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Effects of castration on growth performance and carcass characteristics of Awassi lambs fed high concentrate diet
Small Ruminant Research 65 (2006) 149–153
Technical note
Effects of castration on growth performance and carcass characteristics of Awassi lambs fed high concentrate diet S.G. Haddad ∗ , M.Q. Husein, R.W. Sweidan Department of Animal Production, Jordan University of Science and Technology, P.O. Box 3030, Irbid 22110, Jordan Received 6 July 2004; received in revised form 12 April 2005; accepted 12 May 2005 Available online 22 June 2005
Abstract New born male Awassi lambs were randomly assigned to one of two groups: intact (12 lambs) and castrated (12 lambs). After weaning (body weight = 21.0 kg) at the age of 70 days, lambs consumed a high concentrate diet ad libitum for 60 days after which all lambs were sacrificed. The metabolizable energy and CP content of the diet were 2.90 Mcal/kg and 16%, respectively (all in DM basis). Dry matter intake was higher for the castrated lambs as compared to intact animals. Castration had no effect on average daily gain (ADG). Feed to gain ratio for castrated lambs was significantly higher compared to intact lambs. Hot carcass weight, cold carcass weight and dressing percentages were all unaffected by castration. However, kidney fat for castrated lambs was significantly higher compared to the intact lambs. As a percentage of cold carcass weights, intact lambs had greater leg weights compared to the castrated lambs. Fat thickness on the loin area was higher for the castrated lambs. Castrated lambs’ legs had more total and subcutaneous fat compared to the intact lambs. Intact lambs had greater percentages of lean and bone in their legs as compared to the castrated lambs. In conclusion, castration did not affect ADG, cold carcass weight or dressing percentage of Awassi lambs. However, it reduced efficiency of feed utilization, increased subcutaneous fat and decreased carcass leanness. Therefore, due to local consumer preference of leaner carcasses with minimum subcutaneous fat, castration of Awassi lambs to be slaughtered approximately 130 days is not recommended under an intensive feeding system. © 2005 Elsevier B.V. All rights reserved. Keywords: Castration; Testosterone; Carcass characteristics; Awassi lambs
1. Introduction Awassi is the only sheep breed in Jordan and is well adapted to its harsh environment. The growth rate for ∗ Corresponding author. Tel.: +962 2 7201000x22220; fax: +962 2 7095069. E-mail address: [email protected] (S.G. Haddad).
0921-4488/$ – see front matter © 2005 Elsevier B.V. All rights reserved. doi:10.1016/j.smallrumres.2005.05.029
Awassi lambs is consistently lower than that obtained with Western breeds. Through intensive farm management practices, the growth performance of Awassi lambs appears to show sign of increased productivity (Haddad et al., 2001). One practice that is becoming more common in feedlotting Awassi lambs is castration. Castration reduces the aggressive behavior and simplifies husbandry practices (Fahmy et al., 1999;
150
S.G. Haddad et al. / Small Ruminant Research 65 (2006) 149–153
Ulker et al., 2002). However, rams are in some cases superior to castrated lambs in terms of live weight gain, feed consumed per unit of gain and the percentage of lean tissue in the carcass (Wellington et al., 2003). No data are available on the growth performance of castrated Awassi lambs. Therefore, our objective was to investigate the effects of castration on growth performance and carcass characteristics of Awassi lambs fed high concentrate diet.
