females and used to inseminate females maintained in
thermoneutral conditions resulted in similar fertilization
rates but lower embryonic survival than pregnancies
arising from inseminations with spermatozoa
retrieved from females maintained in thermoneutrality.
The oviductal or intrauterine environment could
thus be compromised in heat stressed cows owing to
decreased blood flow to the uterus and an increase in
uterine temperature under heat stress conditions [8].
Given the multiple factors affecting conception rate
and their interactions, we performed two logistic
regressions, one including mean and maximum THI
and temperature variables and the other one only
including the mean and maximum temperature variables.
Although temperature and THI are related
variables, two different results were observed. However,
the two logistic regression models showed similar fits
and the Hosmer–Lameshow index indicated a good
model fit in both analyses (P = 0.88 versus P = 0.98).
Thus, we could not conclude that the temperature–
humidity index is a better predictor of conception rate
than temperature alone. More studies on the direct
effects of temperature and THI are needed to determine
which index is more appropriate to predict the
reproductive performance of high producing dairy
cows