This study examined the effects of HS on follicular
dynamics and luteal function during the development
of the preovulatory follicle of lactating dairy cows. In
this study (Figure 3) and a companion study (29),
serum estradiol was lower in HS cows than in TN
cows. Other researchers ( 9 ) have reported a smaller
proestrus rise in estradiol in HS cows housed in environmental
chambers. When follicular growth was
monitored, HS cows had lower estradiol when the
first wave dominant follicle was establishing
dominance (31). Although some studies show an adverse
effect of HS on estradiol, others reported
equivalent (23) or greater (24) estradiol in HS cows.
The inconsistencies in estradiol response to HS may
be due to differences in the physiological status of the
cattle or the severity or nature (chronic vs. acute) of
the HS in the experiment.