Evaluation of Carcass Characteristics and Egg Quality Traits of Kuroiler and Sasso Chickens Reared Under On-Station and On-Farm Management Conditions in Tanzania

Two studies were conducted to evaluate the carcass characteristics and egg quality traits of Sasso and Kuroiler chickens under on-farm and on-station management conditions. Carcass characteristics were evaluated under on-station only while egg quality was evaluated under both management conditions. A total of 240 hens and 240 cocks were raised under on-station condition and evaluated for egg and carcass quality respectively. Meanwhile, 320 hens were raised under on-farm condition and evaluated for egg quality only. At the end of each of the 16 th and 20 th weeks of age, a sample of 10 cocks per breed was randomly selected and sacriced for carcass traits evaluation. To study egg quality, a total of 666 fresh eggs (246 eggs from on-farm and 420 eggs from on-station) were used to evaluate the external and internal egg quality traits. The recorded data were analyzed using the General Linear Models (GLM) procedure of SAS software ( SAS 2009). The results show that except for shell, yolk and albumen ratios, the mean values of other egg quality traits studied were higher for on-station than on-farm. Kuroiler chickens had higher values for egg weight, egg length, yolk weight, albumen height and Haugh unit than Sasso chickens. Live weight, carcass weight and carcass parts weight were found to be higher for Sasso than for Kuroiler at both ages of slaughter. It is concluded that there are variations between managements and breeds on egg quality traits. Carcass characteristics are affected by both breed and slaughter age.


Introduction
Poultry production in the world has undergone an enormous expansion and development during the last four decades. Advances in genetics, nutrition and husbandry have contributed to substantial improvement in poultry productivity which resulted in high consumption of poultry meat and eggs globally (Magdelaine et al. 2008;Kearney 2010). The poultry industry in Tanzania comprises both commercial and traditional sub-sectors. The traditional sub-sector is dominated by indigenous poultry in particular chickens. These chickens have low productivity characterized by three laying cycles per annum with 12 eggs per cycle. It is estimated that only 5% of these eggs are marketed and the rest are retained for hatching and household consumption (BFAP and SUA 2018).
Commercial poultry production is mostly practised in urban and peri-urban areas and it contributes a signi cant amount of poultry meat and eggs consumed in urban areas. However, the expansion of commercial chicken production in Tanzania is constrained by the inadequate supply of high performing chicken stocks. In general, the high-yielding chicken breeds had been bred solely for meat or table eggs, thus they require a high level of inputs in terms of nutritional and health management, to fully express their genetic potential (FAO 2014). The introduction of improved breeds such as Kuroiler and Sasso chickens, which are known to produce more meat and eggs than their counterpart local chickens, is an attempt to improve traditional poultry production in Tanzania. These dual-purpose chickens can thrive well in a typical scavenging free-range system and are less costly compared to specialized layers and broilers and hence, can be raised as alternative breeds in place of indigenous chickens (Murawska 2017; BFAP and SUA 2018). The productive performance in terms of growth, egg production and survival rate of these breeds has been evaluated under different management conditions in Tanzania (Sanka et al. 2021a; Guni et al. 2021b). Sanka et al. (2021a) reported variations in carcass yield when Sasso and Kuroiler birds were subjected to varying levels of supplementations under simulated on-farm conditions. While Guni et al. (2021b) reported breed x location interaction for the body weight of the two breeds.
However the information available on the carcass yield and egg quality traits of these breeds under varying management conditions is scant. This study intended rst to compare carcass yield parameters for fully-fed Sasso and Kuroiler raised on station and secondly, establish if there are signi cant breed and management system effects on egg quality characteristics.

Materials And Methods
Location of the study area Two studies were conducted for a period of 52 weeks from December 2018 to December 2019 using Kuroiler and Sasso chickens under on-station and on-farm conditions. The on-station study was conducted at Sokoine University of Agriculture (SUA). The University is located at the foothills of the Uluguru Mountains in Morogoro, Eastern Tanzania, about 550 m above sea level. The on-farm study was conducted in two villages i.e., Wami-Sokoine and Wami-Luhindo about 45 Km from the University.

Management of chicks during brooding
A total of 1200 (600 Kuroiler and 600 Sasso) day-old chicks were purchased from AKM Glitters in Dar es Salaam and Silverlands in Iringa regions respectively to be used in this study. Brooding was done for six weeks at the Poultry farm of the Sokoine University of Agriculture. On arrival these chicks were weighed, wing tagged and thereafter placed into the brooding pens. During the brooding period chicks were fed a commercial starter diet in form of crumbles containing 2941 Kcal ME/kg and 21.2% CP from day old up to the end of 2nd week and chick mash containing 3049 Kcal ME/kg and 20.3% CP from the 3rd up to end of the 6th week. Clean water was provided in ad-libitum. Chick sexing was done at the end of the brooding period.

