The time after feeding alters methane emission kinetics in Holstein dry cows fed with various restricted diets

This study aims to investigate shifts in methane (CH4) emission in cattle in relation to the time after feeding, diet composition, and feed allowance. Four non-cannulated dry Holstein cows were equipped with activity and infrared sensors to monitor feeding behavior and CH4 and carbon dioxide (CO2) levels in the breath, continuously and at a frequency of 4 Hz. The second goal pursued, was to assess the methane emission estimation (CH4, L/h) by the CO2-method based on the ratio between CH4 and CO2 in the exhaled air, using metabolic CO2 as a marker. All cows were fed twice a day at 12 h intervals with contrasting isoenergy diets in a cross-over design: LIN100 diet (5562 VEM, i.e. Voedereenheid Melk, Dutch energy unit for milk production, 1 VEM = 6.9 kJ net energy for lactation) composed of haylage, linseed and wheat, and HAY100 (5367 VEM) diet containing only haylage. After a 2 week adaptation period to the diets, 3 days were required for the measurements and immediately after, two additional experimental treatments were applied by reducing the feed allowance to 70% with the same diets to evaluate the impact of the dry matter intake, yielding the two additional treatments HAY70 and LIN70. In addition, two other rumen-cannulated cows were used to monitor time after feeding short-chain fatty acid concentrations in the rumen. On a daily basis, all indicators (daily CH4:CO2 ratio, eructation frequency and CH4 emission) followed the same trend and showed that cows on a hay-based diet produced more CH4 and feed restriction induced different production levels for the same type of diet. The average CH4 emission for the different diets were 6.86 L/h for HAY100 > 6.25 L/h for HAY70 > 4.26 L/h for LIN100 > 3.97 L/h LIN70 (P < 0.001). The LIN100 diet produced 38% lower daily CH4 emissions than HAY100 and reduced the eructation frequency by 44%. During feeding, the eructation frequency was higher (P < 0.001) for HAY than LIN diets.This work underlines the daily CH4 emission dynamics observed using the CH4:CO2 ratio in the cow's exhaled air. Methane emissions (L/h) are strongly influenced by the time after feeding time (P < 0.001). They increased for up to 2 h after the distribution of the meal, and then decreased until the next meal, with shifts between the maximum and the minimum emission of more than 100% for LIN100 and 22% for HAY100. Consistently, the acetate:proprionate ratio was smaller for the LIN100 diet between 2 to 5 h after the meal (P < 0.001).