CASE STUDY: Evaluation of cooling in 3 grazing dairy farms in Georgia, USA

Objective: Our objective was to evaluate cooling systems in grazing dairy farms in Georgia during summer. Materials and Methods: This study was conducted during summer 2016 in 3 dairy farms. Farms were managed similarly and used rotary parlors with open holding pens with misters. When grazing during the day, cows were cooled by misters attached to pivots without access to shade. Cows were milked at 0400 and 1500 h and fed a partial mixed ration. In farm A, cows were fed for 3.5 h after each milking in an open feeding; pad with concrete bunks equipped with misters, which operated only during afternoon feeding. In farm B, cows were fed 2 h before and 2 h after each milking in an open ridge barn with concrete feed bunks equipped with overhead sprinklers, which only operated before afternoon milking. In farm C, cows were fed for 3.5 h after milking in an open ridge barn with concrete bunks fitted with fans and soakers over the feed bunks. Ten cows per farm were randomly selected to have their vaginal temperature (VT) measured for 3 d. Cow's genotype (Holstein or Holstein x Jersey) was determined by phenotype. Environmental data were obtained from local weather stations. Results and Discussion: Average air temperature and relative humidity over the 3-d period were 29 degrees C and 70%. A farm by hour interaction (P < 0.01) was observed for VT. From morning milking to departure from feeding areas, VT of all cows gradually decreased, but VT of cows in farm C decreased the most rapidly. After leaving the feeding areas, cows in farms B and C experienced a small increase in VT, but cows in farm A maintained VT. Cows in farm A maintained lower VT than cows in farms B and C while in feeding areas after afternoon milking. The VT of all cows increased after leaving feeding pens, but the highest VT was observed in cows in farm B. Regardless of farms, Holstein cows had lower VT than Holstein x Jersey cows during afternoon milking but higher VT after leaving the feeding areas. Implications and Applications: In summary, holding pen misting was effective for reducing body temperatures, and pivot cooling: maintained VT. Holstein and crossbred cows responded differently to cooling and solar radiation.