Evaluation of Growth, Carcass and Meat Quality of a Two-way Cross Developed for Rural Poultry Farming

Rural poultry farming with improved chicken varieties is fast growing with its proven potential to improve the livelihood and nutritional security in the country. Backyard chickens are excellent transformers of low value natural food base in to highly nutritious human food i.e. egg and meat (Rajkumar et al., 2010). Pure line chickens including native and exotic strains were being utilized to develop crossbreds for free range poultry farming (Ayyagari 2008; Padhi et al., 2016; Rajkumar et al., 2019).  Higher shank length with moderate body weight and multi coloured plumage are desirable traits for a rural variety which help the birds to run faster and escape from predators thus protecting themselves under free range conditions. Many dual purpose varieties have been developed and popularized across the country for rural poultry in a big way (Rajkumar and Rao 2018; Sarma et al., 2018). The rural chicken varieties i.e., Vanaraja, Gramapriya, Srinidhi,Giriraja, Rajasri etc. were developed using exotic strains, while the two-way cross was developed using PD-1, derived from Red Cornish and PD-4, which is an improved Aseel breed (Rajkumar et al., 2019). Both Cornish and Aseel are known for their meat quality over the years (Rajkumar et al., 2016; 2017). Chicken meat is the cheapest source of animal protein and mostly preferred meat across the world (Rajkumar et al., 2016; Le Behan-Duval 2004). Meat quality and its taste determine the consumer acceptability which in turn plays a major role in success of the variety and its suitability for rural poultry farming. The presence of Aseel and Cornish inheritance makes the birds more suitable for meat purpose as both the breeds are known for meat quality. The newly developed variety is being propagated as a dual purpose variety at ICAR-Directorate of Poultry Research, Hyderabad, Telangana. Since the birds are propagated for meat and egg purpose, there is need to understand and document the meat quality traits of the variety. Therefore, the present study was carried out to study the growth, carcass and meat quality traits in a two- way cross developed for rural poultry farming.

The data collected from 232 birds of  a two-way (PD-1 x PD-4) cross survived up to 12 weeks of age produced using PD-1 males and PD-4 females during the year 2018-19 at ICAR-Directorate of Poultry Research, Hyderabad, Telangana were utilized in the present study. PD-1 line was evolved from a mediocre red Cornish population, being selected for higher  6 week shank length (Ayyagari 2008) and PD- 4 line evolved from Aseel peela is being improved for body weight and egg production (Haunshi et al., 2019). Chicks were wing banded and reared in deep litter system in an open-sided house under standard management practices. The temperature inside the shed was 33^oC during first week and gradually decreased to 23^oC at the end of fifth week. The chicks were fed ad-libitum with broiler starter (2900 kcal/kg: ME and 22%: CP) diet based on maize-soybean meal up to 6 weeks of age and with broiler grower ration (2600 kcal/kg: ME and 18%: CP) up to 12 weeks of age. The birds were vaccinated against major diseases as per the standard protocol followed for the rural poultry. The body weights (day old to 12 weeks) and shank length (4 to 12 weeks) were measured at biweekly intervals.
       
A total of 20 birds from each sex were selected randomly and sacrificed by cervical dislocation for evaluating the carcass traits at 12 weeks of age.  The live weight, dressing percentage (DP), relative weights of cutup parts (breast, legs, wings, neck and back), meat, bone, meat: bone ratio, giblets (gizzard, liver and heart), feather and abdominal fat were recorded and expressed as percentage of live weight. Meat quality parameters were estimated in 10 birds from each sex. The pH of meat was determined as per AOAC (1995) using digital pH meter. Colour measurements were conducted on the surface of meat samples (breast muscle) with a Mini scan XE plus (Hunter Associated Labs, Inc, Reston, VA., USA) that had been calibrated against black and white reference tiles (X=78.6, Y=83.4, Z=89.0). The CIE L* (lightness), a* (redness) and b* (yellowness) values were obtained using a setting of D65 (daylight, 65-degree light angle). An average value from four random locations in each sample surface was used for statistical analysis. Shear force value (SFV) was estimated using Texturometer (Tinius Olsen, Model H1KF, Redhill, RH1 5DZ, England) by determining the peak force required to pierce through the uncooked meat sample of a prescribed diameter. Three shear values obtained per core (anterior, middle and posterior) were averaged to get the mean SFV and expressed in Newtons (N).The concentration of Hydroxy Proline (HP) was determined (Newman and Lohan 1950) and expressed in µg/g of meat. An experienced panel evaluated cooked chicken meat on an 8-point descriptive scale (8, extremely desirable; 1, extremely undesirable) for appearance, flavor, texture, juiciness and overall acceptability (Keeton 1983). The experiment was approved by the Institutional Animal Ethics Committee.
       