2. Materials and methods New born male Awassi lambs were assigned to two groups of intact and castrated (12 lambs/group). At 7 days of age, lambs in the castrated group were castrated using elastrator rubber band techniques (Chase et al., 1995). All lambs were then left with their dams until weaning at the age of 70 days (S.D. = 8). After weaning, all lambs were removed and placed in individual pens and were offered a high concentrate diet ad libitum that contained 15% chopped alfalfa hay, 35% ground corn grain, 35% barley grain, 12% soybean meal, 1% salt, 1% limestone and 1% mineral and vitamin mix (DM basis). The mineral and vitamin mix supplies per kilogram of diet: 4.9 mg of Zn, 4.05 mg of Mn, 0.45 mg of Cu, 0.075 mg of I, 0.1 mg of Se, 2.500 IU Vitamin A, 400 mg of Vitamin D and 2.5 IU Vitamin E. Feed was offered as total mixed diet and was fed twice daily in amounts to insure 10% orts. Body weights were measured once weekly. Feed samples were oven-dried (60 ◦ C), ground through a 1 mm screen and analyzed for crude protein
(CP; 988.05) and fat (920.39) by the procedures of AOAC (1990) and NDF (Van Soest et al., 1991). Metabolizable energy of the diet was calculated from NRC (1985). At the end of the 60 days fattening period, all lambs were slaughtered after a 16 h fast. Body weights were recorded before slaughter. Measures included hot carcass weight (after 4 h), liver, heart, lung and trachea and spleen weights. Carcasses were then wrapped with nylon bags and refrigerated at 2 ◦ C for 24 h. Cold carcass weights were recorded; visceral tissues, fat tail, kidney and kidney fat were removed from the carcasses and weighed. Carcasses were split into four major cuts: legs, loin, rack and shoulders and weighed as described by Kadim et al. (1989). Randomly selected right legs (eight from each treatment) were frozen for further analyses. The right hind legs were then thawed at room temperature for 16 h then dissected into separable lean, fat and bone. The three components were weighted separately to determine relative proportions within the cuts. The traits analyzed are listed in the Tables 1 and 2. The mathematical model included fixed effects due to treatment (intact and castrated lambs) and residual error (SAS, 1991).
3. Results and discussion No health problems were noted for the castrated lambs throughout the experiment. Pre-weaning growth of Awassi lambs was not affected by castration and averaged 243 g/day (S.E. = 19) for the intact and castrated lambs. All lambs weighed 21 kg on average
Table 1 Nutrient intake and growth performance of intact and castrated Awassi lambs Item
Lambs Intact
Castrated
S.E.
P-value
Dry matter intake (g/day) Organic matter intake (g/day) Crude protein intake (g/day) Neutral detergent fiber intake (g/day) Metabolizable energy intake (Mcal/day) Initial body weight (kg) Final body weight (kg) Weight gain (kg) Average daily gain (g/day) Feed to gain ratio
1098 1019 175 204 3.18 20.8 37.5 16.7 279 3.91
1226 1138 196 228 3.56 21.1 37.9 16.8 280 4.40
44 32 7.1 7.5 0.1 0.4 0.7 0.6 19 0.1
0.04 0.04 0.04 0.04 0.04 0.04 0.12 0.37 0.88 0.001
S.G. Haddad et al. / Small Ruminant Research 65 (2006) 149–153
(Table 1). Dry matter intake for the castrated lambs was 128 g/day higher compared to intact lambs (Table 1). Final body weight of 38 kg, 16.8 kg weight gain and 280 g/day average daily gain (ADG) were not affected by castration. Feed to gain ratio was 0.51 higher for castrated lambs compared to intact lambs. Hot carcass weight, cold carcass weight and dressing percentages were all unaffected by castration and averaged 20.2 kg, 19.7 kg and 53.6%, respectively (Table 2). Liver weights for the castrated lambs were significantly higher by 38 g compared with the intact
151
lambs. Heart, spleen, kidney, lung and trachea weights were all unaffected. However, kidney fat for the castrated lambs was 84 g higher compared to the intact lambs. Mesenteric fat showed similar response to that of kidney fat. Intact lambs had a significant heavier leg weights (33%) as compared to castrated lambs (31%) when major carcass cut weights were expressed as a percentage of cold carcass weights (Table 2). Percentages of shoulder, rack and fat tail were not affected by castration as shown in Table 2. However, loin weight as
Table 2 Effect of castration on slaughtering characteristics, major cut weights, loin characteristics and distribution of the leg tissue of Awassi lambs Item
Lambs Intact
Castrated
S.E.
