ObjectiveThe performance, health, and behaviour of cattle can be strongly affected by climate. The objective of this study was to determine the effect of heat stress on blood parameters, blood proteins (haptoglobin [Hp]; heat shock protein 70 [HSP70]), rectal temperature (RT), heart rate (HR) and rumination time in Korean native beef calves.MethodsThirty-two Korean native beef calves were randomly assigned to 8 groups with 4 animals per group. They were kept in environmental condition with temperature-humidity index (THI) ranging from 70.01 to 87.72 in temperature-humidity controlled chamber for 7 days.ResultsTheir HR, RT, and serum cortisol and HSP70 levels were increased (p<0.05) in high THI compared to those at low THI. But, serum Hp level was decreased (p<0.05) in high THI compared to these at low THI. In addition, HR, RT, serum cortisol and HSP70 were positively correlated with THI (R2 = 0.8368, p<0.01; R2 = 0.6162, p<0.01; R2 = 0.581, p<0.01; R2 = 0.2241, p = 0.0062, respectively). There was also positive association between HR and cortisol (R2 = 0.4697, p<0.01). Similarly, RT and cortisol were positively associated (R2 = 0.4581, p<0.01). But, THI and HR were negatively correlated with Hp (R2 = 0.2157, p = 0.02; R2 = 0.3362, p = 0.003). Hematology and metabolites results were different among treatment groups. Standing position was higher (p<0.05) in the high THI group compared to that in the low THI group.ConclusionBased on these results, it can be concluded that HR, RT, blood parameters (Cortisol, HSP70, Hp) and standing position are closely associated with heat stress. These parameters can be consolidated to develop THI chart for Korean native beef calves.

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Heat shock proteins (HSPs) consist of highly preserved stress proteins that are expressed in response to stress. Two studies were carried out to investigate whether HSP genes in hair follicles from beef calves can be suggested as indicators of heat stress (HS). In study 1, hair follicles were harvested from three male Hanwoo calves (aged 172.2 ± 7.20 days) on six dates over the period of 10 April to 9 August 2017. These days provided varying temperature–humidity indices (THIs). In study 2, 16 Hanwoo male calves (aged 169.6 ± 4.60 days, with a BW of 136.9 ± 6.23 kg) were maintained (4 calves per experiment) in environmentally controlled chambers. A completely randomized design with a 2 × 4 factorial arrangement involving two periods (thermoneutral: TN; HS) and four THI treatment groups (threshold: THI = 68 to 70; mild: THI = 74 to 76; moderate THI = 81 to 83; severe: THI = 88 to 90). The calves in the different group were subjected to ambient temperature (22°C) for 7 days (TN) and subsequently to the temperature and humidity corresponding to the target THI level for 21 days (HS). Every three days (at 1400 h) during both the TN and HS periods, the heart rate (HR) and rectal temperature (RT) of each individual were measured, and hair follicles were subsequently collected from the tails of each individual. In study 1, the high variation (P < 0.0001) in THI indicated that the external environment influenced the HS to different extents. The expression levels of the HSP70 and HSP90 genes at the high-THI level were higher (P = 0.0120, P = 0.0002) than those at the low-THI level. In study 2, no differences in the THI (P = 0.2638), HR (P = 0.2181) or RT (P = 0.3846) were found among the groups during the TN period, whereas differences in these indices (P < 0.0001, P < 0.0001 and P < 0.0001, respectively) were observed during the HS period. The expression levels of the HSP70 (P = 0.0010, moderate; P = 0.0065, severe) and HSP90 (P = 0.0040, severe) genes were increased after rapid exposure to heat-stress conditions (moderate and severe levels). We conclude that HSP gene expression in hair follicles provides precise and accurate data for evaluating HS and can be considered a novel indicator of HS in Hanwoo calves maintained in both external and climatic chambers.

We assessed the growth performance, physiological traits, and gene expressions in steers fed with dietary rumen-protected L-tryptophan (RPT) under a cold environment. Eight Korean native steers were assigned to two dietary groups, no RPT (Control) and RPT (0.1% RPT supplementation on a dry matter basis) for six weeks. Maximum and minimum temperatures throughout the experiment were 6.7 °C and −7.0 °C, respectively. Supplementation of 0.1% RPT to a total mixed ration did not increase body weight but had positive effects of elevating average daily gain (ADG) and reducing the feed conversion ratio (FCR) on days 27 and 48. The metabolic parameter showed a higher glucose level (on day 27) in the 0.1% RPT group compared to the control group. Real-time PCR analysis showed no significant differences in the expression of muscle (MYF6, MyoD, and Desmin) metabolism genes between the two groups, whereas the expression of fat (PPARγ, C/EBPα, and FABP4) metabolism genes was lower in the 0.1% RPT group than in the control group. Thus, we demonstrate that long-term (six weeks) dietary supplementation of 0.1% RPT was beneficial owing to enhanced growth performance by increasing the ADG and glucose level, decreasing FCR, and maintaining homeostasis in immune responses in beef steers in a cold environment.

The objective of the present study was to determine the effect of vitamin A restriction on serum metabolites and carcass performance in Korean native steers during a fattening period. In Study 1, 61 steers were divided into three groups and supplied diets with concentrate and roughage containing 890 IU/kg of provitamin A and then supplemented with either 8000 IU (control), 3000 IU (T1) or 0 IU (T2) of premix vitamin A per kilogram of dry matter. In Study 2, 19 steers were divided into two groups and provided with the same basic diets then supplemented with 8000 IU (control) or 0 IU (T) of premix vitamin A per kilogram of dry matter. In Study 1, we found that serum vitamin A concentrations were significantly (P &lt; 0.05) lower in the T2 group, along with significant (P &lt; 0.05) increases in blood urea nitrogen, albumin, creatinine and non-esterified fatty acid concentrations. In Study 2, the T group had a higher (P &lt; 0.05) skeletal muscle mRNA expression levels of myogenic factor 6 and a trend for the greater yield grade (P=0.095). However, marbling scores in the study showed no significant. Therefore, vitamin A restriction with vitamin premix during the fattening period was associated with a trend for a higher yield grade, but marbling scores that were not significantly higher. Metabolic parameters in this stage could be used as indicators in future metabolic studies and as early health status markers in Korean native steers.