.5 cm thick) were cut at 2 days post-mortem for measurement of drip-loss according to the procedure of Honikel (1987) and sarcomere length according to the procedure of Cross, West and Dutson (1980). 2.4. Measurements on pre-frozen meat Frozen vacuum-packed steaks were thawed overnight at ambient temperature before cooking for sensory and
P. French et al. / Meat Science 57 (2001) 379±386
WBSF analysis and mincing for compositional analysis. Sensory analysis was performed by an eight member, inhouse trained panel on steaks grilled to an internal temperature of 70 C, according to the American Meat Science Association Guidelines (AMSA, 1978). Panelists were asked to assess the samples for the following attributes: tenderness (scale 1±8; 1=extremely tough, 8=extremely tender) moistness/juiciness (scale 1±8; 1=extremely dry, 8=extremely juicy). overall ¯avour (scale 1±6; 1=very poor, 6=very good) residual chewiness (scale 1±6; 1=not chewy, 6=extremely chewy) overall texture (scale 1±6; 1=very poor, 6=very good) overall acceptability (scale 1±6; 1=not acceptable 6=extremely acceptable). Warner±Bratzler shear force was measured according to the procedure of Shackelford, Koohmaraie, Cundi, Gregory, Rohrer, and Savell (1991). Steaks (2.5 cm) were cooked in retortable vacuum pack bags to an internal temperature of 70 C, by immersing in a water bath (Model Y38, Grant Instruments Ltd.) at 80 C. The internal temperature of the steaks was measured using a Hanna Foodcare digital thermometer (HI 9041). Five cores (1.25 cm diameter) were cut from the steaks parallel to the direction of the muscle ®bres and sheared using an Instron Universal testing machine equipped with a Warner±Bratzler shearing device. The crosshead speed was 5 cm/min. Instron Series IX Automated Materials Testing System software for Windows (Instron Corporation, High Wycombe, Bucks, UK) was employed in the analysis. 2.5. Chemical analyses Intra-muscular fat and moisture concentrations of thawed minced LD samples were determined using an automated, integrated microwave moisture and methylene chloride fat extraction method (Bostian, Fish, Webb, & Arey, 1985) on a CEM moisture/solids analyser (Model AVC 80, CEM corp., Matthews, NC, USA). Protein was determined by the method of Sweeney and Rexroad (1987) using a LECO protein analyser (LECO FP428, LECO Corp., St. Joseph, MI, USA). The dotriacontane and tritriacontane concentrations of the grass, faeces and concentrate were measured according to Vulich, Hanrahan, and Crowley (1995). All other feed analyses were carried out as previously described by Moloney and O'Kiely (1995) 2.6. Statistical analyses Variables that were measured at a single time point were subjected to analysis of variance using a model
381
that had block and treatment as main eects. The LD temperature data at various times post-mortem were logarithmically transformed and linear regression was used to derive a cooling constant for each carcass. These values were then analysed using a model that had slaughter day and treatment as main eects. Where a signi®cant eect of treatment was detected, means were separated using the least signi®cant dierence procedure. Variables measured 2, 7 and 14 days post slaughter were subjected to analysis of variance using a model that had treatment as a main eect and days post slaughter as a split-plot on treatment. The pH data were subjected to analysis of variance using a model that had treatment as a main eect and hours post slaughter as a split-plot on treatment. Relationships between variables were examined by correlation analysis. 3. Results The chemical composition of the dietary ingredients is shown in Table 1. Animals oered grass only (treatment 1) had higher (P<0.05) grass intake and lower (P>0.05) carcass weight and carcass gain than all other treatments (Table 2). Animals oered concentrates ad libitum (treatment 6) consumed 13.33 kg DM daily and had higher (P<0.05) carcass fat scores and LD fat concentration and lower (P<0.05) LD moisture concentration than all other treatments. They also had the highest (P<0.05) carcass gain and carcass weight, other than treatment 3 from which they did not dier signi®cantly. There was an interaction (P<0.001) between time post-slaughter and diet pre-slaughter for LD pH (Fig. 1). Thus, LD from animals oered grass only had higher (P<0.05) pH at 4, 5, 6, 7 and 8 h post-slaughter than all other treatments. The LD from animals oered the high grass and high concentrate allowance (treatment 3) had lower (P<0.05) pH at 6, 7 and 8 h postslaughter than all other treatments. There was no eect of diet on pH 24 h and 48 h post slaughter. The LD from animals oered the low grass and high concentrate allowance (treatment 4) or concentrates ad libitum (treatment 6) cooled more slowly than LD from all other animals. Table 1 The chemical composition of grass and concentrates
Dry matter (DM) (g/kg) Crude protein (g/kg DM) Ash (g/kg DM) Dry matter digestibility (g/kg ) Crude ®bre (g/kg DM) Oil (g/kg DM)
Grass
Concentrate
198 225 125 738 287 29
872 143 48 843 101 24
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Table 2 The eect of diet on grass intake, carcass characteristics and M.l. dorsi composition Dieta
1
2
3
4
5
6
S.E.
Signi®canceb
Grass dry matter (DM) intake (kg/day) Concentrate DM intake (kg/day) Carcass weight (kg) Carcass gain/day (g) Fat scorec KCFd/carcass (g/kg) Intra-muscular fat (g/kg muscle) Ash (g/kg muscle) Moisture (g/kg muscle) Protein (g/kg muscle)
10.67d 0 330e 360e 4.03e 24 23 12 737 225
7.72g 2.25 355g,h 631g,h 3.97e 26 24 17 736 227
7.78g 4.50 363g,f 727g,f 4.14e 28 29 12 733 224
4.49e 4.50 352g,h 617g,h 3.79e 25 23 12 735 226
6.78f 2.25 348h 551h 4.15e 22 25 12 734 228
± 13.3 371f 809f 4.64f 29 44 12 717 226
0.368 ± 4.9 39.2 0.133 2.3 3.6 0.4 3.8 2.2
*** ± *** *** * NS *** NS ** NS
a Steers oered (1) 18 kg grass DM, (2) 18 kg grass DM and 2.5 kg concentrate, (3) 18 kg grass DM and 5 kg concentrate, (4) 6 kg grass DM and 5 kg concentrate, (5) 12 kg grass DM and 2.5 kg concentrate and (6) concentrates ad-libitum. b Means in rows without a common superscript are signi®cantly dierent (P< 0.05). c 1=leanest 5=fattest. d KCF, Kidney plus channel fat.
Fig. 1. The eect of diet and time post-mortem on muscle pH. (^) 18 kg grass dry matter (DM), (&) 18 kg grass DM and 2.5 kg concentrate, (~) 18 kg grass DM and 5 kg concentrate, () 6 kg grass DM and 5 kg concentrate, () 12 kg grass DM and 2.5 kg concentrate and (*) concentrates adlibitum. Diettime post-mortem s.e.=0.038.
There was no eect of pre-slaughter diet on LD colour, sarcomere length or drip loss (Table 3). An increase in aging time post mortem decreased (P<0.001) WBSF value of the LD and increased (P40.05) tenderness, texture, ¯avour, juiciness, chewiness and acceptability scores and cooking loss (Table 4). There was no eect of treatment and no interaction between treatment and ageing time post mortem for any of these variables. Correlations between live animal/carcass variables and meat quality attributes are presented in Table 5.
The LD pH at 4, 5, 6 and 7 h post-mortem was negatively correlated with carcass gain and the LD pH at 8 h post-mortem positively correlated with carcass gain. The LD pH at 1, 2, 3, 5 and 8 h post mortem was positively correlated with carcass fat score. The proportion of grass in the diet was not correlated with any of the meat quality variables measured. In contrast, carcass growth rate was negatively correlated (P<0.05) with WBSF and LD pH at 4, 5, 6 and 7 h post-mortem.
P. French et al. / Meat Science 57 (2001) 379±386
383
Table 3 The eect of diet on M.l dorsi characteristics Dieta
1
Cooling rate (hÿ1) Muscle colour ``L'' ``a'' ``b'' Sarcomere length (m m) Drip loss (g/100 g) pH (48 h)
2 0.040c
3
0.043c
34.3 13.9 7.3 1.68 2.73 5.54
4
0.043c
33.6 14.1 7.4 1.66 2.65 5.47
5 0.031b
34.5 14.5 7.6 1.76 2.11 5.53
6
0.049c
33.9 14.5 7.4 1.70 2.35 5.52
34.2 14.4 7.6 1.73 2.51 5.53
0.032b 34.9 14.6 7.7 1.78 2.13 5.49
S.E.