P-value
36.2 19.8 19.3 53.2 579 143 68 489 103 179 310
37.1 20.6 20.1 54.1 617 153 70 478 109 263 437
1.1 0.3 0.3 0.9 12 4.6 3.4 12 4.7 12 39
0.22 0.12 0.14 0.31 0.02 0.14 0.67 0.64 0.22 0.03 0.01
Major cuts (% of cold carcass weight) Shoulders Racks Legs Loins Fat tail
35.6 8.4 32.9 8.9 14.2
34.9 8.8 31.0 10.3 14.9
0.8 0.2 0.4 0.4 0.9
0.15 0.06 0.01 0.02 0.32
Loin characteristics (mm) Fat thickness Loin depth Loin width
4.0 30.8 61.6
6.7 30.9 58.3
0.7 0.8 2.1
0.01 0.88 0.28
Fasting weight (kg) Hot carcass weight (kg) Cold carcass weight (kg) Dressing (%) Liver weight (g) Heart weight (g) Spleen weight (g) Lung and trachea weight (g) Kidney weight (g) Kidney fat (g) Mesenteric fat (g)
Leg weight (g) Total lean (g) Total bone (g) Total fat (g) Subcutaneous (g) Intermuscular (g) Meat to bone ratio Proportions of leg tissue (%) Lean Bone Fat Others
3102 1723 497 766 612 154
3152 1668 477 902 740 161
92 39 11 46 45 12
0.72 0.49 0.25 0.04 0.03 0.66
3.4
3.5
0.07
0.71
55.6 16.1 25 1.8
53.0 15.1 29 1.6
0.8 0.3 1.0 0.1
0.02 0.25 0.01 0.10
152
S.G. Haddad et al. / Small Ruminant Research 65 (2006) 149–153
a percentage to cold carcass weight was 1.4% higher for the castrated lambs compared to the intact lambs. Fat thickness on the loin area was 2.7 mm higher for the castrated lambs compared to the intact lambs. Loin depth and width were not affected by castration and averaged 31 and 60 mm, respectively. The lean and bone weights in intact and castrated legs were similar. However, in castrated lambs, legs had 136 g more total fat and 128 g more subcutaneous fat compared to the intact lambs. Intermuscular fat weights were not affected by castration. Intact lambs had 2.6% more lean and 1.1% more bone in legs compared to the castrated lambs. Total fat percentage in the castrated lambs legs were 4% higher compared to the intact lambs. The desirable market live weight for Awassi lambs in Jordan is 30–35 kg, which usually corresponds with a carcass weight of 15–20 kg. In the current study, animals were slaughtered at this desirable market weight. Pre-weaning growth of Awassi lambs was not affected by castration. In contrast, Mahgoub and Lodge (1994) stated that Omani lambs castrated with the surgical removal of the testes within a week of birth had slower growth rates compared to intact lambs. According to Chase et al. (1995), castration using rubber band minimizes blood loss, reduce trauma and reduce exposure to infections. Post-weaning growth was not affected by castration as well. Correspondingly, Ulker et al. (2002) reported no significant difference in growth rate and body weight of intact and castrated Karakas lambs. In contrast, it has been reported that weight gain in intact lambs exceeded that of castrated lambs (Fahmy et al., 1999; Mahgoub et al., 1998). Possibly, Awassi lambs slaughtered at 130 days, failed to express the effect of castration. The age of lambs at slaughter has usually been 170 days (Fahmy et al., 1999; Mahgoub et al., 1998). Feed to gain ratio was lower for intact than castrated lambs in agreement with several researchers (Arthaud et al., 1977; Mahgoub et al., 1998; Schanbacher et al., 1980). In contrast, Mahgoub et al. (1995) reported Omani ram lambs consumed more feed post-weaning than did wether or ewe lambs, however, despite higher weight gains, rates of feed efficiency were similar. The heavier leg weight of intact lambs was compensated for by a heavier loin weight of castrated lambs and the tendency to have a heavier fat tail, which resulted in the absence of differences in carcass weights and dressing percentage between intact and castrated lambs.
