Partial replacement of high-fibre forages with corn silage across the lactation cycle: effects on methane emission,...

Feeding high-fibre forages to ruminants facilitates enteric methane emission but may also compromise milk yield. The aim of the present study was to investigate the possibility of reducing methane emission and improving feed conversion efficiency with a forage-based ration by replacing high-fibre forages with corn silage across the whole lactation cycle. Twenty-eight Holstein dairy cows were fed the same close-up diet for 21 days before their second parturition. After calving, cows with a divergent breeding value for functional herd life were equally allocated to a lactation diet containing forage (66% of DM) of either low (LCS; 31.1% DM) or high corn silage (HCS; 37.7% DM) proportion. The increase in the proportion of corn silage was achieved by partial replacement of grass silage, straw, and hay with corn silage. Diets were fed during the whole lactation period for ad libitum intake, and DM intake and milk production were recorded daily. Cows were weighed and evaluated for their body condition score, milk samples were analysed for fat, protein, and lactose, and blood samples were taken for the analysis of glucose, non-esterified fatty acid, beta-hydroxybutyrate, insulin, adiponectin, and IGF-1. In the respiration chambers, methane production, energy balance, and digesta mean retention time were measured and rumen fluid samples were taken for short-chain fatty acid analysis. Cows fed the HCS diet had greater DM intake, milk and energy-corrected milk yield during the whole lactation period than counterparts fed the LCS diet. The molar percent of acetate was lower and that of propionate and butyrate was higher in the rumen fluid of HCS compared to LCS cows. Methane production was not different between groups but methane yield and intensity were lower in the HCS than in the LCS group. Plasma glucose and IGF-1 concentrations were higher and adiponectin, beta-hydroxy butyrate and non-esterified fatty acid concentrations were lower in HCS compared to LCS cows. In contrast, plasma insulin concentrations were not different between groups. In conclusion, partial replacement of high-fibre forages with corn silage in a lactation diet for dairy cows increased metabolisable energy supply via an increase in DM intake and ruminal fermentation efficiency all of which led to an increase in milk production, a better metabolic status, improved feed and energy use efficiency, and reduced methane yield and intensity.