Comparison of three cooling management systems to reduce heat stress in lactating Holstein cows during hot and dry ambient conditions

The aim of this study was to compare three cooling management systems to improve the physiological status and lactation performance of Holstein cows during summer heat. Multiparous Holstein cows, 32, were blocked according to milk yield divided into four treatments being: C) Control group, cows cooled before milking time (0500 and 1700 h daily); AM) cows cooled at 1100 h and before milking; PM) cows cooled at 2300 h and before milking; and AM + PM) cows cooled at 1100 and 2300 h, as well as before milking. Total cooling time per group was 1 h for the Control group, 2 h for AM and PM groups, and 3 h for the AM + PM group. Cows were moved to a holding pen daily to be cooled. Respiration rate (RR) and rectal temperatures (RT) were lowered (P < 0.05) by treatment in AM + PM compared to control, but body condition scores were similar among groups. Glucose levels of control cows (48.41 mg/dL) were higher (P < 0.01) than cooled cows (44.9 mg/dL) and AM + PM cows (43.12 mg/dL). Other metabolites (i.e., cholesterol, triglycerides) did not differ among treatments, and thyroid hormones (i.e., thyroxin, triiodothyronine) were also similar among the groups. Milk production and milk energy output were higher (P < 0.05) in group AM + PM cows (21.12 kg of milk and 13.6 Mcal per day) than control cows (19.1 kg of milk and 12.6 Mcal per day), but milk fat and protein proportions were similar among the four groups. Even though cows under the cooling management system with the higher number of coolings per day had better performance, their physiological status does not correspond to a those non-heat stressed lactating cows. Results show that it is necessary to increase the time of cooling to effectively reduce heat stress during severe summer heat conditions.