Effect of body weight on the carcass composition of French Lop rabbits

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1 Effect of body weight on the carcass composition of French Lop rabbits D. Michalik, A. Lewczuk, W. Brzozowski, and K. Wawro Department of Commodity Science and Animal Improvement, University of Warmia and Mazury, Olsztyn, Poland. Received 27 May 2008, accepted 10 October Michalik, D., Lewczuk, A., Brzozowski, W. and Wawro, K Effect of body weight on the carcass composition of French Lop rabbits. Can. J. Anim. Sci. 89:4751. The experiment was performed on 60 male French Lop rabbits reared under extensive conditions and sacrificed at body weights of approximately 3 kg at the age of 150 d (30 animals) and approximately 4.5 kg at the age of 210 d (30 animals). Chilled carcasses without heads were divided into the front, middle and hind sections, which were then dissected to separate lean meat (including intramuscular fat), fat and bones. An increase in the body weight of rabbits at slaughter was accompanied by a decrease, of about 0.60%, in the proportion of the head and giblets (kidneys, liver, heart and lungs) in the carcass, and by an increase in the perirenal fat content from 0.66 to 1.69%. The average carcass dressing percentage of rabbits sacrificed at an average body weight of 3054 g reached 49.13%, and it was 2.49% higher than in rabbits slaughtered at a body weight of 4427 g. The percentage content of the front, middle and hind sections of the carcasses of the lighter rabbits was 38.50, and 39.74%, respectively. In the carcasses of the heavier rabbits, the proportion of the front section was 2.29% higher, the proportion the hind section was 2.45% lower, while the proportion of the middle section remained at a similar level as in the lighter rabbits. The carcasses of the lighter rabbits, compared with the carcasses of the heavier rabbits, had a higher percentage content of meat (82.60 vs %; P50.01) and a lower percentage content of fat (1.78 vs. 4.38%). In addition, rabbits sacrificed at a body weight of approximately 3.0 kg were marked by a higher content of lean meat in the middle and front sections of the carcass (by 1.89 and 3.07%, respectively), and by a slightly lower content of lean meat in the hind section (by 0.85%). Key words: Rabbit, body weight, slaughter quality Michalik, D., Lewczuk, A., Brzozowski, W. et Wawro, K Incidence du poids sur la composition de la carcasse des lapins be liers français. Can. J. Anim. Sci. 89:4751. L expe rience portait sur 60 lapins be liers franc ais maˆ les. Les animaux ont e te e leve s de manie` re intensive puis sacrifie s au poids d environ 3 kg à l aˆ ge de 150 jours (30 sujets) ou d environ 4,5 kg a` l aˆ ge de 210 jours (30 sujets). Les carcasses refroidies, sans la tête, ont e te de bitées en trois sections (avant, milieu, arrière) qui ont elles-meˆ mes été disse quées pour se parer la viande maigre (graisse intramusculaire incluse), le gras et les os. La hausse du poids corporel s accompagne d une diminution d environ 0,60 % de la teˆ te et des abats (reins, foie, cæur, poumons) ainsi que d une augmentation de la capsule adipeuse du rein, dont la proportion passe de 0,66 à 1,69 %. Le pourcentage de parage de la carcasse moyenne des lapins abattus au poids moyen de g s e lève a` 49,13 %, soit 2,49 % de plus que celui des sujets abattus au poids de g. Chez les lapins moins lourds, l avant, le milieu et l arrie` re de l animal repre sentaient respectivement 38,50, 21,76 et 39,74 % de la carcasse. Chez les plus lourds, la section avant e tait 2,29% plus importante et la section arrière, 2,45% moins importante, celle du centre gardant la meˆ me proportion. Comparativement a` celle des sujets lourds, la carcasse des sujets légers contenait un pourcentage de viande plus e leve (82,60 c. 81,15 %; P50,01) et une plus faible proportion de gras (1,78 c. 4,38 %). De plus, les lapins abattus au poids d environ 3,0 kg contenaient plus de viande maigre dans leurs parties avant et centrale (1,89 et 3,07 % respectivement), ainsi que le ge` rement plus de viande maigre dans leur partie arrie` re (0,85 %). Rabbits are bred primarily for their meat, which is a low-calorie source of high-quality protein, vitamins and microelements, low in fat and cholesterol (Stalin ski et al. 1993; Zajac 1999, 2001; Bernardini Battaglini et al. 1995; Sikora et al. 1995; Skrˇ ivanova et al. 2000; Da nicke et al. 2004). Due to its high eating quality, rabbit meat is in great demand worldwide (Barabasz and Bieniek 2003; Frindt 2004). Consumers prefer carcasses high in meat and low in fat. The body proportions and the percentage content of particular tissues, which determine the overall quality of a carcass, are affected by the age and body Mots clés: Lapin, poids corporel, qualité à l abattage weight of rabbits (Stobiecka 1990; Stalin ski et al. 1993; Bieniek et al. 1994; Zajac 1999, 2001, 2002). Studies conducted by the above authors generally involved medium rabbit breeds, while information on the slaughter quality of large rabbit breeds is scant. Zajac (2003, 2004) investigated crosses between New Zealand White rabbits and the French Lop, Flemish Giant and Checkered Giant breeds and found that their carcass dressing percentage increased with age, proportionally to slaughter weight, whereas the content of primal cuts in the carcass remained at the same level. According to Zajac, 47

