Growth performance
For the growing period, ADG was lower in W130C180 than that of the other treatment groups (Table 2); however, there was no statistically significant difference. FCR was lower in W80C180 than that of W130C180 (P < 0.05); however, results were similar between the other treatment groups. For the early and late fattening periods, ADGs were higher in W80C90 than that of the other treatment groups; however, there was no statistically significant difference. FCRs were lower in W80C90 than that of the other treatment groups. For the entire experimental period, there were no effects of the weaning and castration ages on ADG and FCR of Hanwoo steers. There were no differences in concentrate, rice straw, and dry matter intakes between treatment groups because concentration and rice straw were restricted by the weight of steers over the entire experimental period.
For the growing period, ADG was lower in W130 than that of W80 (Table 3); however, there was no statistically significant difference. There were no effects of weaning age on ADG, feed intake, and FCR over the entire experimental period.
For the growing period, there were no differences in ADG and FCR based on the castration age (Table 4). Final body weight was 5.4 kg higher in C180 than that in C90; however, there was no statistically significant difference. There were no effects of castration age on ADG, feed intake, and FCR over the entire experimental period.
In the present study, there were no overall effects of weaning and castration ages on ADG, feed intake, and FCR of Hanwoo steers; however, the final body weight was considered to be slightly advantageous in the customary weaning and castration ages than that in the early weaning and castration ages. Previous studies [24, 25] reported that the early weaned calves had higher ADG. However, ADG tended to be slightly higher for the growing period owing to the early weaning in the present study, yet they were similar between the other treatment groups over the entire experimental period. These results are caused by differences in calf management methods, experimental periods (weaning to growing vs. weaning to late fattening), and feeding method of concentrate (ad libitum or restricted feeding).
Kwon et al. [15] reported that there was no effect of the weaning ages (90 and 120 days) on concentrates, rice straw, dry matter, crude protein, and TDN intakes, which is in agreeance with our results. In the present study, there was no difference in feed intake until 3 months of age, as the amount of milk suckling was limited to two times per day from 1 month after birth. The results of no significant difference in feed intake were due to restricted feeding of concentrates (1.7% of BW for growing and early fattening periods and 1.3% of BW for late fattening period) and fixed feeding of rice straw by months of age. In the present study, the purpose of limited milk suckling was to increase concentrate and hay intake considering the rapid increase in energy demand of calves from 3 weeks of age and the rapid decrease in milk yield of mother cows [11]. Therefore, the ADG of calves was not lower than that of the early weaning age if the amount of milk suckling is restricted from 1 month after birth. This result would be useful to share with farmers for incorporation into their management systems.
In the present study, we did not investigate return to estrus, services per conception, and calving interval based on the weaning age. However, it is desirable to shorten the weaning age as much as possible, considering shortening of return to estrous [31] and improvement of reproductive efficiency [8, 17, 24].
In the experimental design process of the present study, the early castration was predicted to be disadvantageous to ADG and FCR compared to the customary castration age. However, from the results, there was no effect of castration age on ADG and FCR, which appears to be related to castration age and feeding methods. Regardless of the treatment group, there was no significant difference in stress between the treatment groups as all calves were castrated before puberty. In addition, although there was a slight difference in ADG and FCR over the growing period, there was no difference in ADG and FCR based on the castration age over the entire experimental period because there was similar feed intake owing to the restricted feeding of concentrate.
In general, delayed castration is known as being advantageous to ADG [10, 34] and feed efficiency [2, 6]. However, Worrell et al. [35] reported that early castration before puberty did not reduce ADG. This finding supports the results of the present study. In addition, previous studies [5, 7] reported similar results as the present study that there was no difference in ADG in relation to the castration age. When castration is delayed, increased stress [12, 13] occurs and the extension of the fattening period [5, 13] is inevitable to produce the same meat quality grade. Therefore, early castration is advantageous to shorten the age of slaughter taking into consideration the meat quality grade.
Blood metabolites
There were no effects of weaning and castration ages on concentrations of albumin, BUN, total protein, glucose, creatinine, cholesterol, total glyceride, NEFA, Ca, P, GOT, GPT, and GGT of Hanwoo steers (Table 5).
