Evaluating management strategies for a pasture-based extended lactation system with 24-month calving intervals

Extended lactation (EL) systems, with calving interval voluntarily extended beyond 12 months, may alleviate dairy sector challenges of labour scarcity and non-replacement calves. This study used bio-economic simulation to investigate how the profitability of an EL system could be improved through strategic management and tested system robustness across different climate and economic years. An EL system with half of cows calving each spring at 24-month intervals was compared with a conventional (Control) system calving all cows each spring. Both systems were modelled with Ruakura climate and Friesian cows at 2.8 cows/ha with > 80% of feed from grazed pasture. Profitability of the EL system was better during years with greater pasture growth, particularly in summer and autumn, and in years with low supplement feed costs relative to milk price. The EL system profitability was improved by shortening grazing rotations in autumn and winter to harvest more pasture. Overall, a strategically managed EL system could achieve similar or improved production, profit and environmental outcomes to Control, provided the herd achieves similar days in milk to the control and has sufficiently lower feed, health and breeding expenses.