Objective: To describe effects of season on milk production in Holstein dairy cows and to determine the location and effectiveness of fans and sprinklers in the management of stress attributable to season.
Design: Longitudinal observational study.
Animals: 141 dairy herds for which owners used the Dairy Herd Improvement Association's database for production and reproduction record keeping.
Procedure: Owners were interviewed to identify location of fans, shade structures, and sprinklers. Production and reproduction data were retrieved from the database, and a mixed model ANOVA was used to estimate effects of season, parity, and use of sprinklers, and fans on milk production.
Results: Daily peak milk production decreased for all parity groups in the summer, but the effect decreased with increasing days in lactation. Use of sprinklers increased peak milk production in parity-1 and -3 or higher cows, but use of fans did not significantly alter effects of season. After calving in the summer, 305-day milk production decreased in parity-2 and -3 cows. This decrease was not significantly modified by the presence of sprinklers or fans.
Clinical implications: Use of sprinklers may increase peak milk production in high-producing cows and could be recommended for reducing heat and total stress during this time. Production-oriented veterinarians should be cautious when recommending use of sprinklers and fans to increase production because of the wide confidence intervals describing their effectiveness. Management of parity-2 or higher cows so that they calve from October to June could increase 305-day milk production.