Using a Model to Compare Cooling System Design Factors For Lactating Cows

Abstract

Highlights Cow mass, milk yield, solar load, air velocity, dry-bulb and dew-point temperature impact lactating cow respiration rates. Modeled respiration rates align with published studies dealing with milk yield, solar load, and evaporative cooling. The model can be used to assess cooling systems for conditions that might be difficult to capture in field measurements. Abstract. The risk of lactating cows experiencing heat stress is increasing because of increased productivity. A steady-state process-based model described by Nelson and Janni (2023) and assessed by Janni et al. (2023) was used to compare additional combinations of environmental conditions (e.g., air dry-bulb and dew-point temperatures, air velocity, solar load) and lactating cow characteristics (e.g., body mass and daily milk yield) on modeled respiration rate. Respiration rate was linked to qualitative heat stress levels, based on work by Renaudeau et al. (2012). The model demonstrates how cows with greater body mass have larger inspired volumes of respired air (i.e., liters per minute) because they have larger tidal volumes (i.e., liters per breath) while they have lower respiration rates (i.e., breaths per minute) compared to cows with smaller body masses. The modeled results support previous studies that demonstrated heat stress increases with greater daily milk yields, solar load, and air dry-bulb and dew-point temperatures. The model finds conditions where increasing air velocity at cow level can help cows reduce heat stress levels due to solar load, and high air dry-bulb and dew-point temperatures. A comparison to a field study demonstrates the need to align field data collection and model input needs to explore the actual or potential impacts of mitigation methods like shade, evaporative cooling, and air velocity (i.e., via fans). This report demonstrates how the model can be used by engineers to investigate the impact of ventilation system designs on respiration rates using current and future technologies. Keywords: Air velocity, Cow mass, Dairy, Dew-point temperature, Dry-bulb temperature, Heat stress, Milk yield, Respiration rate, Solar load.