2 48 CANADIAN JOURNAL OF ANIMAL SCIENCE rabbits sacrificed at body weight of around 2.5 kg are marked by a low carcass dressing percentage, ranging from 50 to 52%. An increase in body weight to about 3.5 kg is followed by an increase in carcass dressing percentage to 56%. Sikora et al. (1995) demonstrated that the carcass dressing percentage of Flemish Giant rabbits sacrificed at body weights of 4.5 and 5.5 kg reached 68.9 and 69.1%, respectively, which means that the difference between the lighter and heavier animals was as low as 0.2%. Large rabbit breeds differ in body conformation from medium and small breeds, which may have an impact on their slaughter quality. Flemish Giants are long-bodied, with broad, well-filled and welldeveloped shoulders and chest, rounded hindquarters, a broad head and long ears with bent tips. French Lops are stocky and short-bodied, with cut off hindquarters, a broad head, floppy and fleshy ears, and their pelt has a large surface area (Frindt 2004). Very few publications address the carcass quality of large rabbit breeds, which are becoming more and more popular among breeders, and are increasingly used for both pure- and crossbreeding. Therefore, the objective of this study was to determine selected slaughter quality traits of French Lop rabbits sacrificed at body weights of approximately 3.0 kg and 4.5 kg. MATERIALS AND METHODS The experimental procedures were conducted in accordance with Council Directive 98/58/EC of 1998 Jul. 20 concerning the protection of animals kept for farming purposes. The experiment was performed on 60 male French Lop rabbits reared over the same period of time under extensive conditions, and fed ad libitum farmproduced feed (grass-legume mixtures, meadow hay, oat, steamed potatoes, carrots, cabbage). The animals were sacrificed at body weight of approximately 3 kg at the age of 150 d (30 animals) and approximately 4.5 kg at the age of 210 d (30 animals), in accordance with Council Directive 93/119/EC of 1993 Dec. 22 on the Protection of Animals at the Time of Slaughter or Killing. After slaughter, bleeding and skinning, the front feet were removed at the carpal joint, and the hind feet at the hock joint. The ears were cut off at the skin. Skinned carcasses were eviscerated, and the liver, heart, lungs and perirenal fat were weighed to an accuracy to 1 g. After evisceration the carcasses were cold-stored for 24 h at 2778K. Chilled carcasses were weighed, including head and kidneys. Following the removal and weighing of kidneys, the head was cut off between the first and second cervical vertebra, and it was weighed. Carcasses without heads were divided into three primal cuts (front, middle, hind), as follows: Cut 1 between the last dorsal vertebra and the first lumbar vertebra; Cut 2 between the last lumbar vertebra and the first sacral vertebra. Primals were weighed and their proportion of total carcass weight was calculated based on the formula: weight of a primal cut (g) 100 total carcass weight (g) The primals were dissected into lean meat (including intramuscular fat), fat and bones. The percentage content of lean, fat and bones in the primal cuts was calculated as a ratio between the weight (g) of a given tissue component in a primal cut and the total weight (g) of this primal cut 100. The percentage content of lean meat, fat and bones in the whole carcass was determined in the same way. The percentage content of lean meat from the front, middle and hind sections of the carcass was compared to total weight by dissection using the formula: meat weight in a carcass section (g) meat weight in the whole carcass (g) 100 A statistical analysis (STATISTICA 7.1; StatSoft, Inc. 2006) of numerical data involved the determination of the characteristics of the experimental materials (arithmetic means x and standard deviations s) and of the significance of differences between the mean values of the investigated traits of rabbits sacrificed at different body weight ( t test). RESULTS AND DISCUSSION The average body weights of rabbits were similar to the values assumed in the methodology, and they reached 3054 g and 4427 g, respectively (Table 1). The hot carcass weights (without head) were 1491 g and 2064 g, respectively. The results obtained for the hot carcass weight of the lighter rabbits are comparable with those reported by other authors for rabbits of medium breeds Table 1. Weight of body, carcass and cuts, and carcass dressing percentage Weight of (g) Body 3054B A 236 Carcass without head 1491B A 197 Head 197B A 19 Perirenal fat 20B 13 75A 53 Kidneys 16B 2 22A 4 Liver 90B A 16 Heart and lungs 24B 4 40A 6 Carcass dressing percentage z (%) 49.13A B 2.44 z Ratio between hot carcass weight (without head) to live weight. A, B Significance of differences between means at P50.01.

