Modelling the impact of increasing herd size on milking interval, milk yield and profit in a forage based automatic milking system

The aim of this modelling study was to investigate the effect of herd size on walking distances and milking interval (MI), and their impact on milk yield (MY) and profit when 50% of the total diet was provided from home grown feed either as pasture or grazeable complementary forage rotation (CFR) in an automatic milking system (AMS). Twelve scenarios consisting of 3 AMS herd sizes (400, 600, 800 cows), 2 levels of pasture utilisation (15.0 t dry matter [DM]/ha, termed as ‘moderate’ and 19.7 t DM/ha, termed as ‘high’) and 2 rates of incorporation of grazeable complementary forage system (CFS [pasture+CFR], % farm planted into CFS; 0, 30%) were investigated. Modelled results showed that increased herd size and associated increased walking distances, resulted in increased energy loss and MI of cows, and reduced MY in a pasture-based AMS. However, modelling the integration of grazeable CFR showed the potential to increase MY and financial performance compared to the pasture only, large herd, AMS.