Lipid-tannin in vivo
The use of rapeseed as fat source in dairy diet has been known to reduce enteric methane emission. Grape marc, a by-product of wine production, as tannin source has also been observed to reduce methane. However, the effect of feeding rapeseed and grape marc in combination is not known. Four intact lactating Norwegian Red cows were fed four diets in a Latin square cross over design with 11 days of adaptation and 3 days of sample and data collection over 4 periods. The treatments were without additional rapeseed and grape marc in the diet (CON), 4.3 % DM whole cracked rapeseed (FAT), 27% DM dried grape marc (TAN), and 4.2% DM and 27% dried grape marc (FAT&TAN). Methane emissions were measured using GreenFeed System. Feed intake was significantly higher (P < 0.001) due to grape marc treatment. Milk yield and energy-corrected milk were no different due to treatments, but reduction of milk protein (2.9%) was observed in cows fed combination of whole cracked rapeseed and grape marc. Methane yield was reduced when grape marc was part of the diet (28.2%), but reduction was not improved when fed in combination with whole cracked rapeseed. This study highlights the importance of careful consideration for potential interactions between different mitigation strategies, especially those containing compound other than targeted substances.