ALLOMETRIC GROWTH PATTERNS OF BODY AND CARCASS COMPONENT IN DOCKED AND INTACT KARADI LAMBS

To study the allometric growth of body and carcass traits, twelve new born Karadi lambs were docked within 3 days of their birth using rubber-rings, and left with their mothers till weaning (2.5 months). Another 12 weaned Karadi lambs obtained from local market were left intact. Following an adaptation period of a week, the docked and intact lambs with an average initial weight of 16.83±1.522 and 19.92± 0.748kg, respectively were randomly divided into three equal groups to be slaughtered at 20, 30 and 40kg. Results revealed that the allometric growth coefficients of both docked and intact lambs of dissectible lean and bone were negative heterogenic (b<1), indicating an early maturing tissues, while the growth of dissectible fat is a late maturing tissues. In both groups, loin, shoulder, foreshank and rack are an early maturing cuts, neck is isogonic, while leg in intact lambs is an early maturing whereas in docked lambs grew at a similar rate to carcass. In docked and intact lambs, carcass fat relative to empty body weight is an early and late maturing tissues, whereas non-carcass fat is isogonic and grew at a similar rate to empty body weight in both groups. The growth of pelt, liver, lung and trachea and heart were isogonic and grew at a similar rate to empty body weight in both groups


INTRODUCTION
Sheep have historically been essential meatproducing animals in many parts of the world, including Iraq (1,3,16). Moreover, producing lambs with a high rate of lean meat and enough fat cover is also one of the options for approaching the need for sheep meat production (47). Although, docking fat tail is not common practice in the area that raises fat tail sheep (4), however, it is assumed that docking early in live will be improve the efficiency of growth (45) as well as dressed lamb carcasses have neater appearance and thus receive higher marked prices (15). Thus, the understanding of sheep carcass composition, quantitative accretion of each carcass component, and variations in growth patterns at various phases of growth is essential in both nutrition research and production system evaluations that try to maximize profit (29). Furthermore, allometry studies provide for a better understanding of the rate of growth and development of carcass areas, as well as a more precise slaughter time for each breed (17). Sheep carcass assessment and body composition research has received a major interest, particularly in developing nations where sheep are consumed a lot for meat production (32). Therefore, there is a need to characterize tissue partitioning and carcass composition of local breeds in Iraq, and particularly to the effect of docking fat tail. Thus, the main objective of the present study was to determine the growth pattern and carcass traits of docked and undocked Karadi lambs.

MATERIALS AND METHODS Animal and experimental design:
In the current work, twelve new born lambs were docked within 3 days of their birth using rubber-rings and left with their mothers till weaning (2.5 months). Another 12 weaned male lambs obtained from local market were left intact. After an adaptation period of a week, the docked and intact lambs with an average initial weight of 16.83± and 19.92± kg respectively, were randomly divided into three equal groups to be slaughtered at 20, 30 and 40kg, and each group was housed in a separate pen and fed a pelleted diet containing 16% crude protein and 2769 Kcal energy and straw ad libitum. Full details of the experiment are described in our previous paper (8) Slaughtering of the animals When each lamb reached its desired slaughter weight (20, 30 and 40 kg), they were slaughtered after fasting for 12 hours, with unlimited access to water. The lambs were slaughtered at abattoir according to Islamic method, by severing the necks and major blood vessels. Immediately after skinning was completed, evisceration was carried out and the carcass and non-carcass components were weighted. Hot carcass includes kidney and kidney fat, edible offal's constitute of heart, testes, liver, lung and trachea, spleen and inedible offal's comprised skin, head and feet were weighed. Omental, mesenteric, scrotal and cardiac fat were separated and weighed. The gastro-intestinal tract was weighed, then emptied of its contents, cleaned, and reweighed in order to calculate the empty body weight by subtracting the weight of the digestive tracts content from the slaughter weight.

