The study was conducted from October 2017 to May 2018 on cattle purchased from different places and slaughtered at Elfora Bishoftu export abattoirs which found at bishoftu town. Arsi and Harar breeds purchased from cattle market at West Arsi (kofale) and West Hararghe (Chiro) respectively. However, Boran breed from Dida tuyera ranch, Borena Zones (Yabello). West Arsi is located at 7˚19' to 7˚40'N and 38˚30' to 38˚35'E with an elevation of 2695 meters above sea level. West Hararghe zone is located at altitude between 970 and 1410 meter above sea level. The annual rainfall ranges from 650 mm - 950 mm and mean temperature range between 17.5˚C - 27˚C. Borana zone located at 3˚26' - 6˚32'N latitude and 36˚43' - 40˚46'E longitudes with altitude below 1500 m above mean sea level. The area characterized by semi-arid lowland with an average rainfall ranging from 300 to 600 mm and average daily temperature from 19˚C to 26˚C. Mixed crop-livestock production system is practiced in the Arsi and Hararghe regions in which grazing and crop residue feeding were common. Pastoral range livestock production system is practiced in Borena zone in which cattle mostly depend on grazing natural pasture which is dominated by perennial grasses (Cenchrus, Pennisetum, and Chrysopogon species).

A total of 39 bulls consisting of three breeds (Boran, Harar and Arsi) were used for the study. The bulls were grouped into three age groups as group I contained cattle with 2 - 3 years of age, group II contained cattle with 3 - 6 years of ages and group III contained cattle with 6 - 9 years of ages. Ages of cattle were determined by dentition according to [9]. Bulls from Boran breed were directly loaded from ranch while a bull from Arsi and Harar breeds directly from the market. Bulls of each breed were transported by FSR trucks to export abattoir for the same distance. On arrival at the abattoirs, unloading activities were monitored and cattle were provided with feed and water ad-libtium according to abattoir animal handling guideline. Cattle were stayed in lariage for 18 hours without provision of feed. Later they were stunned and slaughtered using standard operating procedures of the abattoir.

Carcass bruise score assessment was done for 39 beef carcasses using a method based on the Australian Carcass Bruise Score System [10]. After dressing, the carcasses were examined for the numbers of bruises per carcass and bruises by anatomical site (butt, rump-loin, ribs, forequarter, back, pin and hip. The size, colour and shape of every bruise were recorded. The size of each bruise was measured on the basis of its diameter as: little (<2 cm), slight (2 - 8 cm), medium (8 - 16 cm) or heavy (>16 cm) by using a ruler. When a bruise was not circular, the diameter was measured as the longest length of the lesion. To assist with the visual appraisal of the bruises, a hard paper indicating circular areas of 2, 8 and 16 cm was used. Bruise scores were calculated for each bruised carcass by multiplying the number of bruises in each size class (little, slight, medium or heavy) by a weighing factor (little 0, slight 1, medium 3 and heavy 5) and adding these values. Little bruises (<2 cm) were not considered. These bruise scores then divided by the number of bruised carcass to give a mean bruise score per carcass. Level of bruise by size category was counted for different breed and age categories from the total bruise. Bruise age was estimated using the method of [11] as described in Table 1.

The pH measurement done according to procedure described by [12]. The pH and temperature measured using Portable HANNA pH or temperature meter (model number-HI99163) in the Muscularis longisimus thoracis et. Lumborum (LTL) at the depth of 3 - 4 cm while carcasses were at hanging position and by removing samples from the loin region. The pH meter was calibrated before taking measurement and in every measurement using pH 4 and pH 7 standard buffer solutions. During each pH measurement series the immersed sensor tip or electrode was rinsed immediately and thoroughly with distilled water and dried carefully with a clean paper towel. After measurement the carcasses with pH₂₄ hours lower than 5.8 were classified as normal quality and carcasses with pH₂₄ hours value greater than or equal to 5.8 as DFD meat according to previous recommendation [12] [13].

