CARCASS QUALITY OF CHICKENS OF DIFFERENT CONFORMATION

The aim of this study was to investigate the effect of conformation of chickens of different genotype on the yield of breast meat. As a typical example of the chickens of very poor conformation pure breed Naked neck chickens were taken, fattened 8 and 10 weeks (groups K8 and K10). As an example of good conformation, an imported hybrid of chickens was taken, known for its broiler qualities and as medium growing hybrid, Red Bro (R). The second experiment included commercial hybrids of fast growth (Ross, Cobb and Hubbard) reared according to all technological standards of intensive fattening until the age of 42 days. The results obtained were contrary to the conclusion obtained a few decades ago, at the beginning of the study the conformation of chicken, by Scots and Darrow (1953), according to which the selection of chickens of heavy type, despite the fact that, to some extent, it had improved meat yield of the breast, did not significantly improve slaughter traits of fattening chickens, confirming that better conformation and higher body weight had a positive impact on improving relative share of breast, i.e. white meat. The results regarding the slaughter traits of chicken genotypes of different conformation suggest that breeding selection work to improve the conformation of broilers significantly improved slaughter yields and breast meat yield. In this sense, the conformation can be treated as an indicator of the slaughter value of carcasses, rather than an aesthetic category. Key wards: genotype, conformation, share of meat


Introduction
In recent decades, in the selection of heavy-type hens, considerable attention has been given to body type or structure, or conformation of the body of chickens in broiler age, and in this regard has made remarkable progress.Even though, in broiler hybrids, in modern production certain minor differences in conformation may be established, virtually there are no significant differences in slaughter output ratios.Possible differences in these traits appear to be predominantly in genotypes of different body weight before slaughter (Hopić 1999;Hopić et al., 2002;Vračar et al., 1996;Pavlovski et al., 2006;Pavlovski et al., 2007;Blagojević et al., 2009).
Back in 1951, Asmundson and Lerner (1951) have expressed the opinion that the selection to improve the conformation rather concerns vague aesthetic standards by which a consumer evaluates the appearance of dressed carcass than the actual amount of meat on the carcass.On the other hand, the results of some authors indicate no significant differences in the characteristics in slaughter traits of chicken of different conformation.If we compare the results of the research obtained in the last 20 years, it can be concluded that the genetic selection testing made a significant contribution to the increase in body weight of chickens and share of breast (white meat), and thus a better conformation.The results of our study in 2014 confirmed that genotype and body mass directly affect better conformation and a higher share of breast meat.
It seemed interesting to perform tests with genotypes of chickens of distinctly different conformations: Red Bro and indigenous breed Naked neck, on the one hand and commercial fast-growing hybrids, on the other hand, in terms of carcass quality.

Materials and Methods
The experimental research was conducted through two experiments.In the first experiment, as an example of good conformation, an imported hybrid of chickens was taken, known for its broiler qualities and as medium growing hybrid, Red Bro (R).In contrast, as the representative of the old, unimproved type of conformation, native breed Naked neck was taken, grown in pure blood without applying selection measures.Since the body weight of this population at the age of 8 weeks was significantly lower than that of the modern hybrids, in addition to these groups, a group of chickens was slaughtered at 10 weeks of age K 8 and K 10 ).Chickens of these groups were grown extensively in the same building, in the same conditions of keeping and feeding, except for the differences in the duration of fattening.
The second experiment included commercial fast growing hybrids (Ross, Cobb and Hubbard) which were reared according to all technological standards of intensive fattening until the age of 42 days.
Prior to slaughtering chickens spent 12 hours without food and water.After measuring of body weight, chickens were slaughtered in the experimental poultry slaughterhouse of the Institute for Animal Husbandry, Belgrade-Zemun.The following body dimensions (measures conformation) were measured: shank length, keel length, breast angle and thigh girth according to the method of Pavlovski and Mašić (1983), on 15 and 12 chickens, respectively, per genotype and gender, and the obtained results are shown in absolute values.In recent years the presentation of conformation less precise but more comprehensive indexes are used which show the relationship of live weight and linear measures or simply body weight (g) at 1 mm of corresponding body measure.
Slaughter yields (dressing percentage): traditionally dressed carcass, ready to cook, ready to grill were taken according to Pravilnik o kvalitetu pernate živine (1981) (Rulebook on quality of poultry meat).
The software package STATISTICA, version 12 (Stat Soft inc.) was used for statistical analyses.The level of statistical significance of differences betwen groups was determined by Tukey-test.

Results and Discussion
Data on individual body measures that in some way reflect the body conformation of chickens are given in table 1.Based on the data from the table, the following can be concluded: -The difference in the average live weight of chickens between groups R and K 10 was very strong and almost 500 g, so it does not seem justified to compare these groups in other traits; -The average live weight of K 10 chickens was less than the weight of chicks of group R, and in males by just over 500 g, and in females more than 300 g -in both cases the difference was statistically significant; -Despite the significantly lower body weight, K 10 chickens had greater shank length and the keel length compared to chickens of R group -in both case the difference was statistically significant; -The breast angle was about 40 degrees lower in chicks of group K, and the difference compared to the R group was statistically significant; -The differences in thigh girth of all the groups were statistically significant and approximately proportional to the difference in live weight; -A relatively greater keel length and much smaller breast angle in chickens of group K 10 indicated a significantly less favourable conformation of these chickens compared with chickens of group R. Table 2 shows the index values of conformation measures measured on typical 15 chickens for each provenience and gender.Due to the uneven live weight of investigated chicken proveniences, as an relative comparable indicator of the conformation the ratio between the live weight and certain linear measures (index g / mm) was taken.Most suitable index for all the studied measures were recorded in chickens of both sexes of genotype Red Bro (R).Table 3 shows the values obtained for slaughter yields of tested chickens per genotype and gender.The most favourable yield "traditionally dressed carcass" had male and female chickens of genotype K10 (85.91% and 85.14%), which were not statistically significant.The resulting yields were significantly better than the yield in the trials with the same pure breed (Pavlovski et al., 2009), which can be correlated with a higher body mass live chickens the measured before slaughter.

Conclusion
The results of the study of slaughter traits of chicken genotype of different conformation suggest that breeding -selection work to improve the conformation of broilers significantly improved slaughter yields and meat yield of chicken breast.In this sense, the conformation can be treated as an indicator of the slaughter value of carcasses, rather than an aesthetic category.

Acknowledgment
This research is part of the Project EVB: TR-31033 financial by suported by Ministry of Education, Science and Technological Development of the Republic of Serbia.