higher slaughter weight (22n26 kg), empty body weight (20n39 kg), hot carcass ... slaughter, whereas carcass fat, including subcutaneous ...... Slough: Com-.
Journal of Agricultural Science, Cambridge (1998), 131, 329–339. Printed in the United Kingdom # 1998 Cambridge University Press
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A comparative study on growth, body composition and carcass tissue distribution in Omani sheep and goats O. M A H G O U B* G. A. L O D G E† Department of Animal and Veterinary Sciences, College of Agriculture, Sultan Qaboos University, PO Box 34, Al Khod 123, Sultanate of Oman (Revised MS received 8 April 1998)
SUMMARY Growth, body composition and distribution of carcass tissues were compared in Omani sheep and goats. Animals had ad libitum access to Rhodes-grass hay (8 % CP) and a concentrate diet (16 % CP) from weaning until slaughter. The two species had similar birth weights but sheep had higher preweaning (181 g}day), postweaning (175 g}day) and overall (179 g}day) growth rates than goats (120, 102 and 111 g}day, respectively) and thus they reached slaughter weights earlier. Sheep had higher slaughter weight (22±26 kg), empty body weight (20±39 kg), hot carcass weight (12±48 kg) and dressing out percentage (55±94 %) than goats (21±17, 18±82, 11±48 kg and 53±97 %, respectively). Sheep also had higher proportions of skin, liver and lungs and trachea (P ! 0±01) than goats, which had higher proportions of head, feet and gut contents. As proportions of carcass weight, sheep had higher fat (25±08 %) but lower muscle content (57±24 %) than goats (15±72 and 65±88 %, respectively). There were no significant differences between the two species in proportion of carcass bone (13±76 and 14±17 %). These effects resulted in sheep having a lower muscle : bone ratio (4±19 and 4±68) and higher fat : muscle ratio (0±44 and 0±24). Sheep had higher proportions of non-carcass, carcass and total body fat in the empty body weight (EBW) than goats. However, sheep had less non-carcass but more carcass fat than goats when fats were expressed as proportions of total body fat. Sheep had higher proportions of muscles in the proximal hind limb, distal hind limb (P ! 0±01), around the spinal column, connecting forelimb to thorax and high-priced muscle group (P ! 0±05), but lower proportions of muscles in the abdominal wall, proximal forelimb (P ! 0±05), distal forelimb (P ! 0±01), connecting neck to forelimb, intrinsic muscles of neck and thorax (P ! 0±05) and total forequarter muscles (P ! 0±01) than goats. As proportions in carcass bone, sheep had higher axial skeleton (P ! 0±05) but lower forelimb than goats. Among species}sex}slaughter weight groups, castrated male and female goats had the lowest growth rates. Castrates and female sheep, particularly at heavier liveweights, had higher carcass and non-carcass fat contents than intact males and goats of all sexes. Although Omani goats produced leaner carcasses and had higher proportions of some non-carcass offals than Omani sheep, they had slower growth rates and a less attractive muscle distribution. This may negatively affect their potential for large scale meat production under Omani conditions. INTRODUCTION Sheep have been important meat-producing animals worldwide, whereas goats are more important meat animals in the tropics, including Oman. Growth and development are the bases for meat production whereas distribution of carcass tissues is significant in determining carcass quality. Lean muscle, and to a * To whom all correspondence should be addressed. Email : osmahgob!squ.edu.om † Present address : RR2, Lanark, Ontario, Canada K06 1K0.
lesser extent fat, are the major edible tissues of the carcass. In countries where meat is sold in cuts, the lean content of each cut is an important factor in determining its value. Amount and site of fat in the carcass influences its quality. Non-carcass fats (kidney, scrotal, pelvic etc) are easily separable after slaughter, whereas carcass fat, including subcutaneous and intermuscular, is more difficult to remove. Excess carcass fat has to be trimmed when meat is processed and results in considerable losses, thus reducing carcass value. Bone is not an edible tissue, but its proportion in the carcass affects those of other edible carcass tissues such as lean meat.
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. . .
