Pasture growth curve impacts the economic merit of extended lactation: a simulation study

Abstract

Voluntarily increasing the calving interval beyond 12-months (extended lactation; EL) has possible benefits in reducing labour requirements, herd replacement rate, and surplus calf numbers. With limited information on feed balance and economic effects with EL, reductions in profitability were hypothesised. A MS Excel spreadsheet model was developed to compare calving systems: spring calving annually (Base), two herds between spring and autumn calving with 18-month calving intervals (EL18), or two herds calving in alternating springs with 24-month intervals (EL24). Weekly feed balances using pasture growth curves for four regions (Northland, Waikato, Canterbury, Southland) and partial budget analysis informed estimations of supplement costs and net income (NI). The EL24 system had lower supplement costs (-$240 /ha) and higher NI (+$439 /ha) than the Base system for Northland only. The EL18 systemalways had the highest annual milk production and total revenue, but highest supplement costs and lowest NI in the four regions. Replacement, calving, and mating costs were lower for EL systems than Base; however, costs for milking and repairs and maintenance were higher. This preliminary study indicates there is merit in investigating EL systems, particularly for Northland. Further data from EL systems are needed to increase confidence in the system’s potential.