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The quality of meat and fatness of bulls offered ad libitum concentrates, indoors or at pasture
Livestock Production Science 87 (2004) 271 – 276 www.elsevier.com/locate/livprodsci
Short communication
The quality of meat and fatness of bulls offered ad libitum concentrates, indoors or at pasture A.P. Moloney a,b,*, R.J. Fallon a, M.T. Mooney b, D.J. Troy b a b
Teagasc, Grange Research Centre, Dunsany, Co. Meath, Ireland Teagasc, The National Food Centre, Ashtown, Dublin 15, Ireland
Received 21 January 2003; received in revised form 14 July 2003; accepted 28 July 2003
Abstract The darker coloured meat sometimes reported when cattle finished at pasture are compared to cattle finished indoors may reflect breed, diet, age at slaughter, exercise and/or environment. To determine the contribution of exercise/environment to beef colour, 24, 24-week-old Holstein/Friesian bulls were either housed (H, 2.5 m2/animal) or maintained at pasture (P, 133 m2/ animal) for 180 days prior to slaughter. The bulls were offered a barley-based concentrate ad libitum and minimum roughage (straw for H and grass for P) to maintain rumen function. Changes in fat deposition were used as an index of exercise. Concentrate intake (group basis) was 7.0 and 6.5 kg dry matter for H and P, respectively. Mean carcass weight was 234 and 246 (sed 4.63) kg for H and P, respectively. Corresponding values for carcass fat score, kidney fat weight and longissimus thoracis (LT) muscle lipid concentration were 3.13 and 2.67 (sed 0.165), 17.9 and 13.9 (sed 2.08) g/kg carcass and 6.7 and 5.4 (sed 0.172) g/kg. Neither LT lightness (Hunter L value) at 2 (mean 35.5) or 7 days (mean 35.7) post-mortem, redness (Hunter a value) at 2 (mean 11.1) or 7 days (mean 13.8) post-mortem nor the pattern of pH fall post-mortem, differed between H and P. It is concluded that exercise/environment sufficient to alter body composition did not affect LT muscle colour in bulls. D 2003 Elsevier B.V. All rights reserved. Keywords: Bulls; Meat; Concentrates; Indoors; Pasture
1. Introduction Meat colour has a large influence on the purchase decision of consumers (Baardseth et al., 1988). The preferred colour of beef is market dependent with Mediterranean consumers preferring light or pink coloured meat while British/Irish consumers prefer darker, redder coloured meat (Anon, 1999). Consis* Corresponding author. Present address: Teagasc, Grange Research Center, Dunsany, Co. Meath, Ireland. Tel.: +353-46-9061100; fax: +353-46-90-26154. E-mail address: [email protected] (A.P. Moloney). 0301-6226/$ - see front matter D 2003 Elsevier B.V. All rights reserved. doi:10.1016/j.livprodsci.2003.07.009
tently satisfying beef market colour specifications requires information on all factors that influence colour development. Animal production factors that may influence beef colour include breed, feed consumption, age at slaughter and ante-mortem handling practices (Lawrie, 1998). Beef from cattle slaughtered off pasture is often darker than beef finished indoors (Muir et al., 1998; Priolo et al., 2001) but in many such comparisons, variation in the factors listed above likely confound identification of individual factors causing this difference in meat colour. In addition, the opportunity for greater exercise/activity in grazing animals has led to speculation that this is also a
272
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contributory factor to darker meat in grazing animals (Vestergaard et al., 2000; Varnam and Sutherland, 1995). French et al. (2000), however, found no difference in colour of meat from animals slaughtered at a similar age and energy intake whether they were offered grazed grass or concentrates indoors, prior to slaughter. This suggests that provided plane of nutrition and animal management is adequate to ensure sufficient reserves of glycogen in muscle prior to slaughter, exercise/activity per se is not a cause of darker meat in grazing animals. The objective of this study was to confirm the above suggestion by offering cattle a high energy concentrate ration ad libitum indoors and at pasture, thus removing the possible confounding effect of ration composition on meat colour.
