Reduced fertility / reproduction. In a US trial the percent of inseminated cows that were confirmed pregnant dropped from 30% in winter to 10 to 15% in summer evaluated over three consecutive years. In another study conception rate declined by 5% units for every 10°F above 50°F at the time of insemination (conception rate 67% at 20°F and only 21% at 80°F). Early embryonic deaths account for significant losses in heat stressed cows.