A higher-output grass-based spring-calving dairy production system in Ireland-Factors influencing performance...

The competitiveness of the Irish dairy industry relies on the efficient utilization of grazed grass. Growth in milk output over the last decade was primarily achieved by increasing herd size rather than cow yield. However, limitations on land, labor, and environmental regulations restricting stocking rates mean higher concentrate input grazing systems, which focus on increased output per cow, merit consideration. From 2016, a multiyear study commenced at University College Dublin investigating a higher-output grazing system, characterized by increased milk solids (MSo; fat kg + protein kg) output and higher concentrate supplementation per cow, by integrating the most recent advances in grassland management, nutrition, and genetics. Approximately 57 spring-calving dairy cows were selected and managed as one herd. The 9-year average herbage yield was 12,560 kg DM/ha, and grass utilization (>4 cm) was 88.4%. Annual grazed grass intake per cow averaged 2,931 kg DM. Interannual variability in daily grass growth and total DM grown led to a wide range in grazed grass consumed per cow (2,260-3,410 kg DM). On average, cows were allocated 1,906 kg DM of grass silage and 1,299 kg DM of concentrate. Farm-gate nitrogen (N) use efficiency, used to estimate the ratio of N input versus output in farm produce, averaged 35% but increased in years when fertilizer use was reduced. Average MSo production (583 kg/cow) and the 6-wk in-calf rate (76.4%) both exceeded national averages over the same period. This study highlights the potential of higher-output grass-based systems to achieve efficient grassland performance and high levels of MSo production per cow. Future research should focus on strategies to improve interyear performance consistency of milk production, fertility, and grassland management, particularly in managing the impacts of climatic variation affecting grass growth. This may include more flexible and responsive concentrate supplementation approaches to offset yield depressions during periods of reduced grass availability.