Title Page
Contents
ABSTRACT 12
Ⅰ. Literature review 16
A. Introduction 16
B. Heat stress 17
1. Economic losses of livestock by global warming and abnormal weather 17
2. Changes in Korean temperature over 107 years 17
C. Effects of heat stress on cattle 18
1. Changes physical parameters under heat stress in cattle 19
2. Endocrine parameters during heat stress in cattle 27
3. Changing blood metabolites during heat stress in cattle 32
4. Changing rumen environment during heat stress in cattle 35
D. Summary of ruminant physiological changes under heat stress condition 37
E. How to overcome heat stress 39
1. Physical modification of the environment 39
2. Genetic improvement of heat tolerant breeds 40
3. Improved feeding and nutritional management practices 42
F. The objectives of this study 56
Ⅱ. Heat stress effects on rumen microorganisms and the role of protein or energy levels in rumen fermentation properties 57
A. Abstract 57
B. Introduction 59
C. Materials and Methods 60
1. Collecting ruminal inoculum and In vitro incubation procedures 60
2. Chemical analysis 61
3. Analyzes of fermentation properties 71
4. Protein analysis of liquid associated bacteria 72
5. Statistical analysis 73
D. Results 73
1. Chemical composition of feed ingredients and formulation in trial 1 and trial 2 73
2. In vitro fermentation properties according to heat stress 74
3. In vitro fermentation properties according to protein levels of diet in trial 1. 84
4. In vitro fermentation properties according to energy levels of diet in trial 2. 86
5. Changes in protein amount of liquid-associated bacteria 89
E. Discussion 90
1. Effects of heat stress on fermentation properties and liquid associated bacteria 90
2. Effects of protein levels on in vitro fermentation properties and liquid-associated bacteria 93
3. Effects of energy levels on in vitro fermentation properties and liquid associated bacteria 94
F. Conclusion 97
Ⅲ. Comparative analysis of ruminal temperature, pH, fermentation, microbial composition, and microbial amino acids between spring and summer seasons in Korea 99
A. Abstract 99
B. Introduction 101
C. Materials and Methods 102
1. Animal management and diet 102
2. Temperature and humidity index 103
3. Chemical composition analysis 105
4. Measurements of ruminal temperatures 106
5. Rumen fluid sampling 107
6. Analyzing pH, volatile fatty acid, and NH₃-N 108
7. Collecting rumen microbes and analyzing amino acids 109
8. DNA extraction, PCR and 16S rRNA gene sequencing 110
9. Bioinformatics analysis. 110
10. In-situ procedure 111
11. Statistical analysis 111
D. Results 114
1. Experimental environment 114
2. Ruminal fermentation 114
3. The digestibility of dry matter, neutral detergent fiber, and crude protein in rumen 120
4. Richness, diversity estimates, and rumen bacteria and archaeal composition 121
5. Differences in bacterial community composition between spring and summer 125
6. Microbial amino acids composition 127
E. Discussion 129
F. Conclusion 137
Ⅳ. Effects of different energy levels and two levels of temperature–humidity indices on growth, blood metabolites, and stress biomarkers in Hanwoo calves 138
A. Abstract 138
B. Introduction 140
C. Material and methods 142
1. Animals and climatic chambers 142
2. Management conditions and treatment 142
3. Chemical analysis of experimental diets 145
4. Physiological parameters under heat stress 148
5. Blood hematology analysis under heat stress 148
6. Blood metabolites analysis under heat stress 152
7. Sampling and isolation of PBMCs 155
8. Total RNA extraction and real-time PCR analysis 155
9. Statistical analysis 157
D. Results 158
1. The effects of dietary energy levels and THI levels on DMI, energy intake, growth performance, and physiological parameters 158
2. Dietary energy levels effects on blood metabolites and amino acids under heat stress 159
3. The effect of dietary energy levels on heat shock protein expression under heat stress 160
