Effects of calcareous marine algae on performance, rumen fermentation and methane emissions of high-yielding dairy cows

Calcareous marine algae (CMA) products are included in dairy diets as buffers and sources of slow-release calcium. Studies have shown that milk yield, feed intake and rumen fermentation responses to CMA depend on baseline diet. In vitro studies suggest that CMA buffers might lower methane emissions, but this has never been tested in dairy cows. The objective of this study was to determine whether CMA products influence milk yield, feed intake, feed efficiency, rumen pH and volatile fatty acids (VFA), and methane emissions, in high-yielding dairy cows. Products investigated were Acid Buf and Acid Buf 10 (Celtic Sea Minerals, Carrigaline, Ireland), both derived from CMA, with additional Mg of marine origin in the latter. Two experiments were conducted, both involving partial-mixed rations (PMR) and concentrates fed during robotic milking. Experiment 1 used a Latin square design with four diets fed in four three-week periods to 48 cows. The control diet (CON1) was the normal farm diet containing limestone and MgO; these were replaced by Acid Buf for Diet AB1, by Acid Buf 10 for Diet AB+Mg1, and by Acid Buf plus garlic powder for Diet AB+GP. Experiment 2 used a randomised complete block design with three diets fed to 16 cows per treatment for 12 weeks. Diets CON2, AB2 and AB+Mg2 were the same as CON1, AB1 and AB+Mg1, except formulation of the baseline diet changed to allow for different forage composition. Energy-corrected milk yield was higher for AB+Mg1 and lower for AB+GP, compared with CON1. Milk yield was higher for AB2 compared with CON2. Diet did not affect feed intake in either experiment. Rumen pH was higher for AB+Mg1 compared with CON1 and was below pH 6.0 for fewer hours per day for AB+Mg1 and AB+GP. Rumen VFA were not affected by treatment in Experiment 1, but AB+Mg2 had higher total VFA and lower acetate to propionate ratio in Experiment 2. Methane production was lower for all CMA treatments. Methane yield was lower for AB1, AB+Mg1, AB+GP and AB+Mg2, and tended to be lower for AB2. These results suggest that CMA lower enteric methane synthesis by providing an alternative hydrogen sink. It is concluded that milk production and rumen fermentation responses were variable, but CMA products consistently lowered methane emissions in high-yielding dairy cows. • Calcareous marine algae were included in dairy diets as buffers and sources of calcium. • Milk yield was increased by some treatments with no change in feed intake. • Rumen pH was stabilised by long-term feeding of calcareous marine algae. • Calcareous marine algae consistently lowered methane production in all treatments.