Distribution of carcass tissues has been well studied in cattle (Berg & Butterfield 1976) and sheep (Butterfield 1988). Both studies investigated the issue with emphasis on the effects of mature body size. Limited work of this nature has been done in goats (Warmington & Kirton 1990 ; Colomer-Rocher et al. 1992). Comparative studies on sheep and goats, especially tropical unimproved breeds, are especially lacking. Sheep and goats in Oman are traditionally raised in mixed flocks and slaughtered over a similar weight range regardless of their sex or mature body size. However, Omani goats are preferred by locals and, therefore, they fetch higher prices (almost three times more than local sheep). For each of the species, meat is sold at more or less the same price regardless of its site on the carcass. Besides the dressed carcass, many parts of the animal body are also consumed (e.g. head, feet, liver, heart, stomach and intestines) or sold (e.g. skin). The current study was designed to compare meat production capabilities of Omani sheep and goats through studying their growth, body composition and carcass tissue distribution. MATERIALS AND METHODS Animals and management Sixty Omani sheep and goats (Batina breed) comprising equal numbers of intact males, castrated males (wethers) and females were used in a factorial study in 1990–91. Animals were housed in open pens with access to shade. Male animals were allocated to the wether group by castrating (with elastrator rubber rings) during the first 2 weeks of life every second male born. Five animals in each species}sex group were randomly allocated to be slaughtered at 18 or 28 kg liveweight. These weights encompass the range at which Omani sheep and goats are usually marketed. Lambs and kids were fed ad libitum concentrate creep feed (16 % CP) from 1 month of age and weaned at an average age of 58 days. From weaning until slaughter, animals were housed as separate species} sex groups in partially shaded 6¬10 m pens (10 animals}pen) and fed ad libitum on the same pelleted concentrate (DM 92±7 % ; CP 16±5 % ; CF 2±26 % ; EE 3±34 ; ash 5±89 %) plus Rhodes-grass hay (DM 93±4 % ; CP 8±8 % ; CF 40±0 ; EE 1±80 ; ash 9±38). Water and salt blocks were also available ad libitum. Animals were weighed weekly from birth to slaughter.
ethylene bags and stored at ®15 °C for dissection. Non-carcass components included head, skin, feet, digestive tract, liver (plus gall bladder), spleen, heart, pancreas, lungs plus trachea, diaphragm and genitals (testes, epididymis and spermatic cord in males and uterus, oviduct and ovaries in females). Weight of digestive contents was computed as the difference between full and empty digestive tract ; empty body weight (EBW) was computed as the difference between slaughter weight and weight of digestive content. Omental, mesenteric, scrotal or udder, pelvic and kidney fats were separated and weighed. The rest of the non-carcass fat was separated and weighed as channel fat. Weights of omental, mesenteric, scrotal (or udder), kidney, pelvic and channel fats were added as total non-carcass fat (TNCF). Prior to dissection, the tail, kidneys, bladder, connective tissue, blood vessels and scrotal or udder, pelvic and kidney fats were removed. The carcass was then split along the vertebral column into left and right halves using a band saw. The left half was dissected into muscle, bone, fat (subcutaneous and intermuscular) and connective tissue. The amounts of muscle, bone and fat were multiplied by 2 to give total carcass muscle, bone and fat (TCF). Total body fat (TBF) was calculated as TNCF plus TCF. The muscular tissue of the left half-carcass was separated into individual muscles which were then combined into nine groups following the procedures of Butterfield (1988) for sheep. The nine muscle groups included : muscles of the proximal hind limb (MG1), muscles of the distal hind limb (MG2), muscles surrounding the spinal column (MG3), muscles of the abdominal wall (MG4), muscles of the proximal forelimb (MG5), muscles of the distal forelimb (MG6), muscles connecting the thorax to the forelimb (MG7), muscles connecting the neck to the forelimb (MG8) and intrinsic muscles of the neck and thorax (MG9). Muscles were named according to the conventions of the Nomina Anatomica Veterinaria (1973). Individual bones of the left half-carcass were dissected out, weighed and grouped as : the axial skeleton, forelimb and hind limb. The axial skeleton included cervical, thoracic, lumbar, sacral and coccygeal vertebrae, ribs, pelvis and sternum. The forelimb included scapula, humerus, radius and ulna, and carpus whereas the hind limb included femur, tibia, patella and tarsus plus tuber calcanei.
Experimental measurements
Statistical methods
Feed was withheld overnight and animals were slaughtered the Muslim (Halal) way when each individual animal had reached its designated body weight. Carcass and non-carcass components were weighed immediately after slaughter and carcasses chilled overnight at 4 °C, then wrapped in poly-
Weights of internal organs were expressed as percentages of EBW and carcass tissues as percentages of respective total carcass side tissue weight. Data were analysed using PC SAS (1991) General Linear Models procedures for windows. Model equation for a 2¬3¬2 (2 species, 3 sexes and 2 slaughter weights)
Growth, composition and carcass tissue distribution in Omani sheep and goats factorial arrangement was used to analyse main effects of species, sex and slaughter weight and their interactions. Least square means were computed and tested for treatment differences and main effects of species are presented. Least square means (population marginal means) are the expected value of class or subclass means for a balanced design involving the class variable with all covariates at their mean value (SAS 1991). Some interaction effects are presented on selected components of growth, composition and carcass tissue distribution. Throughout the results, characters stated to be greater or smaller than the alternative are different at P ! 0±001 except where indicated. RESULTS Omani sheep and goats had a similar birth weight (2±93 and 2±81 kg, respectively). In absolute terms, sheep grew faster and reached slaughter weights earlier than goats (Table 1). At weaning (8 weeks), sheep were 4 kg heavier and at 16 weeks they were 8 kg heavier than goats. Sheep reached 28 kg liveweight by the 20th week when the goats were only 18 kg. There was an 11 kg difference between the two species in favour of sheep by 24 weeks of age. Sheep had higher preweaning (181 g}day), postweaning (175 g}day) and overall (179 g}day) growth rates than goats (120, 102 and 111 g}day, respectively).