Signi®cance
0.0036
**
0.43 0.41 0.29 0.038 0.271 0.026
NS NS NS NS NS NS
a Steers oered (1) 18 kg grass dry matter (DM), (2) 18 kg grass DM and 2.5 kg concentrate, (3) 18 kg grass DM and 5 kg concentrate, (4) 6 kg grass DM and 5 kg concentrate, (5) 12 kg grass DM and 2.5 kg concentrate and (6) concentrates ad-libitum. b Means in rows without a common superscript are signi®cantly dierent (P<0.05).
Table 4 The eect of diet and ageing time post-mortem on WBSFa and taste panel assessment of M.l dorsi Dietb (D)
1
Days aged (T) WBSF (kg) % Cook loss Tendernessc Textured Flavoure Juicinessf Chewinessg Accepabilityh
2
2 7
14
2
3 7
14
2
4 7
14
2
5 7
14
6 2
7
14
2
S.E. Signi®cance 7
14
D
T DxT
8.0 5.9 4.8 7.5 6.1 4.1 6.6 5.2 4.2 7.0 6.5 4.3 6.4 5.7 4.0 6.1 4.9 3.9 0.43 NS *** 30.0 29.4 31.3 29.5 30.3 31.4 28.7 28.1 29.9 29.3 29.7 30.3 29.1 30.9 30.8 29.8 28.9 30.6 0.69 NS ** 3.5 4.8 5.2 4.2 4.7 5.6 4.5 5.2 5.8 4.0 5.0 5.7 4.8 4.7 5.7 4.4 5.2 6.2 0.26 NS *** 2.9 3.4 3.6 3.2 3.3 3.7 3.3 3.4 3.7 3.1 3.5 3.7 3.2 3.5 3.9 3.3 3.5 3.8 0.13 NS *** 3.5 3.7 3.8 3.6 3.5 3.8 3.7 3.8 3.8 3.8 3.7 3.8 3.6 3.9 3.9 3.7 3.8 3.9 0.10 NS ** 4.8 4.6 5.3 5.2 4.6 4.6 5.3 4.3 4.8 5.2 4.7 5.2 4.7 4.7 4.9 5.2 5.1 5.0 0.24 NS * 4.2 3.5 3.1 3.7 3.5 3.0 3.7 3.2 2.8 4.0 3.3 3.0 3.6 3.6 3.1 3.9 3.3 2.7 0.15 NS *** 3.2 3.2 3.7 3.1 3.6 3.8 3.4 3.6 3.8 2.8 3.4 3.6 3.2 3.4 3.9 3.3 3.6 3.9 0.15 NS ***
NS NS NS NS NS NS NS NS
a
Warner±Bratzler shear force. Steers oered (1) 18 kg grass dry matter (DM), (2) 18 kg grass DM and 2.5 kg concentrate, (3) 18 kg grass DM and 5 kg concentrate, (4) 6 kg grass DM and 5 kg concentrate, (5) 12 kg grass DM and 2.5 kg concentrate and (6) concentrates ad-libitum. c 1=extremely tough, 8=extremely tender. d 1=very poor, 6=very good. e 1=very poor, 6=very good. f 1=extremely dry, 8=extremely juicy. g 1=not chewy, 6=extremely chewy. h 1=not acceptable, 6=extremely acceptable. b
4. Discussion The composition of the grass was typical of grass harvested in autumn with low digestibility and high crude protein (CP) concentration relative to that reported for grass harvested earlier in the grazing season (Munro & Walters, 1987). The concentrate had higher digestibility and lower CP concentration than the grazed grass. Assuming that the growth potential of the cattle was realised by the ad libitum concentrate group (treatment 6), grazed grass, at an allowance of 30 g DM/kg bodyweight (treatment 1), only supported 0.45 of the potential carcass growth. However, animals oered treatment 3 achieved 0.90 of potential carcass growth but 630 g/kg of the diet was grazed grass. While the grass only treatment resulted in a slower rate of pH decline, LD pH at 24 h post slaughter was similar for all dietary treatments. Meat colour, tenderness, ¯avour, juiciness and shelf life, are in¯uenced by pH (Hofmann, 1988). Muir, Beaker, and Brown (1998)
indicated that grass-fed steers had higher ultimate pH values than grain-fed steers and suggested that grass-fed steers were more susceptible to pre-slaughter stress than grain-fed steers as the latter would be more accustomed to penning and handling and would be less likely to suer glycogen depletion in the factory pre-slaughter. In the present study, all animals were accustomed to handling and penning due to frequent weighing (French et al., 2000b). Bidner, Schupp, Montgomery, and Carpenter (1981), Bidner et al. (1986), Morris, Purchas, and Burnham (1997) and Wander-stock and Miller (1948), also observed similar ultimate muscle pH in grass and grain-®nished cattle. Bidner et al. (1981) and Reagan, Carpenter, Bauer, and Lowrey (1977) reported darker lean in forage-fed animals in comparison with concentrate-fed animals. Bidner et al. (1986) attributed the darker lean in foragefed animals to higher myoglobin concentrations. The haem pigment, myoglobin, is mainly responsible for the colour of meat. Varnam and Sutherland (1995)
384
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Table 5 Correlations of meat quality attributes with live animal/carcass variables Grass proportion
Drip loss WBSF 14 daysa Colour L a b Tendernessb Juicinessb Flavourb Textureb Chewinessb Acceptabilityb
0.16 0.22 ÿ0.15 ÿ0.11 ÿ0.11 ÿ0.23 0.07 ÿ0.05 ÿ0.11 0.18 ÿ0.16
Carcass weight
Carcass gain
ÿ0.02 ÿ0.05
ÿ0.01 ÿ0.31*
0.12 ÿ0.14 ÿ0.28* ÿ0.03 ÿ0.09 ÿ0.03 0.00 0.12 ÿ0.04
0.32* 0.20 0.18 0.16 ÿ0.13 ÿ0.03 0.07 ÿ0.10 0.11
Longissimus dorsi pH (hours post-mortem) 1 ÿ0.07 0.24 2 0.08 ÿ0.08 3 0.09 ÿ0.05 4 0.13 ÿ0.11 5 0.13 0.00 6 0.15 ÿ0.14 7 0.12 ÿ0.14 8 0.15 0.03 24 0.10 0.09 48 0.10 0.06 a b
0.04 ÿ0.19 ÿ0.22 ÿ0.30* ÿ0.25* ÿ0.36** ÿ0.39** 0.32* ÿ0.17 ÿ0.16
Carcass fat score
Internal fat weight
Internal fat carcass
0.09 0.11
0.13 ÿ0.13
ÿ0.03 ÿ0.18 ÿ0.32* ÿ0.14 0.04 ÿ0.11 ÿ0.09 0.29* ÿ0.17 0.30* 0.25* 0.26* 0.21 0.25* 0.19 0.22 0.32* 0.10 0.24
Longissimus composition Moisture (%)
Protein (%)
Lipid (%)
Ash (%)
0.14 ÿ0.14
0.09 0.02
0.15 0.18
ÿ0.17 ÿ0.12
ÿ0.03 0.16
ÿ0.04 ÿ0.12 ÿ0.22 ÿ0.04 0.04 0.13 ÿ0.03 0.03 ÿ0.02
ÿ0.05 ÿ0.08 ÿ0.16 ÿ0.05 0.05 0.14 ÿ0.03 0.01 ÿ0.02
ÿ0.02 ÿ0.14 ÿ0.12 ÿ0.13 ÿ0.04 ÿ0.15 ÿ0.03 0.03 ÿ0.07
ÿ0.23 ÿ0.05 ÿ0.09 ÿ0.14 0.04 0.04 ÿ0.04 0.18 ÿ0.04
0.07 0.17 0.15 0.15 ÿ0.01 0.17 0.00 ÿ0.10 0.05
0.09 0.05 0.05 0.00 0.09 ÿ0.22 ÿ0.06 0.00 ÿ0.09
0.41** 0.18 0.23 0.17 0.17 0.14 0.20 0.18 ÿ0.02 0.16
0.38* 0.20 0.24 0.19 0.17 0.16 0.23 0.18 ÿ0.05 0.14
ÿ0.01 ÿ0.05 ÿ0.03 ÿ0.06 ÿ0.02 0.01 ÿ0.05 ÿ0.01 0.12 0.12
ÿ0.03 ÿ0.06 0.00 0.01 ÿ0.06 ÿ0.01 0.02 0.08 0.08 0.00
0.03 0.08 0.07 0.08 0.07 0.04 0.05 ÿ0.04 ÿ0.11 ÿ0.10
ÿ0.13 ÿ0.05 ÿ0.09 0.00 0.02 ÿ0.09 ÿ0.10 0.05 ÿ0.06 ÿ0.04
Warner±Bratzler shear force. After 14 days ageing.
