Meat Production Characteristics of Black Bengal Goat

Black Bengal goat is primarily reared for meat, skin comes here as a by-product. The present trial describes the effect of age on different carcass characteristics of Black Bengal goats of either sex. A total of 61 Black Bengal goats of different age and sex groups were slaughtered. They were reared under semi-intensive management on milk alone or with concentrates (of 10.14 MJ ME and 10.48 g M/kg DM) and freshly cut Napier grass (2 MJ ME and 25 g CP/kg of fresh matter) that provides the estimated NRC (1981) requirement. The four age groups were: pre-weaned kids (0-90 day), post-weaned kids (91-180 days), growing (181-365 days) and adult (>365 days). Goats were slaughtered according to ‘Halal’ method by severing the major vessels of the throat by a transverse cut. Different slaughter parameters of Black Bengal goat can be best predicted from the equations as follows: live weight (kg)=0.801 (shoulder height (cm))-24.32, (r=0.94); carcass weight (kg)=0.364 (height at hind legs (cm))-11.54, (r=0.91); edible weight (kg)=0.623 (shoulder height (cm))-19.94, (r=0.91) and saleable weight (kg)=0.701 (shoulder height (cm))-21.99, (r=0.92). Live weight, carcass weight, edible weight and saleable weight of castrated goat at one-year onward ranges from 20-22, 9.4-10.5, 14-16 and 16.6-18.8 kg, respectively, which are about 80% higher than most of the reported observations on Black Bengal goat of same age and sex. Slaughter weight, warm carcass weight, edible weight and saleable weight increased curvilinearly with age of slaughter but not affected (p>0.05) by sex. However, linearity of the response curve of affect of age on mentioned parameters ends at around 9 months. Visceral fat as per cent of live weight increased curvilinearly with age and attain its maximum (about 6%) at about 500 days. However, linear part of the quadratic model ends at about 300 days when visceral fat content is about 4.8% of body weight. Blood and skin yield for one-year old male goat was 797 g and 1.61 kg, respectively. Absolute yield of blood and skin increased curvilinealry and attained maximum level at about 400 days (13.3 months). Average proportion of different carcass cut were round 27%, rump 7%, loin 10%, ribs (6-12th) 14%, shoulder 21%, Neck 7%, chest 14%. Thigh and shoulder constituted about 48.3% of the cold carcass weight. Overall crude protein content of meat samples of different carcass cuts progressively decreased with age starting from 57 at 0-90 days to 58, 47 and 33 per cent, respectively at 91-180, 181-365 and >365 days, respectively. Overall meat fat content increased almost linearly from 11.1% during 91-180 days to 22.9 and 39.5% during 181-365 and >365days, respectively. Results from this trial suggest that both carcass yield and carcass composition changes with age; and sex have little or no effect on carcass yield and carcass composition. However, caution should be made in using second conclusion as there were few female animals slaughtered relative to the male. Optimum slaughter age for Black Bengal goat reared under semi-intensive management with adequate feeding and management would be about 9 months when their live weight, warm carcass weight, edible and saleable weight of carcass can be about 16.74, 7.28, 12.05 and 13.81 kg, respectively. (Asian-Aust. J. Anim. Sci. 2004. Vol 17, No. 6 : 848-856)


INTRODUCTION
Meat production is the most important function of goats in the tropics (Devendra, 1991).Devendra and Burn (1983) reviewed the meat production characteristics of different meat type goat breeds in the tropics.These studies assessed the growth and development of kids from birth to slaughter, carcass characteristics, and meat quality in relation to breed, age, sex and nutritional regime.Black Bengal goat is primarily a meat type breed, although it is also valued for its skin.Relatively fewer studies conducted on meat production characteristics of Black Bengal goat.Singh and Sengar (1979) compared the meat production characteristics of male Black Bengal or its crosses to that of the Jamnapari, Beetal, Barbari or their crosses.They showed that the dressing percentage and percentage of total edible meat was the lowest in Black Bengal goat (44.62 and 74.15%, respectively) and the highest in Barbari (49 and 80%,respectively).Black Bengal goat found to attain optimum slaughter weight at the shortest period (8.9 months) than the Jamnapari (23.48 months), Beetal (19.46 months) and Barbari (13.46 months).However, this was not a direct measurement rather was an estimation: slaughter weight= (Birth weight×7)-(Birth weight-2).This estimation was based on the assumption that postnatal growth is the function of living cells delivered at birth as the birth weight (Singh and Sengar, 1979).However, these measurements have not been validated on the Black Bengal goats.Shajalal et al. (2000) studied the effect of dietary protein concentration and feeding level on the growth and carcass characteristics of 8 months old castrated Black Bengal goat.They showed that goat having ad libitum feeding with high protein (20.3%) concentrate have better growth rate and carcass characteristics than those raised on restricted feeding of low protein (16.9%) diet.Moniruzzaman et al. (2002) studied the effect of stall-feeding, tethering, restricted grazing or free grazing on the carcass characteristics of 1 year old Black Bengal does.They showed that stall-fed does had better meat production than the other systems.Quality and quantity of meat produced is generally a function of age, sex, genotype and management (feeding in particular).To our knowledge, effect of age groups on yield and carcass characteristics of Black Bengal goat of either sex has not been studied.The present research programme has therefore been designed to determine the effect of age on different carcass characteristics of Black Bengal goats of either sex.