3 MICHALIK ET AL. * CARCASS COMPOSITION OF FRENCH LOP RABBITS 49 slaughtered at body weight of 3.0 kg (Bieniek et al. 1994; Zajac 1999, 2001, 2002; Bielan ski 2000). The carcass weight of the heavier rabbits was found to be lower than reported by Sikora et al (1995) in Flemish Giants, which could result from different body characteristics of these two breeds, and primarily from differences in body length, shape of hindquarters and the weight of ears and pelt. One of the key slaughter quality traits in rabbits is carcass dressing percentage, which significantly affects production profitability, sale price and the processing suitability of raw material. In the present study the average carcass dressing percentage of rabbits sacrificed at body weight of around 3.0 kg reached 49.13%, and it was 2.49% higher (P50.05) than that reported for rabbits weighing 4.5 kg. This could result from higher values for perirenal fat and hide in older rabbits. The above results differ from those obtained by Zajac (2001, 2002, 2003, 2004), who analyzed the effect of different slaughter times on carcass quality in medium rabbit breeds and their crosses, and demonstrated that the greater the slaughter weight the higher the carcass dressing percentage, which is most probably due to inter-breed differences. Average head weight reached 197 g in the lighter rabbits, and it was 69 g lower than in the heavier animals (P 50.01; Table 1). An increase in the body weight of rabbits was correlated with an increase in the weight of the liver (from 90 to 102 g), kidneys (from 16 to 22 g), heart and lungs (from 24 to 40 g) and perirenal fat (from 20 to 75 g). When the above values were expressed as a percentage content of body weight, the proportion of head and giblets decreased in the heavier rabbits, in comparison with the lighter ones (3.70 and 4.27%, respectively), while the proportion of perirenal fat increased (1.69 and 0.66%, respectively). These results correspond with the findings of other authors (Skrˇ ivanova et al. 2000; Zajac 2001, 2002; Tu mova et al. 2003; Da nicke et al. 2004), who also determined that the percentage content of retail cuts in rabbit carcasses is dependent on slaughter weight. Another important indicator of slaughter quality in rabbits is the percentage content of primal cuts in the carcass. An analysis of the data in Fig. 1 shows that the content of the front, middle and hind sections in the carcasses of the lighter rabbits was 38.50, and 39.74%, respectively. In the carcasses of the heavier rabbits, the content of the front and hind sections was 2.29% higher and 2.45% lower, respectively, in comparison with rabbits sacrificed at body weight of around 3.0 kg (P50.01). The percentage content of the middle section was at a similar level in both groups of rabbits: 21.80%. The percentage content of primal cuts in the carcasses of rabbits weighing approximately 3.0 kg is comparable with that reported by other authors (Stalin ski et al. 1993; Bieniek et al. 1994; Skrˇ ivanova et al. 2000; Lewczuk et al. 2000, 2001; Zajac 2003, 2004). An analysis of the tissue composition of primal cuts (Table 2) revealed that the middle section of the carcass Fig. 1. Percentage content of carcass parts (carcass weight 100%). had the highest content of lean meat, in rabbits sacrificed at body weight of around 3.0 kg and 4.5 kg (87.74 and 85.85%, respectively). It should be stressed that the difference in the meat content of this carcass section, determined at 1.89% to the advantage of the lighter rabbits, was