Development of Carcass Evaluation System for Baggara Cattle Raised to Different Slaughter Weights

Abstract

This research was conducted to study changes and variations in carcass quality associated with age, weight and fatness. Also, to develop procedures for evaluating beef carcasses quantitatively and qualitatively to solve meat marketing problems. Forty-eight Western Sudan Baggara bulls were used. They were divided into two groups according to their ages, young (1-2 years) and mature (3-4 years). The bulls were kept for a period of 25 weeks, during which they were adlib fed on concentrated diet (20% CP and 11.1 MJ/kg DM ME), and representative animals from each group slaughtered at weeks 5, 10, 15, 20 or 25 of the feeding period. The results indicated that mature bulls consumed more feed and had better daily weight gain than young ones. But young bulls showed better feed conversion ratio than mature bulls. The results revealed no significant treatment effect (P>0.05) on trunk length, heart girth, height at withers, height at hip, neck and hump length. But there were significant effect on chest depth (P<0.05), pelvic width (P<0.01), shank width and barrel circumference (P<0.001). Mature bulls showed higher dressing percentages (54.2, 59.3) than young (53.9, 58.7) bulls on full and empty body basis, respectively. Body weight had a significant effect (P<0.001) on the weights of all offal parts except spleen and rumen fill weight. At an equally adjusted slaughter weight, young bulls had heavier omentum, mesenteric, head and hide weights, while mature bulls had higher liver, spleen and rumen fill weights. viii There was no significant treatment effect (P>0.05) on carcass measurements. Mature bulls had longer carcasses and legs and more developed fat over eye-muscle than young bulls. The results revealed that mature bulls had heavier carcasses, total muscle, bone and fat weight, and greater muscle: bone ratio (4.0), but lighter kidney fat weight. There was a significant treatment effect on moisture (P<0.01), crude protein and ash (P<0.05). Young bulls had higher moisture, but lower protein and ash percentage. There was no significant effect (P>0.05) on chemical fat, but mature bulls had higher value for this trait than young bulls. The results revealed significant treatment effect (P<0.001) on cooking loss but not on water holding capacity, pH value or meat colour. Cooking loss was greater in young than mature bulls. Mature bulls had more intense red coloured meat than young ones. Young bulls had higher sensory scores (P<0.05) for all parameters than mature bulls. The meat from young bulls was superior in eating quality and more acceptable to panelists than that of mature bulls. The results indicated that all live body measurements, had high positive correlation with slaughter weight. The best association was found between heart girth and slaughter weight (r = 0.90, P<0.001). Regression equation relating body weight (y) and heart girth (x) is: Y = 4.2 x – 363.3±0.31. There was very high positive correlation (r = 0.98, P<0.001) between carcass weight and total muscle weight. The regression equation to predict total muscle (y) from carcass weight is: Y = 0.68 x – 3.11±0.02. ix Kidney, omentum and mesenteric fat showed very low coefficient of determination for predicting weight of carcass tissues. Multiple regression equation using external body measurements (heart girth, height at withers and hip, chest depth and barrel circumference) had very high accuracy in predicting live body weight (R2 = 0.87). Also, slaughter weight and omental fat weight had very high accuracy in predicting muscle weight (R2 = 0.97), bone weight (R2 = 0.81), fat weight (R2 = 0.71) and joint weight (R2 = 0.99). Consumer and butcher questionnaire results indicated that the majority (87.5%) of consumers were able to identify meat quality but only (43%) asked for certain cuts from the carcass. They preferred fresh meat (86.7%) of young animals (73.4%). Roasting is preferred method of cooking (60%) followed by moist cooking (24%). The results indicated that meat colour is the main tool by which butcher identify carcass age. The majority (66.7%) of the butchers agreed to sell meat according to cuts quality. To encourage improvement in cattle meat quality, buying and selling of beef should be based on a grading system. Two market classes of slaughtered cattle, young and mature are proposed. Three grades of beef carcasses are proposed for young bulls, while four and five grades were recommended for mature bulls and mature cows respectively.