Management of birds for egg quality evaluation under the on-farm condition
At the end of brooding, three hundred and twenty (320) growing pullets were distributed to selected farmers in the two villages. The selection of villages and households participating in the study was done in collaboration with District and Ward livestock o cers. In each village, 16 farmers/households were recruited for the study. One half of the household in each village received 10 Sasso pullets each and the remaining eight households received 10 Kuroiler pullets. Allocation of the strains was done randomly. The pullets were reared under a semi-scavenging system of management. Each household was required to provide a house/shelter with a simple enclosure around the house which allowed restriction of birds especially during the provision of supplementary feeds. All along farmers were responsible for providing housing, supplementary feeding and basic health care. They were encouraged to make simple formulations to include energy, some protein sources and mineral in addition to kitchen leftover and what they could get from scavenging.

Management of birds for egg quality and carcass characteristics evaluation under the on-station condition
Under the on-station experiment, a total of two hundred and forty (240) pullets were randomly allocated to 6 deep litter pens (3 for Kuroiler and 3 for Sasso) of 40 birds each and reared under total con nement.
They were provided with a commercial grower ration containing 15.5% CP and 2762 Kcal ME/kg, from the 7th to the end of the 19th week of the age. Thereafter, layer rations containing 18.5% CP and 2965 Kcal ME/kg were provided from the 20th week of age up to the rest of the study period. Alongside, the cockerels were distributed using a 2 x 2 factorial design i.e. 2 breeds (Kuroiler and Sasso) and 2 slaughter ages (16 and 20 weeks), with six replications of 40 birds each (3 replications per each breed) making a total of 240 birds. The feeding system was similar to that of pullets up to the end of the 19th week of age.

Measurement of the external egg quality traits
A total of 666 fresh eggs (246 eggs from on-farm and 420 eggs from on-station) were used to evaluate the external egg quality traits. External egg quality traits such as egg weight, length, width, shape index, shell weight, shell thickness and shell ratio were determined. Egg weights were obtained by weighing individual eggs using a digital weigh balance whereas the length and width of the eggs were measured using a digital vernier calliper. Egg shape index (%) was calculated as the ratio of egg width to egg length times 100 (Anderson et al. 2004). The eggshells with their membranes were dried on open-air and weighed using a digital weighing balance. The shell weight was divided by egg weight to get the shell ratio. The thickness of shells was measured using a digital vernier calliper.

Measurement of the internal egg quality traits
The eggs used for external egg quality measurements were also used to measure the internal egg quality traits. The internal egg quality traits that were evaluated include yolk weight, albumen weight, yolk ratio, albumen ratio, albumen height and Haugh unit. The internal egg quality measurements were obtained by carefully breaking the egg followed by separation of the albumen and the yolk contents. The weight of albumen was obtained by taking total internal egg weight (i.e. yolk weight + albumen weight) minus yolk weight. The albumen weight and yolk weight were determined using a digital weighing balance, whereas albumen height was measured using a digital vernier calliper. Albumen and yolk ratios were calculated by taking their weights as the percentage of total egg weight. Haugh Unit (HU) was calculated according to Haugh (1937)

Measurement of carcass and carcass parts
At the end of the 16th and 20th weeks of age, a sample of 20 male birds in each age category, i.e.10 birds/breed were randomly selected and slaughtered to determine carcass weight as well as carcass parts weights. Sampled birds were fasted for 12 hours before slaughtered. The carcass weight was taken after de-feathering and removal of feet, head and the viscera (gizzard, heart, spleen, liver and intestine). The eviscerated carcass, breast, thighs, drumsticks, wings, back and neck were weighed using a digital balance. These data were used to calculate the dressing percentage and carcass part yields (%) by taking the weight of the individual parts as the percentage of the live weight of the chicken.

Statistical data analysis
The General Linear Models (GLM) procedure of SAS software (SAS 2009) was used to analyze all traits measured by considering management system and breed as xed effects for egg quality traits, as well as the interaction between them. Breed and slaughter age was considered as the xed effects for carcass traits under the on-station management. Individual farmer or pen effect within a management condition was taken as a random effect for egg quality traits while individual bird was taken as a random effect for carcass traits.
The following statistical model was used to analyze the external and internal egg quality traits observed on a pen or household basis (i.e. the pen or household was the observation unit): Where: Y ijk = observation (Egg quality traits) from the k th farmer/pen within the j th breed and i th management system; µ = General mean common to all observations in the study; M i = Effect of the i th management system (i = on-station, on-farm); B j = Effect of the j th breed (j = Kuroiler, Sasso); (MB) ijk = Effect associated with the interaction between management system and breed; FP(MB) ijkl = Random effect of the k th farmer/pen within the j th breed and i th management system; E ijklm = Random effects peculiar to each bird;