hypothesized that grass-fed animals have more muscle myoglobin, due to more activity pre-slaughter than their feedlot counterparts. However, the controlled manner in which the grazing animals were managed pre-slaughter in the current study should have resulted in similar levels of activity as those animals oered concentrates ad libitum. Improved lean colour is sometimes associated with increased intramuscular fat concentration (Muir et al., 1998) but no such relationship was observed in the present study. It has been proposed that early post mortem pH in¯uences the activity of endogenous enzyme systems and, thus, aects ultimate meat tenderness (O'Halloran, Troy, & Buckley, 1996). Marsh, Ringkob, Russell, Swartz, and Pagel (1987) used dierent forms of electrical stimulation and various cooling rates to produce a wide range of early post-mortem glycolytic rates and concluded that tenderness was highest when glycolysis proceeded at a rate which resulted in a pH at 3 h post mortem (pH3) of 6.1. In the present study, WBSF after 14 days ageing was most highly correlated with the pH at 8 h post mortem (r=0.45) and the corresponding sensory perception of tenderness with pH at 48 h postmortem (r=ÿ0.42). The in¯uence of carcass fatness on LD pH seen in the present study may have contributed to the dierence between this and other studies with
respect to the relationship between LD pH and tenderness. The coecient of variation for tenderness score and WBSF value within the population of animals used in this study was approximately 25 and 30% respectively. This re¯ects the intrinsic variability in the animals used but may also re¯ect the procedures used. Forage-®nishing of cattle has been shown to decrease tenderness of the meat when compared to grain-®nishing (Mitchell, Reed, & Rogers, 1991; Rumsey, Bond, Berry, Hammond, & Dinius, 1987). This may re¯ect lighter and/or leaner carcasses from forage-®nished cattle since numerous authors (Bowling, Smith, Carpenter, Dutson, & Oliver, 1977; Bowling et al., 1978; Dolezal, Smith, Savel, & Carpenter, 1982; Lochner, Kauman, & Marsh, 1980; Smith, Dutson, Hostetler, & Carpenter, 1976) have reported a positive correlation between muscle tenderness and carcass weight and fatness. Large quantities of fat insulate the carcass and slow postmortem chilling, which, in turn, improves tenderness by decreasing the extent of cold-induced muscle shortening in the LD and some other muscles. Slow post mortem chilling may also enhance post mortem muscle autolysis (Lochner et al., 1980; Smith et al., 1976). However, the correlation between carcass weight or carcass fat score (a subjective measure of subcutaneous fat) and WBSF was not signi®cant in
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this study. Moreover, there was no dierence in sarcomere length which was within the range previously observed in our laboratory (O'Halloran et al., 1996) and by others, Koohmaraie, Seideman, Schollmeyer, Dutson, and Babiker (1988). These ®ndings indicate that no treatment-induced cold-shortening occurred despite the dierences in carcass weight and rates of LD cooling observed. In this study, the cattle oered concentrates ad libitum had higher carcass gains than animals oered grass only. Cattle grown rapidly prior to slaughter have been shown in some studies to produce more tender meat than their slower growing counterparts (Aberle, Reeves, Judge, Hunsley, & Perry, 1981; Fishell, Aberle, Judge, & Perry, 1985). Cattle which grow more rapidly pre-slaughter have increased rates of protein turnover, resulting in higher concentrations of proteolytic enzymes in the carcass tissues at slaughter which, in turn, may aect collagen solubility and (or) myo®bril fragmentation (Aberle et al., 1981; Hall & Hunt, 1982; Miller, Tatum, Cross, Bowling, & Cole, 1983). While there were no treatment eects on tenderness in this study, carcass growth rate accounted for 10% of the variation in WBSF and 3% of the variation in sensory tenderness in 14 day-aged steaks. Moloney, Keane, Mooney, and Troy (2000) found no decrease in WBSF or increase in tenderness in LD from steers when pre-slaughter growth rate was increased from 0.36 to 1.08 kg/day. Oltjen, Rumsey, and Putman (1971) and Young and Kauman (1978) found dierences in juiciness between forage- and grain-fed beef. In both studies, there were dierences in carcass fatness, which paralleled the increasing juiciness scores. Muir et al. (1998) concluded that the increased juiciness of beef from grain-fed cattle relative to grass-fed cattle was due to dierences in carcass growth rate and/or fat cover. However, in this study, juiciness was poorly correlated with both intra-muscular fat content and carcass growth rate which may re¯ect the narrow range in fatness and drip loss, especially across treatments 1 to 5, in the dataset. Meat ¯avour is in¯uenced by a number of factors including animal age and genetics, pre-slaughter dietary regimen, environment, length of post-slaughter aging and the particular primal cut examined (Spainer et al., 1990). Early studies (Meyer, Thomas, Buckley, & Cole, 1960; Wander-stock & Miller, 1948) indicated lower palatability of grass-fed beef than grain-fed beef, but the carcasses in those studies diered in weight and composition. In subsequent studies, Dinius and Cross (1978), Oltjen et al. (1971) and Young and Kauman (1978) found that forage-fed beef had eating qualities equal or superior to those of grain-fed beef of similar carcass composition. Muir et al. (1998) concluded that the dierences in ¯avour and acceptability due to feed type could be accounted for by dierences in carcass fatness. The relatively narrow range in fatness in the present study and the lack of treatment on ¯avour and acceptability support this suggestion.
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5. Conclusion Although the animals used in this study were selected to be of similar breed type and age only a small proportion of the large variation in both sensory and instrumental assessments of tenderness could be attributed to diet pre-slaughter, carcass growth rate pre-slaughter and carcass fatness. A rate of carcass growth close to the genetic potential of beef cattle can be achieved on a grass-based diet without a deleterious eect on meat quality. Acknowledgements This research was part funded by grant aid under the Food Sub-Programme of the Operational Programme for Industrial Development, which is administered by the Irish Department of Agriculture and Food and supported, by national and EU funds. Technical assistance of Mr. P. Collins and Mr. F. McGovern and ®nancial support from the Agricultural Trust, I.A.W.S., Waterford Foods, Golden Vale PLC, Lakelands Co-Op, Dairygold Co-Op and N.C.F. Co-Op is gratefully acknowledged. References Aberle, E. D., Reeves, E. S., Judge, M. D., Hunsley, R. E., & Perry, T. W. (1981). Palatability and muscle characteristics of cattle with controlled weight gain: time on a high energy diet. Journal of Animal Science, 52, 757±763. AMSA (1978). Guidelines for cookery and sensory evaluation of meat. National Livestock and Meat Board, Chicago: American Meat Science Association. Baardseth, P., Skrede, G., Naes, T., Thomassen, M. S., Iversen, A., & Kaaber, L. (1988). A comparison of CIE L*A*B values obtained from two dierent instruments on several food commodities. Journal of Food Science, 53, 1737±1742. Bidner, T. D., Schupp, A. R., Montgomery, R. E., & Carpenter, J. C. (1981). Acceptability of beef ®nished on all-forage, forage-plusgrain or high energy diets. Journal of Animal Science, 53, 1181± 1187. Bidner, T. D., Schupp, A. R., Mohamad, A. B., Rumore, N. C., Montgomery, R. E., Bagley, C. P., & McMillin, K. W. (1986). Acceptability of beef from Angus±Hereford or Angus±Hereford± Brahman steers ®nished on all-forage or a high energy diet. Journal of Animal, 63, 381±387. Bostian, M. L., Fish, D. L., Webb, N. B., & Arey, J. J. (1985). Automated methods for determination of fat and moisture in meat and poultry products: collaborative study. Journal of Association of Ocial Analytical Chemists, 68, 6877±6882. Bowling, R. A., Smith, G. C., Carpenter, Z. L., Dutson, T. R., & Oliver, W. M. (1977). Comparison of forage-®nished and grain-®nished beef carcasses. Journal of Animal Science, 45, 209±215. Bowling, R. A., Riggs, J. K., Smith, G. C., Carpenter, Z. L., Reddish, R. L., & Butler, O. D. (1978). Production, carcass and palatibility characteristics of steers produced by dierent management systems. Journal of Animal Science, 46, 333±341. Cross, H. R., West, R. L., & Dutson, T. R. (1980). Comparison of methods for measuring sarcomere length in beef semitendinosus muscle. Meat Science, 5, 261±269.
