Lactational performance of dairy cows fed ad libitum grass silages of different quality supplemented with concentrates high or low in locally sourced ingredients.

Grass silage is central to Nordic dairy cow diets, but its variable quality - affected by weather and growing conditions - necessitates protein supplements. High-protein concentrates are used to optimize diets, but often include significant amounts of imported protein ingredients, negatively impacting sustainability and regional feed self-sufficiency. We evaluated possible interactive effects between concentrates containing a higher share of imported ingredients with soy (Control) as a protein source or higher share of locally sourced ingredients with alkalized barley (Alka) as a protein source, combined with two grass silage qualities differing in organic matter digestibility (OMD; HighOMD and LowOMD), on dry matter intake (DMI), digestibility, and milk production. The study involved 40 Norwegian Red (NRF) dairy cows in a continuous 2 × 2 factorial design experiment over 63 days (21-d adaptation, 42-d measurements). All cows received grass silage ad libitum, with concentrate allowance optimized based on Control, then replaced quantitatively by Alka for relevant groups. Results revealed no interactions between concentrate type and grass silage quality. HighOMD silage improved grass silage DMI and nutrient digestibility (P < 0.001). A greater concentrate allowance for cows fed LowOMD silage compensated for the lower nutritional value of the basal diet in terms of milk production. Feed use efficiency was lower for cows fed LowOMD silage (P = 0.007). In conclusion, concentrates with a higher inclusion of locally produced ingredients and alkalized barley as a protein source can replace concentrates with a higher share of imported ingredients and soy protein when fed in combination with differing grass silage qualities.