Phenotypic traits related to methane emissions from Holstein dairy cows challenged by low or high forage proportion
Limited literature is available identifying phenotypical traits related to enteric methane (CH4) production from dairy cows, despite its relevance in relation to breeding for animals with a low CH4 yield (g/kg DMI), and the derived consequences hereof. This study aimed to investigate the relationships between CH4 yield and different animal phenotypes when 16 2nd parity dairy cows, fitted with a rumen cannula, were fed 2 diets differing in forage:concentrate ratio in a cross-over design. The diets had either a low forage proportion (35% on DM basis, F35) or a high forage proportion (63% on DM basis, F63). Gas exchange was measured by means of indirect calorimetry. Spot samples of feces were collected, and INDF was used as an internal marker to determine total tract digestibility. In addition, rumen evacuations, monitoring of chewing activity, determination of rumen VFA concentration, analysis of relative abundance of methanogens, and measurement of liquid passage rate were performed. Rumen samples were taken directly though the cannula or via a ruminator. DNA and RNA was extracted from samples and they were subjected to metagenomic and metatranscriptomic sequencing.