statistically significant (P 50.01). The lighter rabbits were also marked by a higher (by 3.07%; P50.01) meat content of the front section. The meat content of the hind section of the carcass in the lighter rabbits reached 82.79%, and it was 0.85% lower than in the heavier rabbits (P 50.05). In studies conducted on rabbits of different breeds, the meat content of a whole carcass ranged from 66 to 83% in the front section, from 76 to 84% in the middle section, and from 75 to 84% in the hind section (Labecka and Gardzielewska 1990; Stalin ski et al. 1993; Bieniek et al. 1994). This indicates that French Lop rabbits weighing 3.0 kg are characterized by a very high content of lean meat in the middle section. The bone content of primal cuts in rabbits sacrificed at a body weight of around 3.0 and 4.5 kg was comparable, i.e., and 14.03% in the front section, 8.77 and 8.44% in the middle section, and and 13.93% in the hind section, respectively (Table 2). The percentage content of fat in the front, middle and hind sections of the carcass in rabbits weighing approximately 4.5 kg, in comparison with rabbits weighing approximately 3.0 kg, was higher by, respectively, 4.40, 2.59 and 0.26% (P 50.01). According to the authors cited above, the bone content of a carcass in medium rabbit breeds ranges as follows:front section 14.1 to 24.3%, middle section 6.4 to 15.6%, hind section 14.1 to 21.6%; the respective values for fat content are 5.6 to 7.9%, 2.4 to 10.3% and 1.5 to 3.1%. This indicates that in French lops, in comparison with medium-breed rabbits, primal cuts are characterized by a relatively low bone and fat content. The low proportion of fat in primals was a consequence of both the breed effect and the extensive system of management.

4 50 CANADIAN JOURNAL OF ANIMAL SCIENCE Table 2. Weight of primal cuts and carcass composition Weight of the front section (g) 575B A 101 Composition of the front section Meat (g) 457B A 69 (%) 79.49A B 4.75 Fat (g) 17B 12 65A 54 (%) 2.87B A 5.28 Bones (g) 83B A 12 (%) Weight of the middle section (g): 325A A 63 Composition of the middle section Meat (g) 285B A 51 (%) 87.74A B 3.01 Fat (g) 6B (%) 1.69B A 3.49 Bones (g) 28B 5 38A 8 (%) Weight of the hind section (g) 592B A 56 Composition of the hind section Meat (g) 490B A 51 (%) 82.79b a 1.22 Fat (g) 5B 2 9A 5 (%) 0.77b a 0.70 Bones (g) 89B A 11 (%) 14.97a b 1.70 Significance of differences between means: A, B at P50.01 a, b at P Analysis of tissue composition (Table 3) confirmed the higher quality of the carcasses of rabbits sacrificed at a body weight of approximately 3.0 kg, reflected in a high meat content (82.60% on average) and a low fat (1.78%) and bone content (13.47). The carcasses of the heavier rabbits contained less meat (81.15%, P 50.05) and more fat (4.38%, P50.01). Table 3. Content of meat, fat and bones in carcass and meat-to-bone ratio Analysis of the proportions of meat in primals compared with total meat weight in the carcass shows that in rabbits of approximately 3.0 kg, the meat content of the front section was 3% higher and the meat content of the hind section was 0.85% lower than in 4.5 kg rabbits (Table 2). The carcasses of lighter rabbits, Content in carcass Meat (g) 1232B A 150 (%) 82.60a b 2.81 Fat (g) 27B 16 94A 77 (%) 1.78B A 3.23 Bones (g) 200B A 24 (%) Mat-to-bone ratio Significance of differences between means: A, B at P50.01 a, b at P Fig. 2. Percentage content of meat in the front (a) front section, (b) middle section, (c) hind section (meat weight in the carcass100%).

