LAUSR

Due to climate change, periods of drought might be longer and occur more frequently, which challenges roughage production and requires changed feeding of dairy cattle by increasing the grain content of the diet. This study investigated the effect of diets with concentrate proportions up to 91% of dry matter on dry matter intake (DMI), milk production, enteric methane emission, rumen fermentation, rumen bacterial community structure, nutrient digestibility, and feeding behavior of Holstein and Jersey dairy cows. Twelve Danish Holstein and 12 Danish Jersey cows were fed ad libitum with one of 3 total mixed rations differing in concentrate proportion in a continuous design with staggered approach over 19 to 29 d. Dietary concentrate proportions were 49% (C49), 70% (C70), and 91% (C91) on dry matter basis, and were based on increasing proportions of chopped barley straw, dried beet pulp, barley, NaOH-treated wheat, dried distillers grain, and rapeseed cake at the expense of grass/clover silage, corn silage and soybean meal. Cows were adapted to the diets over a 12- to 19-d period, before rumination activity was measured over 3 d. Subsequently, spot samples of feces were collected for digestibility determination over 2 d, and gas exchange was measured on the last 3 d of the experimental period. Shortly after chamber stay, rumen liquid was collected using an oro-ruminal device. Dry matter intake was higher for Holstein than Jersey. Methane emissions (all expressions) were affected by the interaction between breed and diet. Methane per kilogram of DMI was lowered by 18 and 48% for Holstein fed C70 and C91, respectively, compared with C49, whereas this was 17 and 22% respectively for Jersey. Rumen propionate molar proportion increased more, rumen bacterial community was less diverse, and rumination time and rumination chews relative to DMI reduced less for Holstein than for Jersey cows with increasing concentrate level. In conclusion, Holstein dairy cows responded stronger to increased dietary concentrate level regarding methane mitigation, changes in rumen VFA profile, and effect on the rumen bacterial community structure than Jersey cows, whereas Jersey cows responded stronger with regard to rumination time and rumination chews (per kilogram of DMI and per kilogram of neutral detergent fiber intake) than Holstein cows. Thus, diets high in concentrates are a less effective methane mitigation strategy for Jersey than for Holstein.