Abdullah et al. (1994) reported no differences between intact and castrated Dorset × Malin lambs in slaughter weight, carcass weight and dressing percentage while Grabarski et al. (1970) reported higher dressing percentages of castrated than intact Hampshire lambs. The higher liver weight for the castrated lambs was possibly due to increased nutrient intake, the liver being regarded as a highly metabolically active organ (Ferrell et al., 1986). Kidney, mesenteric and subcutaneous fat weights were also heavier in castrated lambs, whereas leg intermuscular fat was not affected by castration, which is in agreement with Fahmy et al. (1999) and Wellington et al. (2003). Castration is reported to raise the proportion of total fat in the subcutaneous depot (Abdullah et al., 1994). Moreover, the magnitude of the increase in fat weight was greater for the non-carcass fat (kidney fat 46%, mesenteric fat 40%) compared with the carcass fat (leg subcutaneous fat 16%). Mahgoub and Lodge (1994) stated that fat depots in the carcass grew at a slower rate than that in the non-carcass components of castrated Omani lambs. Reports on the effect of castration on fat distribution are not consistent. In general, the higher fat content of castrated lambs may be attributed to higher proportions of subcutaneous fat. In this study, subcutaneous fat in the leg was 80% of the total leg fat for the intact lambs, whereas the corresponding proportion, for the castrated lambs was 82%. In conclusion, castration did not affect ADG, cold carcass weight or dressing percentage of Awassi lambs. However, it reduced efficiency of feed utilization, increased subcutaneous fat and decreased carcass leanness. Therefore, due to local consumer preference of leaner carcasses with minimum subcutaneous fat, castration of Awassi lambs to be slaughtered approximately 130 days is not recommended under an intensive feeding system
Acknowledgements The authors would like to thank the Deanship of Research at the Jordan University of Science and Technology (JUST) for financial support (Project no. 52/2001). The assistance of the farm staff led by I. Tahat at the Center for Agriculture and Production at JUST is greatly appreciated.
S.G. Haddad et al. / Small Ruminant Research 65 (2006) 149–153
References Abdullah, F.M., Salleh, R.M., Khusahry, M.Y.M., 1994. Body components and carcass characteristics of induced cryptorchid, wethers and intact males. In: Proceedings of the Seventh Conferences of the Asian Austral-Asian Association of Animal Production Societies, vol. 3, Indonesia, pp. 69–70. Arthaud, V.H., Mandigo, R., Koch, R.M., Kotula, A.W., 1977. Carcass composition, quality and palatability attributes of bulls and steers fed different energy levels and killed at four stages. J. Anim. Sci. 44, 55–64. AOAC, 1990. Official Methods of Analysis, 15th ed. Association of Official Analytical Chemists, Arlington, VA, pp. 69–78. Chase Jr., C., Larsen, R.E., Randel, R.D., Hammond, A.C., Adams, E.L., 1995. Plasma cortisol and white cell responses in different breeds of bulls: a comparison of two methods of castration. J. Anim. Sci. 73, 975–980. Fahmy, M.H., Sairam, M.R., Proulx, J.G., Petit, H.V., Jiang, L.G., Dufour, J.J., 1999. Effect of active immunization against luteinizing hormone on carcass and meat quality of Romanov lambs. Small Rumin. Res. 34, 87–96. Ferrell, C.L., Koong, L.J., Nienaber, J.A., 1986. Effect of previous nutrition on body composition and maintenance energy costs of growing lambs. Br. J. Nut. 56, 505–605. Grabarski, C., Wilson, L.L., Merritt, T.L., Rugh, M.C., Ziegler, J.H., Simpson, M.J., Varela-Alvarez, H., Watkins, J.L., 1970. Ram, cryptorchid and wether performance on two energy regimes. J. Anim. Sci. 31, 173–179. Haddad, S.G., Nasr, R.E., Muwalla, M.M., 2001. Optimum dietary crude protein level for finishing Awassi lambs. Small Rumin. Res. 39, 41–46.
