Voluntary heat stress abatement system for dairy cows: Does it mitigate the effects of heat stress on physiology and behavior?

Many cooling strategies are used to keep cows in thermal homeostasis; however, most of them are applied to the group level, commonly at the feed bunk or milking parlor. The variance of heat stress effects on animals are well known, but with more individualized management in dairy farms, group cooling opportunities are becoming restricted. It is known that dairy cattle are variable in their responses to an increase in heat load. Thus, the first objective of this study was to investigate the effect of 2 mandatory soakings at the exit of the milking parlor and free access to a voluntary soaking system compared with cows with access to a voluntary soaking system only, with no mandatory soakings. The second objective of this study was to assess the heat abatement capability of voluntary soaking of cows by assessing cow physiology, behavior, and milk production. Last, this study aimed to determine the individual use of the voluntary heat abatement system and its relationship with temperature-humidity index (THI). Fifteen mid-lactation Holstein cows were enrolled in this study and had free access to a motion-activated soaker (Cool Sense, Edstrom) located adjacent to the research pen for an 8-wk data collection period. Cows were paired according to parity, milk production, and body weight, and assigned a treatment with or without mandatory soakings twice per day. In the mandatory soaking treatment (MS), cows were soaked using a motion-activated soaker at the exit of the milking parlor and had free access to the voluntary soaker in the pen. Cows in the treatment without mandatory soakings (NMS) were not soaked at the exit of the milking parlor and had free access to the voluntary soaker in the pen. The effects of soaker treatment were analyzed using mixed linear models. The model included treatment, soaker uses per day, pair, mean daily THI, days in milk, daily milk yield, and interaction of treatment with mean daily THI. Study day was specified as a repeated measure, and cow as the subject, using an autoregressive structure. Also, we assessed the relationship of mean soaker use and THI against all variables. There was great individual variation in voluntary soaker use, ranging from 0 to 227 soakings/d (mean ± standard deviation, 13 ± 30 voluntary soakings/d). Treatment did not affect voluntary soaker use (MS, 12.4 ± 1.4 soakings/d; NMS, 14.8 ± 1.4 soakings/d), respiration rate (MS, 57.3 ± 0.4 breaths/min; NMS, 56.4 ± 0.4 breaths/min), or milk yield (MS, 36.5 ± 0.6 kg/d; NMS, 36.2 ± 0.6 kg/d). However, MS cows spent more time ruminating (MS, 558.6 ± 5.2 min/d; NMS, 543.4 ± 5.4 min/d). Temperature-humidity index had a positive relationship with voluntary soaker use and mean respiration rate. In conclusion, voluntary soaker use related positively to the THI, but no major productive, physiological, or behavioral differences were observed between soaking treatments. Furthermore, we found that voluntary soaker use is highly variable among cows and it was related positively to milk yield, where higher producing cows used the soaker more frequently.