Effect of body weight on slaughtering performance and carcass measurements of Sudan Baggara bulls

I E E Khalafalla, M Atta*, I E Eltahir and A M Mohammed

Department of Livestock Fattening Researches, Animal Production Researches Centre, Khartoum – Sudan
* Administration of Animal Resources, Ministry of Environment, Qatar State
muzamilata@yahoo.com

Abstract

Eighty fattened Sudan Baggara bulls were used to examine the variations on slaughtering performance and carcass measurements due to slaughter weight variation. The work also aimed at studying the use of carcass measurements to predict carcass weight. Animals were divided into four groups of 20 animals each (200 - 250, 251 - 300, 301 - 350 and 351 – 400 kg body weight groups). After slaughtering, dressing and evisceration, carcass and all organs were individually weighed. The carcass was also weighed after chilling at 4ºC for 24 hours. Measurements of carcass length, leg length, leg circumference, chest circumference, barrel circumference were taken on the cold carcass. One way analysis of variance was used to examine the effect of slaughter weight on the obtained data. Regressions of cold carcass weight on its measurements were also calculated.

Hot and chilled dressing percentages as well as the carcass measurements increased with the increase of slaughter weight. The opposite trend was observed for gut fill, total, internal and external non carcass components percentages. Leg circumference correlation with carcass weight had the highest coefficient. The study concluded that the Western Sudan Baggara bulls are promising beef animals. The optimum finishing weight range of this type of cattle was 301 - 350 kg. The leg circumference measurement can be used satisfactorily for prediction of carcass weight using the following equation: y = 4.62x - 273.

Key words: Carcass prediction, dressing percentage, finishing weight

Introduction

Western Sudan Baggara cattle constitute the most dominant and highly efficient meat producer in Sudan. They provide the majority of meat consumed locally and contribute considerably to the export trade, hence to the national economy of the country. Western Sudan Baggara cattle are found in the Savannah regions between White Nile and western frontier of Sudan. They are raised mainly under open range conditions and are owned by nomads (Khalil 1961). Economically beef animal is evaluated by consumer and producer on the basis of dressing percentage that defines the marketable proportion of the animal weight. Preston and Willis (1974) found that dressing percentage increased with the increase of weight and fattening of animal to a certain weight after which it tended to cease. This weight is intrinsic to breeds and bulls should be slaughtered at it (Mohammed et al 2007). They added that slaughtering animals beyond this weight was not feasible.

The shape and dimensions of animal carcass were used to describe carcass fatness (Allen and Kilkenny 1980). Preston and Willis (1974) added that some measurements of carcass like length, width and depth had been recommended as useful predictors for carcass yield and composition. Sudan Baggara cattle are raised under conditions of no weighing devices to determine animal body weight. At present, animal owners and cattle traders depend on eye judgment to estimate live body and carcass weights. The accuracy of such subjective method depends on individual experience. The importance of conformation as an indicator of commercial value is based on the assumption that carcasses with better conformation have advantages in terms of lean meat yield, proportion of higher priced cuts and possibly greater muscle size or area (Kempster et al 1986). Mohammed (2004) found that all carcass measurements were significantly affected by slaughter weight.

The objective of this research was to study the variations in slaughtering characteristics and carcass measurements of Baggara bulls due to variation in slaughter weight. The study also aimed to examine prediction of zebu cattle carcass weight using carcass measurements.

Materials and methods

This research was done at the Department of Livestock Fattening and Meat Production Researches of the Animal Production Research Centre, Khartoum North. The fattening herd of the department was accommodated in groups and fattened on concentrate diet (19.6% CP and 11.60 MJ/Kg, M.E) consisted of molasses (52%), wheat bran (39%), ground nut cake (5%), urea (3%) and common salt (1%). In addition sorghum straw was offered. The feed was offered ad libitum at the ratio of 80% concentrate and 20% sorghum straw. Fresh water and salt licks were freely available for animals.

