Cooling cows with sprinklers: Effects of soaker flow rate and timing on behavioral and physiological responses to heat load and production.

Spray strategies (e.g., flow rate and spray timing) may affect the surrounding microclimate and how cows use soakers, affecting cooling efficiency. Our objective was to evaluate the combined effects of spray timing (i.e., frequency, low: 3 min on, 6 min off; or high: 1.5 min on, 3 min off) and flow rates (3.3 or 4.9 L/min) on behavioral and physiological responses to heat load and production in Holstein cows managed in a freestall barn. In a 2 × 2 Latin square design, 3 cohorts of 4 pairs of cows averaging (±standard deviation) 36.7 ± 5.4 kg/d of milk were tested for 3 d/treatment. Water was sprayed at the feedline from 0815 to 2330 h when air temperature and relative humidity averaged 27 ± 3°C and 37 ± 7%, respectively. The overall quantity of water sprayed was not affected by spray timing; it varied only as a function of flow rate. Cows' posture and location within the pen were measured continuously, whereas feeding and body temperature were recorded every 3 min over 24 h/d. Respiration rates were recorded daily every 45 min from 0900 to 2000 h. Neither spray timing nor flow rates affected posture, location in the pen, feeding activity, or respiration rates. Overall, on average, cows spent 12.6 ± 0.4 h/d lying down and 5.8 ± 0.3 h/d in the feed bunk area. While in the feed bunk area, cows spent 78 ± 3% of their time feeding. Average respiration rate ranged from 57 to 59 ± 3 breaths/min across treatments. Although body temperature tended to be reduced when using higher flow rate, this difference was 0.1°C when comparing 24-h averages (4.9 vs. 3.3 L/min: 38.6 vs. 38.7 ± 0.1°C). Body temperature differences, however, were more marked and statistically different when soakers were cycling, especially between 1100 and 2200 h. Despite this, the magnitude of the hourly differences were <0.2°C. Milk production also tended to increase by 1.5 kg/d when using higher flow rates. When using the same water volume, spray timing did not affect cow behavior, physiology, or production. Flow rate had a small effect on milk production and body temperature but the biological relevance of these differences is unclear, especially in this situation where all cows were relatively cool.