331
Therefore, the mean age at which sheep reached a predetermined slaughter weight (120 days) was significantly lower than for goats (191 days). To account for differences between the two species in body size, daily growth rates were expressed as percentages of birth weight, weaning weight and weight at 20 weeks. This indicated that sheep had higher growth rates relative to birth weight as well as to weights at weaning and 20 weeks of age than goats. Omani sheep had higher slaughter weight (22±26 kg), EBW (20±39 kg), hot carcass weight (12±48 kg) and dressing out (DO) percentage (55±94 %) than goats (21±17, 18±82, 11±48 kg, and 53±97 %, respectively). As proportions of EBW, sheep had heavier skin, liver, lungs and trachea than goats, which had higher proportions of head, feet and digestive tract contents (Table 2). Sheep had higher fat (25±08 %) but lower muscle content (57±24 %) than goats which had 15±72 and 65±88 %, respectively. There were no significant differences between the species in proportion of bone in the carcass (13±76 and 14±17 %). Therefore sheep had a lower muscle : bone ratio (4±19 v. 4±68) but higher fat : muscle ratio (0±44 v. 0±24). Fat contents in the body of sheep and goats were expressed as proportions in EBW and TBF (Table 3). As proportions of EBW, sheep had higher omental, scrotal}udder and kidney fats which contributed to
Table 1. Growth performance of Omani sheep and Omani Batina goats (least square means) over 24 weeks Species Sheep Item Liveweight (kg) Birth weight Weaning weight Weight at 16 wk Weight at 20 wk Weight at 24 wk Daily gain (g}day) Birth–weaning Weaning–20 wk Birth–20 wk Birth–24 wk Relative growth Birth–weaning* Birth–weaning† Weaning–20 wk* Weaning–20 wk‡ Birth–24 wk† Birth–24 wk‡
Goats
Mean
.. (.. 59)
Mean
.. (.. 59)
2±93 14±29 23±31 28±09 31±49
0±063 0±264 0±436 0±425 0±536
2±81 10±34 15±55 18±47 20±51
0±063 0±267 0±445 0±444 0±518
181 175 179 170 6±37 1±26 6±12 0±64 1±20 0±62
* Daily growth rate as percentage of birth weight. † Daily growth rate as percentage of weaning weight. ‡ Daily growth rate as percentage of week 20 weight.
4 3 3 3 0±14 0±01 0±13 0±002 0±04 0±01
120 102 111 105 4±28 1±15 3±88 0±60 0±96 0±54
4 4 3 3 0±14 0±01 0±14 0±002 0±04 0±01
. . .
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Table 2. Slaughter weight (kg), empty body weight (EBW) and proportions of body, EBW and carcass tissue components in Omani sheep and Omani Batina goats (least square means) Species Sheep Mean
.. (.. 59)
Mean
.. (.. 59)
120 22±26 20±39 12±48 55±94
5 0±161 0±163 0±120 0±40
191 21±17 18±82 11±48 53±97
5 0±169 0±181 0±126 0±42
6±06 10±27 2±75 6±54 8±33 2±03 0±47 1±55 0±29
0±07 0±19 0±03 0±11 0±34 0±03 0±04 0±05 0±03
6±94 8±48 3±18 6±72 11±71 1±89 0±53 1±47 0±31
0±07 0±21 0±03 0±12 0±37 0±04 0±05 0±04 0±03
57±24 25±08 13±76 4±19 0±44
0±46 0±58 0±15 0±05 0±01
65±88 15±72 14±17 4±68 0±24
0±48 0±60 0±16 0±05 0±01
Item Slaughter age (days) Slaughter weight (kg) Empty body weight (EBW) (kg) Hot carcass weight (kg) Dressing out percentage* As proportion of EBW Head Skin Feet Empty digestive tract† Gut-fill Liver Heart Lungs and trachea Genitals As proportion of carcass weight Muscle Fat Bone Muscle : bone ratio Fat : muscle ratio
Goats
* Calculated on overnight fasted weight. † Calculated as a proportion of slaughter weight.