2. Materials and methods 2.1. Experimental design and animal management Fifty-four, 24-week-old autumn-born Holstein/Friesian bull calves with an initial weight of 233 kg were blocked in groups of three on a descending bodyweight basis. Within block the animals were assigned at random to a barley soyabean meal ration (rolled barley (850), soyabean meal (130) and vitamins (20) g/kg) offered either housed (H), at pasture (P) throughout a 180-day experimental period or at pasture initially for subsequent removal (Treatment 3). All animals were adapted to the barley soyabean meal ration prior to the beginning of the study such that they had ad libitum access at the start of the experimental period. The H animals were accommodated on concrete slats in a naturally ventilated house with six animals per pen. Each animal had a pen area allowance of 2.5 m2. For P animals a pasture area of 0.96 ha was available. At one corner of this area, the concentrates were offered in a covered ‘‘lean-to’’ shed such that concentrates were protected from the environment and vermin. The animals were managed such that grass consumption would be minimised to a level required to maintain rumen health and therefore optimise concentrate consumption. Thus, the pasture area was divided into three paddocks of 3213 m2. Within each paddock, the space allowance was 85 m2/animal and, based on the mean grass growth curve for Grange Research
Centre for the previous 4 years (O’Riordan and O’Kiely, 1996), an expected forage supply of 0.5 kg dry matter (DM)/animal (based on a mean daily grass growth of 75 kg DM/ha and a utilisation of 75%). Grass height was 15 –18 cm when cattle entered a paddock. Cattle remained in a paddock until sward height decreased (due to less than average grass growth) or ground conditions deteriorated (due to rainfall). The other paddocks were managed in parallel, to maintain the target grass height. On July 1 (after 77 days), coincident with the expected seasonal decline in grass growth (to 50 kg DM/ha on average), the 18 cattle on treatment 3 were removed to maintain the target forage supply for the remaining cattle. The animals in treatment 3 are not considered in the remainder of this study. The space allowance for the remainder of the study was 170 m2/animal. The mean space allowance for the duration of the study was therefore 133 m2/animal. Concentrate feed intakes were recorded weekly and fresh water was available at all times. Indoor animals each received a daily allowance of 500 g straw. 2.2. Post-slaughter carcass measurements and sampling All animals were slaughtered after 180 days. On the day of slaughter, animals were weighed, transported 15 km to a commercial slaughter facility and slaughtered within 2 h of removal from Grange Research Centre. During transport and lairage, animals were maintained in their treatment/pen groups. After slaughter, cold carcass weight (hot carcass weight 0.98, assuming a weight loss of 20 g/kg during cooling) was recorded. Carcass weight gain was estimated as the difference between final carcass weight and estimated initial carcass weight (assuming a killing-out rate of 550 g/ kg liveweight). The weight of kidney and channel fat (KCF) on each carcass was recorded. The carcasses were classified for fat score (1 = leanest and 5 = fattest) using the EU Beef Carcass Classification Scheme (Anon, 1981). Meat quality assessments were only carried out on carcasses from animals in the first 12 blocks. One hour post-mortem, the pH of the m. longissimus thoracis (LT) was measured by making a scalpel incision and inserting a glass electrode (Model EC2010-11, Amargruss Electrodes, Castlebar,
A.P. Moloney et al. / Livestock Production Science 87 (2004) 271–276
Mayo, Ireland) attached to a portable pH meter (Model no. 250 A, Orion Research, Boston, USA) approximately 2.5 cm into the muscle. This measurement was repeated hourly for 8 h and again at 24 h and 48 h post mortem. The sides were cold-boned at 48 h post-mortem. Steaks, 2.5 cm thick, were frozen for compositional analysis. Further samples of LT were vacuum packed (SuperVac GK-166T) and aged at 4 jC for 7 days post-mortem. Steaks, 2.5 cm thick, were then cut for Warner –Bratzler shear force (WBSF) measurement. These were vacuum-packed and frozen at 30 jC for subsequent analysis. Steaks (2.5 cm thick) were cut at 2 and 7 days post-mortem for colour measurements according to the procedure of Strange et al. (1974). Freshly cut samples were wrapped in an oxygen permeable PVC wrap and left to bloom at 4 jC for 3 h. The Hunter ‘L’, ‘a’ and ‘b’ values of each sample was then measured using a Hunter lab Ultra Scan XE colorimeter with Universal Software Version 2.2.2 (Hunter Associates Laboratory, 11491 Sunset Hills Road, Reston, VA, 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). Warner – Bratzler shear force was measured according to the procedure of Shackelford et al. (1991). Steaks (2.5 cm) were cooked in retortable vacuum pack bags to an internal temperature of 70 jC, by immersing in a water bath (Model Y38, Grant Instruments) at 80 jC. 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 fibres and sheared using an Instron Universal testing machine equipped with a Warner – Bratzler shearing device. The crosshead speed was 5 cm/min. Instron Series 1X Automated Materials Testing System software for Windows (Instron, High Wycombe, Bucks, UK) was employed in the analysis. Intra-muscular fat and moisture concentration of thawed minced LT samples were determined using an automated, integrated microwave moisture and methylene chloride fat extraction method (Bostian et al., 1985) on a CEM moisture/solids analyser (Model AVC 80, CEM, Matthews, NC, USA). Protein was determined by the method of Sweeney and Rexroad (1987) using a LECO protein analyser (LECO FP 428, LECO, St. Joseph, MI, USA.
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2.3. Statistical analyses Data were subjected to analysis of variance using a model that had block and treatment as main effects. pH data were analysed according to a split-plot design with treatment in the main plot and time of measurement and the treatment by time interaction in the sub-plot.
