Sep 2, 2010 - subcutaneous, tail, scrotal, intermuscular and pelvic fats respectively. This study ... fat deposition in Omani sheep raised under intensive.
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Growth and body composition of Omani local sheep 1. Liveweight growth and carcass and non-carcass characteristics O. Mahgoub and G. A. Lodge Animal Science / Volume 58 / Issue 03 / June 1994, pp 365 - 372 DOI: 10.1017/S0003356100007303, Published online: 02 September 2010
Link to this article: http://journals.cambridge.org/abstract_S0003356100007303 How to cite this article: O. Mahgoub and G. A. Lodge (1994). Growth and body composition of Omani local sheep 1. Live-weight growth and carcass and non-carcass characteristics. Animal Science, 58, pp 365-372 doi:10.1017/ S0003356100007303 Request Permissions : Click here
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Aniin. Prod. 1994, 58: 365-372 © 1994 British Society of Animal Production
0003-3561 /94/21550365S02-00
Growth and body composition of Omani local sheep 1. Live-weight growth and carcass and non-carcass characteristics O. Mahgoubt and G. A. Lodged Department of Animal and Food Sciences, College of Agriculture, Sultan Quaboos University, PO Box 34, Al-khod 123, Sultanate of Oman
Abstract Forty-five local Omani ram, wether and ewe lambs were reared from birth until slaughter at 18, 28 or 38 kg live weight (five of each 'sex' at each weight group) on an ad libitum concentrate diet and Rhodesgrass hay. Ram lambs grew faster from birth and reached -predetermined slaughter weights earlier than wether and ewe lambs. At 28 kg live weight, ram lambs had: heavier heads, feet, reticulo-rumens and livers; higher muscle and bone and lower fat proportions in the carcass; lower muscle : bone and higher muscle : fat ratios; higher proportions of carcass but lower non-carcass fat than had wether and ewe lambs. The head, feet, alimentary tract, liver and heart of Omani sheep grew at a lower rate; the skin grew at a similar rate and the carcass grew at a rate faster than empty body weight (EBW). Relative to EBW, muscle grew at a similar rate, fat faster and bone slower. Both carcass and noncarcass fats grew at a rate higher than that of the growth of EBW, with non-carcass fat growing at a higher rate than that of carcass fat. The growth rate of omental fat was the fastest followed by kidney, mesenteric, subcutaneous, tail, scrotal, intermuscular and pelvic fats respectively. This study demonstrated that Omani sheep have good potential for growth if they are managed and fed satisfactorily. Omani sheep are early maturing for which reason it is recommended that they be slaughtered at lighter weights to avoid higher fat content in the carcass. Castration in Omani sheep is not recommended for production of meat lambs under intensive systems as it resulted in reduced growth rates and deposition of excess fat at lower slaughter weights. Keywords: carcass composition, castration, growth, non-carcass components, Omani sheep.
Introduction
by smallholders in settled villages. Under almost all of these conditions, sheep are grazed on poor-quality range grass or given agricultural by-products and household left-overs, supplemented in some cases with dried fish (Indian oil sardines).
Local sheep numbers in Oman have been estimated at about 153 000 out of a total livestock population of over a million (Anonymous, 1986). Although this number is not large by world animal production standards, sheep are important animals to the natives. Lamb and mutton are preceded only by goat meat in preference by the local population. Sheep are commonly slaughtered for religious and social occasions throughout the Omani calendar. However, local animals contribute only a very small proportion of the total need and therefore substantial numbers of live sheep, as well as frozen and chilled sheep meats, are imported into the country annually (GRM International, 1984). Local sheep in Oman are owned by nomadic and semi-nomadic pastoralists as well as t To whom reprint requests to be addressed. % Present address: R. R. #2, Iroquois, Ontario, Canada K0E 1K0.
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Omani sheep are predominantly black (sometimes patched with brown or white) and coarse-wooled. They are thin-tailed (with slightly thicker base), small in size and unthrifty in appearance; males are mostly horned and females unhorned (Anonymous, 1978). Average adult live weight of Omani sheep raised under traditional systems range between 22 and 25 kg, producing carcasses of about 12 kg (Anonymous, 1978). The low production levels in local Omani sheep have been attributed to a combination of slow growth rate as well as reduced fertility (Lodge, 1989). Information on peformance of Omani sheep under intensive systems is very limited. However, Omani sheep have responded
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Mahgoub and Lodge
well to improved nutrition and management, in the form of higher growth rates (Lodge, 1989) which were comparable with those of tropical breeds such as the Awassi and Najdi (Gatenby, 1986). Further investigation of live-weight growth and its composition is needed to evaluate the potential of Omani sheep as meat-producing animals and to identify the causes that hinder their production. Omani sheep are small in size and appear to be early maturing, and therefore, studies of the pattern of fat deposition in their carcasses are important in assessing their value for production of meat under intensive conditions. Unlike temperate sheep breeds, information on growth and body composition of tropical unimproved breeds is rather limited. This study may add to our understanding of performance of tropical sheep and their potential as meat producing animals. The objective of this experiment was to evaluate the live-weight growth, body composition and pattern of fat deposition in Omani sheep raised under intensive management systems when given food ad libitum to allow maximum live-weight growth.