The color of meat was measured in triplicate 24 hours after slaughter in the Muscularis longisimus thoracis et. Lumborum (LTL), 3 cm thick sample removed from the area between the 12th and 13th ribs from right side carcass at free fat area. Measurements were made after 30-min exposure to air (bloom time) on the different locations of the surface of the muscle using a Mini Scan EZ machine (model number-4500L) with a 20 mm diameter measurements area and illuminant D65-day light, 10˚ standard observer. The machine was standardized before taking measurements using the black and white colour standard samples provided for this purpose. Three readings were taken on each sample by rotating the Colour Guide 90˚ between measurements so as to obtain the average value for the colour and meat colour was expressed using the CIELAB color space (L* = lightness, a* = redness, and b* = yellowness) according to the CIE system [14] [15].

The thickness of subcutaneous fat (TSF) measured by a caliper averaging three points between the 12^th and 13^th ribs of longissimus muscle and expressed in inch.

The data was analyzed by Statistical Analysis System 9.3 version (SAS, 2011). Descriptive statistics were used to determine levels of bruising and DFD. Pearson’s chi-square test was done to compare the level of DFD for the breed and age category. General Linear Model procedure (PROC GLIMMIX; SAS, 2011) was used to compare beef quality parameter (pH, temperature and colour) for normal and DFD meat. Significant differences among least square group means were compared using pdiff when F test was statistically significant (P < 0.05).

The model used was:

Y і ј = μ + α і + β ј + ε і ј

where,

Y_ij = response variable (pH, temperature, WHC, L*, a*, b*).

N = Constant mean common to all observations.

α_і = Breed (Harar, Boran, Arsi).

β_ј = Age (group 1, group 2 and group 3).

E_ij = random error.

The level of DFD beef in slaughtered cattle in the present study is shown in Figure 1. The result of the study showed that from a total of 39 beef cattle slaughtered, 27 bull (69.23%) had ultimate pH (pH₂₄ hours) less than 5.8 (normal meat) and 12 bulls (30.77%) had ultimate pH greater than or equal to 5.8 (DFD meat) in longissimus dorsi muscle. The current level of DFD in slaughtered cattle were high compared to level of DFD for cattle slaughtered at South Africa local commercial abattoir which was 7.3% - 11.8% [16], 4.53% for Brazilian commercial crossbred cattle [17], 3.2% in USA [18], 1.6% in Canada [19] grain finished cattle in USA which were in the range between 1.5% and 5% [20]. The higher proportion of DFD might be associated with the absence of enough glycogen stored by the cattle before slaughter. Most of cattle slaughtered at public abattoirs in Ethiopia had low grade of fat (fat grade 1) based on beef classification system of Ethiopia [21]. Moreover, cattle were exposed to a number of stress which started from farm, transport which was usually trekking, during marketing, lairriage and by methods of slaughter [22] [23]. The present finding alert the need to look for strategies to minimize the incidence of DFD beef produced in Ethiopia.

Quality characteristics of normal and DFD beef are presented in Table 4. The mean ultimate pH of normal and DFD beef were 5.54 ± 0.07 and 6.16 ± 0.04, respectively. Normal beef was relatively lighter (P < 0.05) than DFD Meat with L* values of 34.29 ± 0.59 and 31.53 ± 0.83, respectively. However, difference in terms of pH45 min, Temp24 hours, a* and b*, for the two meat groups were not significant. The pH of normal meat drops from initial pH 6.16 to 5.54 after 24 hours of carcass chilling at 0˚C - 4˚C while in DFD meat did not drop with significant figure. The possible absence of drop in pH of DFD beef might be associated with depletion of glycogen due to stress of the animal which finally didn’t produce significant acidification due inability to produce enough lactic acid.

Experimental cattle were transported up to 16 hours, at high transit temperature up to 36˚C, exposure to cold and rainy environment alternatively, long hours of deprivation water and feed up to 36 hours. Animals exposed to stress during transport from farm to abattoir. The stress trigger depletion of muscle glycogen which might be mobilized by rapid release of stress enzymes and hormones, this results in glycogen depletion in muscle at slaughter, formation of insufficient amount of lactic acid, and correspondingly, low fall in muscle pH post

N = Total number of animals per breed, pH₄₅ = pH measured at 45 minute, pH₂₄ = pH measured at 24 hour (ultimate pH), DFD = Dark, Firm and Dry.

N = Total number of animals per breed, pH₄₅ = pH measured at 45 minute, pH₂₄ = pH measured at 24 hour (ultimate pH), DFD = Dark, Firm and Dry.