3. Results The experiment began in April and animals were slaughtered in October. Monthly rainfall and sunshine averaged 71.5 mm and 135 h, respectively, for April to October, inclusive. The corresponding average
Table 1 Carcass and kidney/channel fat weight and m. longissimus thoracis characteristics in bulls offered ad libitum concentrates indoors or at pasture
Initial weight (kg) Final weight (kg) Growth (g/day) Carcass weight (kg) Kidney/channel fat (kg) (g/kg carcass) Fat score Killing-out (g/kg carcass) Conformation Colour—2 days L a b Saturation Hue angle Colour—7 days L a b Saturation Hue angle Composition (g/kg) Fat Moisture Protein Ash Drip loss (g/kg) Shear force (kg) Cook loss (g/kg) PH48
House
Pasture
sed
Sig
228.3 451.0 1237 234.5 4.18 17.9 3.13 520 1.79
236.6 473.2 1314 245.6 3.46 13.9 2.67 519 1.75
9.53 8.25 59.9 4.63 0.50 2.08 0.165 5.5 0.106
NS * NS * NS 0.068 * NS NS
35.6 11.4 7.4 13.6 0.58
35.5 10.9 7.2 13.0 0.58
0.68 0.49 0.28 0.53 0.011
NS NS NS NS NS
35.5 13.3 8.3 15.7 0.56
35.8 14.2 8.6 16.6 0.55
0.73 0.76 0.41 0.84 0.013
NS NS NS NS NS
6.7 749.3 232.1 11.4 25.8 5.53 319 5.61
5.4 750.2 232.0 11.3 27.7 5.34 328 5.57
1.72 3.13 2.95 0.26 1.34 0.186 1.1 0.039
NS NS NS NS NS NS NS NS
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Fig. 1. Post-mortem pH of LD muscle in bulls offered ad libitum concentrates, indoors ( w ) or at pasture (n) [Treatment time sed 0.075].
maximum and minimum temperatures were 16.5 and 8.8 jC, respectively. Daily concentrate consumption averaged 7.0 and 6.5 kg DM for H and P animals, respectively. On average, P animals were heavier ( P < 0.05) at slaughter, had heavier ( P < 0.05) carcasses that had a lower ( P < 0.05) fat score and a smaller ( P < 0.1) proportion of kidney and channel fat (Table 1). Intra-muscular lipid concentration followed this trend but neither muscle composition nor any of the measured muscle attributes differed between H and P treatments (Table 1). Muscle pH declined ( P < 0.001) post-mortem but there was no evidence that the pattern of decrease differed between treatments (Fig. 1).
4. Discussion In four of the eight studies reviewed by Muir et al. (1998), animals finished at pasture had darker meat. Muir et al. (1998) suggested that this reflected lower energy consumption of the grazing animals but might also reflect the greater activity/exercise of the grazing animals. Varnam and Sutherland (1995) similarly hypothesised that grass-fed animals have more muscle myoglobin due to more activity pre-slaughter than their feedlot counterparts. In previous studies at this institute (French et al., 2000, 2001), there was no evidence that animals finished at pasture had darker meat than animals fed restricted or ad libitum amounts of concentrates indoors. In these studies, the stocking density was tightly controlled and the animals were rotationally grazed. It was unlikely that the animals had the same opportunity for exercise when compared to the grass-
fed animals in the studies examined by Muir et al. (1998). The objective of the present study was to examine the effects of exercise/environment on colour of meat from animals fed a common high energy diet confined inside, or outside with liberal opportunity for exercise/activity. A concentrate diet was used rather than offering the H animals cut grass, as it is difficult to ensure that consumption of ‘‘zero-grazed’’ grass will supply similar nutrients as grazed grass due to selection by grazing animals. The degree of exercise/ activity of P animals was not measured in this study but all indices of fatness were lower in P animals compared to H animals. As energy consumption was similar (the possible slightly higher grass consumption over the final 100 days of the study compensating for the difference in concentrate consumption), we believe the decrease in fatness of P animals is consistent with greater energy expenditure on exercise and/ or partitioning of absorbed energy towards muscle as a result of exercise. This contrasts with the findings of French et al. (2000) who observed no difference in these indices of fatness between indoor and grazing animals. We therefore interpret the body composition data in the present study as reflecting greater exercise/ activity in P animals compared to H animals. It is acknowledged, however, that environmental conditions of temperature, rainfall and photoperiod differed between H and P treatments and that these differences may have contributed to the apparent effects of exercise/activity on body composition, i.e. possibly greater energy expenditure to maintain core body temperature in P animals. That there was no difference in the pattern of pH fall or ultimate pH indicates similar glycogenolysis post-slaughter in animals from both groups. The P
A.P. Moloney et al. / Livestock Production Science 87 (2004) 271–276