Material and methods Forty-five local Omani ram, wether and ewe lambs (15 of each 'sex') were used in this study. Every second male to be born was allocated to the wether group by castrating with 'elastrator' rubber rings, during the 1st week of life. Five animals in each 'sex'group were randomly allocated to be slaughtered at 18, 28 or 38 kg live weight. This resulted in nine sex/ weight groups, i.e. 3 X 3 sex and slaughter weight factors. These slaughter weights were chosen to represent a range beyond which local animals are traditionally marketed and slaughtered. Lambs were born over three consecutive lambing seasons and raised to slaughter weights at Sultan Qaboos University Teaching Farm under a uniform management system. Lambs were offered concentrate creep food from 1 month of age and weaned between 42 and 76 days of age. From weaning until slaughter lambs were continued on the same pelleted food offered ad libitum plus Rhodesgrass hay (Table 1). Free access to water and salt blocks was allowed at all times. Animals were weighed at birth and weekly thereafter and live weight was recorded to the nearest 100 g. Animals were fasted overnight (water was allowed) and slaughtered according to Muslim (Halal) tradition. Non-carcass components: head, skin, feet, omental and mesenteric fats, full and empty alimentary tract, reticulo-rumen, intestines, liver, spleen, pancreas, heart, lungs and trachea, genitals
Table 1 Dry matter and composition of dry matter of experimental foods (g/kg) Type of food Concentrate Rhodesgrass hay
Dry Crude Crude matter protein fibre
Crude fat
Ash
165-0 88-3
33-4 18-0
58-9 93-8
927 934
22-6 409-0
(testes or ovaries) and diaphragm were weighed to the nearest g. Kidneys and kidney fat were left intact on the carcass until dissection. Dressed carcasses were weighed, chilled for 24 h at 4°C then reweighed, and stored in polythene bags at -15 to 20°C. Weight of gut contents at slaughter (gut-fill) was calculated by difference between full and empty alimentary tract, and empty body weight (EBW) was computed by subtracting the weight of gut contents from slaughter weight. Carcasses were thawed overnight and prepared for dissection by removing the tail, kidneys, bladder, connective tissue, blood vessels and glands. Scrotal or udder, pelvic and kidney fat were separated and weighed. Fat inside the carcass other than the above fat depots 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). The prepared carcass was split along the vertebral column into left and right halves using a commercial band saw. The left half was dissected into muscle, bone, fat (subcutaneous and intermuscular) and connective tissue. The amounts of muscle, bone, and fat dissected from the left half-carcass were doubled to give total carcass, muscle, bone and fat (TCF). Total body fat (TBF) was calculated as TCF plus TNCF. The tail, which is thicker in Omani sheep than in breeds of European origin was regarded as a fat depot and added to total body fat. Female lambs had been partially docked and so had smaller tails. Experimental data were analysed utilizing the Statistical Analysis Systems Institute (1985) general linear models (GLM) procedures. Least-square means were computed and tested for significance using Duncan's multiple range test. Orthogonal polynomial contrasts were used to evaluate the effect of sex through unbiased comparisons between rams and ewes and between rams and wethers at different live weights. Mean values of components at 28 kg live weight at this weight are presented for purposes of sex and breed comparisons. Rates of growth of body organs in relation to EBW were evaluated using Huxley's (1932) equation of relative growth in the logarithmic form, log Y = log a + b log X, where Y
Growth of Omani sheep
367
is a body component of X (a whole, e.g. EBW) and b and a are constants.
Results Live-weight growth
There was no significant effect of the season of birth on live-weight growth of experimental lambs and therefore data from all experimental animals were pooled. Male lambs were heavier at birth than females, weighing 3-0 and 2-8 kg respectively (P < 0-05).
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Ram lambs grew faster from birth and reached predetermined slaughter weights earlier than wether and ewe lambs. Thus ram lambs reached the slaughter weights of 18, 28 and 38 kg 13 and 29 days; 25 and 36 days; 70 and 74 days earlier than wether and ewe lambs respectively (Table 2). Over the period of 28 weeks, ram lambs gained 34-8 kg whereas wether and ewe lambs gained 32-1 and 28-0 kg respectively. These figures may be converted into average daily gains of 184, 170 and 148 g for ram, wether and ewe lambs respectively. Liveweight gain in lambs increased from the period from birth to its maximum at 12 to 16 weeks, with an average daily gain of 260 g and then declined. For wether and ewe lambs maximum daily gain was achieved over the 4 to 8 weeks period when growth rates were 193 and 167 g/day respectively.
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EBW, carcass and non-carcass components increased with increased slaughter weight from 18 to 38 kg (Table 2 and 3). Muscle, bone and fat contents of the carcass increased with increased slaughter weight. However the proportion of muscle in the cold carcass decreased, that of fat increased and that of bone slightly decreased. Accordingly, muscle : bone ratio increased and muscle: fat ratio decreased with increased slaughter weight (Table 3). Weights of carcass and non-carcass fat depots increased with increased slaughter weight. Intermuscular, TCF, scrotal/udder, channel and pelvic fats decreased whereas omental, mesenteric, kidney, TNCF and tail increased as a proportion of TBF (Table 4). Effects of sex Rams had lower dressing-out percentage (DO); heavier head, feet, reticulo-rumen and liver; higher carcass muscle and bone and lower carcass fat content than wethers at 28 kg live weight. Rams also had heavier EBW (at 18 and 38 kg), lower DO, heavier head, feet, reticulo-rumen, gut fill and liver; higher muscle and bone and lower carcass fat content at 28 kg than ewe lambs. At 28 kg rams had significantly lower muscle: bone and higher
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