Carcass traits
The cold carcass was weighed after chilling it for 24 hours at 40 degrees Celsius, then the pelvic and kidney fat were removed and weighed separately. An electric saw was used to split the carcass in half along the spinal column. The left side of the carcass was cut into nine whole sale cuts and weighed.

Physical dissection
Each cut of the left half carcasses were weighed and dissected completely into lean, fat and bone. The three components were weighed separately to determine their percentages.
Carcass fat including subcutaneous and intermuscular fat was separated from each cut. Non-carcass fat was the sum of the omental, mesenteric, pelvic, kidney, scrotal and cardiac fat. Statistical analysis: The allometric growth equation of Huxley (18) was performed to analyze the differential growth of dissectible body components relative to carcass side and empty body weight using the slaughter and carcass data. The data was first transformed to logarithms (base 10) and log transformed weights of dissectible body components were regressed on carcass side and empty body weight using the allometric growth equation of the form Y= aX b . The experimental relationship was converted to a logarithmic form as follows: Log 10 Y= log 10 a + b log 10 X Where Y= weight of dissectible body component; X= empty body weight or weight of carcass side; a= the value of Y when X=1; and b= the growth coefficient of dissectible body component relative to weight of carcass or empty body weight. To verify if b=1, the t-test was used, when b=1, growth was denominated isogonic, indicating that growth of both X and Y were similar during the growth period considered. On the other hand, when b ǂ1, growth was denominated heterogonic, being negative with precocious development if b<1 and positive with the late maturation if b>1. The regression procedure of the SAS software (43) was used to obtain the allometric coefficient.