Experimental animals and their management
The experiment was conducted in the Goat Farm of Bangladesh Livestock Research Institute, Savar, Dhaka.A total of 61 Black Bengal goats of different age and sex groups were slaughtered (Table 1).Animals were reared under semi-intensive management.All male animals were castrated during 3rd to 4th week of their life.Pre-weaned kids (0-90 day) were absolutely on milk alone.Post-weaned kids (91-180 days) were given concentrate mixture (of 10.14 MJ meatbolizable energy (ME) and 10.48 g metabolizable protein (MP)/kg DM; Table 2) and freshly cut Napier grass (of 2 MJ ME and 25 g CP/kg of fresh matter) to meet the estimated nutrient requirement of NRC (1981).Depending on the body weight, growing and adult animals were given 350-600 g concentrate mixture (10.31MJ ME and 11.7 g MP/kg DM; Table 2) daily in addition to 6 hours grazing in a mixed natural pasture.

Slaughter procedure and measurements
Prior to slaughter, goats were weighed by a hanging digital balance.Different body measurements including shoulder (wither) height, height at hind legs, chest depth (half of the circumference of chest girth) and body length (point of elbow to point of hip) were then recorded.Goats were slaughtered according to 'Halal' method by severing the major vessels of the throat by a transverse cut.Blood was collected and weighed in a pre-weighed bucket.Before flaying, a 20 cm steel-rod was inserted through left fetlock under the skin towards thigh.Air was then blown into the body through the perforation until the carcass was swelled with air under the skin.This was done to facilitate easy removal of skin.Skin was removed by conventional flaying method.The carcass was hoisted from its hock at a convenient height.Head was removed at the oxipito-atlantal joint and feet below the carpals (knee bones) in the fore legs and tarsals in the hind legs.Entire digestive tract was weighed before and after removing the contents.Data were recorded in terms of live weight, warm carcass weight, dressing percentage, weight of blood, visceral organs (liver, lung, kidney, heart, spleen), head, gut and caul fat, perinephric and channel fat, weight of digestive tract, total edible (carcass, viscera, visceral fat) and total saleable (edible plus skin) weight.Carcass was then chilled at -25°C.Chilled carcass was divided into different cuts (shoulder, loin, ribs, thigh) according to Warris (2000).About 250 g of meat sample from each cut was taken for their chemical analysis.

Chemical analysis
Meat samples from different cuts were analyzed for dry matter, ash, crude protein and ether extract according to the AOAC (1984).Concentrate mixture was also analyzed using the same procedure.

Statistical analysis
The data were analyzed using the statistical package of SPSS 9.05 for Windows (SPSS Ltd., 1998).In the analysis of variance appropriate for 4×2 factorial experiment the results presented for main effects and interactions as follows: A=age effect (0-90, 91-180, 181-365 and >365 days); S=sex (male (M) and female (F)) and A×S= interaction between the age and sex.The effect of age and sex of goat and their interaction on slaughter weight, body measurement, yield of different carcass and non-carcass components and carcass composition, were determined by using the following linear model: where, Y ij is the effect of i th age at j th sex on parameter in question, µ is the general mean, α i is the effect of i th (i=0-90, 91-180, 181-365 and >365 days) age group of goat, β j is the effect of j th (j=male (M) and female (F)) sex, αβ ij is the interaction effect of i th age at j th sex and e ij is the random error.However, for chemical composition of meat, effect of sex was not included in the model.Besides, linear, exponential or quadratic model was used to express the relationship between to related variables using Microsoft Excel programme (Microsoft Office 2000).

