Effect of environmental factors
Table 4 shows the analysis of variance for environmental effects on the carcass traits in Chikso. There were significant differences in CW and BF among sex, regions, birth years, and ages at slaughter, but there was no significant difference between birth seasons and coat colors. The EMA showed significant differences among sex, regions, birth seasons, and ages at slaughter but no significant difference between birth years and coat colors. In MS, sex, regions, birth years, birth seasons, and coat colors were significantly different but there was no significant difference for ages at slaughter.
Least square means (LSM) of sex and region effects show ing significant differences in all carcass traits are shown in
Table 5 and
6. The LSM of CW in bulls and steers were 404.8 kg and 404.9 kg, which weren’t significantly different.
The 2017 Hanwoo (Korean native cattle) grading results reported by KAPE [
14] showed that LSM of CW (439.8 kg) in steers was higher than in bulls (425.6 kg). In general, it would be considered that CW of bulls is higher than of steers when raising them in the same environment, but it seems that there was no significant difference in CW between bulls and steers because they were raised in different environments in different time periods. Likewise, it is presumed that CW in Chikso weren’t significantly different between bulls and steers for the same reason. In particular, this would be one of the reasons why Chikso bulls are used for natural mating, which accounts for the lack of an intensive fattening period.
In EMA, the LSM of bulls, steers and cows was 87.43, 83.94, and 76.14 cm
2, respectively. These are lower than the EMA means of Hanwoo bulls, steers and cows slaughtered in 2017 reported by KAPE [
16], which showed 91.0, 92.1, and 82.9 cm
2. The LSM of BF in steers and cows were 12.32 mm and 11.92 mm, which were not significantly different, and the LSM of BF in bulls was 5.04 mm. These statistics observe a similar tendency to the average BF in Hanwoo steers and bulls reported by KAPE [
16], which were 13.8 mm and 6.2 mm. This shows that the average BF of Chikso was lower than that of Hanwoo. In MS, the LSM of Chikso bulls, steers, and cows were 4.36, 1.37, and 3.40, showing similar tendencies in Hanwoo steers, bulls and cows which had 5.8, 1.4, and 4.3, respectively [
16]. These statistics shows that the average MS of Chikso was lower than that of Hanwoo.
Lee and Choy [
6] compared the monthly weights of Han woo and Chikso. Hanwoo was heavier at 12 months of age than Chikso, and the difference was larger at 18 and 28 months of age, resulting in their respective carcass traits performance. In the meantime, there has only been a management effort by research institutes at the province level to improve Chikso, not the national level. Therefore, it is feasible that there exists a difference in carcass grades between Chikso and Hanwoo because Hanwoo has experienced consistent and various efforts for improvement at the national level. For the Chikso to undergo carcass trait improvement, it is critical that Chikso also undergoes management efforts at the national level like Hanwoo. As shown in
Table 6, the LSM of CW by region were 407.03 kg and 396.94 kg in Jeonnam and Gyeongnam, respectively. The best EMA was 83.98 cm
2 and 83.70 cm
2 in Chungnam and Gangwon. The highest BF was 8.38 mm and 8.46 mm in Jeonnam and Gangwon, while the highest MS was 3.73 and 3.34 in Gyeongbuk and Gyeonggi, respectively. Gangwon, Chungbuk, Jeonbuk, and Gyeongbuk (Ulleung) produced their own semen and distributed them; however, the genetic ability of the distributed semen was not confirmed, and it was high proportion of the farmers that produce semen by themselves or do natural service, which seems to show inconsistent performance on regional carcass traits.
The CW, EMA, and BF were not significantly different under the presence of brindle with black color on a yellow background, but MS was significantly influenced. The highest LSM of EMA in the 3rd level of coat color was 3.22 and the highest LSM of EMA in the 4th level was 3.20.
Lee et al [
17] compared carcass performance between Chik so and black cattle raised in the inland and found that black cattle were heavier in CW, broader in EMA, thicker in BF and higher in MS. In addition, Choi et al [
18] also compared weights at 24 months of age between Chikso and black cattle, and didn’t report any significant difference between them (although the weights of black cattle were heavier numerically).
The livestock-related research institutes at each province are producing semen based on coat color and distributing it to farmers. Therefore, semen with greater carcass traits performance should be provided to them.
Monthly performance of steers in carcass traits
Carcass traits of steers are directly related to profit in the Chikso industry.
Table 7 shows the basic statistics of carcass traits in steers by month when over 100 heads were slaughtered. In comparison with Hanwoo, it was expected that Chikso show longer months of age at slaughter than Hanwoo. However, they were slaughtered the most at 30 months of age, nearly the same age at slaughter of Hanwoo which had about 62% (701 heads) slaughtered between 28 and 32 months of age.
The CWs increased continuously with an increase in months of age at slaughter. The EMA changed little until 31 months of age and slightly increased at 32 months of age.
The BF increased until 31 months of age and decreased at 32 months of age.
In the case of MS, the steady increase was observed based on months of age at slaughter, such as 3.7 at 29 months of age, 4.1 at 30 months of age, 4.3 at 31 months of age, 4.7 at 32 months of age.
Estimation of genetic parameters
Table 8 shows the estimates of heritability, genetic correlations, and phenotypic correlations of the carcass traits in Chikso. The heritability estimates of the CW, EMA, BF, and MS were 0.50, 0.37, 0.35, and 0.53, respectively. It was higher than the heritability estimate of 0.39 in CW and lower than the heritability estimate of 0.62 in MS reported by Sun et al [
19] in Hanwoo. The heritability of CW from this study was estimated higher than that of the study using performance testing records of Hanwoo young bulls (0.37) [
20], and using the data from Hanwoo steers [
21].
Table 8 shows the genetic and phenotypic correlations be tween traits studied. Sun et al [
19] reported that the genetic correlation between EMA and BF in Hanwoo was 0.31 and the genetic correlation between BF and MS was 0.36, which was different from the results in Chikso showing negative genetic correlations. However, Roh et al [
20] used Hanwoo young bulls’ data and reported that the genetic correlation between EMA and BF was −0.17 and the correlation between BF and MS was −0.10. Park et al [
8] also reported that the genetic correlation between EMA and BF was −0.20 and the correlation between BF and MS was −0.02, which agreed with the trends of the results in this study.