Table 3. Proportions of fat depots in the empty body and total body fat of Omani sheep and Omani Batina goats (least square means) As % of empty body weight (EBW) Sheep Fat depot Non-carcass Omental Mesenteric Scrotal}udder Kidney Pelvic Channel Total non-carcass Carcass fat Subcutaneous Intermuscular Total carcass Tail Total body fat Subcutaneous : intermuscular fat ratio
As % of total body fat (TBF)
Goats
Sheep
Goats
Mean
.. (.. 59)
Mean
.. (.. 59)
Mean
.. (.. 59)
Mean
.. (.. 59)
3±07 1±47 1±18 2±31 0±37 0±22 8±62
0±12 0±05 0±04 0±10 0±01 0±01 0±25
2±40 1±38 0±91 1±78 0±34 0±19 7±00
0±13 0±05 0±04 0±10 0±01 0±01 0±26
13±87 6±87 5±62 10±33 1±76 1±04 39±49
0±38 0±27 0±18 0±35 0±09 0±07 0±61
15±39 9±15 5±96 11±51 2±34 1±25 45±59
0±40 0±29 0±19 0±37 0±10 0±07 0±64
6±80 6±03 12±82 1±95 21±44 1±14
0±20 0±17 0±32 0±05 0±51 0±04
3±92 4±39 8±31 0±35 15±38 0±90
0±20 0±17 0±33 0±06 0±53 0±04
31±81 28±69 60±51 9±43
0±62 0±55 0±61 0±28
25±14 29±27 54±41 2±35
0±65 0±58 0±64 0±29
Growth, composition and carcass tissue distribution in Omani sheep and goats
333
Table 4. Proportions of muscle groups in the carcass side muscle weight of Omani sheep and Omani Batina goats (least square means) Species Sheep
Goats
Muscle group
Mean
.. (.. 59)
Mean
.. (.. 59)
Proximal hind limb Distal hind limb Around spinal column Abdominal wall Proximal forelimb Distal forelimb Connect thorax to forelimb Connect neck to forelimb Intrinsic neck and thorax High-priced muscle groups* Fore-quarter†
28±78 5±46 16±34 9±55 11±78 3±11 9±96 4±34 10±67 56±90 36±75
0±15 0±06 0±11 0±13 0±13 0±04 0±07 0±04 0±10 0±19 0±14
27±82 5±20 14±41 11±96 12±28 3±27 9±43 4±57 11±06 54±51 37±34
0±16 0±06 0±12 0±14 0±14 0±04 0±07 0±04 0±11 0±20 0±15
* Muscle groups of proximal hind limb, surrounding spinal column and proximal forelimb. † Muscle groups of proximal forelimb, connecting thorax to forelimb, connecting neck to forelimb, intrinsic muscles of neck and thorax.
Table 5. Proportions of individual bones in the carcass side bone weight of Omani sheep and Omani Batina goats (least square means) Species Sheep Bone or bone group Axial skeleton First rib Sixth rib Twelfth rib Total ribs Total vertebral column Sternum Pelvis Total axial skeleton Forelimb Scapula Humerus Radio-ulna Carpus Total forelimb Hind limb Femur Tibia Patella Tarsus Total hind limb
Goats
Mean
.. (.. 59)
Mean
.. (.. 59)
0±81 1±18 0±44 10±82 30±43 3±04 6±80 51±09
0±02 0±02 0±02 0±10 0±38 0±14 0±08 0±30
0±85 1±10 0±35 9±51 30±30 2±95 7±11 49±88
0±02 0±02 0±02 0±10 0±45 0±16 1±00 0±35
5±12 8±24 6±38 1±30 21±05
0±06 0±06 0±06 0±04 0±15
5±11 9±38 6±85 1±43 22±78
0±08 0±07 0±07 0±04 0±18
10±76 9±12 0±78 3±21 23±87
0±08 0±07 0±02 0±07 0±17
10±63 9±24 0±70 2±90 23±47
1±00 0±09 0±02 0±08 0±20
them having a higher TNCF than goats. Sheep also had higher proportions of subcutaneous, intermuscular, total carcass fat and tail in the EBW than
goats. Higher proportions of carcass and non-carcass fat depots resulted in sheep having 6 % more total body fat (TBF) in the EBW than goats. However, a
31±07 (0±84) 198 (5) 126 (10) 54±6 (0±96) 6±23 (0±16) 11±14 (0±46) 57±96 (1±13) 14±18 (0±37) 23±68 (1±36) 4±10 (0±13) 0±41 (0±03)
28 kg
90 (10) 54±31 (0±96) 6±43 (0±16) 10±00 (0±46) 59±19 (1±13) 14±60 (0±37) 22±16 (1±36) 4±06 (0±13) 0±39 (0±03)
—
—
18 kg 27±50 (0±64) 176 (4) 153 (10) 58±10 (0±89) 5±26 (0±15) 9±88 (0±42) 54±96 (1±04) 12±19 (0±34) 29±46 (1±26) 4±52 (0±12) 0±54 (0±03)
28 kg
Wether
107 (10) 54±85 (0±96) 6±40 (0±15) 10±97 (0±42) 58±42 (1±04) 14±59 (0±34) 22±87 (1±26) 4±01 (0±12) 0±39 (0±03)
—
—
18 kg 25±78 (0±71) 164 (5) 162 (10) 58±41 (0±96) 5±07 (0±16) 9±41 (0±46) 55±02 (1±13) 11±95 (0±37) 29±19 (1±36) 4±61 (0±13) 0±53 (0±03)
28 kg
Female
117 (11) 52±91 (1±06) 7±60 (1±18) 9±20 (0±50) 67±45 (1±23) 15±44 (0±40) 12±72 (1±49) 4±37 (0±14) 0±19 (0±03)
—
—
18 kg
28 kg 23±17 (0±91) 141 (6) 187 (10) 54±40 (0±89) 7±51 (0±16) 9±69 (0±46) 68±24 (1±04) 14±22 (0±34) 13±43 (1±26) 4±80 (0±12) 0±19 (0±03)
Male
* Weight at 20 weeks and gain over 20-week period are analysed for effects of species, sex and their interactions only.