Slaughter weight and carcass yield
Effect of age and sex on slaughter weight and carcass yield characteristics of Black Bengal goat is shown in Table 4. Slaughter weight was significantly (p<0.001)affected by the age but not by the sex.Live weight at slaughter of goat increased curvilinearly (r 2 =0.86) up to 520 days (17.3 months; estimated from the equation Figure 6a) but the linearity of the curve ends at about 270 days (9 months; estimated from the equation Figure 6a).This means that meat production efficiency of Black Bengal goat would be the highest at about 9 months, which is similar to the suggested (theoretical estimation) optimum slaughter age of 8.9 months for Black Bengal goat (Singh and Sengar, 1979).
Live weight of castrated male goat at one-year onward ranges from 20-22 kg, which, is about 78% higher than that reported live weight of 13 kg (Guha et al., 1968), 11.6 kg (Singh andSengar, 1979), 10.3 kg (Shajalal et al., 2000) and 12.3 kg (Monirzzaman et al., 2002) for the Black Bengal goat at one year.One possible reason is that goat under the present trail were given NRC (1983) recommended nutrient right from their in-utero life.While most of the trials (except Singh and Sengar, 1979) referred here are based on short-term observation of 3-5 months feeding under different types of management.Ryan (1990) showed that lambs and calves subjected to nutritional restriction during their in-utero life or soon after birth, may suffer permanent stunting of growth.This is probably due to the fact that pregnant dam can induce life long change in gene expression of many metabolic systems e.g.insulin/ glucose axis, growth hormone/IGF 1 axis and other key metabolic regulator of homeorhsis (Makkar, 2002).Result of this trial probably shows the real potentiality Black Bengal goat as meat animal.
Unlike live weight, carcass weight was significantly affected both by age (p<0.001),sex (p<0.05) and also by their interaction (p<0.001).Carcass weight of goat also increased curvilinearly (r 2 =0.86) up to 525 days (17.3  months).However, linearity of the curve ends at about 260 days (8.67 months; estimated from the equation Figure 6b), which, is slightly higher than the estimated (using an equation mentioned earlier) optimum slaughter age of 248 days (8.26 months) for Black Bengal goat (Singh and Sengar, 1979).In the present trial, carcass weight, at one year on-ward 9.4-10.5 kg, which, is about two times higher than that reported carcass weight of 5.17 kg (Singh andSengar, 1979), 4.65 kg (Shajalal et al., 2000) and 5.17 kg (Moniruzzaman et al., 2002) for one year old male Black Bengal goat.
Total edible and saleable quantity of carcass was significantly (p<0.001)affected by the age and sex of goat and also by their interaction.However, age or sex had no significant (p>0.05)affect on edible or saleable part of carcass as per cent of live weight.With increase live weight, the edible (Figure 6c) and saleable (Figure 6d) quantity of carcass increased curvilinearly (r 2 =0.84 and 0.86, respectively).Edible and saleable quantity increased up to 585 days (19.5 months; estimated from the equation Figure 6c) and 560 days (18.7 months; estimated from the equation Figure 6d), respectively but the linearity of increase, in both cases, ends at about 260 days (8.7 months; estimated from the equation Figures 6b and 6c).However, there is no apparent relationship between ages and edible (Figure 7b) or saleable (Figure 7c) as per cent of live weight.This is different from the observation that showed that percent of saleable bio-mass of East African female goats increased from 45.9% at birth to 61.8% at 4.1 kg weight which then decreased to 60.8, 57.5, 55.5 per cent at 7.3 kg, 11.3 kg and  at maturity, respectively (Wilson, 1958).Overall edible (64.5±1.90) and saleable (79.6±1.67) per cent in this trial were similar to 61.2 and 81.5%, respectively for the Katjang goat of Malaysia (Devendra and Burns, 1983).

Edible by-products
Effect of age and sex on edible by-product yield of Black Bengal goat is shown in Table 5. Weight of dressed carcass, lung, liver, kidney, spleen, total viscera, visceral fat and visceral fat as per cent of live weight increased significantly (p<0.001) with age.However, sex had no significant (p>0.05)affect on edible carcass by-products.Although total visceral content increased curvilinearly with age (r 2 =0.71; Figure 8a) but age of goat had little affect (r 2 =0.26; Figure 8b) on visceral content as per cent of live weight.
However, both total visceral fat (r 2 =0.75; Figure 8c) and visceral fat as per cent of live weight (r 2 =0.64; Figure 8d) increased curvilinearly with age.Using the equation in Figure 8d (Y=-0.00003X 2 +0.0301X-1.5385),it can estimate that maximum visceral fat as per cent of live weight (about 6%) can be achieved at about 500 days.However, linear part of the quadratic model ends at about 300 days when visceral fat content is about 4.8% of body weight.Up to 6 months visceral fat content was about 1.2% of live weight that increased to about 5% during 180-365 days and to 6% for animals over one year old.This trial shows that in Black Bengal goat, viscera as proportion of body weight do not changes but the proportion of visceral fat increases with age.As per as fat deposition is concern, optimum slaughter age will be around 300 days (10 months).

