Prediction of Sheep Carcass Yield using Combinations of Ante-mortem and Post-mortem Measurements

The Algerian sheep herd, increased from 5 million heads at the dawn of Independence (in 1962) to more than 31 million in 2021 (MADR, 2022), of which 61% (19 million heads) are breeding ewes. Indeed, the sheep is one of the few animal species able to survive and produce in the environments of our country such as the steppe, the highlands and the desert (Hadbaoui et al., 2020). The Algerian sheep population is characterized by the presence of several breeds including, the Ouled Djellal (OD) breed (also called “White”) remains the dominant sheep breed in Algeria (60% of total sheep) with its particular specificities; it is an autochthonous breed (Dehimi et al., 2014). The consumption of sheep meat which greatly exceeds beef and knowing that quality is the main objective of fattening livestock. Therefore, the value of a carcass is determined from its conformation which constitutes, with other factors such as live weight and fattening, one of the main elements of the commercial value of sheep, considered as a very important criterion.
       
The assessment of carcass quality by utilizing carcass classification systems might have an important contribution to ensure consumers that the meat is in accordance with the official standards (Dlamini et al., 2020). The EUROP classification system is based on visual assessment of carcass conformation and fatness (Johansen et al., 2006).  Ovine carcasses are classified by using EUROP carcass classification system according to the Commission regulation No 461/93 (Commission Regulation, 1993). Two different schemes are used for lamb classification in the EUROP system, one for carcasses above 13 kg and the other for carcasses under this weight (Sañudo et al., 2000; Ekiz et al., 2021).
       
The ability to estimate the live weight and carcass weight of an animal during its growth, its productive life and then its fattening is of great help to the breeder and the zootechnician. It makes it possible, to measure the effectiveness of breeding but can also guide the farmer in his choice of breeding stock according to his production objectives. Improving the productivity of sheep breeds or maintaining genetic diversity can allow farmers to select animals or create new breeds to cope with environmental changes. Traditionally, it is believed that the meat of Hamra lambs is better tasting than the meat of the other breeds. The present study aims to describe the potential of use of body measurements to predict carcass weight and provided a new insight into the effect of breed meat traits of Ouled Djellal and Hamra sheep breeds.

Description of the study area
 
The test was conducted in the wilaya Tebessa located in the northeast of Algeria (35°20' N, 8°6'E, Altitude: 960 m). Its area is about 13878 km², near the Tunisian border. The wilaya of Tebessa is distinguished by four bioclimatic stages: The sub-humid, the semi-arid, the sub-arid and the arid or mild Saharan (Houssou et al., 2023). The dominant plant species in this wilaya are Artemisia cereals and derivatives, Herba alba, Stipa tenacissima, Rosmarinus tournefortii and Retama sphaerocarpa.
 
Ethical statement
 
The animals used in this study had their origin on semi-arid farms with a traditional management system. They were intended for the production of milk and meat for human consumption. These animals were submitted to practices standardized and regulated by international guidelines for animal welfare (Terrestrial Animal Health Code 2018, section 7. Art 7.1) and national executive decree No. 95-363 of November 11, 1995 (Algeria).
 
Data collection
 
The study was carried out between March and June 2023 at the municipal slaughterhouse in the wilaya of Tebessa on a total of 151 sheep¢s belonged to Ouled Djellal breed (n=118) and Hamra breed (n=33). Age was determined according to the number of permanent incisors counted prior to dressing the carcass. The animals were adult ³12 months. Linear body measurements were taken on each animal before slaughter and Fig 1 schematically shows the locations of measuring. Dactylo-Thoracic Index (DTI) was calculated according to Sotillo and Serrano (1985) and Houssou and Brik (2021). This remaining index is functional, providing information about the type, aptitude and production performance of the animal as described by (Sotillo and Serrano, 1985; Houssou and Brik, 2021).
 