The data collected on various traits were analyzed using standard statistical methods (Snedecor and Cochran 1994). Single factor ANOVA model (SPSS 12.0) was used to assess the effect of sex on different traits.

The least squares means for body weight and shank length up to 12 weeks of age are presented in Table 1. The body weights differed significantly (P≤0.05) between the sexes from six weeks onwards, with higher body weights in males. During the initial period sex did not show any significant effect on growth. The average body weight of 1.7 kg in males and 1.4 kg in females at 12 weeks of age makes the birds suitable for dual purpose variety as the males were disposed of for meat purpose with premium price at 12 weeks of age. The appearance and gait of the birds due to the presence of Aseel inheritance attracts the farmers, thus increases adoption among the farmers and also fetches premium price in the market. In a previous study in the same two-way cross, higher body weights in males were reported while the body weights in hens were similar (Rajkumar et al., 2019).  Lower body weights than the present findings were recorded in three-way cross developed for backyard poultry farming (Rajkumar et al., 2018; Padhi et al., 2016), in Nigerian chicken (Ndofor-Foleng et al., 2015) and in White Leghorn layers (Chandan et al., 2019). The differences in the body weights may be due to different chicken breeds/lines used for their development and also the purpose of their development either for egg or for both egg and meat. The higher body weights and shank length in 2-way cross might be due to the fact that the bird was developed using PD-1 line as male parent which was under selection for higher shank length for last 12 generations and PD-4 as female line, an improved native Aseel chicken known for higher shank length and improved for higher eight week body weight.
 

       
The carcass traits expressed as percentage of live weight are presented in Table 2. The live body weight at 12 weeks of age in sample of birds varied significantly (P≤0.05) between the sexes. Similar significant sex effects were observed by many authors in different chicken populations (Iqbal et al., 2009; Kaya and Yildirim 2018; Mutibvu et al., 2018). Sex had no significant effect on DP, neck, back and breast meat proportions. The DP observed in two-way cross was within the normal range (65-75%) as reported in literature (Rajkumar et al., 2016; Haunshi et al., 2013; Sarsenbek et al., 2013; Rajkumar et al., 2011). The breast meat proportion was lower in the present study compared to the Aseel and normal broilers (Rajkumar et al., 2016), which might be attributable to the selection criterion. The commercial broilers were selected for broader breast resulting in high breast proportion as well as the Aseel breed which is known for broader breasts. Males had strong legs with significantly high proportion of thigh meat similar to the findings of Kaya and Yildirim (2018) in broiler chickens. Leg proportions in the present cross were similar to the findings in Aseel (Rajkumar et al., 2016) as the present cross had 50% Aseel inheritance. High leg proportions in the present study might be due to the native Aseel chicken which had stronger legs and PD-1 line which was under selection for higher shank length. Similar findings were reported by many authors (Rajkumar et al., 2016; Rajkumar et al., 2017; Padhi et al., 2016; Haunshi et al., 2013) in native and crossbred chicken. The strong shanks with high proportion of thigh meat in the present two-way cross is a desirable feature for the bird developed for free range backyard farming. The bone proportion was significantly higher in males as they have stronger and longer bones. The meat and meat bone ratio was statistically similar in both the sexes. Abdominal fat proportion was significantly (P≤0.05) higher in pullets, though it was less compared to the normal broilers. Lower abdominal fat was desirable characters for meat type birds as consumer prefer meat with low fat percentage. Low proportion of abdominal fat was reported (Rajkumar et al., 2016; Haunshi et al., 2013) in native chicken. Giblets (heart, liver and Gizzard) did not show any significant variation in male and female birds. Feather proportion was significantly (P≤0.05) higher in males as they are characterized by long tail feathers and higher body mass. Lower feather proportion was observed in Aseel (Rajkumar et al., 2016; Padhi et al., 2016; Padhi and Chatterjee 2013) compared to the present findings.
 

