Abstract
This experiment was designed to investigate the relation of high and low methane-yield phenotypes with body weight (BW), dry matter intake (DMI), lactation performance, enteric CH4 emissions, and rumen fermentation parameters in lactating dairy cows. A total of 130 multi- and primiparous Holstein cows were screened for enteric CH4 emissions using the GreenFeed system (C-Lock Inc.). Out of these 130 cows, 5 were identified as phenotypically high (HM) and 5 as phenotypically low (LM) CH4 emitters. Cows in the LM group had lower daily enteric CH4 emissions than cows in the HM group (on average 346 vs. 439 g/d, respectively), lower CH4 yield (15.5 vs. 20.4 g of CH4/kg of DMI), and CH4 intensity (13.2 vs. 17.0 g of CH₁/ kg of energy-corrected milk yield). Enteric emissions of CO2 and H2 did not differ between HM and LM cows. These 10 cows were blocked by parity, days in milk, and milk production, and were used in a 5-wk randomized complete block design experiment. Milk composition, production, and BW were also not different between LM and HM cows. The concentration of total volatile fatty acids in ruminal contents did not differ between CH4 phenotypes, but LM cows had a lower molar proportion of acetate (57 vs. 62.1%), a higher proportion of propionate (27.5 vs. 21.6%, respectively), and therefore a lower acetate-to-propionate ratio than HM cows. Consistently, the 16S cDNA analysis revealed the abundance of Succinivibrionaceae and unclassified Veillonellaceae to be higher in LM cows compared with HM cows, bacteria that were positively correlated with ruminal propionate concentration. Notably, Succinivibrionaceae trigger the formation of propionate via oxaloacetate pathway from phosphoenolpyruvate via Enzyme Commission: 4.1.1.49, which showed a trend to be higher in LM cows compared with HM cows. Additionally, LM cows possessed fewer transcripts of a gene encoding for methyl-CoM reductase enzyme compared with HM. In this study, low and high CH4-yield cows have similar production performance and milk composition, but total-tract apparent digestibility of organic matter and fiber fractions was lower in the former group of animals.
Generated Summary
This experiment investigated the relationship between high and low methane-yield phenotypes in lactating dairy cows, focusing on their body weight (BW), dry matter intake (DMI), lactational performance, enteric CH4 emissions, and rumen fermentation parameters. A total of 130 Holstein cows were screened for enteric CH4 emissions using the GreenFeed system. From this initial screening, 5 cows with high methane emissions (HM) and 5 cows with low methane emissions (LM) were identified. The study employed a 5-week randomized complete block design to analyze milk composition, production, and BW differences between the groups. Rumen fermentation variables and microbial composition were also examined, along with an assessment of the relationship between CH4 emission phenotype and genomic estimates in lactating Holstein cows. The researchers hypothesized that selecting for the LM phenotype would lead to shifts in rumen fermentation, similar to chemical CH4 inhibition, which could lead to a decreased acetate proportion and an increased propionate proportion, and subsequent shifts in the microbial community and gene expression without affecting animal production performance.
Key Findings & Statistics
- The LM group had lower daily enteric CH4 emissions than the HM group (346 vs. 439 g/d, respectively), lower CH4 yield (15.5 vs. 20.4 g of CH4/kg of DMI), and lower CH4 intensity (13.2 vs. 17.0 g of CH₁/ kg of energy-corrected milk yield).
- The concentration of total volatile fatty acids in ruminal contents did not differ between CH4 phenotypes.
- LM cows had a lower molar proportion of acetate (57 vs. 62.1%), a higher proportion of propionate (27.5 vs. 21.6%), and therefore a lower acetate-to-propionate ratio than HM cows.
- The HM and LM groups of cows averaged lactation numbers of 1.8 ± 1.09 and 1.8 ± 1.09, DIM 250 ± 10.6 and 247 ± 26.3 d, DMI 21.8 ± 1.73 and 23.4 ± 2.70 kg/d, and MY 32.9 ± 3.94 and 35.0 ± 3.97 kg/d at the beginning of the study, respectively.
- Cows with HM phenotype had 93 g/d greater daily enteric CH4 emissions and 24% greater CH4 emission yield than LM cows (P < 0.03).
- Similarly, CH4 emission intensity (per kg of milk yield or ECM yield) was greater (P = 0.03) for the HM group compared with LM.
- The molar proportion of acetate was 8.2% higher (P = 0.03) in HM than in LM cows.
- The molar proportion of propionate was 21.5% lower (P = 0.01) for the HM phenotype.