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Chrystall, B. (1994). Meat texture measurement. Advances in Meat Research, 9, 316. Dillon, P., & Stakelum, G. (1988). The use of n-alkanes and chromic oxide as markers for determining feed intake, faecal output and digestibility in dairy cows. Proceedings of the 12th General Meeting of the European Grassland Federation, Dublin, 154±158. Irish Grassland Association, Galway. Dinus, A. D., & Cross, H. R. (1978). Feedlot performance, carcass characteristics and meat palatability of steers fed concentrate for short periods. Journal of Animal Science, 47, 1109±1115. Dolezal, H. G., Smith, G. C., Savell, J. W., & Carpenter, Z. L. (1982). Comparison of subcutaneous fat thickness, marbling and quality grade for predicting palatability of beef. Journal of Food Science, 47, 397±401. Fishell, V. K., Aberle, E. D., Judge, M. D., & Perry, T. W. (1985). Palatibility and muscle properties of beef as in¯uenced by preslaughter growth rate. Journal of Animal Science, 61, 151±157. French, P., O`Riordan, E. G., Monahan, F. J., Carey, P. J., Vidal, M., Mooney, M. T., Troy, D. J., & Moloney, A. P. (2000a). Meat quality of steers ®nished on autumn grass, grass silage concentratebased dets. Meat Science, 56, 173±180. French, P., O'Riordan, E. G., O'Kiely, P., Carey, P. J., & Moloney, A. P. (2000b). Intake and growth of steers oered dierent allowances of autumn grass and concentrates. Animal Science, 72, (in press). Hall, J. B., & Hunt, M. C. (1982). Collagen solubility of A-activity bovine longissimus muscle as aected by nutritional regimen. Journal of Animal Science, 55, 321±329. Harrison, A. R., Smith, M. E., Allen, D. M., Hunt, M. C., Kastner, C. L., & Kropf, D. H. (1978). Nutritional regime eects on quality and yield characteristics of beef. Journal of Animal Science, 47, 383± 388. Hofmann, K. (1988). pH. A quality criterion for meat. Fleischwirtschaft, 68, 67. Honikel, K. O. (1987). The water binding of meat. Fleischwirtschaft, 67, 1098. Hutchings, J. B., & Illford, P. J. (1988). The perception of food texture Ð the philosophy of the breakdown path. Journal of Texture Studies, 19, 103±109. Koohmaraie, M., Seideman, S. C., Schollmeyer, J. E., Dutson, T. R., & Babiker, A. S. (1988). Factors associated with the tenderness of three bovine muscles. Journal of Food Science, 53, 407±410. Larick, D. K., Hedrick, H. B., Bailey, M. E., Williams, J. E., Hancock, D. L., Garner, G. B., & Morrow, R. E. (1987). Flavor constituents of beef as in¯uenced by forage and grain-feeding. Journal of Food Science, 52, 245±251. Lochner, J. V., Kauman, R. G., & Marsh, B. B. (1980). Early post mortem cooling rate and beef tenderness. Meat Science, 4, 227±241. Mayes, R. W., Lamb, C. S., & Colgrove, P. A. (1986). The use of dosed herbage n-alkanes as markers for the determination of herbage intake. Journal of Agricultural Science, Cambridge, 107, 161±170. Marsh, B. B., Ringkob, T. P., Russell, R. L., Swartz, D. R., & Pagel, L. A. (1987). Eects of early-post-mortem glycolytic rate on beef tenderness. Meat Science, 21, 241. Medeiros, L. C., Field, R. A., Menkhaus, D. J., & Russell, W. C. (1987). Evaluation of range-grazed and concentrate-fed beef by a trained sensory panel, a household panel and a laboratory test market group. Journal of Sensory Studies, 2, 259±272. Melton, S. L. (1990). Eects of feeds on ¯avor of red meat, a review. Journal of Animal Science, 68, 4421±4435. Meyer, B., Thomas, J., Buckley, R., & Cole, J. W. (1960). The quality of grain-®nished and grass-®nished beef as aected by ripening. Food Technology, 1(1), 4. Miller, R. K., Tatum, J. D., Cross, H. R., Bowling, R. A., & Clayton, R. P. (1983). Eects of carcass maturity on collagen solubility and palatability of beef from grain ®nished steers. Journal of Food Science, 48, 484±486.
Mitchell, G. E., Reed, A. W., & Rogers, S. E. (1991). In¯uence of feeding regimen on the sensory qualities and fatty acid contents of beef steaks. Journal of Food Science, 56, 1102±1106. Moloney, A. P., Keane, M. G., Mooney, M. T., & Troy, D. J. (2000). Fat deposition and muscle tenderness in steers with dierent patterns of concentrate consumption. Irish Journal of Agricultural and Food Research, 39, (in press). Moloney, A. P., & O Kiely, P. (1995). Growth digestibility and nitrogen retention in ®nishing steers oered concentrates ad-libitum. Irish Journal of Agriculture and Food Research, 34, 115±121. Morris, S. T., Purchas, R. W., & Burnham, D. L. (1997). Short-term grain feeding and its eect on carcass and meat quality. Proceedings of the New Zealand Society of Animal Production, 57, 275±277. Muir, P. D., Beaker, J. M., & Bown, M. D. (1998). Eects of forageand grain-based feeding systems on beef quality: A review. New Zealand Journal of Agricultural Research, 41, 623±635. Munro, J. M., & Walters, R. J. K. (1987). The feeding value of grass. In J. Frame, ``Grazing'', British Grassland Society Occasional symposium, no. 19 (pp. 65±77). London: Blackwell Scienti®c Publishers. O'Halloran, G. R., Troy, D. J., & Buckley, D. J. (1996). The relationship between early post-mortem pH and the tenderisation of beef muscles. Meat Science, 45, 239±251. O'Riordan, E. G., & O'Kiely, P. (1996). Potential of Beef Production Systems Based on Grass. Irish Grassland and Animal Production Association Journal, 30, 185±217. Oltjen, R. R., Rumsey, T. S., & Putman, P. A. (1971). All-forage diets for ®nishing beef steers. Journal of Animal Science, 32, 327±333. Reagan, J. O., Carpenter, J. A., Bauer, F. T., & Lowrey, R. S. (1977). Packaging and palatability characteristics of grass and grass- grain fed beef. Journal of Animal Science, 46, 716±721. Rumsey, T. S., Bond, J., Berry, B. W., Hammond, A. C., & Dinius, D. A. (1987). Performance and carcass characteristics of feed-lot steers fed all silage diets. Nutrition Reproduction International, 35, 847±854. Shackelford, S. D., Koohmaraie, M., Cundi, L. V., Gregory, K. E., Rohrer, G. A., & Savell, J. W. (1991). Heritabilities and phenotypic and genetic correlations for bovine postigor calpastatin activity, intramuscular fat content, Warner±Bratzler shear force, retail product yield and growth rate. Journal of Animal Science, 72, 857±863. Smith, G. C., Dutson, T. R., Hostetler, R. L., & Carpenter, Z. L. (1976). Fatness, rate of chilling and tenderness of lamb. Journal of Food Science, 41, 748±756. Spanier, A. M., McMillian, K. W., & Miller, J. A. (1990). Enzyme activity levels in beef; eect of post-mortem ageing and endpoint cooking temperature. Journal of Food Science, 55, 318. Strange, E. D., Benedict, R. C., Gugger, R. E., Metzger, V. G., & Swift, C. E. (1974). Simpli®ed methodology for measuring meat colour. Journal of Food Science, 39, 988±991. Sweeney, R. A., & Rexroad, P. R. (1987). Comparison of LECO FP228 ``Nitrogen Determinator'' with AOAC copper catalyst Kjeldahl metod for crude protein. Journal of Association of Analytical Chemists, 70, 1028±1035. Varnam, A. H., & Sutherland, J. P. (1995). The colour of meat. In Meat and meat products Ð technology, chemistry and micro biology (p. 26). Chapman and Hall: London. Vulich, S. A., Hanrahan, J. P., & Crowley, B. A. (1995). Modi®cation of the analytical procedure for the determination of herbage and faecal n-alkanes used in the estimation of herbage intake. Journal of Agricultural Science, Cambridge, 124, 71±77. Wander-stock, J. J., & Miller, I. (1948). Quality and palatability of beef as aected by method of feeding and carcass grade. Food Research, 13, 291±299. Young, A. W., & Kauman, R. G. (1978). Evaluation of beef from steers fed grain, corn silage or haylage-corn silage diets. Journal of Animal Science, 46, 41±47.
