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

Abstract This study aims to investigate shifts in methane (CH 4 ) 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 CH 4 and carbon dioxide (CO 2 ) levels in the breath, continuously and at a frequency of 4 Hz. The second goal pursued, was to assess the methane emission estimation (CH 4 , L/h) by the CO 2 -method based on the ratio between CH 4 and CO 2 in the exhaled air, using metabolic CO 2 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 CH 4 :CO 2 ratio, eructation frequency and CH 4 emission) followed the same trend and showed that cows on a hay-based diet produced more CH 4 and feed restriction induced different production levels for the same type of diet. The average CH 4 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 4 emissions than HAY100 and reduced the eructation frequency by 44%. During feeding, the eructation frequency was higher ( P 4 emission dynamics observed using the CH 4 :CO 2 ratio in the cow's exhaled air. Methane emissions (L/h) are strongly influenced by the time after feeding time ( P P