^a,b Means in the same row with different letters are significant different (P < 0.05). DFD = Dark firm dry, n = Total number of observation, pH₄₅ min = pH measured at 45 minute (initial pH), pH24 hr = pH measured at 24 hour (ultimate pH), L* = Lightness, a* = Redness, b* = Yellownes.

mortem and meat become dark in colour [26]. Similarly, relatively lower L* value of DFD meat indicated that the meat was dark in colour which might be associated with stress condition of the cattle before slaughter. Similar to the present study [27] reported lower L* value for DFD meat compared to the normal one.

The level of bruising and non bruising carcass in slaughtered beef cattle is shown in Figure 2. From total of 39 cattle slaughtered, 26 (66.7%) carcasses were bruised and the rest 13 (33.3%) were not. Of bruised carcasses, 28.3% had one bruise, 12.8% had two bruise, 17.9% had three bruise, 5.1% had four bruise and 2.6% had greater than four bruise (Figure 3). The 26 bruised carcasses scored a total of 51 bruising cases. Among these, 35% were slight, 11 were medium and 5% were heavy. The mean number of bruise per carcass for bruised carcass was 1.96 ± 0.25 while bruise score per carcass was 3.58 ± 0.68 (Table 5). The current mean number of bruise per carcass was less compared to value reported [28] which was 3.75 point. The present finding of level of bruising was high as compared to cattle slaughtered at South African commercial abattoir which was 5.5% [16]. The level of in the present study was comparable to bruising reported in Uruguay which was 60.0% [29]. The higher level of bruising in the present study might due to poor road condition, lack of loading rump at the market, poor vehicle design, poorly designed unloading rump and stunning box used at slaughter house.

The level of bruise by anatomical site is presented in Table 6. The most frequent anatomical site bruise was observed at the backside middle part of carcass (49%), followed by 17.9% on hip, 14.3% on rump and loin, 5.4% on pin, 5.4% on rib. With respect to position of bruised part of carcass, from a total of 51 bruised

cases, the highest 25 (49%) was found along the middle line of back of carcass, followed by left side of carcass 18 (32.14%) and the right side of carcass 8 (14%). Considering the left side carcass, highest bruise was found around the hip (44.4%) and the lowest around the butt, rib and fore quarter (each 5.6%). Considering the right side of the carcass, the highest bruise (50%) was recorded for rump and loin while the lowest was for rib and hip (each 25%). The highest level of back bruise in current study suggested that the most of slaughtered animals were likely hit by stick during handling (at loading, during driving, weighing), injured from fall down in the stunning box during stunning, collide with facilities such as weighing box and crush. During transporting cattle, appropriate vehicle was not used, instead vehicle (FSR) which were initially meant for transport of goods were used. The drivers of the vehicles drove as if he was carrying goods. The drivers were suddenly holding the brake which had made cattle off balance and the bulls were stacked with the body of the truck or adjacent bulls. The presence of higher level of back bruising in the present study suggested the possibilities for the cause of the bruise at slaughter house. According to [30] most of bruising was occurred at the middle line of carcass which accounts 50.1% of carcass bruising.

The least bruise which was found at left forequarter and at butt indicated that there was less injury of cattle during closing the doors of weighing scale and stunning box at abattoirs. Rump and loin bruises might be associated with mounting on each other during their stay in the abattoir, injury during loading, collision of bulls with abattoirs facilities (scales, gates, crush) and body of the truck. According to [31] the main factors influencing bruising are stockman-ship, facility and vehicle design, driving style, road conditions, mixing of animals before transport or in lairage, presence of horned animals, and animal temperament. Bruising recorded for the different locations in this investigation was much lower than those reported by [32] who found 72.5% on Hips, 36% on rib area and chunk, 31% on rump, 28% on the backside, butt and pin area.

Out 51 bruised cases, 68.62% were slight, 21.57% were medium and 9.80% heavy bruise (Table 7). Likewise, with regarding to colours, 56.86% were bright red, 37.25% were dark red and 5.88% were watery consistency. In current study, most bruises were slight and had a bright red colour which is the indication of fresh bruise. This confirms that most of the bruise was recent and were happen during ante mortem period probably caused during transit, at unloading, or during lairage and at stunning box of the slaughterhouse.