           
The results of meat quality attributes of two-way cross are presented in Table 3. Sex did not show any significant variation on pH, SFV and HP values. The optimum pH of 5.5 to 6.5 may be suitable for better meat quality and longer storage period. The pH values of meat recorded in the present study were in the normal range reported in the literature (Sarsenbek et al., 2013). The meat quality primarily depends on the pH of the meat, low pH improves the shelf life of meat with pale colouration, while high pH results in dark, firm and dry (DFD) meat with poor storage quality due to accelerated microbial growth (Rajkumar et al., 2016). Higher SFVs than the present study were observed in Chinese native chickens (Chen et al., 2007); in Indian Aseel and broiler chicken (Rajkumar et al., 2016). The lower SFV in the present study might be attributable to the age of the slaughter and body weight of the birds as SFV tend to increase with age (Sarsenbek et al., 2013) and body mass (Rajkumar et al., 2016).  Lower SFVs were observed in broiler chicken reared in free range and intensive systems of rearing (Funaro et al., 2014) compared to the present results. HP is directly proportional to the collagen content of the meat (Rajkumar et al., 2016). SFV and HP concentration determines the tenderness and toughness of the meat. The yellowness (b*) differed significantly (P≤0.05) between the sexes and it was lower in males with variable myoglobin content in the muscle. Light (L*) and red (a*) colouration did not show any significant variation. The meat colour was due to the myoglobin content, chemical state of the haem structure and pH of meat (Fletcher 2002). The pH influences the reflectance and transmittance of light in to the tissues and across the muscle fibers resulting in light and dark colouration of meat (Swatland 2008). The fat and moisture content significantly (P≤0.05) differed between the sexes. Fat proportion was significantly (P≤0.05)   higher in females and moisture proportion was significantly (P≤0.05) higher in males. Protein and ash proportions were similar in both the sexes. The quantity and quality of proteins, fats, carbohydrates, minerals and fatty acids present in the meat determines its value and quality (Pearson and Gillet 1996). The chemical composition of protein, fat, ash and moisture observed in the meat of 2 way cross were within the range of earlier findings of protein (17.0-23.3%); fat (1.0-17.4%); ash (0.1-3.6%); moisture (60.4-76.14%) (Rajkumar et al., 2017; Souza et al., 2011). The proximate composition parameters observed in the present findings are in accordance with Aseel chicken meat (Rajkumar et al., 2017) which might be due to the fact that the present 2-way cross had Aseel inheritance as female parent.
 

       
The sensory evaluation of meat by an expert panel revealed that sex had no significant effect on all sensory attributes.  The sensory attributes ranged from 6.55 to 7.15 (Table 4) on an eight point scale in 2 way cross meat indicating better consumer acceptability. The probable reason might be the presence of Aseel native inheritance as well as the Cornish inheritance, the established coloured meat purpose breed. The unique taste, firm texture, rich flavour and higher acceptability of native chicken meat are well documented in the literature (Rajkumar et al., 2016; Jayasena et al., 2013).
 

The new dual purpose variety (Two-way cross) developed for rural poultry farming was having fairly good meat quality characters similar to the native chicken in addition to the optimum growth traits. The study concluded that, two-way cross with ideal growth, carcass and optimum meat quality and reasonable consumer acceptability may be a suitable variety for propagating in rural and tribal areas under free range backyard conditions.