Metagenomic and Metabolomic Insights Into the Mechanism Underlying the Disparity in Milk Yield of Holstein Cows

Abstract

This study was conducted to investigate the metabolic mechanism underlying the disparity in the milk yield of Holstein cows. Eighteen lactating Holstein cows in their second parity and 56 (±14.81 SD) days in milking (DIM) were selected from 94 cows. Based on the milk yield of the cows, they were divided into two groups of nine cows each, the high milk yield group (HP) (44.57 ± 2.11 kg/day) and the low milk yield group (LP) (26.71 ± 0.70 kg/day). The experimental cows were fed the same diet and kept under the same management system for more than 60 days. Rumen metagenomics revealed that two Archaea genera, one Bacteria genus, eight Eukaryota genera, and two Virus genera differ between the HP and LP groups. The analysis of metabolites in the rumen fluid, milk, and serum showed that several metabolites differed between the HP and LP groups. Correlation analysis between the predominant microbiota and milk yield-associated metabolites (MP-metabolites) revealed that four Bacteria and two Eukaryota genera have a positive relationship with MP-metabolites. Pathway enrichment analysis of the differential metabolites revealed that five pathways were enriched in all the samples (two pathways in the milk, two pathways in the serum, and one pathway in the rumen fluid). Further investigation revealed that the low milk yield observed in the LP group might be due to an upregulation in dopamine levels in the rumen fluid and milk, which could inhibit the release of prolactin or suppress the action of oxytocin in the udder resulting in reduced milk yield. On the other hand, the high milk yield in the HP group is attributed to an upregulation in citrulline, and N-acetylornithine, which could be used as substrates for energy metabolism in the citric acid cycle and ultimately gluconeogenesis.

Using a multi-omics approach to explore potential associations with rumen content and serum of cows with different milk production levels based on genomic predicted transmitting ability for milk and phenotypic milk production

“…A study focusing on the rumen microbial genomes observed that the Refseq database classified only about 50% of reads [ 33 ]. However, it is worth noting that the average milk yield for the low-producing group in our study was still greater than the average milk yield (44.57 kg/d) reported by others for their high-producing group [ 12 ]. Additionally, the two groups considered in the study had a difference of milk production of almost 20 kg/d [ 12 ], for the current study the groups only had a difference in milk production of about 10 kg/d when comparing the high versus low production by GPTAM.…”

“…However, it is worth noting that the average milk yield for the low-producing group in our study was still greater than the average milk yield (44.57 kg/d) reported by others for their high-producing group [ 12 ]. Additionally, the two groups considered in the study had a difference of milk production of almost 20 kg/d [ 12 ], for the current study the groups only had a difference in milk production of about 10 kg/d when comparing the high versus low production by GPTAM. Differences in microbial relative abundances of some bacteria such as Proteobacteria were observed in another study comparing rumen microbial communities and metabolites of high versus low producing cows [ 10 ].…”

“…A study was conducted comparing the rumen microbiome of high and low-producing Holstein cows [ 12 ]. It was observed that several Archaea , Bacteria , Eukaryota , and Viruses differed between high versus low producing dairy cows using rumen metagenomics.…”

“…These studies observed that there are different populations and metabolite markers at different levels of milk production [ 8 , 9 ]. Few have considered the effects of the microbiome and metabolome together [ 10 – 12 ]. These studies observed that there were differences in the relative abundance of some bacteria as well as metabolic differences in cows with different milk production levels.…”