• Korean Journal of Poultry Science
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• v.49 no.2
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• pp.89-98
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• 2022

This study compared the production and physiological characteristics of male and female Korean native commercial chickens. We investigated the growth performance, vitality, and stress response of 479 male and 608 female chickens from 1 d to 12 weeks of age. The body weight, feed consumption and feed conversion ratio were measured as growth performance. The survival rate, amount of telomeric DNA, DNA damage rate, heterophil-lymphocyte ratio (H/L ratio), and heat shock protein (HSP)-70, HSP-90α, and HSP-90β gene expression levels were analyzed as indicators of vitality and stress response. Body weight was significantly higher in male chickens than in female chickens after 2 weeks of age (P<0.01). Feed intake was higher in male chickens than in female chickens, whereas the feed conversion ratio showed the opposite trend. The survival rate was significantly higher in female chickens than in male chickens (82.8% vs. 73.8%, P<0.05). Stress response analysis revealed no differences between male and female chickens in terms of telomeric DNA content, DNA damage rate, H/L ratio, and HSP gene expression levels. Taken together, it was concluded that there was a significant difference in the growth performance and survival rate between male and female Korean native commercial chickens, whereas there was no difference in the degree of stress response between them. Therefore, in terms of the productivity of Korean native commercial chickens, it is judged that separate-sex rearing is much more advantageous than mixed rearing, regardless of the physiological characteristics of males and females.

• Korean Journal of Poultry Science
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• v.49 no.4
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• pp.229-237
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• 2022

This study investigated the growth characteristics of four strains of newly developed synthetic Korean native commercial chickens (KNCs). We investigated a suitable growth curve model in KNCs and estimated the number of days to reach a 2 kg market weight. Body weight was measured at 2-week intervals from birth to 12 weeks of age. The growth curves were estimated using von Berteralanffy, Gompertz, and logistic functions. The results showed that males were significantly heavier than females at all ages, but there were no significant differences in body weight between strains, except at birth and 2 and 6 weeks of age. The coefficients of determination and adjusted determination of growth function had high goodness-of-fit (97.4~99.7). Of the growth curve parameters, the mature weight and growth ratio were higher in males than in females, but the maturity rate was similar in males and females. The inflection point occurred at approximately 7 weeks of age for females and 8 to 9 weeks of age for males. The weights estimated from the growth curve functions almost agreed with the actual weights, except for male weights estimated using the von Bertalanffy function. The coefficients of determination of the regression equations for weight to age were 0.9583 to 0.9746. The 8- and 10-week-old body weights estimated using the regression equation, and the 12-week-old weight estimated using the logistic function were most similar to the actual weight. Using these models, the estimated age of KNCs to reach 2 kg was 62.0~64.6 days for males and 74.9~78.6 days for females.

• Korean Journal of Poultry Science
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• v.48 no.4
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• pp.177-184
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• 2021

Sex identification in day-old chicks is essential in the poultry industry. Currently, the feather-sexing using a sex-linked inheritance is a chick sexing method used extensively in the poultry industry. For chicks produced by feather-sexing, all females are early-feathering (EF) chicks and all males are late-feathering (LF) chicks. Therefore, investigating the effects of EF and LF phenotypes on production traits of chickens is critical. The purpose of this study was to analyze and compare the production performance between EF and LF chickens in Korean native commercial chickens. The results showed that the survival rate of the EF chickens was significantly higher than that of the LF chickens, from hatching to 12 weeks of age (P<0.05), with the highest difference observed in females. However, no significant difference was observed in body weight between the EF and LF chickens at almost all ages. In addition, no significant difference was observed between in feed utility, such as average daily feed intake and feed conversion ratio, between the EF and LF groups. In conclusion, although the survival rate of early-feathering chickens was superior to that of late-feathering chickens, no significant difference was observed in growth performance and feed utility among Korean native chickens. The results suggest that production capacity is not influenced by feathering type in the establishment of a breeder structure and production system for feather-sexing Korean native chickens, which is valuable for the practical application of feather-sexing in the poultry industry.

• Korean Journal of Poultry Science
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• v.44 no.4
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• pp.259-265
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• 2017

This study was to investigate the effect of chick weight in the early growth period on market-weight of Korean native chickens (KNCs). We measured the body weights of 1,087 chickens (male 479, female 608) of 13 KNC strains at 1-84 days of age at two week intervals. The growth performance of the 13 KNC strains was investigated. Correlation coefficients among the weights of chickens in each growth period and regression of market-weight on early chick weights were analyzed. The results showed that the average body weight of 70-day-old KNCs was 1,962g: 2,154g and 1,819.7g for males and females, respectively. The equation for regression of body weight on age was estimated as $\hat{Y}=0.1347X^2+18.738X-40.134$ ($R^2=0.9418$). Using this regression equation, the duration required to attain a KNC market-weight of 2 kg was estimated as 71.8 days. All the correlation coefficients between early chick weight and market-weight were significantly positive. Although the correlation coefficients among the chick weights in each growth period decreased with increase in age interval, early growth weight had a significant effect on late growth performance. The correlation coefficient between market-weight at 70-days and chick weight at 1-day was estimated to be a low as 0.10-0.13. In the estimations of market-weight correlation coefficients, correlation coefficient and coefficient of determination were high in the female and male chicks after 28-days and 42-days of age, respectively. The results of the analysis of correlation and regression between early chick weight and market-weight of KNCs showed that market-weight could be predicted based on the weights of 28-day-old females and 42-day-old males.

• Korean Journal of Poultry Science
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• v.51 no.2
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• pp.65-71
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• 2024

The feather-sexing method is widely used commercially for chick sex identification. However, for feather-sexing to be industrially practical, the early-feathering (EF) and late-feathering (LF) genes must existed within the foundation stock, a suitable feather-sexing lines must be established, and the accuracy of sex identification by feather-sexing must be ensured. Therefore, this study introduces the method of constructing the Korean native chickens (KNC) feather-sexing lines using EF and LF genes and evaluates the effectiveness of feather sex determination on commercial chicks produced from the constructed KNC lines. The results showed that both EF and LF chickens existed within the foundation stock, with the frequency of LF genes ranging from 0 to 0.205. In feather-sexing line establishment, the paternal strain of the grandparent stock (GPS) was fixed as EF (kk) for both sexes, while the maternal strain was composed of males with LF homozygotes (Z^KZ^K) and females with EF (Z^kW). Thus, in the parent stock (PS), male breeder had EF (Z^kZ^k) and female breeder had LF (Z^KW), resulting in chicks produced from their crosses having LF (Z^KZ^k) for males and EF (Z^kW) for females, allowing sex determination based on feather development. Additionally, to evaluate the effectiveness of feather-sexing for the produced commercial chicks, a study was conducted on 1,000 samples of the produced chicks to investigate the concordance between vent-sexing and feather-sexing, showing a matching rate of 93.1%.