RESULTS AND DISCUSSION Carcass composition:
The weights in kg of lean, fat and bone in the left side of the carcass increased linearly as the slaughter weight increased in the docked and intact lambs (Tables 1 , 2). This result were close to other workers (5,7,11,30), who reported that as the carcass weight increased, the weights of lean, fat and bone increased. The allometric growth coefficients of dissectible lean and bone weights in docked and intact Karadi lambs were negative heterogenic (b<1), indicating low impetus and early maturing tissue, and the growth of these two tissues are significantly (P<0.01) slower than carcass weight. While, dissectible fat weight was greater than one and their values are 1.694 and 2.203 in docked and undocked lambs respectively, it means high impetus and late maturing tissue, and they grew higher than the carcass weight. This was predicted since tissue development follows the order of bone, lean and fat (36). These results are in agreement with (6,9,11,13) who reported that fat is a late maturing tissue, whereas carcass lean and bone weights are early maturing when compared to empty body weight. However, Rosa et al. (34), working with Texel lambs, Yanez et al. (49) with Saanen goats and Santos et al. (38), with Santa Inês and Bergamasca lambs, also found early bone development and late fat tissue growth. However, they found that muscle tissue growth was identical to carcass growth. These variations might be due to differences in tissue composition and growth in various parts of the carcass. Also, Sousa et al., (46) and Al-Owaimer et al., (5) who found isogonic growth of dissectible lean. Furthermore, Silva et al. (44) discovered that the muscle growth of lambs born from Texel rams with Texel × Ideal ewes is isometric in relation to the carcass and its cuts, revealing that weights above 33 kg may not be the most appropriate at 105 days of age, because high proportions of muscle and good fat deposition in the carcass are obtained up to this weight. Thus, the variations between these experiments are most likely due to environmental factors, such as nutrition quality and the degree of maturity obtained at slaughter body weight. Table 1 In the present experiment, the chilled carcass weight and weights of all wholesale cuts relative to chilled carcass side at different slaughter weights in docked and intact male lambs were increased linearly (p≤0.01) with increasing slaughter weight (Tables 3 , 4). Similarly, Al-Owaimer, et al., (5) reported that the weight of all wholesale cuts was increased linearly with increasing slaughter weight. The allometric growth coefficient of leg weight is differ between treatments in relation to half carcass weight, while it was found that the b value in docked lambs is near to one (1.036), which means isogonic growth and grew at a similar rate to carcass weight, on the other hand, the b value in intact lambs was (0.845), indicating low impetus and early maturing cut and the growth rate was lower than that of carcass weight. Such difference could be attributed to more deposition of fat in the leg of docked lambs compared to intact lambs (20.18 vs. 12.99%) (8). This result for intact lambs are in accordance with Alvarez-Rodriguez, et al., (9) who indicated that the allometric growth of leg cuts in relation to half carcass weight was an early developed. Also, the low relative growth of leg is in line with results noticed by other workers (21,33,41,42). The results obtained for docked lambs is similar to those of Yáňez et al. (49) who found the coefficient of leg equal to one in saanen goats. The growth coefficient of neck in docked and intact lambs are isogonic with b=1 and their values are 1.159 and 1.075, respectively. (Tables 3 , 4) Similarly, Mora, et al., (26) showed isogonic growth of neck cuts with development growth of cold carcass weight. Furthermore, breast cuts (1.031) in docked had similar rate of growth to carcass side, and higher rate (1.350) of growth was observed in undocked lambs. This results were close to other workers (6,48,49), who reported that the breast cut was positive impetus and late growth which had a coefficient value greater than one. In both docked and intact lambs, loin, shoulder, foreshank and rack were low impetus and early maturing tissue, and growth rate of these components grew at slower rate than carcass rate. These results are in agreement with Sabbioni, et al., (37) who reported that the growth coefficient of loin cuts was early growth. Also, Santos, et al., (39) found that the loin proved to be an early growth rate in lambs slaughtered at 33.5 and 42.8kg. While, the growth coefficient of flank cuts in docked lambs is significantly less than one (0.990) indicating that grew at slower rate than the carcass, on the other hand, the b value in undocked lambs was significantly greater than one (1.610) demonstrated high impetus and late maturing tissue. These results are in agreement with Al-Owaimer, et al., (5) and Alvarez-Rodriguez, et al., (9) who found a positive heterogonic growth coefficients of flank cuts, because flank is considered a region with late maturation due to higher fat deposition and lower lean compared to other cuts.   . 0.218 ±0.005 c 0.272 ±0.002 b 0.343 ±0.02 a 0 (Tables 5 , 6), such effect of slaughter weight on carcass composition has been widely reported (25,28,49). Al-Owaimer et al. (5) also observed that as the Ardhi goat kids grew, the percentage of dissectible intramuscular fat as a percentage of the cold carcass side weight increased linearly (P≤0.01) with increasing slaughter weight. The current findings contrasts markedly with those of Mtenga et al. (28) in Saanen goats, who reported that the proportion of subcutaneous fat increased with the increased in slaughter weight from 9.5 to 36.5 kg. At similar carcass weights in general, similar trends of intermuscular fat were reported by Dhanda et al. (12) and Marichal et al. (24) who revealed that the proportions of intermuscular fat were positively impacted by age and slaughter weight. In the current investigation, it appears from Tables 5 and 6 that all non-carcass fat increased linearly with the increasing slaughter weight, except kidney and pelvic fat in docked lambs, whereas in intact lambs heart fat decreased and scrotal fat increased linearly, while all other fat depots including omental, mesenteric, kidney and pelvic and non-carcass fat increased quadraticly (P≤0.05) with the increasing slaughter weight. The allometric coefficients of carcass fat in docked and intact lambs were 0.955 and 1.415 respectively, indicating that low impetus in docked and high impetus in intact lambs, and between carcass fat showed that subcutaneous fat had heterogonic growth, >1, grew at higher rate than intermuscular fat which is <1, in docked and intact lambs (Tables 5 , 6). Similar results were obtained by Yanez, et al., (49); Santos, (40); Mahgoub and Lodge, (22); Mtenga et al., (27) and Al-Owaimer, et al., (5) who observed late growth for subcutaneous fat in relation to empty body weight. In contrast, Yanez, et al., (49); Santos, (40); Mahgoub and Lodge, (22); and Al-Owaimer, et al., (5) who observed later growth for inter-muscular fat in relation to empty body weight. Non-carcass fat of docked and intact lambs showed isogonic growth, it means grew at similar rate to empty body weight. Similarly, mesenteric and kidney fat had isogonic growth of both groups. In contrast, of omental and heart fat in docked and scrotal fat in undocked there were low impetus and early maturing tissue. These results are in agreement by Garcia, et al., (14) who found that allometric coefficients of the mesentery fat in purebred Ile de France x Santa Inês males and the females from all of the genetic groups equal to one for this component (isogonic growth), showing that the mesentery fat grows at a rate equivalent to the empty body weight. However, disagree with McGregor, (25) who found the early growth for mesenteric fat in Angora goats, also disagrees with Teixeira et al. (48); Mahgoub and Lodge, (22) and Alvares-Rodriguez, et al., (9) who found the late growth for omental and mesenteric fat in relation to empty body weight.