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Kadim, I.T., Purchas, R.W., Rae, A.I., Barton, R.A., 1989. Carcass characteristics of Southdown ram from high and low backfat selection lines. N.Z. J. Anim. Res. 32, 181–191. Mahgoub, O., Lodge, G.A., 1994. Growth and body composition of Omani local sheep: growth and distribution of the musculature and skeleton. Anim. Prod. 58, 373–379. Mahgoub, O., Horton, G.M.J., Olvey, F.H., 1995. Effects of castration on growth and carcass characteristics of Omani sheep. In: Proceedings of the International Conference on Animal Production in Hot Climates, Sultan Qaboos University Muscat, Oman, p. A4. Mahgoub, O., Byerley, D.J., Chesworth, J.M., Myhara, R.M., 1998. Effect of status and feeding diets containing palm by-products on composition of the rack cut in Omani sheep. Small Rumin. Res. 28, 281–288. National Research Council, 1985. Nutrient requirement of sheep, sixth rev. ed. National Academy of Sciences, Washington DC. SAS Institute, 1991. SAS for Windows, Version 6.0, ed. SAS Institute Inc., Cary, NC. Schanbacher, B.D., Crouse, J.D., Ferrell, C.L., 1980. Testosterone influences on growth performance, carcass characteristics and composition of young market lambs. J. Anim. Sci. 51, 685–691. Ulker, H., Gokdal, O., Temur, C., Cemal, B., Oto, M, de Avila, D.M., Reeves, J.J., 2002. The effect of immunization against LHRH on body growth and carcass characteristics in Karakas ram lambs. Small Rumin. Res. 45, 273–278. Van Soest, P.J., Robertson, J.B., Lewis, B.A., 1991. Methods for dietary fiber neutral detergent fiber, and non-starch polysaccharides in relation to animal nutrition. J. Dairy Sci. 74, 3583–3592. Wellington, G.H., Hogue, D.E., Foot, R.H., 2003. Growth, carcass characteristics and androgen concentrations of gonad altered ram lambs. Small Rumin. Res. 48, 51–59.
Technical note
Effects of castration on growth performance and carcass characteristics of Awassi lambs fed high concentrate diet S.G. Haddad ∗ , M.Q. Husein, R.W. Sweidan Department of Animal Production, Jordan University of Science and Technology, P.O. Box 3030, Irbid 22110, Jordan Received 6 July 2004; received in revised form 12 April 2005; accepted 12 May 2005 Available online 22 June 2005
Abstract New born male Awassi lambs were randomly assigned to one of two groups: intact (12 lambs) and castrated (12 lambs). After weaning (body weight = 21.0 kg) at the age of 70 days, lambs consumed a high concentrate diet ad libitum for 60 days after which all lambs were sacrificed. The metabolizable energy and CP content of the diet were 2.90 Mcal/kg and 16%, respectively (all in DM basis). Dry matter intake was higher for the castrated lambs as compared to intact animals. Castration had no effect on average daily gain (ADG). Feed to gain ratio for castrated lambs was significantly higher compared to intact lambs. Hot carcass weight, cold carcass weight and dressing percentages were all unaffected by castration. However, kidney fat for castrated lambs was significantly higher compared to the intact lambs. As a percentage of cold carcass weights, intact lambs had greater leg weights compared to the castrated lambs. Fat thickness on the loin area was higher for the castrated lambs. Castrated lambs’ legs had more total and subcutaneous fat compared to the intact lambs. Intact lambs had greater percentages of lean and bone in their legs as compared to the castrated lambs. In conclusion, castration did not affect ADG, cold carcass weight or dressing percentage of Awassi lambs. However, it reduced efficiency of feed utilization, increased subcutaneous fat and decreased carcass leanness. Therefore, due to local consumer preference of leaner carcasses with minimum subcutaneous fat, castration of Awassi lambs to be slaughtered approximately 130 days is not recommended under an intensive feeding system. © 2005 Elsevier B.V. All rights reserved. Keywords: Castration; Testosterone; Carcass characteristics; Awassi lambs
1. Introduction Awassi is the only sheep breed in Jordan and is well adapted to its harsh environment. The growth rate for ∗ Corresponding author. Tel.: +962 2 7201000x22220; fax: +962 2 7095069. E-mail address: [email protected] (S.G. Haddad).