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The eating quality of meat of steers fed grass and/or concentrates P. French a,b, E. G. O'Riordan a, F. J. Monahan b, P. J. Carey b, M. T. Mooney c, D. J. Troy c, A. P. Moloney a,c,* a Teagasc, Grange Research Centre, Dunsany, Co. Meath, Ireland Faculty of Agriculture, University College Dublin, Bel®eld, Dublin 4, Ireland c Teagasc, The National Food Centre, Dunsinea, Castleknock, Dublin 15, Ireland b
Received 7 March 2000; received in revised form 26 August 2000; accepted 2 September 2000
Abstract The objective was to determine, relative to animals expressing their full potential for carcass growth, the impact on meat quality of increasing carcass growth of grazing steers by supplementing with concentrates or by increasing grass supply. Sixty-six continental (Limousin and Charolais) crossbred steers (567 kg) were assigned to one of six diets: (1) 18 kg grass dry matter (DM); (2) 18 kg grass DM grass and 2.5 kg concentrate; (3) 18 kg grass DM and 5 kg concentrate; (4) 6 kg grass DM and 5 kg concentrate; (5) 12 kg grass DM and 2.5 kg concentrate; or (6) concentrates daily. Animals were slaughtered after an average of 95 days. Samples of the M. longissmus dorsi (LD) were collected at the 8±9th rib interface and subjected to sensory analysis and to other assessments of quality following 2, 7, or 14 days aging. Carcass weight gain averaged 360, 631, 727, 617, 551 and 809 g/day for treatments 1 to 6, respectively. There was no dierence between diets for colour, Warner±Bratzler shear force (WBSF) or any sensory attribute of the LD. WBSF was negatively correlated with (P<0.05) carcass growth rate (ÿ0.31) but only a small proportion of the variation in meat quality between animals could be attributed to diet pre-slaughter or carcass fatness. It is concluded that high carcass growth can be achieved on a grass-based diet without a deleterious eect on meat quality. # 2001 Elsevier Science Ltd. All rights reserved. Keywords: Grass; Concentrates; Meat quality
1. Introduction Feed costs are a major proportion of total variable costs in most beef systems and eciently managed grazed grass can be the cheapest feedstu in temperate climates (O'Riordan & O'Kiely, 1996). The value of beef from grass-®nished cattle is often discounted compared with concentrate-fed beef because of perceived dierences in tenderness (Chrystall, 1994), colour (Baardseth, Skrede, Naes, Thomassen, Iversen, & Kaaber, 1988), juiciness (Hutchings & Illford, 1988) and ¯avour (Melton, 1990). There is evidence, particularly from North American beef production systems, that concentrate-fed animals produce more tender and better-¯avored meat than forage-fed animals (Larick et al., 1987; Medeiros, Field, Menkhaus, & Russell, 1987). However, in many of these experiments, dietary eects were confounded by dierences in animal age, pre-slaughter growth rate or * Corresponding author. Fax: +353-46-26154. E-mail address: [email protected] (A.P. Moloney).
carcass weight/fatness at slaughter (e.g. Bowling, Smith, Carpenter, Dutson, & Oliver, 1977; Harrison, Smith, Allen, Hunt, Kastner, & Kropf, 1978) factors that in¯uence meat quality, in particular tenderness and ¯avour (Spanier, McMillian, & Miller, 1990). French et al. (2000a) showed that when steers had a similar mean rate of carcass growth, pre-slaughter diet per se (autumn grazed grass, concentrates or grass silage) did not aect the sensory perception of meat quality. In that study, the rate of carcass growth was restricted to that of animals fed unsupplemented grass and was less than the genetic potential of the animals used. To maximise pro®tability, the growth potential of the animals should be achieved with maximum inclusion of grazed grass but without an impairment of sensory quality. We hypothesised that inclusion of grass in high-energy ®nishing diets for beef cattle would have little eect on meat quality. The objective of this study therefore, was to measure the quality of meat from cattle ®nished on grass alone, on concentrates oered ad libitum (expressing full genetic potential for growth) or on various combinations of both.
0309-1740/01/$ - see front matter # 2001 Elsevier Science Ltd. All rights reserved. PII: S0309-1740(00)00115-7
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2. Materials and methods 2.1. Experimental design and animal management From a larger study concerned with strategies for beef production from autumn grass (French, O'Riordan, O'Kiely, Carey, & Moloney, 2000b), six treatment groups were chosen for assessment of meat composition and eating quality. The six groups (11 continental [Limousin and Charolais] crossbred steers per group: initial body weight 567 [S.D.=34.1] kg) were oered, per animal daily, (1) 18 kg grass dry matter (DM), (2) 18 kg grass DM and 2.5 kg concentrate, (3) 18 kg grass DM and 5 kg concentrate, (4) 6 kg grass DM and 5 kg concentrate, (5) 12 kg grass DM and 2.5 kg concentrate or (6) concentrates ad-libitum+1 kg straw. Animals were blocked on descending bodyweight into blocks of 6 and within block assigned at random to treatment. Groups 1 to 5 inclusive, rotationally grazed a predominantly perennial ryegrass pasture. Daily grass allowances were achieved by varying the size of the grazing area. Animals were oered a fresh allowance daily and did not have access to the previous days allowance. Pre-grazing grass mass was estimated by cutting four strips (each 1.25 m; 4 cm stubble height) three times weekly from the areas to be grazed by each group. Grass intake was estimated using the n-alkane technique of Mayes, Lamb, and Colgrove (1986) as modi®ed by Dillon and Stakelum (1988). Thus, animals were dosed with gelatine capsules containing 500 mg dotriacontane and faeces samples collected twice daily. A pelleted concentrate, which was a mixture of ground barley (0.29), unmolassed beet pulp (0.29), maize gluten (0.29), soya-bean meal (0.05), molasses (0.05) and mineral/vitamin mix (0.03), was oered individually to all animals receiving supplementary concentrates. The appropriate animals were restrained individually in a purpose built mobile feeder in the ®eld and oered 2.5 kg concentrates per head at 08:00h, before being allocated a fresh daily grass allowance. Animals remained restrained until the concentrates were consumed (approximately 20 min). Animals receiving 5 kg concentrates daily were restrained and oered a further 2.5 kg concentrates at 16:00h. Animals oered concentrates and straw were accommodated in a slatted ¯oor shed and oered their diets individually through electronically controlled gates. The average duration of the feeding period was 95 days from 22 August. 2.2. Post-slaughter carcass measurements and sampling Animals from the four heaviest blocks were slaughtered after 89 days, from the next four blocks after 95 days and from the remaining three blocks after 101 days. On the day of slaughter, animals were weighed, mixed during loading onto one truck, transported 120