animals therefore did not suffer excessive glycogen depletion either due to exercise/activity during the study or during transport and lairage. This lack of difference in pH was reflected in the similar muscle colour of both treatment groups after 2 and 7 days storage post-mortem. Vestergaard et al. (2000) reported that bulls slaughtered at 360 kg from pasture had darker LD when compared to bulls slaughtered at a similar weight from a high energy indoor diet. They suggest that ‘‘differences in physical activity are probably the main reason’’ for the differences observed. Nevertheless, in that study, muscle glycogen concentration was lower and consequently muscle ultimate pH was higher in the grazing animals, which contribute to darker meat per se. Moreover, the grazing animals were 100 days older than the indoor animals and their data show that increasing age from 360 to 460 kg on a common diet also resulted in darker meat (Vestergaard et al., 2000). Their conclusion on the effect of exercise is therefore rather weak. In contrast, Andersen et al. (1991) compared tiestalls (width 125 cm) with loose housing at 1.8 m2/ animal on either a slatted floor or deep bedding. Energy consumption for bulls was similar for each group, but the loose housed animals had lower dissected fat trim in the carcass, dissected fat in the loin and intramuscular fat in LT. The latter animals also had darker meat, which appears to be related to decreased time spent lying and more time spent eating than the animals in the tie-stalls. Similar results were recorded by Jensen and Oksama (1996). These data with bulls and those of Andrighetto et al. (1999) with veal calves suggest that exercise/activity in a housed environment can result in darker meat. The lack of an effect on meat colour in the present study may reflect the degree of exercise/activity of the P animals compared to H animals since the space allowance of the H animals in the present study was greater than that of the studies cited above. Thus, there might be a threshold space allowance above which no further effect of exercise per se will occur. The type as well as the intensity of exercise/activity may be important for meat colour. Studies with imposed exercise/activity of varying durations and patterns are required to clarify this issue. A further hypothesis of the effect of exercise on muscle colour is an alteration in muscle pigment
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concentration due to the exercise-induced increase in oxidative fibres that have a higher concentration of myogloblin and a decrease in glycolytic fibres (Vestergaard et al., 2000). Grazed bulls, which had darker longissimus muscle than indoor bulls in the study of Dufrasne et al. (1995), had higher pigment concentrations. Increased pigment concentrations appear to be related to darker muscle in the studies of Andersen et al. (1991) and Jensen and Oksama (1996). It is clear that in the present study, cattle did not exercise sufficiently to effect such a change in muscle structure. It is recognised that the muscle used in this study is predominantly a postural muscle and may therefore be less affected by exercise than locomotor muscles in the hip or legs. It has been shown that feeding regime, housing system and exercise/activity may affect the hypertrophic and metabolic response of individual muscles differently (Aalhus and Price, 1991; Vestergaard et al., 2000). There was no difference in tenderness between H and P animals. Similar results were observed by Andersen et al. (1991) and Jensen and Oksama (1996) despite apparent increases in longissimus muscle growth, thus rejecting the hypothesis that muscle from exercised animals, by virtue of faster growth rate, is more tender, as seen in sheep by Aalhus et al. (1991), and also in veal calves by Andrighetto et al. (1999). It is concluded that the degree of exercise/activity and likely environmental conditions experienced by P animals in this study, while sufficient to alter body composition, did not alter LT colour in bulls. Further studies involving imposed exercise are required to confirm the effect of exercise per se on meat colour. Acknowledgements This research was partially supported by grant aid under the Food Sub-Programme of the Operational Programme for Industrial Development, which was administered by the Irish Department of Agriculture and Food and supported by national and EU funds. References Aalhus, J.L., Price, M.A., 1991. Endurance-exercised growing sheep: 1. Post mortem and histological changes in skeletal muscles. Meat Sci. 29, 43 – 56.
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Aalhus, J.L., Price, M.A., Shand, P.J., Hawrysh, Z., 1991. Endurance-exercised growing sheep: 11. Tenderness increase and change in meat quality. Meat Sci. 29, 57 – 68. Andersen, H.R., Krohn, C.C., Foldager, J., Munksgaard, L., Klastrup, S., 1991. Influence of housing and feeding on behaviour, feed intake, growth and carcass and meat quality. Report 700, Foulum National Institute of Animal Science, 39 pp. (in Danish). Andrighetto, I., Gottardo, F., Andreoli, D., Cozzi, G., 1999. Effect of type of housing on veal calf growth performance, behaviour and meat quality. Livest. Prod. Sci. 57, 137 – 145. Anon., 1981. Community Scale for the Classification of Carcasses of Adult Bovine Animals. E.C. No. 1208/81 and 2930/81 Official Publications of the European Communities, Luxembourg. Anon., 1999. Bord Bia Meat News. Bord Bia (Irish Food Board) Clanwilliam Court, Lower Mount St., Dublin Ireland. 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 different instruments on several food commodities. J. Food Sci. 53, 1737 – 1741. 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. J. Assoc. Off. Anal. Chem. 68, 87 – 6882. Dufrasne, I., Gielen, M., Limbourg, P., van Eenaeme, C., Istasse, L., 1995. Effects of a grazing period on performance of finishing bulls: comparison with an indoor finishing system. Anim. Sci. 60, 75 – 80. French, P., O’Riordan, E.G., Monahan, F.J., Caffrey, P.J., Vidal, M., Mooney, M.T., Troy, D.J., Moloney, A.P., 2000. Meat quality of steers finished on autumn grass, grass silage or concentratebased diets. Meat Sci. 56, 173 – 180. French, P., O’Riordan, E.G., Monahan, F.J., Caffrey, P.J., Mooney, M.T., Troy, D.J., Moloney, A.P., 2001. The eating quality of meat of steers fed grass and/or concentrates. Meat Sci. 57, 379 – 386.
