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 significantly (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 influenced (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.
Variable | Management system | | Breed | SEM | P-value |
On-farm | On-station | Kuroiler | Sasso | Management | Breed |
External egg quality traits |
Egg weight (g) | 53.20b | 59.73a | | 57.13a | 55.80b | 0.32 | < .0001 | 0.0365 |
Egg length (mm) | 55.94b | 57.05a | | 56.89a | 56.10b | 0.16 | < .0001 | 0.0060 |
Egg-width (mm) | 41.28b | 43.00a | | 42.28a | 41.99a | 0.09 | < .0001 | 0.1069 |
Egg Shape index (%) | 73.92b | 75.48a | | 74.73a | 74.97a | 0.25 | < .0001 | 0.1062 |
Shell weight (g) | 6.08b | 6.94a | | 6.58a | 6.44a | 0.06 | < .0001 | 0.1131 |
Shell ratio (%) | 11.47a | 11.67a | | 11.56a | 11.59a | 0.09 | 0.1499 | 0.9683 |
Shell thickness (mm) | 0.53b | 0.56a | | 0.55a | 0.54a | 0.00 | 0.0008 | 0.9921 |
Internal egg quality traits |
Yolk weight (g) | 17.12b | 19.47a | | 18.61a | 17.98b | 0.13 | < .0001 | 0.0029 |
Yolk ratio (%) | 32.30a | 32.66a | | 32.62a | 32.35a | 0.22 | 0.3047 | 0.3481 |
Albumin weight(g) | 29.89b | 33.12a | | 31.87a | 31.14a | 0.26 | < .0001 | 0.1456 |
Albumin ratio (%) | 56.11a | 55.39a | | 55.76a | 55.74a | 0.26 | 0.0892 | 0.9565 |
Albumin height (mm) | 6.80b | 7.58a | | 7.29a | 7.09b | 0.04 | < .0001 | 0.0080 |
Haugh unit | 84.12b | 86.98a | | 85.98a | 85.12b | 0.24 | < .0001 | 0.0243 |
a−b Means with different superscripts within a row and effect differed significantly (P < 0.05), SEM = Standard error of the mean |
The observed difference between the two management systems on egg weight might be partly due to the rearing system but mostly due to insufficient 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 et al. (2021a) which also showed lower performance of on-farm than on-station management in most egg production traits. Similarly, Champati et al. (2020) reported heavier eggs for intensively reared chickens than for semi-intensive while Dong et al. (2017) and Kucukyılmaz et al. (2012) also observed variation in egg weight for different rearing systems. In contrast to the present findings, Patel et al. (2018) and Sokołowicz et al. (2018) did not find significant differences in egg weight between deep litter and other rearing systems. Conflicting reports from these authors are likely due to the effect of a variety of factors, such as genotype, nutrition, and environment (Rakonjac et al. 2014).
Kuroiler chickens had heavier eggs than Sasso chickens which may have been attributed to the hen genotype. However, using similar breeds, Sanka et al. (2021b) did not find significant differences in egg weight. Such dissimilar observations between the present study and that of Sanka et al. (2021b) might be due to differences in the management of the birds, specifically on feeding practices. The overall egg weight (55.80g) for Sasso chickens in the present study is within the range 45.7–59.9g and 48.0–56g reported by Sanka et al. (2021b) and Kidie (2019) respectively for a similar breed. Likewise, the egg weight for Kuroiler in this study (57.13g) is within the range 46.25–57.65g and 47.0–59.0g reported by the same authors in the same order. In contrast, Bamidele et al. (2019) reported that the overall egg weight for Kuroiler and Sasso was 54.0 and 54.9g respectively, which was lower than the egg weight observed in the present study. This difference might be attributed to variation in feeding and other environmental factors affecting egg weight in chickens.
The shape of an egg is important during both, packaging and transportation by reducing possible breakage of eggs and it also plays part in determining market preference (Guni et al. 2013). The observed higher shape index for on-station eggs than those from on-farm could be explained by the size and weight of an egg. Normally egg length and width are the determinants of the shape of an egg, which were also higher for on-station eggs than on-farm. Sokołowicz et al. (2018) had a similar observation where the egg shape index was found to be higher for birds under deep litter than those from free-range and organic systems. Similarly, using Red Island Red (RIR) and Fayoumi Bekele et al. (2009), found a higher egg shape index for eggs from the on-station than from on-farm. On the other hand, insignificant effects of the rearing system on egg shape indices were reported by Sekeroglu et al. (2010), Oke et al. (2014), and Champati et al. (2020). The shape index in the present varied from 73.92–75.48%. This value falls within a value of 72–76% reported by Altuntas and Sekeroglu (2008) as the standard/normal shape. The obtained shape indices were similar to the result by Sanka et al. (2021b), but lower than values of 76.08 to 77.52% reported by Mengsite et al. (2019) for the Sasso strain. The eggs with a shape index below 72% are sharp and those above 76% are roundish (Altuntas and Sekeroglu 2008) which increase the possibility for breakages during transportation.