For the purpose of this experiment eighty fattened Baggara bulls were selected. The animals were divided into four groups (of twenty animals each) according to their slaughter weights. The body weight ranges were 200 - 250, 251 - 300, 301 - 350 and 351 – 400 kg, and were designated 225, 275, 325 and 375, respectively. Before slaughtering the animals were fasted overnight from feed. The animals were slaughtered according to the Muslim practice by severing both jugular veins and carotid arteries by a sharp knife without stunning. After complete bleeding the head was removed at the atlanto-occipital joint and weighed. Blood was collected and weighed after the animal stopped bleeding. The hide was cut along the limbs and down the abdomen then removed manually and weighed. The fore and hind feet were removed with a knife at the proximal end of the metacarpal and metatarsal joints, respectively, and each was weighed with its hide cover. The tail was separated at the first inter-coccygeal articulation and weighed. After dressing and evisceration, the internal organs and offal were individually weighed. The alimentary tract was weighed and then cleaned of its contents (fill) and reweighed. The weight of fill was subtracted from the slaughter weight to determine the empty body weight (E.B.W.). The kidneys and their surrounding fat were left attached to the carcass. The carcass was stored in a chilling room at 4ºC for 24 hours. The cold carcass weight was then weighed.

The following measurements (in centimeters) were taken on the cold carcass while hanging by the hind limbs (Mohammed 2004, Albertí et al 2005, Eltahir 2007):

1. Carcass length (from the last sacral vertebra to the base of the neck).
2. Leg length (from the distal end of the tarsal bone along the inside of the leg to the stifle joint).
3. Leg circumference (from a point in front of the root of the tail, encircling rump).
4. Chest circumference (from the spinous process of the first thoracic vertebra to the mid line of the sternum).
5. Barrel circumference (from the spinous process of 4^th lumber vertebra to the most proximal edge of the flank).

 One way analysis of variance was used to examine the effect of slaughter weight on the obtained data (StatSoft 2010). The same statistical software was used to calculate the regressions of the cold carcass weights on its measurements.

Results

Table 1 showed that empty body, hot carcass, cold carcass and total weights of non-carcass components were significantly (P < 0.05) variable among the experimental groups and they increased with the slaughter weight increase. The same trend was observed for the hot and chilled dressing percentages (on slaughter and empty body weights basis), however there were no significant (P > 0.05) differences between the two heavy (325 and 375) and between the two light (225 and 275) groups. The opposite trend was observed for the gut fill, total, internal and external non-carcass components percentages. The measurements of the carcass (table 2) always increased with the increase of slaughter weight. The differences were significant (P < 0.05) between the four experimental groups for the neck and carcass lengths and leg circumference measurements. For the measurements of shin and leg lengths, shoulder, barrel, chest and waist circumferences, groups 325 and 375 were not different (P > 0.05).

The coefficients of correlations of the carcass measurements with the carcass weight in table 3 revealed that for the pooled data of the four experimental groups all the measurements had significant (P < 0.05) positive correlations. For groups 325 and 375 it was only the leg circumference that correlated significantly (P < 0.05) with carcass weight. For group 275, leg circumference, carcass length, leg length and shin length correlated significantly (P < 0.05) with carcass weight. For group 225, only carcass length and leg circumference correlated significantly (P < 0.05) with carcass weight. The highest correlation coefficient was observed for leg circumference for all groups except group 275 that had the highest coefficient for the carcass length.

 Table 4 shows the regression parameters of the carcass weight on leg circumference for the pooled data and for the four groups separately. The results revealed that the pooled data model showed the highest coefficients of determination and coefficient of regression. The results also showed the percentage of variation of the observed from the predicted (using the pooled data model) carcass weight of the four experimental groups. This variation was significantly lower for group 275 than the other groups, those were similar. 

Discussion

The dressing percentages observed here were comparable to those reported by Mohammed (2004) and Eltahir (2007) for the same type of animals and higher than 49% reported for Kenana bulls by El Khidir et al (1988). Consistently, Gumma (1996) observed that Baggara bulls had dressing percentage higher than Kenana bull of the same slaughter weight. The current results (table 1) indicated that bulls of heavy weight groups gave higher dressing weight (P < 0.001) than those of light weight groups on warm or chilled carcass weight basis. Similar observations were reported by Eltahir (2007). Williams et al (1992) noted that the increase in dressing percentage with the increase of slaughter weight might be attributed to the differences in the maturity of carcass and non-carcass components. Carcass components are late maturing tissues so their percentages increase as the bull weight increases, whereas the percentages of the non-carcass components, the early maturing tissues, decline (Lawrence and Fowler 1997). The insignificant (P > 0.05) difference between groups 325 and 375 was explained by Preston and Willis (1974) who stated that dressing percentage increased with live weight increase till a point at which it tended to cease. This may indicate that weight range of Baggara bull suitable for slaughtering is 301 – 350 kg beyond which no increase in lean meat yield percentage is expected. Similar conclusion was also reported by Mohammed (2004), however, Eltahir (2007) proposed the suitable slaughter weight to be above 400 kg. Dressing percentage of hot carcass weight was greater than that of chilled carcass weight, and this was similar to that noted by Berg et al (1991) who attributed that to the chilling losses. As a result of cooling, carcass loses weight due to loss of tissue water.