       
Immediately after slaughter and after dressing, two photographs of all carcasses, one of the left lateral side and one of the dorsal view, were taken with a digital camera from a distance of 2 meter. These photographs were then used to classify the carcasses. The offal weight was weighted. Mutton carcasses were visually classified for conformation and fatness by the methodology specified according to E.U.R.O.P. classification: five classes, from E=“excellent”, to P=“poor conformation”) and fatness score (five classes from 1=lean to 5=fat) (Commission Regulation, 1993). After the carcass classification processes, we measured carcass weight after bleeding and skinning and removing the head, hooves, tail and viscera. The following measurements were taken on the entire carcasses: carcass length, carcass width, leg length and backfat thickness (measured between 13^th thoracic and first lumbar vertebrae using caliper); (carcass yield) were calculated as described by Belhaj et al., (2021); Ekiz et al., (2021) and Kumar et al., (2022).
 
Statistical analyzes
 
All data were coded and recorded in to excel sheet. The descriptive analysis of the data was established using the SPSS version 20 tool focused on the determination of the mean values, standard deviations, minima and maxima of the studied parameters. In order to study the effect of breed on body measurements and carcass characteristics, difference with value of (P<0.05) was considered to be statistically significant. The Pearson’s correlation coefficients were performed to assess the association between the parameters studied.

Body and carcass measurements
 
Table 1 and 2 shows the effects of animal¢s breed at slaughter on carcass traits using different criteria like body measurements, weight, carcass conformation, fatness (thickness of back fat), thoracic typing index and the carcass yield of the both breeds. In general, there were significant differences (P<0.05) for the body measurements before slaughter: HG; CP; SIL and DTI. The Ouled Djellal breed was significantly longer SIL; developed chest perimeter; more developed canon perimeter CP, the DTI was higher compared to the Hamra breed (P<0.05). There is heterogeneity between the two breeds for these traits: The Ouled Djellal breed was significantly longer; chest perimeter was developed; more developed canon perimeter and the dactyl thoracic index was higher. Consequently, Ouled Djellal have fairly developed bone structure. Our findings are close to those reported by Afri-Bouzebda et al., (2018) and Houssou and Brik (2021) for the same breed in the east of Algeria. The dactylo-thoracic index (DTI) indicates the degree of skeletal thinness; it allows us to establish a correlation between the individual mass of the animal and its limbs, so as to determine whether the body volume corresponds to the bone development (Cerqueira et al., 2011). These parameters show that the Ouled Djellal breed (IDT: 0.103±0.012) has a developed bone structure than the Hamra breed (IDT: 0.099±0.011) (P<0.05).
 

 

       
After slaughter, in one hand, we observed significant differences between the two sheep breeds studied at (P<0.05) on the carcass characteristics: K, CW, BW and carcass yield. On the other hand, we recorded no significant differences (P>0.05) on the carcass characteristics: F, G, SW and the offal weight. Regarding yield carcass, we recorded percentage of 51.51% for Ouled Djellal breed and 49.15% for Hamra breed (P<0.05). The findings in the present study were close to results found by other authors Benyounes et al., (2015) in Ouled Djellal (OD) breed in Algeria and Belhaj et al., (2021) in the both breeds Ouled Djellal and Hamra in Morocco.  Moreover, the breed had a significant effect on these parameters, where the higher values were recorded for OD breed. However, Teixeira et al., (2005) and Yousefi et al., (2012) have noted no significant effect of breed on carcass yield respectively of Portuguese breeds and Iranian lambs. The last author determined greater significantly of breed on back fat thickness. The recorded carcass weight values varying between 34.96±7.82 kg and 30.53±4.33 kg respectively for Ouled Djellal and Hamra breeds studied, which appears that these last to be lower than 37.6±1.73 kg of the Ouled Djellal breed in intensive mode in the region of Guelma (East of Algeria).
 