Non-carcass components
In the current work, in docked lambs, a nonsignificant quadratic increase in carcass, heart and spleen and decrease in liver, lungs and trachea was noticed. Whereas, with the exception of pelt, a significant linear decrease was noticed in head, feet, kidney and empty digestive and testes significantly increased linearly with increasing empty body weight. In intact lambs, a non-significant quadratic difference was noticed in liver, lungs and trachea and heart weights, and a significant decrease was found in empty digestive tract weights. However, with the exception of pelt, a significant linear increase was found in each of hot carcass and testes weight (P≤0.01), and a significant decrease (P≤0.01) was noticed in head, feet, kidney and spleen. These results are similar with those reported by Al-Owaimer et al. (5) who found that empty and hot carcass weight in Aradhi goats increased linearly (P≤0.05) and did not change in the percentage of liver based on empty body weight with increasing slaughter weight.   The allometric growth coefficients of hot carcass weight and spleen are isogonic in docked lambs and grew at similar rate of empty body weight, while, in undocked lambs are negative heterogonic (b<1), which grew at slower rate than empty body weight (Tables 7 ,  8). Similar results were obtained by Alvarez-Rodriguez, et al., (9) who found that spleen had early developing growth in relation to empty body weight. The growth of organs head, feet, kidney and empty digestive tract grew at lower rate than empty body weight, it means low impetus and early maturing tissue and there values were -0.295, -0.375, -0.235 and -0.344 respectively, in docked lambs and -0.276, -0.593, -0.771 and -0.219 respectively, in undocked lambs. Such results were in agreement by (9) and (2) who revealed that the head, feet and kidney were low impetus and early growth compared to the growth of empty body weight. Also, Mahgoub and Lodge, (22) demonstrated that between weights of 18 to 38kg the head and feet grew at rate significantly lower and indicating early growth. However, Kirton,et al.,(20) found that the kidneys growth has a high impetus and late developing relative to empty body weight. At birth, tissues important in life functions (such as metabolism and respiration) should be well developed, while those involved in locomotion and energy storage should be less developed (19). In fact, most visceral and thoracic organs, together with the feet and head, were proportionately greater at birth, with further slow postnatal growth (b<1) ( Tables 7 , 8), similar to previously reports on Segurena (31) and Texel lambs (35). In this approach, Atti et al. (10) and Mahouachi and Atti (23) found that the weight of offal components rich in bone and/or with low metabolic activity (head, feet) is indicative of early maturation. The growth of pelt, liver, lungs and trachea and heart were isogonic, it means grew at similar rate to that of empty body weight of both docked and intact male lambs. This results are in the line with those found earlier by Alvarez-Rodriguez, et al., (9) who concluded that skin and liver in relation to empty body weight were isogonic, and indicating similar growth rate with increasing slaughter weight. Also, Mahgoub and Lodge, (22) demonstrated that the skin grew at a rate similar to empty body weight. However, different results was obtained in testes that's found heterogonic growth in docked had early mature organ and grew at lower rate than empty body weight, while, late mature was noticed in undocked lambs and grew at higher rate than empty body weight. Such results are in agreement with (2) and (14)