The total non carcass components proportion of the empty body weight of Baggara bulls observed in the present study (range between 36.2 and 38.0 %) was similar to the range 34.8 – 38.4% reported by Eltahir (2007) for the same type of animals. Consistently, Goldstrand (1988) reported that the total weight of internal and external offal of cattle is about 39% of the live weight. The decrease of non-carcass components with the increase of slaughter weight in the present study agreed with the findings of Jesse et al (1976). They found that hide percentage decreased from 11.2 to 9.39% and blood declined from 3.66 to 2.76% as the empty body weight increased from 196 to 509 kg. When the current total non-carcass components were grouped into internal and external offal, the percentage of each was also observed to decrease with the increase of slaughter weight from 200 kg to 400 kg (from 18.6 to 17.0 % for the external offal and from 19.9 to 19.2 % for the internal offal). These observations were consistent with the findings of Mohammed (2004) who reported that the percentage of the external non-carcass components decreased from 19.3 to 16.8% and that of internal non-carcass components declined from 21.4 to 17.2% as the slaughter body weight increased from 200 to 350 kg. Similarly, Eltahir (2007) reported that total non-carcass components decreased significantly from 38.4 to 34.8% with the increase of slaughter weight from 200 to 400 kg, the external non-carcass components decreased from 18.2 to 15.9% and the internal non carcass components from 20.25 to 18.97%. This is partly due to the fact that internal non-carcass components contain many early maturing organs such as the heart, liver, stomach and intestine (Hammond 1944).

The present carcass measurements (table 2) were comparable to those observed by Mohammed (2004). Eltahir (2007) obtained similar results for all measurements with the exception of the present higher measurements of shoulder and chest circumferences (66.4 – 79.0 vs. 34.5 – 42.1 cm for shoulder circumference and 130 – 146 vs. 52.8 – 69.6 cm for chest circumference) and the lower measurements for leg length (39.4 – 42.5 vs. 69.0 – 79.3 cm).

The effect of slaughter weight on carcass measurements indicated that all carcass measurements increased (P < 0.001) with the increase of slaughter weight. Similar observations were reported by Mohammed (2004) and Eltahir (2007). The correlation coefficient matrix (table 3) indicated that leg circumference had the highest coefficient for the pooled data and groups 225, 325 and 375. Lawrence and Fowler (1997) stated that all body width measurements are most variable with live weight because they reflect both soft and skeletal tissues growth, while the length measurements reflect mainly the skeletal tissue growth. In the same context Mohammed (2004) reported that the linear relationship between carcass weight and carcass measurements showed that leg circumference had the highest correlation coefficient (R = 0.92). He added that a regression equation (y = -161 + 3.33 x) was applied to predict carcass weight from leg circumference. In the present study, the linear regression of the pooled data of carcass weight on leg circumference explained the relation between the two traits by a high coefficient of determination (R² = 0.87) and the equation obtained was y = 4.62x-273, where y is the carcass weight (kg) and x is the leg circumference (cm). When this model was applied to the data of different groups, it was found to overestimate the weights between 251 and 300 kg by about 7.5%; however it precisely predicted the carcass weight of other slaughter weight ranges.

Conclusions

• The findings of this study indicate that the Western Sudan Baggara bulls are promising beef animals. The optimum finishing weight of this type of cattle could be between 301 and 350 kg with reasonable dressing percentage. The study also concludes that the measurement of leg circumference could be used satisfactorily for prediction of carcass weight using the following equation: y = 4.62x - 273.

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Received 12 November 2010; Accepted 19 January 2011; Published 6 March 2011

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