Abstract #M216

# M216
A case study to evaluate cooling options in Georgia grazing dairies.
R. M. Orellana*1, J. K. Bernard1, S. Tao1, 1University of Georgia, Tifton, GA.

Heat audits were performed on 3 grazing dairies in Georgia to evaluate cooling systems during summer. 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 twice daily (0400 and 1500 h) and fed a partial TMR. Feeding schedules, facilities, and cooling settings varied among farms. In farm A, cows were fed in an open area equipped with misters for 3.5 h after each milking. In farm B, cows were fed 2 h before and 2 h after each milking in an open ridge barn equipped with overhead sprinklers which operated before PM milking. In farm C, cows were fed for 3.5 h after milking in an open ridge barn installed with fans and soakers over feed bunks. Ten cows per farm were randomly selected and vaginal temperature (VT) was measured every 10 min for 3 d. Cow’s genotype (Holstein or Holstein × Jersey) was determined by phenotype. Environmental data were obtained from local weather stations. Average air temperature and relative humidity during heat audits were 29°C and 70%. Data were analyzed using the mixed procedure of SAS. A farm by hour interaction (P < 0.01) was observed for VT. Around midnight, cows from all farms had similar VT. From AM milking to departure from feedlots, all cows showed a gradual decrease in VT, but cows in farm C decreased the most rapidly. After leaving the feedlots cows from farm B and C had a small increase in VT, but cows on farm A maintained VT. All cows had similar VT during PM milking, but cows in farm A maintained lower VT than cows in farms B and C in feedlots. All cows showed an increase in VT after leaving feeding pens, but the highest VT was observed in cows from farm B, which gradually decreased and remained constant until next day. Regardless of farms, Holstein had lower VT than Holstein × Jersey during PM milking, but higher VT after leaving feedlots (genotype × hour, P < 0.01). In summary, holding pen misting was effective to reduce body temperature and pivot cooling helped to maintain it. Holstein and crossbred cows responded differently to cooling and solar radiation.

Key Words: grazing, cooling, vaginal temperature