Improving robustness and accuracy of predicted daily methane emissions of dairy cows using milk mid-infrared spectra

BACKGROUND

A robust proxy for estimating methane (CH₄ ) emissions of individual dairy cows would be valuable especially for selective breeding. This study aimed to improve the robustness and accuracy of prediction models that estimate daily CH₄ emissions from milk Fourier transform mid-infrared (FT-MIR) spectra by (i) increasing the reference dataset and (ii) adjusting for routinely recorded phenotypic information. Prediction equations for CH₄ were developed using a combined dataset including daily CH₄ measurements (n = 1089; g d^-1 ) collected using the SF₆ tracer technique (n = 513) and measurements using respiration chambers (RC, n = 576). Furthermore, in addition to the milk FT-MIR spectra, the variables of milk yield (MY) on the test day, parity (P) and breed (B) of cows were included in the regression analysis as explanatory variables.

RESULTS

Models developed based on a combined RC and SF₆ dataset predicted the expected pattern in CH₄ values (in g d^-1 ) during a lactation cycle, namely an increase during the first weeks after calving followed by a gradual decrease until the end of lactation. The model including MY, P and B information provided the best prediction results (cross-validation statistics: R² = 0.68 and standard error = 57 g CH₄ d^-1 ).

CONCLUSIONS

The models developed accounted for more of the observed variability in CH₄ emissions than previously developed models and thus were considered more robust. This approach is suitable for large-scale studies (e.g. animal genetic evaluation) where robustness is paramount for accurate predictions across a range of animal conditions. © 2020 Society of Chemical Industry.

A comparative study on the experimental and calculated results of mid-infrared and Raman vibrational modes of nucleic acid bases

The MIR (mid-infrared) and Raman spectra of the nucleic acid base powders were tested by Fourier transform infrared spectroscopy and laser Raman spectroscopy. The vibrational modes of nucleic acid base crystals were simulated by the generalized energy-based fragmentation approach under periodic boundary conditions (hereinafter referred as PBC-GEBF) together with Guassian09 software. Taking into account the intermolecular hydrogen bonds in the unit cell and the weak interactions between the unit cells, the PBC-GEBF method adopted by our group was for the first time used for calculating nucleic acid base crystals in the 400-2000cm^-1 band. The theoretical and experimental spectra turn out to be in good agreement with each other. Compared with the calculated results of the nucleic acid base monomer, the calculated results of crystals appear to be in better agreement with the experimental results. Some weak vibration peaks were reproduced by simulation, and the positions of the vibration peaks agree well. By analyzing the vibrational modes, it can be observed that the vibrational modes below 1000 cm^-1 are mainly characterized by the collective vibrations involving all the molecules in the unit cell. In addition to intramolecular interactions, weak intermolecular interactions (including Van der Waals force and weak hydrogen bond) and the lattice stacking force also contribute to the overall vibrations. This study is of great importance to the analysis of the stability of RNA/DNA structures and their genetic properties.