Effects of extending dairy cow longevity by adjusted reproduction management decisions on partial net return and greenhouse gas emissions: A dynamic stochastic herd simulation study

Abstract

Prolonging dairy cattle longevity is regarded as one of the options to contribute to more sustainable milk production. Since failure to conceive is one of the main reasons for culling, this study investigates how adjustments in reproduction management affect partial net return at herd level and greenhouse gas emissions per unit of milk, using a dynamic stochastic simulation model. The effects of reproduction decisions that extend cattle longevity on milk yield, calving interval and pregnancy rate were derived from actual performance of Dutch commercial dairy cows over multiple lactations. The model simulated lactations, calving and health status events of individual cows for herds of 100 cows. Scenarios evaluated differed in the maximum number of consecutive artificial insemination (AI) attempts (4, 5 or 6 services), or the production threshold (20, 15, or 10 kg milk per day) at which cows that failed to conceive are culled (reproductive culling). Annual partial net return was computed from revenues of sold milk, calves and slaughtered cows, and the costs from feed consumption, rearing replacement heifers, AI services and treatment for clinical mastitis and lameness. Greenhouse gas emissions were computed for feed production, enteric fermentation, and manure management, and were expressed as total CO2 equivalents. Average age at culling increased with an increased maximum number of AI services. This increase was larger when going from a maximum of 4 to 5 AI attempts (108 d) than from a maximum of 5 to 6 attempts (47 d). Similarly, the average age at culling increased from 1,968 to 2,040 and 2,132 d when the threshold for reproductive culling decreased from 20, to 15 and 10 kg milk per day, respectively. Average annual partial net return increased by 1.1% from €165,850 per 100 cows at a maximum of 4 AIs to €167,670 per 100 cows at a maximum of 6 AIs, and increased by 4.3% from €161,210 per 100 cows at a reproductive culling threshold of 10 kg/day to €168,190 per 100 cows at a threshold of 20 kg/day. Greenhouse gas emissions decreased by 1.2% from 0.926 to 0.915 kg CO₂ equivalents per kg fat-and-protein-corrected milk (FPCM) with an increase in a maximum number of AIs from 4 to 6 AIs. Conversely, greenhouse gas emissions increased by 0.2% from 0.926 kg at a threshold of reproductive culling of 20 kg/day to 0.928 kg CO₂ equivalents per kg FPCM at a threshold of 10 kg/day. Although lowering the threshold for reproductive culling has the potential to extend cattle longevity more than increasing the maximum number of AI services, only the increase in AI services benefits a farm's partial net return, while reducing greenhouse gas emissions.

Keywords: dairy cow longevity; greenhouse gas emissions; partial net return; reproduction management decisions.