Honikel, K.O., 1987. The water binding of meat. Fleischwirtschaft 67, 1098 – 1103. Jensen, L.R., Oksama, M., 1996. Influence of different housing systems on carcass and meat quality in young bulls. Proceedings 42nd ICOMST, Buenos Aires, Argentina, pp. 436 – 437. Lawrie, R.A., 1998. Lawrie’s Meat Science, 6th ed. Woodhead Publishing, Cambridge. Muir, P.D., Beaker, J.M., Brown, M.D., 1998. Effects of forageand grain-based feeding systems on beef quality: a review. N.Z. J. Agric. Res. 41, 623 – 635. O’Riordan, E.G., O’Kiely, P., 1996. Potential of beef production systems based on grass. Irish Grassland and Animal Production Journal, vol. 30, pp. 185 – 217. Priolo, A., Micol, D., Agabriel, J., 2001. Effects of grass feeding systems on ruminant meat colour and flavour. A review. Anim. Res. 50, 185 – 200. Shackelford, S.D., Koohmaraie, M., Cundiff, L.V., Gregory, K.E., Rohrer, G.A., Savell, J.W., 1991. Heritabilities and phenotypic and genetic correlations for bovine postrigor calpastatin acitivity, intramuscular fat content, Warner – Bratzler shear force, retail product yield and growth rate. J. Anim. Sci. 72, 857 – 863. Strange, E.D., Benedict, R.C., Gugger, R.E., Metzger, V.G., Swift, C.E., 1974. Simplified methodology for measuring meat colour. J. Food Sci. 39, 988 – 995. Sweeney, R.A., Rexroad, P.R., 1987. Comparison of LECO FP-228 ‘‘Nitrogen Determinator’’ with AOAC copper catalyst Kjeldahl method for crude protein. J. Assoc. Off. Anal. Chem. 70, 1028 – 1035. Varnam, A.H., Sutherland, J.P., 1995. The colour of meat. Meat and Meat Products—Technology, Chemistry and Micro Biology. Chapman & Hall, London, p. 26. Vestergaard, M., Oksbjerg, N., Henckel, P., 2000. Influence of feeding intensity, grazing and finishing feeding on muscle fibre characteristics and meat colour of semitendinosus, longissimus dorsi and supraspinatus muscles of young bulls. Meat Sci. 54, 177 – 185.
Short communication
The quality of meat and fatness of bulls offered ad libitum concentrates, indoors or at pasture A.P. Moloney a,b,*, R.J. Fallon a, M.T. Mooney b, D.J. Troy b a b
Teagasc, Grange Research Centre, Dunsany, Co. Meath, Ireland Teagasc, The National Food Centre, Ashtown, Dublin 15, Ireland
Received 21 January 2003; received in revised form 14 July 2003; accepted 28 July 2003
Abstract The darker coloured meat sometimes reported when cattle finished at pasture are compared to cattle finished indoors may reflect breed, diet, age at slaughter, exercise and/or environment. To determine the contribution of exercise/environment to beef colour, 24, 24-week-old Holstein/Friesian bulls were either housed (H, 2.5 m2/animal) or maintained at pasture (P, 133 m2/ animal) for 180 days prior to slaughter. The bulls were offered a barley-based concentrate ad libitum and minimum roughage (straw for H and grass for P) to maintain rumen function. Changes in fat deposition were used as an index of exercise. Concentrate intake (group basis) was 7.0 and 6.5 kg dry matter for H and P, respectively. Mean carcass weight was 234 and 246 (sed 4.63) kg for H and P, respectively. Corresponding values for carcass fat score, kidney fat weight and longissimus thoracis (LT) muscle lipid concentration were 3.13 and 2.67 (sed 0.165), 17.9 and 13.9 (sed 2.08) g/kg carcass and 6.7 and 5.4 (sed 0.172) g/kg. Neither LT lightness (Hunter L value) at 2 (mean 35.5) or 7 days (mean 35.7) post-mortem, redness (Hunter a value) at 2 (mean 11.1) or 7 days (mean 13.8) post-mortem nor the pattern of pH fall post-mortem, differed between H and P. It is concluded that exercise/environment sufficient to alter body composition did not affect LT muscle colour in bulls. D 2003 Elsevier B.V. All rights reserved. Keywords: Bulls; Meat; Concentrates; Indoors; Pasture
1. Introduction Meat colour has a large influence on the purchase decision of consumers (Baardseth et al., 1988). The preferred colour of beef is market dependent with Mediterranean consumers preferring light or pink coloured meat while British/Irish consumers prefer darker, redder coloured meat (Anon, 1999). Consis* Corresponding author. Present address: Teagasc, Grange Research Center, Dunsany, Co. Meath, Ireland. Tel.: +353-46-9061100; fax: +353-46-90-26154. E-mail address: [email protected] (A.P. Moloney). 0301-6226/$ - see front matter D 2003 Elsevier B.V. All rights reserved. doi:10.1016/j.livprodsci.2003.07.009
tently satisfying beef market colour specifications requires information on all factors that influence colour development. Animal production factors that may influence beef colour include breed, feed consumption, age at slaughter and ante-mortem handling practices (Lawrie, 1998). Beef from cattle slaughtered off pasture is often darker than beef finished indoors (Muir et al., 1998; Priolo et al., 2001) but in many such comparisons, variation in the factors listed above likely confound identification of individual factors causing this difference in meat colour. In addition, the opportunity for greater exercise/activity in grazing animals has led to speculation that this is also a
272
A.P. Moloney et al. / Livestock Production Science 87 (2004) 271–276
contributory factor to darker meat in grazing animals (Vestergaard et al., 2000; Varnam and Sutherland, 1995). French et al. (2000), however, found no difference in colour of meat from animals slaughtered at a similar age and energy intake whether they were offered grazed grass or concentrates indoors, prior to slaughter. This suggests that provided plane of nutrition and animal management is adequate to ensure sufficient reserves of glycogen in muscle prior to slaughter, exercise/activity per se is not a cause of darker meat in grazing animals. The objective of this study was to confirm the above suggestion by offering cattle a high energy concentrate ration ad libitum indoors and at pasture, thus removing the possible confounding effect of ration composition on meat colour.