E. Discussion 163
F. Conclusions 169
Ⅴ. General conclusion 170
References 174
Appendix 195
Abstract (in Korean) 199
Table 1.1. Continuous and discrete variables included in the meta-analysis 21
Table 1.2. Relationship of temperature-humidity index and rumination time in previous studies. 26
Table 1.3. Summary of ruminant physiological changes under heat stress condition. 37
Table 1.4. Amino acids composition of rumen microbes. 52
Table 2.1. The chemical composition of the feed ingredients used in trial 1 63
Table 2.2. Feed ingredients and chemical compositions of trial 1 65
Table 2.3. The chemical composition of the feed ingredients used in trial 2 67
Table 2.4. Feed ingredients and chemical compositions in trial 2 69
Table 2.5. The results of in vitro ruminal fermentation after 3, 6, 12, 24, and 48 h of incubations according to five protein levels (CP 12.0, 13.5, 15.0, 16.5, 18.0 % of DM basis) and two incubation temperature (39℃ and 41℃) 76
Table 2.6. The results of in vitro ruminal fermentation after 3, 6, 12, 24, and 48 h of incubations according to five metabolizable energy levels (2.4, 2.5, 2.6, 2.7, and 2.8 Mcal/kg of DM basis) and two incubation temperature (39℃ and 41℃) 80
Table 2.7. Comparative analysis was performed to evaluate the rate of change in in vitro ruminal fermentations at protein levels of 13.5%, 15%, 16.5%, and 18% relative... 85
Table 2.8. Comparative analysis was performed to evaluate the rate of change in in vitro ruminal fermentations at energy levels of 2.5, 2.6, 2.7, and 2.8 Mcal/kg of DM... 88
Table 3.1. Chemical compositions of concentrate and forage 104
Table 3.2. Climate conditions including temperature, relative humidity, and temperature humidity index 105
Table 3.3. Ruminal fluid pH and NH₃-N and volalite fatty acids according to season 115
Table 3.4. Percentage of volatile fatty acids in rumen fluid according to season. 116
Table 3.5. Ruminal digestibility of dry matter, neutral detergent fiber, and crude protein according to season and time. 120
Table 3.6. Changes in ruminal microbial amino acids according to season (spring and summer) 128
Table 4.1. Ingredient and chemical compositions of experimental diets. 146
Table 4.2. Effects of dietary energy levels on dry matter intake, energy intake, growth performance, and physiological thermoregulation in Hanwoo calves under heat stress 149
Table 4.3. Effects of dietary energy levels on blood parameters in Hanwoo calves under heat stress 150
Table 4.4. Effects of dietary energy levels on blood amino acid profiles in Hanwoo calves under heat stress 153
Figure 1.1. Changes in annual average highest, average, and lowest temperature (1912-2020) 18
Figure 1.2. The relationship between temperature-humidity index (THI) and DMI (DMI) was analyzed in a meta-analysis conducted by Chang-Fung-Martel et al. (2021).... 22
Figure 1.3. Effect of temperature-humidity index on percentage of standing in lactating dairy cows under heat stress. 24
Figure 1.4. Production process of steroid hormones 28
Figure 3.1. Ruminal temperaure according to season 107
Figure 3.2. Results of VFAs (volatile fatty acids) in spring and summer depending on the time after feeding 119
Figure 3.3. Bacterial alpha diversity and beta diversity of steers with spring and summer 122
Figure 3.4. Comparison of relative abundances of bacterial phyla and genera in spring and summer 124
Figure 3.5. Comparison of relative abundances of bacterial phyla and genera in spring and summer showing significant differences 126
Figure 3.6. Bacterial phyla and genus changed in spring and summer, its functions, and the results of rumen fermentation properties in this study. 135
Figure 4.1. Effects of different energy levels on growth performance and stress parameters in Hanwoo calves under heat stress 144
Figure 4.2. Effects of dietary energy levels on the mRNA expression of HSP70 and HSP90 in PBMCs during the climate chamber experiment 162