0921-4488/$ – see front matter © 2005 Elsevier B.V. All rights reserved. doi:10.1016/j.smallrumres.2005.05.029
Awassi lambs is consistently lower than that obtained with Western breeds. Through intensive farm management practices, the growth performance of Awassi lambs appears to show sign of increased productivity (Haddad et al., 2001). One practice that is becoming more common in feedlotting Awassi lambs is castration. Castration reduces the aggressive behavior and simplifies husbandry practices (Fahmy et al., 1999;
150
S.G. Haddad et al. / Small Ruminant Research 65 (2006) 149–153
Ulker et al., 2002). However, rams are in some cases superior to castrated lambs in terms of live weight gain, feed consumed per unit of gain and the percentage of lean tissue in the carcass (Wellington et al., 2003). No data are available on the growth performance of castrated Awassi lambs. Therefore, our objective was to investigate the effects of castration on growth performance and carcass characteristics of Awassi lambs fed high concentrate diet.
2. Materials and methods New born male Awassi lambs were assigned to two groups of intact and castrated (12 lambs/group). At 7 days of age, lambs in the castrated group were castrated using elastrator rubber band techniques (Chase et al., 1995). All lambs were then left with their dams until weaning at the age of 70 days (S.D. = 8). After weaning, all lambs were removed and placed in individual pens and were offered a high concentrate diet ad libitum that contained 15% chopped alfalfa hay, 35% ground corn grain, 35% barley grain, 12% soybean meal, 1% salt, 1% limestone and 1% mineral and vitamin mix (DM basis). The mineral and vitamin mix supplies per kilogram of diet: 4.9 mg of Zn, 4.05 mg of Mn, 0.45 mg of Cu, 0.075 mg of I, 0.1 mg of Se, 2.500 IU Vitamin A, 400 mg of Vitamin D and 2.5 IU Vitamin E. Feed was offered as total mixed diet and was fed twice daily in amounts to insure 10% orts. Body weights were measured once weekly. Feed samples were oven-dried (60 ◦ C), ground through a 1 mm screen and analyzed for crude protein
(CP; 988.05) and fat (920.39) by the procedures of AOAC (1990) and NDF (Van Soest et al., 1991). Metabolizable energy of the diet was calculated from NRC (1985). At the end of the 60 days fattening period, all lambs were slaughtered after a 16 h fast. Body weights were recorded before slaughter. Measures included hot carcass weight (after 4 h), liver, heart, lung and trachea and spleen weights. Carcasses were then wrapped with nylon bags and refrigerated at 2 ◦ C for 24 h. Cold carcass weights were recorded; visceral tissues, fat tail, kidney and kidney fat were removed from the carcasses and weighed. Carcasses were split into four major cuts: legs, loin, rack and shoulders and weighed as described by Kadim et al. (1989). Randomly selected right legs (eight from each treatment) were frozen for further analyses. The right hind legs were then thawed at room temperature for 16 h then dissected into separable lean, fat and bone. The three components were weighted separately to determine relative proportions within the cuts. The traits analyzed are listed in the Tables 1 and 2. The mathematical model included fixed effects due to treatment (intact and castrated lambs) and residual error (SAS, 1991).
3. Results and discussion No health problems were noted for the castrated lambs throughout the experiment. Pre-weaning growth of Awassi lambs was not affected by castration and averaged 243 g/day (S.E. = 19) for the intact and castrated lambs. All lambs weighed 21 kg on average
Table 1 Nutrient intake and growth performance of intact and castrated Awassi lambs Item
Lambs Intact
Castrated
S.E.