Fat : muscle ratio
Muscle : bone ratio
Fat in carcass
Bone in carcass
Muscle in carcass
Skin in EBW
Head in EBW
Dressing out percentage
79 (10) 55±14 (0±96) 6±93 (0±16) 10±10 (0±46) 57±96 (1±13) 15±02 (0±37) 23±07 (1±36) 3±87 (0±13) 0±40 (0±03)
—
Daily gain over 20 weeks (g)*
Slaughter age (d)
—
18 kg
Weight at 20 weeks (kg)*
Item
Male
Sheep
160 (11) 53±29 (1±06) 7±16 (0±18) 8±15 (0±50) 66±72 (1±23) 14±99 (0±40) 13±49 (1±49) 4±45 (0±14) 0±20 (0±03)
—
—
18 g
16±83 (0±71) 100 (5) 237 (10) 55±9 (0±96) 6±17 (0±16) 7±41 (0±46) 62±97 (1±13) 12±72 (0±37) 20±72 (1±36) 4±97 (0±13) 0±33 (0±03)
28 g
Wether
Goats
132 (11) 51±82 (1±06) 6±90 (0±23) 8±57 (0±65) 65±84 (1±13) 14±50 (0±37) 14±99 (1±36) 4±75 (0±13) 0±23 (0±03)
—
—
18 kg
15±40 (0±67) 92 (4) 308 (10) 55±49 (0±89) 6±30 (0±15) 8±00 (0±42) 63±89 (1±04) 13±16 (0±34) 19±21 (1±26) 4±90 (0±12) 0±30 (0±03)
28 kg
Female
Table 6. Growth and body composition of Omani sheep and goats slaughtered at 18 and 28 kg liveweight (least square means)
334 . . .
Hind limb in total bone
Forelimb in total bone
Axial skeleton in total bone
Fore-quarter muscle in total muscle
Expensive muscle group in total muscle
Neck muscle in total muscle
Around spinal column in total muscle
Proximal hind limb in total muscle
Total body fat in EBW
Non-carcass fat in EBW
Carcass fat in EBW
11±97 (0±76) 5±82 (0±54) 17±75 (1±14) 28±38 (0±38) 16±49 (0±28) 10±81 (0±24) 56±58 (0±46) 37±19 (0±34) 50±63 (0±70) 21±34 (0±35) 24±03 (0±42)
18 kg 12±11 (0±76) 6±85 (0±54) 18±96 (1±14) 27±98 (0±38) 15±92 (0±28) 11±22 (0±24) 55±74 (0±46) 37±68 (0±34) 52±22 (0±70) 20±51 (0±35) 23±31 (0±42)
28 kg
Male
11±19 (0±76) 7±26 (0±54) 18±44 (1±14) 29±44 (0±38) 15±90 (0±28) 10±91 (0±24) 57±23 (0±46) 36±83 (0±34) 50±37 (0±70) 21±18 (0±35) 24±51 (0±42)
18 kg 14±94 (0±71) 11±38 (0±50) 26±32 (1±65) 29±24 (0±35) 16±54 (0±26) 10±30 (0±23) 57±49 (0±43) 36±30 (0±32) 49±99 (0±64) 21±51 (0±32) 24±37 (0±39)
28 kg
Wether
Sheep
11±58 (0±71) 7±69 (0±50) 19±27 (1±05) 28±84 (0±35) 16±41 (0±26) 10±43 (0±23) 57±14 (0±43) 36±50 (0±32) 51±42 (0±64) 21±04 (0±32) 23±67 (0±39)
18 kg 15±17 (0±76) 12±78 (0±54) 27±95 (1±14) 28±84 (0±38) 16±74 (0±28) 10±40 (0±24) 57±22 (0±46) 36±01 (0±34) 52±11 (0±70) 20±54 (0±35) 23±25 (0±42)
28 kg
Female
6±73 (0±84) 5±41 (0±59) 12±14 (1±24) 26±32 (0±47) 13±50 (0±35) 11±29 (0±30) 53±75 (0±56) 39±35 (0±42) 48±64 (0±76) 23±84 (0±38) 23±58 (0±46)
18 kg 7±14 (0±71) 5±92 (0±50) 13±06 (1±05) 26±78 (0±35) 14±38 (0±26) 12±52 (0±23) 53±05 (0±43) 38±65 (0±32) 48±76 (0±85) 23±00 (0±43) 24±03 (0±51)
28 kg
Male
7±44 (0±84) 6±05 (0±59) 13±49 (1±24) 28±71 (0±42) 14±25 (0±31) 10±35 (0±28) 55±15 (0±50) 36±34 (0±37) 50±84 (0±76) 22±14 (0±38) 23±30 (0±46)
18 kg
11±08 (0±76) 8±87 (0±54) 19±95 (1±14) 28±18 (0±38) 14±73 (0±28) 10±89 (0±24) 54±96 (0±46) 37±23 (0±34) 48±43 (0±76) 23±38 (0±38) 24±25 (0±46)
28 kg
Wether
Goats
7±38 (0±76) 6±46 (0±59) 14±15 (1±24) 27±92 (0±38) 14±44 (0±28) 10±66 (0±24) 54±38 (0±46) 36±48 (0±34) 50±09 (0±85) 22±85 (0±43) 23±18 (0±51)
10±25 (0±71) 9±21 (0±50) 19±46 (1±05) 29±00 (0±35) 15±11 (0±26) 10±45 (0±23) 56±01 (0±43) 36±12 (0±32) 52±53 (0±85) 21±36 (0±43) 22±57 (0±51)
