Genetic Markers Associated with Milk Production and Thermotolerance in Holstein Dairy Cows Managed in a Heat-Stressed Environment

Abstract

Dairy production in Holstein cows in a semiarid environment is challenging due to heat stress. Under such conditions, genetic selection for heat tolerance appears to be a useful strategy. The objective was to validate molecular markers associated with milk production and thermotolerance traits in Holstein cows managed in a hot and humid environment. Lactating cows (n = 300) exposed to a heat stress environment were genotyped using a medium-density array including 53,218 SNPs. A genome-wide association study (GWAS) detected six SNPs associated with total milk yield (MY305) that surpassed multiple testing (p < 1.14 × 10−6). These SNPs were further validated in 216 Holstein cows from two independent populations that were genotyped using the TaqMan bi-allelic discrimination method and qPCR. In these cows, only the SNPs rs8193046, rs43410971, and rs382039214, within the genes TLR4, GRM8, and SMAD3, respectively, were associated (p < 0.05) with MY305, rectal temperature (RT), and respiratory rate. Interestingly, these variables improved as the number of favorable genotypes of the SNPs increased from 0 to 3. In addition, a regression analysis detected RT as a significant predictor (R2 = 0.362) for MY305 in cows with >1 favorable genotype, suggesting this close relationship was influenced by genetic markers. In conclusion, SNPs in the genes TLR4, GRM8, and SMAD3 appear to be involved in the molecular mechanism that regulates milk production in cows under heat-stressed conditions. These SNPs are proposed as thermotolerance genetic markers for a selection program to improve the milk performance of lactating Holstein cows managed in a semiarid environment.

Genetic factors influencing milk and fat yields in tropically adapted dairy cattle: insights from quantitative trait loci analysis and gene associations

“…Cheruiyot et al [ 41 ] found eight enriched genes in the glutamatergic synapse pathway associated with heat tolerance in Australian Holstein cattle. In a similar study, Zamorano-Algandar et al [ 42 ] indicated that the glutamatergic synapse pathway was associated with MY in US Holstein affected by heat stress.…”

Exploring Genetic Markers: Mitochondrial DNA and Genomic Screening for Biodiversity and Production Traits in Donkeys

“…The candidate gene approach is a strategy used to screen genetic markers associated with a particular trait of interest by focusing on specific genes that are known or hypothesized to be involved in the expression of that trait [73,74]. This approach has been applied to many animal species [75,76], including donkeys [77], for identifying genetic markers associated with production traits such as the growth rate, milk yields, and reproductive performance. By focusing on specific genes that are known or hypothesized to be involved in the expression of the trait of interest, this approach can increase the efficiency of genetic marker discovery and accelerate the development of genomic selection tools for donkey breeding programs.…”

Candidate genes associated with heat stress and breeding strategies to relieve its effects in dairy cattle: a deeper insight into the genetic architecture and immune response to heat stress

“…that tend to be polygenic, and as a result, many genetic variants, each with small effects contribute to the phenotype. In these cases, the heat tolerance trait has been associated with a number of QTL regions and candidate genes ( 14 , 15 , 18 , 92 ). This polygenicity of a trait can be a challenge in achieving rapid genetic progress for heat tolerance in dairy cattle, particularly in cases when the heritability of a trait is low.…”

“…Identifying genome-wide markers and pathways underpinning the genetic mechanisms that increase thermotolerance in dairy cattle is at the infancy stage, but it is gaining momentum considering the increasing challenges imposed by climate change, as shown by the recent increase in published studies ( 2 , 11 , 12 , 14 , 18 , 92–96 ). Genome-wide association studies are most commonly used to test tens if not hundreds of thousands of genomic variants to find those statistically associated with heat tolerance traits in cattle.…”

“…In addition, investigation of the physiological systems regulated by genes involved in thermoregulation is an area that requires further study, as understanding the biological control will aid to prioritize candidate genes for genomic selection strategies ( 105 ). A considerable number of GWAS and transcriptome studies have been investigated and identified several candidate causal variants potentially linked with milk production and various physiological indicators of HS in dairy cattle ( 11 , 12 , 14 , 15 , 17–19 , 24 , 92–94 , 96 , 106 , 107 ). Recent work has shown that the SNPs rs8193046 , rs43410971 , and rs382039214 , within the TLR4 , GRM8 , and SMAD3 genes, respectively, appear to be significantly associated with 305-day milk yield, RT and RR in Holstein dairy cows kept under heat-stress condition ( 94 ).…”