Abstract
Abstract Summer season in northwest Mexico is characterized by hot-humid weather conditions that lead to heat stress and affect physiological and productive performance of lactating Holstein cows. Mineral supplementation has been proposed as strategy to alleviate negative effects of heat stress in dairy cattle. Thus, the objective of this study was to evaluate the effect of an injectable mineral supplement on physiological variables and milk production in Holstein cows managed during summer. Sixteen cows were randomly assigned to 1 of 2 experimental groups: Mineral-treated (TRT; n = 8) or control (CON; n = 8). The TRT group received 3 injections of Fosfosan® (10 ml, i.m., Virbac, Uruguay), on days 0, 7 and 17, considering summer onset as day 0 (June 21st), whereas group CON was untreated. Physiological variables such as respiratory rate (RR), vaginal temperature (VT) and skin-surface temperature (SST), were registered twice a week (0500-1700 h) during 6 weeks. Ambient temperature and humidity were collected to calculate the daily temperature and humidity index (THI). Data were analyzed using a mixed model with repeated measures, which included fixed effects of treatment, time and treatment*time, and sire as random effect. According to the THI, Holstein cows were exposed to heat stress during the experiment (>72 units). Cows in the TRT group showed higher (P < 0.05) milk production than CON cows (17.93±0.47 vs 17.02±0.51 kg/day) and lower (P < 0.01) VT (39.14±0.11 vs 39.46±0.15 °C). Relative to CON cows, treated cows also had lower RR (63.16±0.65 vs 64.47±0.76 breaths/min) and lower SST (33.75±0.15 vs 34.02±0.16 °C). All physiological variables showed a significant effect of time (P < 0.01). In conclusion, mineral supplementation during summer appears to improve physiological and productive performance in heat-stressed milking dairy cows; therefore, we suggest to consider this management as strategy to reduce negative effects of summer and heat stress on the dairy industry in northwest Mexico.
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