Effects of dietary active dried yeast (Saccharomyces cerevisiae) supply at two levels of concentrate on energy and nitrogen utilisation and methane emissions of lactating dairy cows

Twenty early lactation dairy cows were used to evaluate the effects of the dietary addition of an active dried yeast product at two levels of concentrate on productive performance, nutrient digestibility, methane (CH4) emissions and energy and nitrogen utilisation. This study was a replicated 4 x 4 Latin square design with a two (concentrate level) x two (yeast supplement) factorial treatment arrangement, with four periods (6 week/period) and a 3-week interval between each period. Cows were offered grass silage-based diets consisting of two levels of concentrate (300 and 600 g/kg), with or without supplement of 0.5 g/day of an active dry yeast (Saccharomyces cerevisiae strain) with a specification of 2 x 10(10) cfu/g. Feed dry matter intake, milk yield, milk composition, bodyweight and body condition score were similar between yeast treatments at both concentrate levels. Nutrient digestibility was not affected by yeast supplementation. Energy intake and faecal, urinary, CH4 and milk energy outputs were also not affected by yeast supplementation. Yeast supplementation had no effects on energy partitioning but tended to increase heat production and decreased energy retention. Yeast supplementation at two levels of concentrate had no effect on total CH4 emissions, but tended to increase CH4 per unit of feed intake and CH4 energy output per unit of gross energy intake. There were no effects of yeast supplementation on CH4 per unit of milk yield. Yeast supplementation had no effect on any variable of nitrogen intake, output or utilisation. Overall, the dietary addition of an active dried yeast product at two concentrate feeding levels had no effects on feed intake, milk production, milk composition, nutrient digestibility, or nitrogen utilisation efficiency and only tended to increase heat production, CH4 per unit of feed intake and CH4 energy output per unit of gross energy intake in lactating dairy cows.