RNA-Seq analysis was used to characterize transcriptome response of Holstein calves to thermal stress. A total of eight animals aged between 2 and 3 months were randomly selected and subjected to thermal stress corresponding to a temperature humidity index of 95 in an environmentally controlled house for 12 h consecutively for 3 days. A set of 15,787 unigenes were found to be expressed and after a threshold of threefold change, and a Q value <0.05; 502, 394, and 376 genes were found to be differentially expressed on days 1, 2, and 3 out of which 343, 261 and 256 genes were upregulated and 159, 133, and 120 genes were downregulated. Only 356 genes out of these were expressed on all 3 days, and only they were considered as significantly differentially expressed. KEGG pathway analysis revealed that ten pathways were significantly enriched; the top two among them were protein processing in endoplasmic reticulum and MAPK signaling pathways. These results suggest that thermal stress triggered a complex response in Holstein calves and the animals adjusted their physiological and metabolic processes to survive. Many of the genes identified in this study have not been previously reported to be involved in thermal stress response. The results of this study extend our understanding of the animal's response to thermal stress and some of the identified genes may prove useful in the efforts to breed Holstein cattle with superior thermotolerance, which might help in minimizing production loss due to thermal stress.

The purpose of this study was to discover genetic variants in the bovine fatty acid desaturase domain family member 6 (FADS6) gene and to test for associations with fatty acid composition (FAC) as well as carcass traits such as backfat thickness (BFT) and marbling scores (MAR). 90 Hanwoo steers were used in the study, and sequence analyses detected 4 genetic variants in intron 2 (approximately 10,890 bp) of FADS6. The FADS6 SNPs showed no significant departures from HWE (Hardy-Weinberg Equilibrium) except g.57772511C > T that did not have heterozygous genotypes. Genotypes of g.57770744A > G and g.57772511C > T were significantly associated with Vaccenic (C18:ln7), Palmitoleic (C16:ln7), and Stearic (C18:0) acids. The analysis confirmed dominance and additive effects for the g.57770744A > G and g.57772511C > T segments, respectively. A positive correlation (31.1%, P = 0.003) between BFT and Linolenic acid (C18:3n3) and a negative (-36.5%, P < 0.001) correlation between MAR and Eicosenoic acids (C20:1n9) were observed.

The bovine fatty acid desaturase (FADS) gene cluster consists of FADS1, FADS2, FADS3, and FADS6, which acts as key enzymes in fatty acid metabolism. Of these, the genetics effects of variants in FADS1, FADS2 and FADS3 have been previously studied. However, the genetic effects of variants of FADS6 gene have not been studied. The aim of this study was to identify genetic variants in the bovine fatty acid desaturase 6 (FADS6) gene and study their association with fatty acid composition in Hanwoo cattle. Six genetic variants were observed, three each in intron 2 and exon 6 by DNA sequencing analyses. The association of genetic variants with fatty acid composition was evaluated in 90 Hanwoo steers. The variants were confirmed and the animals were genotyped by RFLP (Restriction Fragment Length Polymorphism) and AS-PCR (Allele Specific PCR) analyses. The analysis revealed that palmitoleic acid (C16:1n7) was associated with g.3391G > A, g.3660A > C and g.15657C > T, and stearic acid (C18:0) showed highly significant association with g.3660A > C segments. Both g.3391G > A, g.3660A > C also had strong additive and dominance effect for Palmitoleic acid, while g.3660A > C also had a strong dominance effect for stearic acid. These results could be useful for modulating fatty acid composition in beef and produce meat with higher monounsaturated fatty acid to saturated fatty acid ratio (MUFA/SFA), which had been shown to have positive health effect in humans.