Eggshell quality is also associated with levels of resistance to breakages during transportation. In this study, the management system significantly (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. For example, Ogunshola et al. (2018) reported heavier eggshell in the deep litter system than in the cage system but observed no significant difference in shell thickness between these systems. On the other hand, Dahloum et al. (2018) did find differences in shell weight of eggs from different rearing systems. Kuhn et al. (2014) also did not find differences in shell weight and thickness of eggs from the litter-floor and free-range systems. Likewise, Patel et al. (2018) observed no differences in shell thickness of eggs from deep litter, semi-scavenging and backyard management. Inconsistent results might be associated with the interaction of the management system with several factors affecting these traits including genotype used, age, oviposition time, and mineral nutrition (Ketta and Tumova 2016).
Yolk weight and albumen weight differed (P < 0.05) between the two management systems with on-station eggs showing higher values than on-farm. In agreement with the results of the present study Sokolowicz et al. (2018) and Dong et al. (2017) also observed variation in rearing systems on yolk weight. The higher mean values for yolk weight and albumen weight from on-station eggs in this study might be related to the size of an egg as these traits have a significant association with egg weight (Suk and Park 2001). This observation conforms to the arguments put forward by Zhang et al. (2005) and Aygun and Yetisir (2010) that egg weight influences 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 or management system. In agreement, Sanka et al. (2021b) also observed a similarity in yolk and albumen ratio for Kuroiler and Sasso eggs under semi-scavenging management. Moreover, Patel et al. (2018) reported similar observation on the yolk ratio but they reported contrasting result on the albumen ratio. Dong et al. (2018) also found the insignificant effect of rearing systems on egg yolk ratio.
Albumen height and Haugh unit were affected by both, the management system and the breed. The superiority of albumen height and Haugh unit observed in eggs from on-station could be associated with appropriate storage and the fact that the eggs were analyzed on the day of collection. Bekele et al. (2009) observed a similar situation for on-farm and on-station trial in Ethiopia. In addition, Sokolowicz et al. (2018) also found a significant rearing system effect where eggs from the deep litter system outperformed free-range in Haugh unit. However, Dong et al. (2017) did not find any differences between rearing systems on these traits.
Differences in albumen height and Haugh unit were also observed between breeds whereby Kuroiler tended to have a higher score than Sasso birds. This observation is in agreement with that of Kucukyılmaz et al. (2012) where White (Lohmann LSL) outperformed Brown (ATAK-S) hens in these traits. However, the report of Sanka et al. (2021b) that eggs from Kuroiler and Sasso had similar values for the albumen and Haugh unit disagree with the result of the present study. This disagreement in results between this study and that of Sanka et al. (2021b) is likely due to the variation in feeding management prevailing in particular studies.
Effect of slaughter age and breed on carcass characteristics of chickens
Table 3 shows the least-square mean values for the effects of slaughter age and breed on carcass characteristics of chickens. The slaughter weight, carcass weight and all carcass parts weight differed significantly (P < 0.05) between ages of slaughter. Birds slaughtered at 20 weeks of age presented heavier carcass weight and higher carcass parts than those slaughtered at 16 weeks of age. This observation may imply that the carcass parts of the two breeds increased in weight concurrently as the slaughter age increases. This observation is in line with the report of several authors (Albuquerque et al. 2003; Horsted et al. 2005; Nikolova and Pavlovski 2009; Ojedapo et al. 2015). Similarly, slaughter age had also significant 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.
Table 3
Least square mean values for the effects of slaughter age and breed on live weight (g), slaughter weight (g), carcass weight and carcass parts in gram and percentages.