5 MICHALIK ET AL. * CARCASS COMPOSITION OF FRENCH LOP RABBITS 51 compared with those of heavier animals, had a significantly lower proportion of meat in the front section (37.05 and 38.38%, respectively; P 50.05) and a significantly higher proportion of meat in the hind section (39.84 and 38.50%, respectively; P 50.01; Fig. 2). This most probably results from age-related changes in the growth rate and proportions of primals in the carcass (Fig. 1). CONCLUSIONS French Lops rabbits sacrificed at a body weight of around 3.0 kg are characterized by a higher carcass dressing percentage than those slaughtered at a body weight of around 4.5 kg. An increase in the slaughter weight of rabbits is accompanied by a decrease in the proportion of the valuable hind section of the carcass, and by an increase in the front section of the carcass, while the proportion of the middle section remains at a similar level. The carcasses of the lighter rabbits, compared with the carcasses of the heavier rabbits, have a higher percentage content of meat and a lower percentage content of fat. The former are also marked by a higher content of lean meat in the middle and front sections of the carcass, and by a slightly lower content of lean meat in the hind section. The results of this study indicate that the carcasses of French Lop rabbits reared under extensive conditions are of better quality when slaughtered at 3.0 as opposed to 4.5 kg body weight. Barabasz, B. and Bieniek, I Rabbits commercial meat production. PWRiL, Warsaw, Poland. 132 pp. Bernardini Battagalini, M., Castellini, C. and Lattailip, P Effect of sire strain, feeding, age and sex on rabbit carcass. World Rabbit Sci. 3: 914. Bielan ski, P Effect of environmental factors on growth of rabbits of some breeds and their slaughter performance. Ann. Anim. Sci. 27: Bieniek, J., Dorozyńska, D., Stalin ski, Z. and Kolczak, T Studies on meat production from rabbits. II. Effect of age on meat quality. Pr. i Mat. Zoot. 46:6573. Council Directive 93/119/EC of 22 December 1993 on the Protection of Animals at the Time of Slaughter or Killing OJ L 340, pp Council Directive 98/58/EC of 20 July 1998 concerning the protection of animals kept for farming purposes OJ L 221, pp Da nicke, S., Ahrens, P., Strobel, E., Brettschneider, J., Vicke, M. and Lengerken, G Effects of feeding rapeseed to fattening rabbits on performance, thyroid hormone status, fatty acid composition of meat and meat quality traits. Arch. Geflugelk. 68:1524. Frindt, A Fundamentals of rabbit raising. Wyd. Oficyna Wydawnicza Hoza, Warsaw, Poland. 68 pp. Lewczuk, A., Janiszewska, M., Mohomet Ayman Al. Saadi and Michalik, D The utility of certain intravital and post slaughter traits for the evaluation of carcass tissue composition in Californian rabbits. Natur. Sci. 7: Lewczuk, A., Postek, A., Brzozowski, W., Michalik, D. and Janiszewska, M The value of chosen pre- and postslaughter traits for the estimation of lean yield in valuable carcass parts of Danish White rabbits. Anim. Sci. Pap. Rep. 19: Labecka, S. and Gardzielewska, J The effect of interbreed crossing of rabbits on their slaughter values. Rocz. Nauk. Zoot., 17:2540. Sikora, T., Waciak, A. and Kaim, D Physicochemical and sensory properties of meat of selected breeds of rabbits. Zesz. Nauk. AE, Krako w 462: 519. Skrˇ ivanowa, V., Marounek, M., Tumowa, E., Skrˇ ivan, M. and Lasˇ tovkova, J Performance, carcass, yield and quality of meat in broiler rabbits:a comparison of six genotypes. Czech J. Anim. Sci. 45:9195. Stalin ski, Z., Bieniek, J., Krelowska-Kulas, M., Dorozyńska, D. and Jaros, J The effect of crossing New Zealand White and Black Bay rabbits on the slaughter and meat value of crossbreds. Pr. i Mat. Zoot. 44:3343. Stobiecka, D The effect of breed, sex and age on the quality attributes of rabbit meat. Acta Agr. Silv. 29: Tumowa, E., Skrˇ ivanowa, V. and Skrˇ ivan, M Effect of restricted feeding time and quantitative restriction in growing rabbits. Arch. Geflugelk. 67: Zajac, J Effect of slaughter weight on slaughter value and meat quality in the rabbit. Rocz. Nauk. Zoot. 26:5972. Zajac, J Comparison of fattening traits slaughter and meat quality in rabbits of different breeds and their crossbreeds. Rocz. Nauk. Zoot. 28: 923. Zajac, J Analysis of slaughter performance in three breeds of rabbits with regard different slaughter weight. Rocz. Nauk. Zoot. 29:4960. Zajac, J Results of commercial crossing of rabbits. Rocz. Nauk. Zoot. 30:2535. Zajac, J Using males of large breeds for commercial crossbreeding of rabbits. Rocz. Nauk. Zoot. 31:5565.