28 kg
Female 18 kg
Table 7. Carcass tissue parameters of Omani sheep and goats slaughtered at 18 and 28 kg liveweight (least square means)
Growth, composition and carcass tissue distribution in Omani sheep and goats 335
336
. . .
different picture emerged when weights of various fat depots were expressed as proportions of TBF. Sheep had lower omental, mesenteric, kidney, pelvic and channel fats as well as TNCF but had higher subcutaneous, TCF and tail than goats. Sheep had a higher ratio of subcutaneous to intermuscular fats than goats (Table 3). There were significant differences between Omani sheep and goats in muscle distribution, which was studied by expressing the weight of individual muscle groups as proportions of total side muscle weight (Table 4). Sheep had higher proportions of muscles in the proximal hind limb, distal hind limb, around spinal column, connecting forelimb to thorax and high-priced muscle group (total of proximal hind limb, surrounding the spinal column and proximal forelimb), but lower proportions of muscles in the abdominal wall, proximal forelimb, distal forelimb, connecting neck to forelimb, intrinsic muscles of neck and thorax and total fore quarter muscles than goats. Distribution of bone weight in Omani sheep and goats was studied by expressing the weight of individual bones as proportions of total side bone weight (Table 5). Sheep had higher proportions of 6th rib, 12th rib, total ribs and total axial skeleton than goats. However, they had lower proportions of humerus, radio-ulna, carpus and total forelimb than goats. Within the hind limb they had higher proportions of the patella and tarsus than goats. Goats, particularly castrates and females, grew at the slowest rates and thus took a much longer time to reach predetermined slaughter weights than intact male goats and sheep of all sexes. Intact male goats had a higher proportion of the head in EBW than castrated and female goats and sheep of all sexes. Wether and female sheep had the highest proportions of carcass fat among all species}sex}weight groups. Therefore, they had the highest fat : muscle ratio. Intact male goats at both liveweights had the lowest fat : muscle ratio and they also had, with the wethers and females, higher bone : muscle ratio than those slaughtered at 18 kg and sheep of all sexes and weights. Sheep, especially wethers and females slaughtered at higher weights, had the highest whereas intact male goats had the lowest, proportions of carcass, noncarcass and total body fat as proportions of EBW (Table 6). Males had higher proportions of intrinsic neck muscles and total fore-quarter muscle groups than castrates and females (Table 7). This effect was maximal in intact male goats slaughtered at both 18 and 28 kg. Intact males, especially goats, had the lowest proportions of high-priced muscle groups at both slaughter weights. Species}sex}weight interaction effects on bone distribution were of small magnitude, including a lower axial skeleton but lower forelimb proportions with males having higher proportions than females (Table 7).