Non-edible by-products
Effect of non-edible age and sex on non-edible by products is shown in Table 6.Both absolute quantity and the proportions of different non-edible by products (except proportion of head) were affected by the age but not by the sex or by their interaction.Absolute yield of blood (Figure 9a) and skin (Figure 9c) increased curvilinealry and attained maximum level at about 400 days (13.3 months).However, age had little or no effect on blood (Figure 9b) or skin (Figure 9d) as proportion of live weight.Blood yield for one-year old male goat was 797 g in the present trial, while  it was about 500 g in Black Bengal goats of same age and sex (Monirzzaman et al., 2002).However, when expressed as per cent of live weight, blood yield was higher in the later (5.05%) than the former (3.57%).Similarly, for oneyear old male goat, yield of skin both absolute quantity (1.61 kg) and as proportion of live weight (7.95%) were higher in the present trial than those of 0.75 kg and 7.5%, respectively observed by Moniruzzaman et al. (2002).

Carcass cuts
Effect of age and sex on carcass cuts of Black Bengal goats is shown in Table 7. Quantity of thigh, loin, ribs,

Chemical composition
Effect of age on chemical composition of dressed meat from some carcass cuts is given in Table 8.Dry matter content of hind leg (p<0.01),shoulder (p<0.06),eye muscle and chest (p>0.05)increased with age.Overall increase in carcass DM content followed a sigmoid trend with relatively lower values at 91-180 days and at >365 days (Figure 10).Ash content was the highest during 91-180 days but decreased with progress in age.Overall crude protein content, on the other hand, progressively decreased with age starting from 57 at 0-90 days to 58, 47 and 33 per cent, respectively at 91-180, 181-365 and >365 days, respectively (Figure 10).The highest overall protein content was observed in the eye muscle (53%) and the lowest (35%) in chest cut (Table 8).Overall protein content of 33-58% of meat was much higher in this trial than 21-22.8%(Shahjalal et al., 2000) or 20.8-22.4% (Moniruzzaman et al., 2002), but it was lower than 61% (Singh and Sengar, 1979) observed in Black Bengal goat.
Unfortunately we do not have the data on carcass fat content during 0-90 days.Overall meat fat content increased almost linearly from 11.1% during 91-180 days to 22.9 and 39.5% during 181-365 and >365 days, respectively (Figure 10).Overall fat content was the highest in the chest cut (44%) and the lowest in the eye muscle (22%).Overall fat content of 11-40% of meat was much higher in this trial than 6-6.9% (Shahjalal et al., 2000) or 4.9-9.2%(Moniruzzaman et al., 2002) or 7.77% (Singh and Sengar, 1979) observed in Black Bengal goat.Relatively higher fat content in this trial was probably due to higher body weight of goats in this trial of 20-22 kg than those of 9.63-11.4(Shahjalal et al., 2000), 9-12.3 kg (Moniruzzaman et al., 2002) and 11.6 kg of (Singh and Sengar, 1979).

CONCLUSION
Results from this trial suggest mainly two things i) both carcass yield and carcass composition changes with age; ii) sex have little or no effect on carcass yield and carcass composition.However, caution should be made in using second conclusion as there were few female animals slaughtered relative to the male.Optimum slaughter age for Black Bengal goat reared semi-intensive management with adequate feeding and management would be about 9 months when their live weight, warm carcass weight, edible and saleable weight of carcass can be about 16.74, 7.28, 12.05 and 13.81, respectively.

Figure 1 .Figure 2 .
Figure 1.Relationship between age and wither height (a), or height at the hind legs (b) chest depth (c) or body length (d) of Black Bengal goat.Each point represents record of individual goat.

Figure 4 .Figure 5 .Figure 6 .
Figure 4. Relationships of edible weight with body height at shoulder (a), hind legs (b), chest depth (c) and body length (d) of Black Bengal goat at different ages and sex groups.

Figure 7 .Figure 8 .
Figure 7. Relationship between slaughter age with dressing per cent (a), edible per cent (b) and saleable per cent (c) of Black Bengal goat reared under semi-intensive management.

Figure 9 .
Figure 9.Effect of age on blood (a), blood as per cent of live weight (b), skin (c) and skin as per cent of live weight (d) of Black Bengal goat.

Figure 10 .
Figure 10.Overall chemical composition of Black Bengal goat carcass at different ages.

Table 1 .
Number of goats slaughtered at different age and sex groups

Table 2 .
Composition of kid starter used for feeding pre weaned

Table 3 .
Effect of age and sex on body measurements of Black Bengal goat under semi-intensive management

Table 4 .
Effect of age and sex on slaughter weight and dressing percentage Black Bengal goat

Table 5 .
Effect of age and sex on edible product and by-products of Black Bengal goat Values in the parenthesis indicate standard error of the mean.* , ** , *** and NS indicate significant at (p<0.05), (p<0.01),(p<0.001) and (p>0.05),respectively.

Table 6 .
Effect of age and sex on non-edible carcass components of Black Bengal goats

Table 7 .
Effect of age and sex on carcass cuts of Black Bengal goats

Table 8 .
Chemical composition of dressed meat of some carcass cuts of Black Bengal goats slaughtered at different ages Values in the parenthesis indicate standard error of the mean.NS indicate not significant at (p<0.05).