Micro-cooling interventions improved the resilience to heat stress of Italian Holstein heifers

The trial was aimed to evaluate nutritional strategies and microstructural interventions to improve the resilience of Italian Holstein heifers under heat stress. The trial lasted 42 d and was performed during summer in Northern Italy. Thirty-six heifers (13.7 mo old; 374.96 ± 35.09 kg live body weight [LBW]) were allocated to 3 experimental groups (n = 12): F, with water-cooled mattresses and a micro-cooling system of feeders and waterers; N, fed twice a day at 0600 h and 2300 h with no coolers; C, fed once a day at 1200 h with no coolers. Temperature and relative humidity were continuously monitored, and temperature-humidity index (THI) calculated. Twice a day, rectal and skin temperature and respira- tion rate were measured. Feed, dry matter, and water intakes (FI, DMI, WI) were measured daily. LBW was recorded weekly, and average daily gain (ADG) and feed conversion ratio (FCR) were assessed. Data were analyzed by the Mixed procedure of SAS for repeated measurements. A significant treatment effect was observed in DMI and FI, but no dif- ference was observed among the groups in WI and LBW. ADG was highest in group F in the third week of the trial (F: 0.76 ± 0.22; C: −0.66 ± 0.22; N: −0.43 ± 0.22 kg/d; P < 0.05), with no differences observed in FCR. Lower respiration rate (F:45.1 ± 1.6; C:54.9 ± 1.6; N:55.1 ± 1.6 breaths/min; P < 0.05), rectal temperature (F:38.7 ± 0.07; C: 38.99 ± 0.07; N: 39.09 ± 0.07°C; P < 0.05), and skin temperature (F: 34.07 ± 0.12; C: 34.7 ± 0.12; N: 34.68 ± 0.12°C; P < 0.05) were recorded when THI was above 75 in group F. Results suggest that heifers subjected to micro-cooling interventions were better able to withstand the summer heat compared with other groups.