Effect of dairy cows cooling on milk production in Slovakian lowlands

Abstract

<b><sc>Abstract.</sc></b> The study aimed to evaluate the effect of high temperatures on milk production of dairy cows in southern Slovakia in the 2015 year. The hypotheses that milk yield is influenced by the evaporative cooling (fogger and fan) was tested. Production data included 227,500 test-day records belonging to 34 Holstein breed herds situated in lowlands (130 m to 182 m above sea level) and kept in free-stall housing. Herds were allotted into groups according to manner of cooling. The first group of cows (19 herds) was cooled evaporative and forced ventilation, the second group (15 herds) was cooled using only forced ventilation (automatically controlled fans in housing and feeding areas). The meteorological data were recorded continuously at each farm by electronic probes. The data were analyzed using a General Linear Model ANOVA. During the period from May to September, 36 summer and 22 tropical days were recorded, 37 days were with a mean thermal humidity index value above 72.0, on 34 days we recorded mean values above 78.0. Dairy cows cooled by fans with water foggers produced significantly more milk than cows cooled only with forced ventilation (9650.4 kg vs 8528.0 kg; P<0.001). Fat and protein production differed also significantly (364.0 kg vs 329.5 kg, P<0.001; 312.2 kg vs 279.7 kg, P<0.001). It can be concluded that heat stress can cause significant production reduction. Evaporative cooling combined with air movement is the best protection against high temperature stress.