P-value
Dry matter intake (g/day) Organic matter intake (g/day) Crude protein intake (g/day) Neutral detergent fiber intake (g/day) Metabolizable energy intake (Mcal/day) Initial body weight (kg) Final body weight (kg) Weight gain (kg) Average daily gain (g/day) Feed to gain ratio
1098 1019 175 204 3.18 20.8 37.5 16.7 279 3.91
1226 1138 196 228 3.56 21.1 37.9 16.8 280 4.40
44 32 7.1 7.5 0.1 0.4 0.7 0.6 19 0.1
0.04 0.04 0.04 0.04 0.04 0.04 0.12 0.37 0.88 0.001
S.G. Haddad et al. / Small Ruminant Research 65 (2006) 149–153
(Table 1). Dry matter intake for the castrated lambs was 128 g/day higher compared to intact lambs (Table 1). Final body weight of 38 kg, 16.8 kg weight gain and 280 g/day average daily gain (ADG) were not affected by castration. Feed to gain ratio was 0.51 higher for castrated lambs compared to intact lambs. Hot carcass weight, cold carcass weight and dressing percentages were all unaffected by castration and averaged 20.2 kg, 19.7 kg and 53.6%, respectively (Table 2). Liver weights for the castrated lambs were significantly higher by 38 g compared with the intact
151
lambs. Heart, spleen, kidney, lung and trachea weights were all unaffected. However, kidney fat for the castrated lambs was 84 g higher compared to the intact lambs. Mesenteric fat showed similar response to that of kidney fat. Intact lambs had a significant heavier leg weights (33%) as compared to castrated lambs (31%) when major carcass cut weights were expressed as a percentage of cold carcass weights (Table 2). Percentages of shoulder, rack and fat tail were not affected by castration as shown in Table 2. However, loin weight as
Table 2 Effect of castration on slaughtering characteristics, major cut weights, loin characteristics and distribution of the leg tissue of Awassi lambs Item
Lambs Intact
Castrated
S.E.
P-value
36.2 19.8 19.3 53.2 579 143 68 489 103 179 310
37.1 20.6 20.1 54.1 617 153 70 478 109 263 437
1.1 0.3 0.3 0.9 12 4.6 3.4 12 4.7 12 39
0.22 0.12 0.14 0.31 0.02 0.14 0.67 0.64 0.22 0.03 0.01
Major cuts (% of cold carcass weight) Shoulders Racks Legs Loins Fat tail
35.6 8.4 32.9 8.9 14.2
34.9 8.8 31.0 10.3 14.9
0.8 0.2 0.4 0.4 0.9
0.15 0.06 0.01 0.02 0.32
Loin characteristics (mm) Fat thickness Loin depth Loin width
4.0 30.8 61.6
6.7 30.9 58.3
0.7 0.8 2.1
0.01 0.88 0.28
Fasting weight (kg) Hot carcass weight (kg) Cold carcass weight (kg) Dressing (%) Liver weight (g) Heart weight (g) Spleen weight (g) Lung and trachea weight (g) Kidney weight (g) Kidney fat (g) Mesenteric fat (g)
Leg weight (g) Total lean (g) Total bone (g) Total fat (g) Subcutaneous (g) Intermuscular (g) Meat to bone ratio Proportions of leg tissue (%) Lean Bone Fat Others
3102 1723 497 766 612 154
3152 1668 477 902 740 161
92 39 11 46 45 12
0.72 0.49 0.25 0.04 0.03 0.66
3.4
3.5
0.07
0.71
55.6 16.1 25 1.8
53.0 15.1 29 1.6
0.8 0.3 1.0 0.1
0.02 0.25 0.01 0.10
152
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a percentage to cold carcass weight was 1.4% higher for the castrated lambs compared to the intact lambs. Fat thickness on the loin area was 2.7 mm higher for the castrated lambs compared to the intact lambs. Loin depth and width were not affected by castration and averaged 31 and 60 mm, respectively. The lean and bone weights in intact and castrated legs were similar. However, in castrated lambs, legs had 136 g more total fat and 128 g more subcutaneous fat compared to the intact lambs. Intermuscular fat weights were not affected by castration. Intact lambs had 2.6% more lean and 1.1% more bone in legs compared to the castrated lambs. Total fat percentage in the castrated lambs legs were 4% higher compared to the intact lambs. The desirable market live weight for Awassi lambs in Jordan is 30–35 kg, which usually corresponds with a carcass weight of 15–20 kg. In the current study, animals were slaughtered at this