Note
Effects of the management system and breed for egg quality variables were tested using the farmer/pen variation within the management system and breed (i.e. FP(MB) ijk ) as the error term.
For Live weight, carcass and parts yield the following model was used.
Where: Y ijk = observation (Live weight, carcass and parts yield) from the i th breed within the j th age; µ = General mean common to all observations in the study; B i = Effect of the i th breed (i = Kuroiler, Sasso); A j = Effect of the j th age (week), (j = 16, 20) (BA) ij = Effect associated with the interaction between breed and age; E ijk = Random effect peculiar to each bird.

Results And Discussion
Effects of management system and breed on external and internal egg quality traits Table 1 presents the least-square mean values for the effect of management system and breed on external and internal egg quality traits of chickens. Management system signi cantly (P < 0.05) affected almost all egg quality traits except shell ratio, yolk ratio and albumen ratio. On the other hand, egg weight, egg length, yolk weight, albumen height and Haugh unit were in uenced (P < 0.05) by the breed of chickens. Table 1 Least square mean values for the effect of management system and breed on external and internal egg quality traits of chickens. The observed difference between the two management systems on egg weight might be partly due to the rearing system but mostly due to insu cient feeding prevailing under on-farm that does not support the birds with adequate levels of nutrition needed to exploit their production potential. This observation concurs with the previous observation of Guni  Eggshell quality is also associated with levels of resistance to breakages during transportation. In this study, the management system signi cantly (P < 0.05) affected shell weight and shell thickness in favour of on-station. The lower values for on-farm eggs for shell quality is most likely to be associated with poor feeding and inadequate Calcium and other trace minerals intake. Several authors have reported varying results on the effect of the management system on shell weight and shell thickness. Aygun and Yetisir (2010) that egg weight in uences the weight of components of eggs especially albumen and yolk. Thus the heavier yolk weight observed for eggs from Kuroiler than Sasso might have been due to such a bigger size of Kuroiler eggs.
Yolk ratio and albumen ratio were neither affected by the management system nor by the breed. This may imply that the share of these traits to the total egg weight of the two breeds is similar regardless of breed Effect of interaction between management system and breed on external and internal egg quality traits Table 2 shows the interaction effect between management system and breed on external and internal egg quality traits. The results show that there was no signi cant (P > 0.05) interaction effects between the management system and breed for all egg quality traits except for egg weight and eggshell ratio. This implies that with exception of egg weight and shell ratio, the response of the two breeds on egg quality traits is similar regardless of    Ojedapo et al. 2015). Similarly, slaughter age had also signi cant effects on dressing percentage as well as drumstick, back and wing percentages. It was observed that while the dressing percentage and the proportions of drumstick, back and wing were increasing with the age of slaughter, the proportion of wing weight decreased. The increase in proportions of other parts such as drumstick likely led to a decrease in wing proportion. The present study also shows that there were signi cant (P < 0.05) differences between the two breeds on live weight, slaughter weight and all carcass traits studied except for thigh, drumstick and wing percentages. The slaughter weight, carcass weight and carcass parts weight were found to be higher for Sasso chickens than for Kuroiler chickens. This observation indicates variation in the genetic potential of the two breeds in growth rate and muscle deposition. The higher carcass weight of Sasso than Kuroiler was expected due to a heavier bodyweight of the former at slaughter. This observation concurs with the report of Rezaei et al. (2018) and several authors who indicated higher carcass weight for heavier birds. parts between this study and of the other authors might be due to differences in the breed and the rearing system. According to Marapana (2016), the dressing percentage and relative meat yield in the different parts could be affected by several factors such as strain, sex, length of feed withdrawal before processing, length of starvation before slaughtering, the birds' transport distance from farm to slaughter plant, the life span of birds and the birds rearing system.

Effect of interaction between breed and slaughter age on carcass traits
The least-square means for the interaction between breed and slaughter age on carcass traits are presented in Table 4. Only the percentage of thigh and neck showed signi cant (P < 0.05) interaction between breed and age of slaughter. It was observed that, while Kuroiler had a higher thigh percentage than Sasso at the 16th week of slaughter age, the reverse was the case at 20 weeks of slaughter age.

Conclusion
Based on the results of the present study, it is concluded that both the external and internal quality of eggs were in uenced by the management condition. Eggs from on-station appeared to be better in quality than those of on-farm. Breed in uenced some egg quality traits and most of the carcass traits. Sasso outperformed Kuroilers in carcass weight and the weight of its parts, whereas Kuroiler had heavier eggs with a higher Haugh unit score than Sasso.