- The acetate-to-propionate ratio was greater (P = 0.01) in the HM animals.
- The molar proportion of isobutyrate was greater (P = 0.04) for the HM phenotype compared with LM.
- Cows with the HM phenotype had greater (P = 0.03) total-tract DM and OM digestibility.
- Similarly, the digestibility of NDF and ADF was also greater (P < 0.02) in HM than in LM cows.
- In the current study, gPTA parameters revealed that HM animals had genetic potential for an overall greater frame size, accompanied by a greater composite BW.
- The relative abundance of Methanobrevibacter showed a numerical increase (P = 0.15) in HM compared with LM cows, whereas Methanosphaera was higher (P = 0.02) in LM cows.
- The bacteria-to-archaea ratio was approximately 50% in LM cows and only 34% in HM cows.
- HM emitters differ by 21% in daily CH4 emissions, 24% in CH4 yield, and 22% in CH4 intensity compared with LM cows.
- Transcripts for the MCR enzyme averaged at 12,033 cpm, which showed a trend to be higher (P = 0.069) in HM cows than the 6,050 cpm in LM cows.
Other Important Findings
- The 16S cDNA analysis revealed that the abundance of Succinivibrionaceae and unclassified Veillonellaceae was higher in LM cows compared with HM cows.
- Succinivibrionaceae trigger the formation of propionate via oxaloacetate pathway.
- LM cows possessed fewer transcripts of a gene encoding for methyl-CoM reductase enzyme compared with HM.
- The study found that low and high CH4-yield cows have similar production performance and milk composition.
- Total-tract apparent digestibility of organic matter and fiber fractions was lower in the former group of animals.
- Enteric emissions of CO2 and H2 did not differ between HM and LM cows.
- Milk composition, production, and BW were also not different between LM and HM cows.
- In the current study, LM cows had a numerically greater DMI compared with HM cows, and LM cows appeared to select for a bacterium that directs H₂ from methanogens toward more propionate formation.
- HM cows had a genetic potential to be taller in stature (P = 0.003), have greater body depth (P = 0.03), and have a tendency for a greater rump width (P = 0.09).
- Differences between HM and LM cows were observed for weighted communities at 12 h and 16 h in the cDNA-based archaeal communities.
- The relative abundance (percentage) of Methanosphaera was higher and Methanobrevibacter was lower in cDNA-based communities compared with DNA-based communities.
- Bacteroidetes and Proteobacteria had greater relative abundance in the LM group compared with the HM group of cows.
- In the LM cows, the enzyme that converts formate to CO2 had lower gene copy and transcript counts.
- Transcripts of the same genes coding for MCR enzymes were much higher in copy numbers relative to the respective gene copy numbers across all animals, suggesting a greater activity of this enzyme.
Limitations Noted in the Document
- The study involved a relatively small sample size, which may have limited the statistical power to detect significant differences in some parameters.
- The authors noted that observations related to milk yield and milk composition reported here must be interpreted with caution due to variability.
- The study did not detect Quinella lineages in the rumen of dairy cows.
- The magnitude of increase in the specific bacterial genera in LM cows was not comparable to the findings of Kamke et al. (2016).
Conclusion
The study successfully identified differences in methane emissions between high and low emitting dairy cows, which were associated with specific rumen fermentation profiles and microbial community compositions. The HM cows had higher methane emissions, yield, and intensity compared to LM cows. The findings suggest that the LM phenotype leads to changes in fermentation, with a decrease in acetate and an increase in propionate, a shift which resembles chemical CH4 inhibition. The distinct microbial communities, with an increased abundance of Succinivibrionaceae in the LM cows, are associated with propionate production. The genomic analysis indicated that HM cows showed a potential for a larger frame size and greater BW, while the gPTA parameters related to milk yield and composition did not differ between the two phenotypes. However, it should be noted that observations related to milk yield and milk composition reported here must be interpreted with caution due to variability. The study’s findings highlight that differences in CH4 emissions are linked to the activity of the MCR enzyme, and also correlate with shifts in bacterial and archaeal networks and pathways that lead to propionate formation in LM cows. This study provides an understanding of the relationship between host genetics and the microbiome. As with past studies, it appears that differences in CH4 emissions were accompanied by differences in the gene and transcript copy numbers of the enzyme that is responsible for CH4 formation in the rumen. The results suggest that host genotype may influence the selection of specific bacterial populations. Ultimately, this research provides insight into the potential for selective breeding to reduce methane emissions in dairy cows, although caution is advised regarding potential impacts on milk production and digestibility.