km to a commercial slaughter facility and slaughtered at random within 6 h of removal from Grange Research Centre. After slaughter, cold carcass weight (hot carcass weight0.98) was recorded. Carcass weight gain was estimated as the dierence between ®nal carcass weight and 55% of initial liveweight The carcasses were classi®ed for fat score (1=leanest and 5=fattest) using the EU Beef Carcass Classi®cation Scheme. The weight of kidney and channel fat (KCF) on each carcass was also recorded and expressed as a proportion of carcass weight. The pH of the M. longissimus dorsi (LD) was measured at hourly intervals for 8 h and at 24 h and 48 h post-mortem by making a scalpel incision at the 5th/6th rib and inserting a glass electrode (Model EC2010-11, Amargruss Electrodes Ltd., Castlebar, Co. Mayo, Ireland) attached to a portable pH meter (Model no. 250 A, Orion Research Inc., Boston, USA) approximately 2.5 cm into the muscle. During each of the second and third slaughter times, the temperature of the LD muscle was measured in 3 randomly chosen carcasses/treatment. Temperature probes were inserted approximately 6 cm into the LD muscle immediately anterior to the 9th rib and temperature was recorded at 15 min intervals up to 24 h post-mortem using a data logger (Grant Squirrel Series 1250). The sides were cold-boned at 24 h post-mortem. Samples of LD were vacuum packed (SuperVac GK-166T) and aged at 4 C for 2, 7 or 14 days post-mortem. Steaks, 2.5 cm thick, were cut after 2 days for compositional analysis and after 2, 7 and 14 d post-mortem, for sensory analysis and Warner±Bratzler shear force (WBSF) measurements. These were vacuum packed and frozen at ÿ30 C for subsequent analysis. 2.3. Measurements on fresh meat Steaks (2.5 cm thick) were cut at 14 days post-mortem for colour measurements according to the procedure of Strange, Benedict, Gugger, Metzger, and Swift (1974). Freshly cut samples were wrapped in an oxygen permeable PVC wrap and allowed to bloom at 4 C for 3 h. The Hunter `l', `a' and `b' value of each sample was then measured using a Hunter lab Ultra Scan XE colorimeter with Universal Software Version 2.2.2 (Hunter Associates Laboratory, Inc., 11491 Sunset Hills Road, Reston, Virginia, USA). Steaks (2.5 cm thick) were cut at 2 days post-mortem for measurement of drip-loss according to the procedure of Honikel (1987) and sarcomere length according to the procedure of Cross, West and Dutson (1980). 2.4. Measurements on pre-frozen meat Frozen vacuum-packed steaks were thawed overnight at ambient temperature before cooking for sensory and
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WBSF analysis and mincing for compositional analysis. Sensory analysis was performed by an eight member, inhouse trained panel on steaks grilled to an internal temperature of 70 C, according to the American Meat Science Association Guidelines (AMSA, 1978). Panelists were asked to assess the samples for the following attributes: tenderness (scale 1±8; 1=extremely tough, 8=extremely tender) moistness/juiciness (scale 1±8; 1=extremely dry, 8=extremely juicy). overall ¯avour (scale 1±6; 1=very poor, 6=very good) residual chewiness (scale 1±6; 1=not chewy, 6=extremely chewy) overall texture (scale 1±6; 1=very poor, 6=very good) overall acceptability (scale 1±6; 1=not acceptable 6=extremely acceptable). Warner±Bratzler shear force was measured according to the procedure of Shackelford, Koohmaraie, Cundi, Gregory, Rohrer, and Savell (1991). Steaks (2.5 cm) were cooked in retortable vacuum pack bags to an internal temperature of 70 C, by immersing in a water bath (Model Y38, Grant Instruments Ltd.) at 80 C. The internal temperature of the steaks was measured using a Hanna Foodcare digital thermometer (HI 9041). Five cores (1.25 cm diameter) were cut from the steaks parallel to the direction of the muscle ®bres and sheared using an Instron Universal testing machine equipped with a Warner±Bratzler shearing device. The crosshead speed was 5 cm/min. Instron Series IX Automated Materials Testing System software for Windows (Instron Corporation, High Wycombe, Bucks, UK) was employed in the analysis. 2.5. Chemical analyses Intra-muscular fat and moisture concentrations of thawed minced LD samples were determined using an automated, integrated microwave moisture and methylene chloride fat extraction method (Bostian, Fish, Webb, & Arey, 1985) on a CEM moisture/solids analyser (Model AVC 80, CEM corp., Matthews, NC, USA). Protein was determined by the method of Sweeney and Rexroad (1987) using a LECO protein analyser (LECO FP428, LECO Corp., St. Joseph, MI, USA). The dotriacontane and tritriacontane concentrations of the grass, faeces and concentrate were measured according to Vulich, Hanrahan, and Crowley (1995). All other feed analyses were carried out as previously described by Moloney and O'Kiely (1995) 2.6. Statistical analyses Variables that were measured at a single time point were subjected to analysis of variance using a model
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that had block and treatment as main eects. The LD temperature data at various times post-mortem were logarithmically transformed and linear regression was used to derive a cooling constant for each carcass. These values were then analysed using a model that had slaughter day and treatment as main eects. Where a signi®cant eect of treatment was detected, means were separated using the least signi®cant dierence procedure. Variables measured 2, 7 and 14 days post slaughter were subjected to analysis of variance using a model that had treatment as a main eect and days post slaughter as a split-plot on treatment. The pH data were subjected to analysis of variance using a model that had treatment as a main eect and hours post slaughter as a split-plot on treatment. Relationships between variables were examined by correlation analysis. 3. Results The chemical composition of the dietary ingredients is shown in Table 1. Animals oered grass only (treatment 1) had higher (P<0.05) grass intake and lower (P>0.05) carcass weight and carcass gain than all other treatments (Table 2). Animals oered concentrates ad libitum (treatment 6) consumed 13.33 kg DM daily and had higher (P<0.05) carcass fat scores and LD fat concentration and lower (P<0.05) LD moisture concentration than all other treatments. They also had the highest (P<0.05) carcass gain and carcass weight, other than treatment 3 from which they did not dier signi®cantly. There was an interaction (P<0.001) between time post-slaughter and diet pre-slaughter for LD pH (Fig. 1). Thus, LD from animals oered grass only had higher (P<0.05) pH at 4, 5, 6, 7 and 8 h post-slaughter than all other treatments. The LD from animals oered the high grass and high concentrate allowance (treatment 3) had lower (P<0.05) pH at 6, 7 and 8 h postslaughter than all other treatments. There was no eect of diet on pH 24 h and 48 h post slaughter. The LD from animals oered the low grass and high concentrate allowance (treatment 4) or concentrates ad libitum (treatment 6) cooled more slowly than LD from all other animals. Table 1 The chemical composition of grass and concentrates
Dry matter (DM) (g/kg) Crude protein (g/kg DM) Ash (g/kg DM) Dry matter digestibility (g/kg ) Crude ®bre (g/kg DM) Oil (g/kg DM)
Grass
Concentrate
198 225 125 738 287 29
872 143 48 843 101 24
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Table 2 The eect of diet on grass intake, carcass characteristics and M.l. dorsi composition Dieta
1
2
3
4
5
6
S.E.
Signi®canceb
Grass dry matter (DM) intake (kg/day) Concentrate DM intake (kg/day) Carcass weight (kg) Carcass gain/day (g) Fat scorec KCFd/carcass (g/kg) Intra-muscular fat (g/kg muscle) Ash (g/kg muscle) Moisture (g/kg muscle) Protein (g/kg muscle)
10.67d 0 330e 360e 4.03e 24 23 12 737 225
7.72g 2.25 355g,h 631g,h 3.97e 26 24 17 736 227
7.78g 4.50 363g,f 727g,f 4.14e 28 29 12 733 224
4.49e 4.50 352g,h 617g,h 3.79e 25 23 12 735 226
6.78f 2.25 348h 551h 4.15e 22 25 12 734 228
± 13.3 371f 809f 4.64f 29 44 12 717 226
0.368 ± 4.9 39.2 0.133 2.3 3.6 0.4 3.8 2.2
*** ± *** *** * NS *** NS ** NS
a Steers oered (1) 18 kg grass DM, (2) 18 kg grass DM and 2.5 kg concentrate, (3) 18 kg grass DM and 5 kg concentrate, (4) 6 kg grass DM and 5 kg concentrate, (5) 12 kg grass DM and 2.5 kg concentrate and (6) concentrates ad-libitum. b Means in rows without a common superscript are signi®cantly dierent (P< 0.05). c 1=leanest 5=fattest. d KCF, Kidney plus channel fat.
