Between-cow variation in milk fatty acids associated with methane production

Area of Science:

• Animal Science
• Nutritional Biochemistry
• Ruminant Physiology

Background:

• Methane (CH4) production in ruminants is influenced by diet and rumen fermentation.
• Milk fatty acids (FA) are potential indicators of rumen function and CH4 emissions.
• Understanding the variation and repeatability of milk FA is crucial for their use as biomarkers.

Purpose of the Study:

• To evaluate the between-cow (b-cow) variation and repeatability of omasal and milk fatty acids (FA) in relation to methane (CH4) emission.
• To investigate the relationship between specific milk FA and stoichiometric CH4 production (Y_CH4VFA).
• To explore the influence of diet and energy balance on milk FA profiles and their association with CH4 emission.

Main Methods:

• Analysis of data from 9 studies involving rumen-cannulated dairy cows using switch-back or Latin square designs.
• Calculation of CH4 production per mole of volatile fatty acids (VFA) based on stoichiometry (Y_CH4VFA).
• Application of univariate and bivariate mixed model regression analysis to assess variation and relationships.

Main Results:

• Dietary variation exceeded b-cow variation for most milk FA, with low to moderate repeatability.
• Odd- and branched-chain fatty acids (OBCFA) showed low repeatability, suggesting potential endogenous synthesis.
• Specific milk FA (e.g., C4:0, anteiso C15:0, C15:0) were related to Y_CH4VFA, but energy balance significantly influenced these associations.

Conclusions:

• Diet is a major driver of milk FA variation, with repeatability varying by FA type.
• Endogenous synthesis of some OBCFA may limit their utility as direct markers for CH4 prediction.
• Energy balance plays a significant role in milk FA composition and their relationship with CH4 emission.