AI. Our assessment of the conception rate of high
producing dairy cows by climate factors proved to be
very valuable (P = 0.98).
Our findings indicate that when the maximum THI
units for Day 3 before AI increased, conception rate
decreased [14,21]. Heat stress can affect many
reproductive variables in cattle including follicular
dynamics [22]. Environmental and stress factors
promote ovulation failure, cows that had failed to
ovulate by Day 50 postpartum following either natural
or synchronized estrus, which is considered the major
cause of infertility in dairy cattle by some authors [23–
25]. In our geographical area of study, Lo´pez-Gatius
et al. [26] described that the only factor that
dramatically affected ovulation was the AI season.
Ovulation failure was 3.9 times higher in cows
inseminated during the warm period (May–September)
compared to the cool period (October–April). High
producing dairy cows commonly suffer metabolic stress
and this added to another stressful effect such as a hot
environment could cause an endocrine imbalance and
finally compromise folliculogenesis