Fig. 1. The eect of diet and time post-mortem on muscle pH. (^) 18 kg grass dry matter (DM), (&) 18 kg grass DM and 2.5 kg concentrate, (~) 18 kg grass DM and 5 kg concentrate, () 6 kg grass DM and 5 kg concentrate, () 12 kg grass DM and 2.5 kg concentrate and (*) concentrates adlibitum. Diettime post-mortem s.e.=0.038.
There was no eect of pre-slaughter diet on LD colour, sarcomere length or drip loss (Table 3). An increase in aging time post mortem decreased (P<0.001) WBSF value of the LD and increased (P40.05) tenderness, texture, ¯avour, juiciness, chewiness and acceptability scores and cooking loss (Table 4). There was no eect of treatment and no interaction between treatment and ageing time post mortem for any of these variables. Correlations between live animal/carcass variables and meat quality attributes are presented in Table 5.
The LD pH at 4, 5, 6 and 7 h post-mortem was negatively correlated with carcass gain and the LD pH at 8 h post-mortem positively correlated with carcass gain. The LD pH at 1, 2, 3, 5 and 8 h post mortem was positively correlated with carcass fat score. The proportion of grass in the diet was not correlated with any of the meat quality variables measured. In contrast, carcass growth rate was negatively correlated (P<0.05) with WBSF and LD pH at 4, 5, 6 and 7 h post-mortem.
P. French et al. / Meat Science 57 (2001) 379±386
383
Table 3 The eect of diet on M.l dorsi characteristics Dieta
1
Cooling rate (hÿ1) Muscle colour ``L'' ``a'' ``b'' Sarcomere length (m m) Drip loss (g/100 g) pH (48 h)
2 0.040c
3
0.043c
34.3 13.9 7.3 1.68 2.73 5.54
4
0.043c
33.6 14.1 7.4 1.66 2.65 5.47
5 0.031b
34.5 14.5 7.6 1.76 2.11 5.53
6
0.049c
33.9 14.5 7.4 1.70 2.35 5.52
34.2 14.4 7.6 1.73 2.51 5.53
0.032b 34.9 14.6 7.7 1.78 2.13 5.49
S.E.
Signi®cance
0.0036
**
0.43 0.41 0.29 0.038 0.271 0.026
NS NS NS NS NS NS
a Steers oered (1) 18 kg grass dry matter (DM), (2) 18 kg grass DM and 2.5 kg concentrate, (3) 18 kg grass DM and 5 kg concentrate, (4) 6 kg grass DM and 5 kg concentrate, (5) 12 kg grass DM and 2.5 kg concentrate and (6) concentrates ad-libitum. b Means in rows without a common superscript are signi®cantly dierent (P<0.05).
Table 4 The eect of diet and ageing time post-mortem on WBSFa and taste panel assessment of M.l dorsi Dietb (D)
1
Days aged (T) WBSF (kg) % Cook loss Tendernessc Textured Flavoure Juicinessf Chewinessg Accepabilityh
2
2 7
14
2
3 7
14
2
4 7
14
2
5 7
14
6 2
7
14
2
S.E. Signi®cance 7
14
D
T DxT
8.0 5.9 4.8 7.5 6.1 4.1 6.6 5.2 4.2 7.0 6.5 4.3 6.4 5.7 4.0 6.1 4.9 3.9 0.43 NS *** 30.0 29.4 31.3 29.5 30.3 31.4 28.7 28.1 29.9 29.3 29.7 30.3 29.1 30.9 30.8 29.8 28.9 30.6 0.69 NS ** 3.5 4.8 5.2 4.2 4.7 5.6 4.5 5.2 5.8 4.0 5.0 5.7 4.8 4.7 5.7 4.4 5.2 6.2 0.26 NS *** 2.9 3.4 3.6 3.2 3.3 3.7 3.3 3.4 3.7 3.1 3.5 3.7 3.2 3.5 3.9 3.3 3.5 3.8 0.13 NS *** 3.5 3.7 3.8 3.6 3.5 3.8 3.7 3.8 3.8 3.8 3.7 3.8 3.6 3.9 3.9 3.7 3.8 3.9 0.10 NS ** 4.8 4.6 5.3 5.2 4.6 4.6 5.3 4.3 4.8 5.2 4.7 5.2 4.7 4.7 4.9 5.2 5.1 5.0 0.24 NS * 4.2 3.5 3.1 3.7 3.5 3.0 3.7 3.2 2.8 4.0 3.3 3.0 3.6 3.6 3.1 3.9 3.3 2.7 0.15 NS *** 3.2 3.2 3.7 3.1 3.6 3.8 3.4 3.6 3.8 2.8 3.4 3.6 3.2 3.4 3.9 3.3 3.6 3.9 0.15 NS ***
NS NS NS NS NS NS NS NS
a
Warner±Bratzler shear force. Steers oered (1) 18 kg grass dry matter (DM), (2) 18 kg grass DM and 2.5 kg concentrate, (3) 18 kg grass DM and 5 kg concentrate, (4) 6 kg grass DM and 5 kg concentrate, (5) 12 kg grass DM and 2.5 kg concentrate and (6) concentrates ad-libitum. c 1=extremely tough, 8=extremely tender. d 1=very poor, 6=very good. e 1=very poor, 6=very good. f 1=extremely dry, 8=extremely juicy. g 1=not chewy, 6=extremely chewy. h 1=not acceptable, 6=extremely acceptable. b
4. Discussion The composition of the grass was typical of grass harvested in autumn with low digestibility and high crude protein (CP) concentration relative to that reported for grass harvested earlier in the grazing season (Munro & Walters, 1987). The concentrate had higher digestibility and lower CP concentration than the grazed grass. Assuming that the growth potential of the cattle was realised by the ad libitum concentrate group (treatment 6), grazed grass, at an allowance of 30 g DM/kg bodyweight (treatment 1), only supported 0.45 of the potential carcass growth. However, animals oered treatment 3 achieved 0.90 of potential carcass growth but 630 g/kg of the diet was grazed grass. While the grass only treatment resulted in a slower rate of pH decline, LD pH at 24 h post slaughter was similar for all dietary treatments. Meat colour, tenderness, ¯avour, juiciness and shelf life, are in¯uenced by pH (Hofmann, 1988). Muir, Beaker, and Brown (1998)
indicated that grass-fed steers had higher ultimate pH values than grain-fed steers and suggested that grass-fed steers were more susceptible to pre-slaughter stress than grain-fed steers as the latter would be more accustomed to penning and handling and would be less likely to suer glycogen depletion in the factory pre-slaughter. In the present study, all animals were accustomed to handling and penning due to frequent weighing (French et al., 2000b). Bidner, Schupp, Montgomery, and Carpenter (1981), Bidner et al. (1986), Morris, Purchas, and Burnham (1997) and Wander-stock and Miller (1948), also observed similar ultimate muscle pH in grass and grain-®nished cattle. Bidner et al. (1981) and Reagan, Carpenter, Bauer, and Lowrey (1977) reported darker lean in forage-fed animals in comparison with concentrate-fed animals. Bidner et al. (1986) attributed the darker lean in foragefed animals to higher myoglobin concentrations. The haem pigment, myoglobin, is mainly responsible for the colour of meat. Varnam and Sutherland (1995)
384
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Table 5 Correlations of meat quality attributes with live animal/carcass variables Grass proportion
Drip loss WBSF 14 daysa Colour L a b Tendernessb Juicinessb Flavourb Textureb Chewinessb Acceptabilityb
0.16 0.22 ÿ0.15 ÿ0.11 ÿ0.11 ÿ0.23 0.07 ÿ0.05 ÿ0.11 0.18 ÿ0.16
Carcass weight
Carcass gain
ÿ0.02 ÿ0.05
ÿ0.01 ÿ0.31*
0.12 ÿ0.14 ÿ0.28* ÿ0.03 ÿ0.09 ÿ0.03 0.00 0.12 ÿ0.04
0.32* 0.20 0.18 0.16 ÿ0.13 ÿ0.03 0.07 ÿ0.10 0.11
Longissimus dorsi pH (hours post-mortem) 1 ÿ0.07 0.24 2 0.08 ÿ0.08 3 0.09 ÿ0.05 4 0.13 ÿ0.11 5 0.13 0.00 6 0.15 ÿ0.14 7 0.12 ÿ0.14 8 0.15 0.03 24 0.10 0.09 48 0.10 0.06 a b
0.04 ÿ0.19 ÿ0.22 ÿ0.30* ÿ0.25* ÿ0.36** ÿ0.39** 0.32* ÿ0.17 ÿ0.16
Carcass fat score
Internal fat weight
Internal fat carcass
0.09 0.11
0.13 ÿ0.13
ÿ0.03 ÿ0.18 ÿ0.32* ÿ0.14 0.04 ÿ0.11 ÿ0.09 0.29* ÿ0.17 0.30* 0.25* 0.26* 0.21 0.25* 0.19 0.22 0.32* 0.10 0.24
Longissimus composition Moisture (%)