2. Materials and methods 2.1. Experimental design and animal management Fifty-four, 24-week-old autumn-born Holstein/Friesian bull calves with an initial weight of 233 kg were blocked in groups of three on a descending bodyweight basis. Within block the animals were assigned at random to a barley soyabean meal ration (rolled barley (850), soyabean meal (130) and vitamins (20) g/kg) offered either housed (H), at pasture (P) throughout a 180-day experimental period or at pasture initially for subsequent removal (Treatment 3). All animals were adapted to the barley soyabean meal ration prior to the beginning of the study such that they had ad libitum access at the start of the experimental period. The H animals were accommodated on concrete slats in a naturally ventilated house with six animals per pen. Each animal had a pen area allowance of 2.5 m2. For P animals a pasture area of 0.96 ha was available. At one corner of this area, the concentrates were offered in a covered ‘‘lean-to’’ shed such that concentrates were protected from the environment and vermin. The animals were managed such that grass consumption would be minimised to a level required to maintain rumen health and therefore optimise concentrate consumption. Thus, the pasture area was divided into three paddocks of 3213 m2. Within each paddock, the space allowance was 85 m2/animal and, based on the mean grass growth curve for Grange Research
Centre for the previous 4 years (O’Riordan and O’Kiely, 1996), an expected forage supply of 0.5 kg dry matter (DM)/animal (based on a mean daily grass growth of 75 kg DM/ha and a utilisation of 75%). Grass height was 15 –18 cm when cattle entered a paddock. Cattle remained in a paddock until sward height decreased (due to less than average grass growth) or ground conditions deteriorated (due to rainfall). The other paddocks were managed in parallel, to maintain the target grass height. On July 1 (after 77 days), coincident with the expected seasonal decline in grass growth (to 50 kg DM/ha on average), the 18 cattle on treatment 3 were removed to maintain the target forage supply for the remaining cattle. The animals in treatment 3 are not considered in the remainder of this study. The space allowance for the remainder of the study was 170 m2/animal. The mean space allowance for the duration of the study was therefore 133 m2/animal. Concentrate feed intakes were recorded weekly and fresh water was available at all times. Indoor animals each received a daily allowance of 500 g straw. 2.2. Post-slaughter carcass measurements and sampling All animals were slaughtered after 180 days. On the day of slaughter, animals were weighed, transported 15 km to a commercial slaughter facility and slaughtered within 2 h of removal from Grange Research Centre. During transport and lairage, animals were maintained in their treatment/pen groups. After slaughter, cold carcass weight (hot carcass weight 0.98, assuming a weight loss of 20 g/kg during cooling) was recorded. Carcass weight gain was estimated as the difference between final carcass weight and estimated initial carcass weight (assuming a killing-out rate of 550 g/ kg liveweight). The weight of kidney and channel fat (KCF) on each carcass was recorded. The carcasses were classified for fat score (1 = leanest and 5 = fattest) using the EU Beef Carcass Classification Scheme (Anon, 1981). Meat quality assessments were only carried out on carcasses from animals in the first 12 blocks. One hour post-mortem, the pH of the m. longissimus thoracis (LT) was measured by making a scalpel incision and inserting a glass electrode (Model EC2010-11, Amargruss Electrodes, Castlebar,
A.P. Moloney et al. / Livestock Production Science 87 (2004) 271–276
Mayo, Ireland) attached to a portable pH meter (Model no. 250 A, Orion Research, Boston, USA) approximately 2.5 cm into the muscle. This measurement was repeated hourly for 8 h and again at 24 h and 48 h post mortem. The sides were cold-boned at 48 h post-mortem. Steaks, 2.5 cm thick, were frozen for compositional analysis. Further samples of LT were vacuum packed (SuperVac GK-166T) and aged at 4 jC for 7 days post-mortem. Steaks, 2.5 cm thick, were then cut for Warner –Bratzler shear force (WBSF) measurement. These were vacuum-packed and frozen at 30 jC for subsequent analysis. Steaks (2.5 cm thick) were cut at 2 and 7 days post-mortem for colour measurements according to the procedure of Strange et al. (1974). Freshly cut samples were wrapped in an oxygen permeable PVC wrap and left to bloom at 4 jC for 3 h. The Hunter ‘L’, ‘a’ and ‘b’ values of each sample was then measured using a Hunter lab Ultra Scan XE colorimeter with Universal Software Version 2.2.2 (Hunter Associates Laboratory, 11491 Sunset Hills Road, Reston, VA, 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). Warner – Bratzler shear force was measured according to the procedure of Shackelford et al. (1991). Steaks (2.5 cm) were cooked in retortable vacuum pack bags to an internal temperature of 70 jC, by immersing in a water bath (Model Y38, Grant Instruments) at 80 jC. 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 fibres and sheared using an Instron Universal testing machine equipped with a Warner – Bratzler shearing device. The crosshead speed was 5 cm/min. Instron Series 1X Automated Materials Testing System software for Windows (Instron, High Wycombe, Bucks, UK) was employed in the analysis. Intra-muscular fat and moisture concentration of thawed minced LT samples were determined using an automated, integrated microwave moisture and methylene chloride fat extraction method (Bostian et al., 1985) on a CEM moisture/solids analyser (Model AVC 80, CEM, Matthews, NC, USA). Protein was determined by the method of Sweeney and Rexroad (1987) using a LECO protein analyser (LECO FP 428, LECO, St. Joseph, MI, USA.