The results in the study showed that overall the Ouled Djellal carcasses were leaner than the Hamra carcasses (Table 2). This found translate into significant differences in yield carcass. Kempster (2003) reported that the proportion of lean meat in the carcass is of major importance since this is the principal determinant of meat yield and commercial value. The results showed that the Ouled Djellal in this research had higher carcass percentage (51.51%) that their Hamra counterpart (49.15%). These results however were closer that the report from Benyounes et al., (2015) which mentioned that the carcass percentage of Ouled Djellal was 51.7% and in agreement with the findings from Belhaj et al., (2021) and Djenontin et al., (2017) which mentioned that the carcass yield of Djallonke and Sahel sheeps breeds were 50.87% and 52.59 % in Benin. 
       
The results showed that the conformity of Ouled Djellal and Hamra sheep carcass were affected positively (P<0.05). Nevertheless, fatness score was unaffected in both breeds (Table 1 and 2). This result showed that the breed had an impact on the subjective classification of carcasses. The higher values of conformity were recorded for Hamra sheep carcasses. Consequently, Hamra sheep carcasses showed better subjective characteristics in terms of conformity; therefore, carcasses required by consumers. Moreover, Exploring the variation in meat quality between muscles is a pivotal step to design strategies for better utilization (Gangadhar et al., 2021).
       
The weight of offal was 12.28±2.51 kg in the Ouled Djellal against 12.02±1.28 kg among the Hamra (P>0.05) which appears higher than 10.33 kg in the Sahelian against 6.20 kg among the Djallonké reported by Djenontin et al., (2017), these variations  can be explained by the effect of the genetic potential.
       
Mutton in the present study were not fully grain-fed inside. This may have meant that some sheep did not reach their full genetic potential for fat deposition it is an important parameter; it provides valuable information on the relevance of feeding, particularly with lactogenic plants present on the pastures, according El-Amaiem and Abd El Kareem (2022), the sheep are able to produce meat without consuming large quantities of feed concentrates. Several factors influenced Lamb meat quality, such as breed (Fogarty et al., 2000; Safari et al., 2001; Aksoy et al., 2019; Pelmuº et al., 2020), age (Belhaj et al., 2021), slaughter weight (Arsenos et al., 2002) and sex (Hoffman et al., 2020). Moreover, other factors could influence meat quality such as pre-slaughter stress, system of production and feed ration (De Araújo et al., 2017; Hoffman et al., 2020; Shibeshi et al., 2022).
 
Correlation coefficients of carcass and measurements traits
 
A summary of the correlations among traits is shown in Table 3. Results showed a positive correlation between carcass yield and pelvis width, chest width, carcass weight and body weight (r=0.346, r=0.247, r=0.435 and r=0.476; p<0.01) respectively and there was also a positive correlation between dactyl-thoracic index and heart girth (r=717; p<0.01) in the both lambs. There were negative correlations between dactyl-thoracic index Scapular-ischial length, leg length, carcass weight and carcass yield for both breeds (r=-0.248, r=-0.303, r=-0.346; r=-0.46 and r=-0.458) (P<0.01).
 

       
The correlation between carcass weight and heart girth, appear to be the most important traits of sheep live affecting yields (Table 3). The importance of carcass length, chest width and pelvis width and their greater participation in the variance than the other conformational criteria corroborate the work of Flamant and Boccard (1966). These authors sorted the measures in the same order according to the degree of correlation, which can explain with accuracy the choice of these three factors, additionally to the length of the legs, in most works dealing with the characteristics of the carcass. However, professionals were not content to define carcasses of good conformation by a short leg. They want a wide and short carcass. In addition, other ²conformation² measures were used quite frequently and relate to the length and width of the carcasses.

The results showed that carcass yield was variable, probably reflecting the wide range of sheep destined for slaughter. In general, these results showed the interaction effects of breed on objective and subjective carcass characteristics. Furthermore, we have demonstrated the multiple zootechnical tools by which the ovine product can be qualified and classified, in a general context of characterization of the sheep implying the choice of the breed and the type of food in response to the specific requirements of the Algerian consumer. Likewise, these results could contribute to the development of automated carcass grading systems.

All authors declare that they have no conflict of interest.