desirable market weight. Pre-weaning growth of Awassi lambs was not affected by castration. In contrast, Mahgoub and Lodge (1994) stated that Omani lambs castrated with the surgical removal of the testes within a week of birth had slower growth rates compared to intact lambs. According to Chase et al. (1995), castration using rubber band minimizes blood loss, reduce trauma and reduce exposure to infections. Post-weaning growth was not affected by castration as well. Correspondingly, Ulker et al. (2002) reported no significant difference in growth rate and body weight of intact and castrated Karakas lambs. In contrast, it has been reported that weight gain in intact lambs exceeded that of castrated lambs (Fahmy et al., 1999; Mahgoub et al., 1998). Possibly, Awassi lambs slaughtered at 130 days, failed to express the effect of castration. The age of lambs at slaughter has usually been 170 days (Fahmy et al., 1999; Mahgoub et al., 1998). Feed to gain ratio was lower for intact than castrated lambs in agreement with several researchers (Arthaud et al., 1977; Mahgoub et al., 1998; Schanbacher et al., 1980). In contrast, Mahgoub et al. (1995) reported Omani ram lambs consumed more feed post-weaning than did wether or ewe lambs, however, despite higher weight gains, rates of feed efficiency were similar. The heavier leg weight of intact lambs was compensated for by a heavier loin weight of castrated lambs and the tendency to have a heavier fat tail, which resulted in the absence of differences in carcass weights and dressing percentage between intact and castrated lambs.
Abdullah et al. (1994) reported no differences between intact and castrated Dorset × Malin lambs in slaughter weight, carcass weight and dressing percentage while Grabarski et al. (1970) reported higher dressing percentages of castrated than intact Hampshire lambs. The higher liver weight for the castrated lambs was possibly due to increased nutrient intake, the liver being regarded as a highly metabolically active organ (Ferrell et al., 1986). Kidney, mesenteric and subcutaneous fat weights were also heavier in castrated lambs, whereas leg intermuscular fat was not affected by castration, which is in agreement with Fahmy et al. (1999) and Wellington et al. (2003). Castration is reported to raise the proportion of total fat in the subcutaneous depot (Abdullah et al., 1994). Moreover, the magnitude of the increase in fat weight was greater for the non-carcass fat (kidney fat 46%, mesenteric fat 40%) compared with the carcass fat (leg subcutaneous fat 16%). Mahgoub and Lodge (1994) stated that fat depots in the carcass grew at a slower rate than that in the non-carcass components of castrated Omani lambs. Reports on the effect of castration on fat distribution are not consistent. In general, the higher fat content of castrated lambs may be attributed to higher proportions of subcutaneous fat. In this study, subcutaneous fat in the leg was 80% of the total leg fat for the intact lambs, whereas the corresponding proportion, for the castrated lambs was 82%. In conclusion, castration did not affect ADG, cold carcass weight or dressing percentage of Awassi lambs. However, it reduced efficiency of feed utilization, increased subcutaneous fat and decreased carcass leanness. Therefore, due to local consumer preference of leaner carcasses with minimum subcutaneous fat, castration of Awassi lambs to be slaughtered approximately 130 days is not recommended under an intensive feeding system
Acknowledgements The authors would like to thank the Deanship of Research at the Jordan University of Science and Technology (JUST) for financial support (Project no. 52/2001). The assistance of the farm staff led by I. Tahat at the Center for Agriculture and Production at JUST is greatly appreciated.
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