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Ten years of records from a 150- head beef cow herd were used to determine the relationship of temperature and temperature-humidity index (THI) on pregnancy rate in beef cows. Pregnancy rate of the herd for the duration of the experiment averaged 92%. There was a linear relationship between average 30-day temperature and pregnancy rate during the first 30 days of the breeding season. Average THI greater than 65 for the first 30 days of the breeding season tended to decrease pregnancy rate in the first 30 days, but there was no effect on herd pregnancy rate. If the 60-day average THI was greater than 70, pregnancy rate for 60 days tended to decrease. Breeding season THI had no effect on pregnancy rate. High temperatures and high temperature-humidity index decrease the pregnancy rate during the first 30 days of the breeding season. Cows acclimate to environmental conditions and if the length of the breeding season is 60 days or more, pregnancy rate is not compromised.