DISCUSSION The major objective of this study was to compare growth, body composition and carcass tissue distribution in Omani sheep and Batina goats. Effects of sex and slaughter weight on Omani sheep and goats have been described (Mahgoub & Lodge 1994 a, b, 1996 ; Mahgoub & Lu 1998). Omani sheep and Batina goats differ in growth and body size, especially early in life, which indicates differences in maturity patterns. Comparing body components of animals of different sizes has always been a problem (Butterfield 1988). Comparing sheep and goats of different mature body sizes at the same weight may indicate differences which are related more to stages of maturity rather than species per se. Various criteria have been suggested to compare such animals including age, body weight, carcass weight, multiples of birth weight, and levels of fatness. Tissues in the animal body grow at different rates. From a commercial point of view, in countries like Oman where consumers prefer sheep and goats of certain weights regardless of the size or sex, comparison at equal weights appears to be more appropriate. In spite of differences in body size, between Omani sheep and goats, especially early in life, there were no significant differences in birth weight in the current study. Al-Nakib et al. (1996) reported that Omani goats were 0±26 kg heavier at birth than Omani sheep. Sheep in the current study grew faster and reached slaughter weights earlier than goats. This is similar to reports on these animals elsewhere in Oman where sheep were 4 and 6 kg heavier at weaning and at 6 months of age, respectively, than goats (Al-Nakib et al. 1996). There are no published reports on pattern of liveweight growth of Omani sheep and goats to maturity but available information suggests that sheep grow faster than goats early in life although they finish having similar mature weights of 50–60 kg (M. G. El Hag & T. A. Eisa, personal communication). Interestingly, differences in growth performance between Omani sheep and Batina goats are not reflected in feed intake or kg feed}kg gain conversion ratio (FCR). Intact Omani sheep had a daily intake of 3–4 % of body weight and 5±8 FCR (Mahgoub et al. 1998), whereas Batina goats raised on diets based on by-products and a concentrate diet had a 3±63 and 3±4 % body weight and 5±0–5±9 FCR (El Hag & El Khanjari 1992). The slower rate of growth of kids early in life compared to that of lambs, suggests that milk yield may be lower in goats than in sheep. Once kids start to fall behind, then feed intake expressed as percentage of body weight could be the same for the two species. Related tropical breeds such as the Awassi lambs grew faster than Desert Iraqi goats both on high and low levels of rumen undegradable protein (Al Jassim et al. 1991). This is in line with the general view that
Growth, composition and carcass tissue distribution in Omani sheep and goats goats grow at a slower rate than sheep (Naude! & Hofmeyr 1981 ; Devendra & Burns 1983). There are some exceptions including some improved goat breeds such as the Boer goat of South Africa, which had a faster growth rate than many South African improved sheep breeds (Naude! & Hofmeyr 1981). Larger animals grow faster than smaller ones (Warmington & Kirton (1990) in goats ; Butterfield (1988) in sheep). To investigate the efficiency of growth of sheep and goats, daily growth rates were expressed as percentages of both birth weight and weight at 20 weeks according to the formula suggested by Purchas (1986). This confirmed the superior growth ability of sheep over goats. Goats are reputed not to perform well under closed intensive management systems. For example, goats raised under intensive management but allowed access to part time natural range browsing in Zimbabwe grew faster than those raised only intensively (J. M. Chesworth, personal communication). Lodge (1989) suggested that the superior performance of local sheep over goats may be explained on the grounds that sheep are less adapted to the prevailing environment than are the goats, with the result that they have the potential to respond to better management, whereas the goats are already close to their limitations and can be improved only by genetic means rather than through improved management. Omani sheep in the current study dressed out higher than Omani goats. There are contradicting reports on DO in sheep compared with goats. Riley et al. (1989) reported lower DO for goats than for sheep, whereas Naude! & Hofmeyr (1981) reported higher DO in Boer goats than in Merino sheep. Gaili et al. (1972) did not find any significant differences between Sudanese sheep and goats of three different high and low liveweight groups. Apparently these discrepancies arise from comparing goats and sheep which are raised under different systems and subjected to different periods of fasting prior to slaughter. They may have also arisen from differences in the thickness of the coat cover which is usually heavier in fleeceproducing sheep such as Merino or Lincoln. Higher DO in sheep in the current study resulted mainly from their smaller gut contents as well as from the lower proportions of head and feet in spite of higher proportions of skin, liver and lungs and trachea. Goats had a greater proportion of gut content than sheep (Thonney et al. 1987 a). Although high DO is a desirable trait in meat producing animals, one of the causes of higher dressing out is higher carcass fat content. Excess carcass fat is much less desirable and needs to be trimmed, thereby reducing carcass value. Differences in proportions of head may be attributed to variations in horn size, where the Batina goats have a relatively large twisted horn compared to the small or absent horns of sheep at this age. Higher proportions of the skin in sheep can be attributed to