Protein (%)
Lipid (%)
Ash (%)
0.14 ÿ0.14
0.09 0.02
0.15 0.18
ÿ0.17 ÿ0.12
ÿ0.03 0.16
ÿ0.04 ÿ0.12 ÿ0.22 ÿ0.04 0.04 0.13 ÿ0.03 0.03 ÿ0.02
ÿ0.05 ÿ0.08 ÿ0.16 ÿ0.05 0.05 0.14 ÿ0.03 0.01 ÿ0.02
ÿ0.02 ÿ0.14 ÿ0.12 ÿ0.13 ÿ0.04 ÿ0.15 ÿ0.03 0.03 ÿ0.07
ÿ0.23 ÿ0.05 ÿ0.09 ÿ0.14 0.04 0.04 ÿ0.04 0.18 ÿ0.04
0.07 0.17 0.15 0.15 ÿ0.01 0.17 0.00 ÿ0.10 0.05
0.09 0.05 0.05 0.00 0.09 ÿ0.22 ÿ0.06 0.00 ÿ0.09
0.41** 0.18 0.23 0.17 0.17 0.14 0.20 0.18 ÿ0.02 0.16
0.38* 0.20 0.24 0.19 0.17 0.16 0.23 0.18 ÿ0.05 0.14
ÿ0.01 ÿ0.05 ÿ0.03 ÿ0.06 ÿ0.02 0.01 ÿ0.05 ÿ0.01 0.12 0.12
ÿ0.03 ÿ0.06 0.00 0.01 ÿ0.06 ÿ0.01 0.02 0.08 0.08 0.00
0.03 0.08 0.07 0.08 0.07 0.04 0.05 ÿ0.04 ÿ0.11 ÿ0.10
ÿ0.13 ÿ0.05 ÿ0.09 0.00 0.02 ÿ0.09 ÿ0.10 0.05 ÿ0.06 ÿ0.04
Warner±Bratzler shear force. After 14 days ageing.
hypothesized that grass-fed animals have more muscle myoglobin, due to more activity pre-slaughter than their feedlot counterparts. However, the controlled manner in which the grazing animals were managed pre-slaughter in the current study should have resulted in similar levels of activity as those animals oered concentrates ad libitum. Improved lean colour is sometimes associated with increased intramuscular fat concentration (Muir et al., 1998) but no such relationship was observed in the present study. It has been proposed that early post mortem pH in¯uences the activity of endogenous enzyme systems and, thus, aects ultimate meat tenderness (O'Halloran, Troy, & Buckley, 1996). Marsh, Ringkob, Russell, Swartz, and Pagel (1987) used dierent forms of electrical stimulation and various cooling rates to produce a wide range of early post-mortem glycolytic rates and concluded that tenderness was highest when glycolysis proceeded at a rate which resulted in a pH at 3 h post mortem (pH3) of 6.1. In the present study, WBSF after 14 days ageing was most highly correlated with the pH at 8 h post mortem (r=0.45) and the corresponding sensory perception of tenderness with pH at 48 h postmortem (r=ÿ0.42). The in¯uence of carcass fatness on LD pH seen in the present study may have contributed to the dierence between this and other studies with
respect to the relationship between LD pH and tenderness. The coecient of variation for tenderness score and WBSF value within the population of animals used in this study was approximately 25 and 30% respectively. This re¯ects the intrinsic variability in the animals used but may also re¯ect the procedures used. Forage-®nishing of cattle has been shown to decrease tenderness of the meat when compared to grain-®nishing (Mitchell, Reed, & Rogers, 1991; Rumsey, Bond, Berry, Hammond, & Dinius, 1987). This may re¯ect lighter and/or leaner carcasses from forage-®nished cattle since numerous authors (Bowling, Smith, Carpenter, Dutson, & Oliver, 1977; Bowling et al., 1978; Dolezal, Smith, Savel, & Carpenter, 1982; Lochner, Kauman, & Marsh, 1980; Smith, Dutson, Hostetler, & Carpenter, 1976) have reported a positive correlation between muscle tenderness and carcass weight and fatness. Large quantities of fat insulate the carcass and slow postmortem chilling, which, in turn, improves tenderness by decreasing the extent of cold-induced muscle shortening in the LD and some other muscles. Slow post mortem chilling may also enhance post mortem muscle autolysis (Lochner et al., 1980; Smith et al., 1976). However, the correlation between carcass weight or carcass fat score (a subjective measure of subcutaneous fat) and WBSF was not signi®cant in
P. French et al. / Meat Science 57 (2001) 379±386
this study. Moreover, there was no dierence in sarcomere length which was within the range previously observed in our laboratory (O'Halloran et al., 1996) and by others, Koohmaraie, Seideman, Schollmeyer, Dutson, and Babiker (1988). These ®ndings indicate that no treatment-induced cold-shortening occurred despite the dierences in carcass weight and rates of LD cooling observed. In this study, the cattle oered concentrates ad libitum had higher carcass gains than animals oered grass only. Cattle grown rapidly prior to slaughter have been shown in some studies to produce more tender meat than their slower growing counterparts (Aberle, Reeves, Judge, Hunsley, & Perry, 1981; Fishell, Aberle, Judge, & Perry, 1985). Cattle which grow more rapidly pre-slaughter have increased rates of protein turnover, resulting in higher concentrations of proteolytic enzymes in the carcass tissues at slaughter which, in turn, may aect collagen solubility and (or) myo®bril fragmentation (Aberle et al., 1981; Hall & Hunt, 1982; Miller, Tatum, Cross, Bowling, & Cole, 1983). While there were no treatment eects on tenderness in this study, carcass growth rate accounted for 10% of the variation in WBSF and 3% of the variation in sensory tenderness in 14 day-aged steaks. Moloney, Keane, Mooney, and Troy (2000) found no decrease in WBSF or increase in tenderness in LD from steers when pre-slaughter growth rate was increased from 0.36 to 1.08 kg/day. Oltjen, Rumsey, and Putman (1971) and Young and Kauman (1978) found dierences in juiciness between forage- and grain-fed beef. In both studies, there were dierences in carcass fatness, which paralleled the increasing juiciness scores. Muir et al. (1998) concluded that the increased juiciness of beef from grain-fed cattle relative to grass-fed cattle was due to dierences in carcass growth rate and/or fat cover. However, in this study, juiciness was poorly correlated with both intra-muscular fat content and carcass growth rate which may re¯ect the narrow range in fatness and drip loss, especially across treatments 1 to 5, in the dataset. Meat ¯avour is in¯uenced by a number of factors including animal age and genetics, pre-slaughter dietary regimen, environment, length of post-slaughter aging and the particular primal cut examined (Spainer et al., 1990). Early studies (Meyer, Thomas, Buckley, & Cole, 1960; Wander-stock & Miller, 1948) indicated lower palatability of grass-fed beef than grain-fed beef, but the carcasses in those studies diered in weight and composition. In subsequent studies, Dinius and Cross (1978), Oltjen et al. (1971) and Young and Kauman (1978) found that forage-fed beef had eating qualities equal or superior to those of grain-fed beef of similar carcass composition. Muir et al. (1998) concluded that the dierences in ¯avour and acceptability due to feed type could be accounted for by dierences in carcass fatness. The relatively narrow range in fatness in the present study and the lack of treatment on ¯avour and acceptability support this suggestion.
385
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