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2.3. Statistical analyses Data were subjected to analysis of variance using a model that had block and treatment as main effects. pH data were analysed according to a split-plot design with treatment in the main plot and time of measurement and the treatment by time interaction in the sub-plot.
3. Results The experiment began in April and animals were slaughtered in October. Monthly rainfall and sunshine averaged 71.5 mm and 135 h, respectively, for April to October, inclusive. The corresponding average
Table 1 Carcass and kidney/channel fat weight and m. longissimus thoracis characteristics in bulls offered ad libitum concentrates indoors or at pasture
Initial weight (kg) Final weight (kg) Growth (g/day) Carcass weight (kg) Kidney/channel fat (kg) (g/kg carcass) Fat score Killing-out (g/kg carcass) Conformation Colour—2 days L a b Saturation Hue angle Colour—7 days L a b Saturation Hue angle Composition (g/kg) Fat Moisture Protein Ash Drip loss (g/kg) Shear force (kg) Cook loss (g/kg) PH48
House
Pasture
sed
Sig
228.3 451.0 1237 234.5 4.18 17.9 3.13 520 1.79
236.6 473.2 1314 245.6 3.46 13.9 2.67 519 1.75
9.53 8.25 59.9 4.63 0.50 2.08 0.165 5.5 0.106
NS * NS * NS 0.068 * NS NS
35.6 11.4 7.4 13.6 0.58
35.5 10.9 7.2 13.0 0.58
0.68 0.49 0.28 0.53 0.011
NS NS NS NS NS
35.5 13.3 8.3 15.7 0.56
35.8 14.2 8.6 16.6 0.55
0.73 0.76 0.41 0.84 0.013
NS NS NS NS NS
6.7 749.3 232.1 11.4 25.8 5.53 319 5.61
5.4 750.2 232.0 11.3 27.7 5.34 328 5.57
1.72 3.13 2.95 0.26 1.34 0.186 1.1 0.039
NS NS NS NS NS NS NS NS
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Fig. 1. Post-mortem pH of LD muscle in bulls offered ad libitum concentrates, indoors ( w ) or at pasture (n) [Treatment time sed 0.075].
maximum and minimum temperatures were 16.5 and 8.8 jC, respectively. Daily concentrate consumption averaged 7.0 and 6.5 kg DM for H and P animals, respectively. On average, P animals were heavier ( P < 0.05) at slaughter, had heavier ( P < 0.05) carcasses that had a lower ( P < 0.05) fat score and a smaller ( P < 0.1) proportion of kidney and channel fat (Table 1). Intra-muscular lipid concentration followed this trend but neither muscle composition nor any of the measured muscle attributes differed between H and P treatments (Table 1). Muscle pH declined ( P < 0.001) post-mortem but there was no evidence that the pattern of decrease differed between treatments (Fig. 1).