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their heavier wool cover compared with the hair of the Batina goats. The current study confirmed reports that goats are leaner than sheep (Naude! & Hofmeyr 1981 ; Devendra & Burns 1983). Omani goats have c. 9 % less fat but more muscle in their carcasses than sheep. There were no differences between the two species in carcass bone content, despite the high proportions of bone reported for goat carcasses compared with those of sheep (Naude! & Hofmeyr 1981). This resulted in lower muscle : bone but higher fat : muscle ratios in sheep than in goats. This phenomenon has economic implications for meat production, indicating that Omani sheep should be slaughtered at a lower body weight than Batina goats to avoid the need for trimming excess carcass fat. Sheep had higher carcass and non-carcass fat proportions in the EBW. As reported by ColomerRocher et al. (1992), proportions of subcutaneous fat in sheep were higher than those in goats, reflected in a high subcutaneous : intermuscular fat ratio. This confirms reports that goats have poorer subcutaneous fat cover than sheep. However, the amount of subcutaneous fat obtained in the current study would be unlikely to negatively affect storage qualities as reported for other tropical goat breeds (Naude! & Hofmeyr 1981). Interestingly, there were some differences between the two species in the pattern of fat deposition when fat depots were expressed as proportions of TBF rather than of EBW. Omani goats had higher proportions of non-carcass and less carcass fat than sheep. Differences between sheep and goats in partitioning of body fat have been reported. Nuade! & Hofmeyr (1981) reported that the Boer goats had higher kidney and non-carcass fat than Merino and Dorper breeds of sheep. This is a desirable trait in goats raised for meat production, as non-carcass fat is readily separable at time of slaughter. It should be noted that Omani sheep have a larger semi-fat tail which made a proportion of 2 % in EBW and 9 % in TBF. This heavier tail should have contributed to the higher total body fat content in sheep than goats which had a much smaller and leaner tail. There is a lack of information on muscle distribution in carcasses of goats and also a lack of comparative studies between sheep and goats in this respect. In the current study, sheep had more muscle in the regions towards the rear of the carcass, whereas goats had more muscles in regions towards the cranium. Most importantly, sheep had higher proportions of the highly-valued muscle groups and lower proportions of the inferior forequarter region than goats. The former muscle groups were defined by Butterfield (1988) as : muscles of proximal hind limb, surrounding the spinal column and proximal forelimb. This is in agreement with findings of Thonney et al. (1987 b) that feral goats had an above average amount
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. . .
of total muscle, but they had a lower proportion in the high-priced cuts than sheep of different breeds (except the Jacob sheep) and thus had the least attractive muscle distribution. Naude! & Hofmeyr (1981) found that the content of the high priced leg joint in the Boer goat carcass was significantly lower than that in sheep of comparable carcass weight. Goat carcasses generally have poorer conformation than sheep carcasses, especially early in life (MorandFehr 1981 ; Naude! & Hofmeyr 1981). However, differences in muscle distribution in the current study were not large and ranged from 1 to 3 %. This supports findings in sheep (Kirton & Pickering 1967 ; Butler-Hogg & Whelehan 1987 ; Butterfield 1988) and cattle (Berg & Butterfield 1976) that differences in carcass muscle distribution are small and unlikely to affect body conformation or have economic significance. The amount of fat (especially subcutaneous fat) remains the major determinant of differences in conformation in meat animals. There were some differences between Omani sheep and Batina goats in individual bone distribution, where sheep had higher proportions of axial skeleton and lower proportions of forelimb than goats. These differences were small (c. 1 %) and were unlikely to produce large commercial effects on meat production from the two species. They are similar to reports on sheep where Butterfield (1988) stated that large sheep breeds do not need to have higher proportions of bone in the limbs to be able to carry the extra weight. Analysis of data for interactions between species, sex and body weight revealed some findings which may have significant implications on meat production from sheep and goats. The lower growth rate of goats compared to sheep was most evident in wethers and
females. This indicates that castration is undesirable, as also the use of females, for meat production from goats under conditions similar to those of the current study. Castration of male goats is widely practised in Oman, as in many parts of the world, mainly to eliminate the so-called ‘ male goat odour ’. However, there are reports that meat from male goats, especially those slaughtered at younger ages, as in the current study, do not have this undesirable odour (Kirton 1970 ; Gaili et al. 1972). The apparent superiority of sheep over goats in growth rate is negatively affected by their higher carcass and non-carcass fat proportions, especially in the wethers and females. This also indicates, as for goats, that intact males are better for meat production. It also indicates that sheep should be slaughtered at lower weights to avoid the deposition of excess carcass fat. The current study showed that Omani Batina goats, especially castrated males and females, did not match Omani sheep in their growth rate or carcass conformation but yielded leaner carcasses. Improvements in genetics and husbandry are needed to improve the potential of these animals for efficient large scale meat production. The authors wish to thank Sultan Qaboos University staff : F. H. Olvey and R. Bello of the Agricultural Experiment Station for animal management ; A. L. Olvey, N. M. Al-Saqry and R. M. Al-Busaidi of the Department of Animal and Veterinary Sciences for technical assistance. This paper is published with the approval of the College of Agriculture, Sultan Qaboos University as paper number 220797.
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