There were no effects of weaning and castration ages on concentrations of blood metabolites, which was due to no difference in feed intake between the treatment groups in the present study (Tables 2, 3, and 4). In the present study, there was no difference in concentration of blood metabolites owing to similar nutrient supply and utilization efficiency between the treatment groups because of castration before puberty, limited feeding of concentrates, and fixed feeding of rice straw.
Carcass characteristics
The carcass weight tended to be lower in W80C90 than that of the other treatment groups (Table 6). The rib eye area was wider in W130C90 than that of the other treatment groups; however, there was no statistically significant difference. There were only small effects of weaning and castration ages on the overall yield traits (carcass weight, back fat thickness, rib eye area, yield index, and yield grade score) of Hanwoo steers. The marbling and meat quality scores were higher in W130C90 than that of the other treatment groups; however, there was no statistically significant difference. There were no effects of weaning and castration ages on meat color, fat color, and texture.
Although there was no statistically significant difference, carcass weight (456.52 vs. 466.78 kg), rib eye area (93.81 vs. 99.13 cm2), and meat quality grade score (1.86 vs. 2.04) was higher in W130 than that in W80, respectively (Table 7). The marbling score, meat color, fat color, texture, and meat quality score were similar between the treatment groups.
The carcass weight tended to be higher in C180 (469.24 kg) than that of C90 (455.17 kg); however, there was no statistically significant difference (Table 8). Although there was no statistically significant difference, the back fat thickness (13.17 vs. 12.33 mm) and rib eye area (97.26 vs. 95.86 cm2) was higher in C90 than that of C180, respectively. The marbling score (6.96 vs. 6.52) and meat quality score (4.22 vs. 4.14) was higher in C90 than that in C180, respectively; however, there was no statistically significant difference.
In the present study, there were small effects of weaning and castration ages on meat quantity and yield traits of Hanwoo steers. This result was probably due to the influence of calf management, feeding methods, and castration age. First, there was no difference in feed intake until 3 months of age as the amount of milk suckling was limited to two times per day from 1 month after birth. Second, there was no difference in the supply of nutrients (energy, protein, and so on) because feed intake (Tables 2, 3, and 4) was similar between the treatment groups due to restricted feeding of concentrates and fixed feeding of rice straw regardless of the treatment groups. Finally, the level of stress caused by castration was similar because calves were castrated before puberty, regardless of the treatment groups. As a result, it is considered that carcass grades were similar as there was no difference in the nutrient utilization efficiency.
In general, early castration has been known to be disadvantageous to carcass weight [18], yet advantageous to marbling score [5, 9, 13]. Although there was no statistically significant difference, results of the present study showed a decrease in carcass weight and increase in marbling with early castration. These results are similar to previous studies. However, the weaning age was considered together with the castration age in the present study, which is different to previous studies. Although there was no positive effect on carcass quality as in previous studies [19, 22], there was no negative effect of the early weaning on the carcass grade of Hanwoo steers and the reproduction efficiency of mother cows. Therefore, considering these points, early weaning is expected to have a positive influence on calves and mother cows.
Although the data are not presented in the present study, ultrasound results at 26 months of age showed smaller rib eye areas owing to the early weaning but higher rib eye areas and marbling due to the early castration. At 28 months of age, the marbling score by ultrasound increased owing to the early weaning and castration. Considering these ultrasound results, when the slaughter age is adjusted from 31 months to 28–29 months of age, the early weaning and castration is favorable to the rib eye area and marbling score except for carcass weight.
Therefore, the results of the present study suggest that the weaning and castration ages have a small effect on ADG, feed intake, FCR, blood metabolism, and carcass characteristics of Hanwoo steers. However, it is considered that early castration is advantageous when the slaughter age is shortened with marbling reduction (i.e., meat quality grade) minimized. Furthermore, early weaning is favorable when reproductive efficiency of mother cows is considered.
The present findings indicated that weaning and castration ages resulted in similar growth performance and carcass characteristics without any negative effect on marbling score in Hanwoo steers. Therefore, early weaning and castration is recommended to reduce the age of slaughter considering meat quality of Hanwoo steers and reproductive efficiencies of Hanwoo cows.
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