4. Discussion In four of the eight studies reviewed by Muir et al. (1998), animals finished at pasture had darker meat. Muir et al. (1998) suggested that this reflected lower energy consumption of the grazing animals but might also reflect the greater activity/exercise of the grazing animals. Varnam and Sutherland (1995) similarly hypothesised that grass-fed animals have more muscle myoglobin due to more activity pre-slaughter than their feedlot counterparts. In previous studies at this institute (French et al., 2000, 2001), there was no evidence that animals finished at pasture had darker meat than animals fed restricted or ad libitum amounts of concentrates indoors. In these studies, the stocking density was tightly controlled and the animals were rotationally grazed. It was unlikely that the animals had the same opportunity for exercise when compared to the grass-
fed animals in the studies examined by Muir et al. (1998). The objective of the present study was to examine the effects of exercise/environment on colour of meat from animals fed a common high energy diet confined inside, or outside with liberal opportunity for exercise/activity. A concentrate diet was used rather than offering the H animals cut grass, as it is difficult to ensure that consumption of ‘‘zero-grazed’’ grass will supply similar nutrients as grazed grass due to selection by grazing animals. The degree of exercise/ activity of P animals was not measured in this study but all indices of fatness were lower in P animals compared to H animals. As energy consumption was similar (the possible slightly higher grass consumption over the final 100 days of the study compensating for the difference in concentrate consumption), we believe the decrease in fatness of P animals is consistent with greater energy expenditure on exercise and/ or partitioning of absorbed energy towards muscle as a result of exercise. This contrasts with the findings of French et al. (2000) who observed no difference in these indices of fatness between indoor and grazing animals. We therefore interpret the body composition data in the present study as reflecting greater exercise/ activity in P animals compared to H animals. It is acknowledged, however, that environmental conditions of temperature, rainfall and photoperiod differed between H and P treatments and that these differences may have contributed to the apparent effects of exercise/activity on body composition, i.e. possibly greater energy expenditure to maintain core body temperature in P animals. That there was no difference in the pattern of pH fall or ultimate pH indicates similar glycogenolysis post-slaughter in animals from both groups. The P
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animals therefore did not suffer excessive glycogen depletion either due to exercise/activity during the study or during transport and lairage. This lack of difference in pH was reflected in the similar muscle colour of both treatment groups after 2 and 7 days storage post-mortem. Vestergaard et al. (2000) reported that bulls slaughtered at 360 kg from pasture had darker LD when compared to bulls slaughtered at a similar weight from a high energy indoor diet. They suggest that ‘‘differences in physical activity are probably the main reason’’ for the differences observed. Nevertheless, in that study, muscle glycogen concentration was lower and consequently muscle ultimate pH was higher in the grazing animals, which contribute to darker meat per se. Moreover, the grazing animals were 100 days older than the indoor animals and their data show that increasing age from 360 to 460 kg on a common diet also resulted in darker meat (Vestergaard et al., 2000). Their conclusion on the effect of exercise is therefore rather weak. In contrast, Andersen et al. (1991) compared tiestalls (width 125 cm) with loose housing at 1.8 m2/ animal on either a slatted floor or deep bedding. Energy consumption for bulls was similar for each group, but the loose housed animals had lower dissected fat trim in the carcass, dissected fat in the loin and intramuscular fat in LT. The latter animals also had darker meat, which appears to be related to decreased time spent lying and more time spent eating than the animals in the tie-stalls. Similar results were recorded by Jensen and Oksama (1996). These data with bulls and those of Andrighetto et al. (1999) with veal calves suggest that exercise/activity in a housed environment can result in darker meat. The lack of an effect on meat colour in the present study may reflect the degree of exercise/activity of the P animals compared to H animals since the space allowance of the H animals in the present study was greater than that of the studies cited above. Thus, there might be a threshold space allowance above which no further effect of exercise per se will occur. The type as well as the intensity of exercise/activity may be important for meat colour. Studies with imposed exercise/activity of varying durations and patterns are required to clarify this issue. A further hypothesis of the effect of exercise on muscle colour is an alteration in muscle pigment
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concentration due to the exercise-induced increase in oxidative fibres that have a higher concentration of myogloblin and a decrease in glycolytic fibres (Vestergaard et al., 2000). Grazed bulls, which had darker longissimus muscle than indoor bulls in the study of Dufrasne et al. (1995), had higher pigment concentrations. Increased pigment concentrations appear to be related to darker muscle in the studies of Andersen et al. (1991) and Jensen and Oksama (1996). It is clear that in the present study, cattle did not exercise sufficiently to effect such a change in muscle structure. It is recognised that the muscle used in this study is predominantly a postural muscle and may therefore be less affected by exercise than locomotor muscles in the hip or legs. It has been shown that feeding regime, housing system and exercise/activity may affect the hypertrophic and metabolic response of individual muscles differently (Aalhus and Price, 1991; Vestergaard et al., 2000). There was no difference in tenderness between H and P animals. Similar results were observed by Andersen et al. (1991) and Jensen and Oksama (1996) despite apparent increases in longissimus muscle growth, thus rejecting the hypothesis that muscle from exercised animals, by virtue of faster growth rate, is more tender, as seen in sheep by Aalhus et al. (1991), and also in veal calves by Andrighetto et al. (1999). It is concluded that the degree of exercise/activity and likely environmental conditions experienced by P animals in this study, while sufficient to alter body composition, did not alter LT colour in bulls. Further studies involving imposed exercise are required to confirm the effect of exercise per se on meat colour. Acknowledgements This research was partially supported by grant aid under the Food Sub-Programme of the Operational Programme for Industrial Development, which was administered by the Irish Department of Agriculture and Food and supported by national and EU funds. References Aalhus, J.L., Price, M.A., 1991. Endurance-exercised growing sheep: 1. Post mortem and histological changes in skeletal muscles. Meat Sci. 29, 43 – 56.
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