Milk production and methane emissions from dairy cows fed a low or high proportion of red clover silage and an incremental level of rapeseed expeller

This study evaluated the effects of including increasing levels of rapeseed expeller in dairy cow diets with a low or high proportion of red clover silage on milk production and methane emissions. A total of 32 lactating Swedish Red dairy cows were used in a cyclic change-over design with three periods of 21 days, in a 2×4 factorial arrangement of treatments. The total mixed ration consisted of 600 g/kg dry matter (DM) of forage and 400 g/kg DM of concentrate on a DM basis. The forage treatments consisted of a 30:70 or 70:30 ratio of grass to red clover silage (RC30 and RC70). A basal supplement consisted of crimped barley and premix, formulated to contain 130 g CP/kg DM. For the three additional concentrate supplements, crimped barley was gradually replaced with incremental levels of rapeseed expeller to reach 170, 210 or 250 g CP/kg DM. No differences in feed intake were found between RC30 and RC70, but a positive response was found to increased dietary CP concentration from rapeseed expeller. Increasing proportion of red clover silage did not have any effect on production, while increasing dietary CP concentration increased yield of milk, energy corrected milk (ECM) and milk protein. Nitrogen efficiency was higher with diet RC30 than with RC70 and decreased with increasing dietary CP concentration, while milk urea nitrogen increased. Methane (CH4) emissions per unit feed intake decreased with dietary CP concentration and tended to increase with increasing proportion of red clover silage in the diet. Increased CP intake from red clover silage in the diet of dairy cows had no positive effect on CH4 emissions.