Variable | Slaughter age (week) | | Breed | SEM | P-value |
16 | 20 | Kuroiler | Sasso | Slaughter age | Breed |
Live weight (g) | 2169.30b | 2656.80a | | 2261.90b | 2564.20a | 51.16 | < .0001 | 0.0002 |
Slaughter weight (g) | 2106.25b | 2559.30a | | 2186.70b | 2478.80a | 50.55 | < .0001 | 0.0002 |
Carcass weight (g) | 1484.55b | 1883.65a | | 1552.05b | 1816.15a | 38.18 | < .0001 | < .0001 |
Breast weight (g) | 377.05b | 483.70a | | 380.35b | 480.40a | 13.13 | < .0001 | < .0001 |
Thigh weight (g) | 259.80b | 322.70a | | 271.45b | 311.05a | 7.52 | < .0001 | 0.0007 |
Drumstick weight (g) | 236.95b | 303.75a | | 255.95b | 284.75a | 6.34 | < .0001 | 0.0028 |
Back weight (g) | 296.30b | 392.20a | | 312.80b | 375.70a | 9.03 | < .0001 | < .0001 |
Wing weight (g) | 200.15b | 234.20a | | 205.70b | 228.65a | 4.49 | < .0001 | 0.0009 |
Neck weight (g) | 101.65b | 130.20a | | 105.65b | 126.20a | 3.31 | < .0001 | < .0001 |
Dressing % | 68.38b | 70.79a | | 68.54b | 70.63a | 0.49 | 0.0015 | 0.0052 |
Breast (%) | 17.31a | 18.34a | | 16.83b | 18.63a | 0.35 | 0.1040 | 0.0009 |
Thigh (%) | 12.00 | 12.12 | | 12.03 | 12.09 | 0.18 | 0.6538 | 0.8163 |
Drumstick (%) | 10.94b | 11.44a | | 11.32 | 11.06 | 0.13 | 0.0119 | 0.1756 |
Back (%) | 13.60b | 14.74a | | 13.74b | 14.60a | 0.21 | 0.0005 | 0.0064 |
Wing (%) | 9.27a | 8.82b | | 9.17a | 8.93a | 0.13 | 0.0220 | 0.2152 |
Neck (%) | 4.66a | 4.90a | | 4.64b | 4.91a | 0.08 | 0.0634 | 0.0355 |
a−b Means with different superscripts within a row and effect differed significantly (P < 0.05), SEM = Standard error of the mean |
The present study also shows that there were significant (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. Unlike the present observation, Sanka et al. (2021a) reported the absence of significant differences between Kuroiler and Sasso chickens on carcass traits when birds were reared under a simulated scavenging system with varying levels of supplementations. Contrasting results between the present study and that of Sanka et al. (2021a) might be due to differences in the rearing system, and in particular feeding management and the ability of the breed to respond to that particular management. For example, in a previous study on the effect of management systems by Guni et al. (2021a), results showed a better performance for Sasso than Kuroiler under the on-station while under the on-farm the performance was similar. The overall mean of the carcass weight for Kuroiler chickens observed in the present study is higher than 1400.6g for Koekoek chickens reported by Ibrahim et al. (2019) but comparable to (1585g) and (1552g) for Hubbard S757 and Lohman dual genotypes respectively, reported by Muller et al. (2018).
Breast meat yield is the carcass component with the highest economic value followed by legs (thigh + drumstick). These parts are considered the most valuable parts in broiler and dual-purpose male chickens kept for meat production, while the back, wing and neck are less valuable parts (Biazen et al. 2021). The higher breast weight relative to other carcass parts might be related effect of selection for meat production where more attention is placed on the breast proportion (Marapana 2016). Though the breeds used are not pure meat birds, by being dual-purpose birds, they thus carry genes from meat breeds.
The difference between breeds in terms of carcass parts is directly related to the slaughter weight, whereby Sasso gave higher proportions than Kuroiler. It has been reported by Olawumi (2013) that the slaughter weight has significant positive correlation with breast weight (r = 0.89), thigh weight (r = 0.95), back weight (r = 0.96) and drumstick weight (r = 0.92) in broiler chickens. Additionally, Katekhaye (2017) and Biazen et al. (2021) reported higher breast, wing, neck and back weight in chickens with heavier slaughter weight. The two breeds also differed (P < 0.05) in dressing percentage as well as the proportions of breast, back and neck in favour of Sasso, while the proportions of the thigh, drumstick and wing were similar between the two breeds.. This observation is in agreement with that Lichovníkova et al. (2009) who also reported similar proportions of leg muscle (thigh and drumstick) when fast-growing chickens were compared to layer male chickens. However, the dressing percentages observed in this study for both Kuroiler (68.54%) and Sasso (70.63%) are higher than (66.75%) for Kuroiler chickens reported by Aline (2015) in Uganda. The difference in dressing percentage and the proportions of various 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.