In the cow, estrus is stimulated by the rise in estradiol from the preovulatory follicle. This rise also triggers the surge of LH that occurs near the onset of estrus. When the preovulatory surge of LH occurs, it causes estrogen secretion by the  follicle to cease and the follicle is gradually converted to the progesterone-secreting corpus luteum. Ovulation typically occurs in cattle about 25-30 hours after the onset of estrus and the LH surge that occurs around the same time. Estrogen secretion does not continue much beyond the onset of estrus.

Estrogen hormone (the cause of external signs of estrus) is secreted by the theca interna of the active growing dominant follicle. This follicle is called estrogen dominant (E2/P4 ration is high = estrogen is higher than progesterone content). After LH surge, the follicle is stopped growing (plateau stage) and changed from estrogen to progesterone  dominant (E2/P4 ratio is low = progesterone more than estrogen).

see also the attached paper  

Cows that have been primed with progesterone, either through secretion of progesterone by the corpus luteum or with a progesterone device like a CIDR, will show estrus much more strongly and longer than cows that are exposed to estrogen without priming with progesterone. That is why many cows do not show estrus at 1st ovulation.

Thanks for your responses. 

In the cow several follicles mature before and during oestrus. The early follicle(s) produces oestrogen with resultant oestrus and is followed by the development of a corpus luteum secreting progesterone. Then follows maturation and ovulation of the second follicle. At this time oestrus is inhibited by the progesterone produced by the earlier developing CL. As mentioned by Dr Britt cows do not show oestrus at first ovulation see ((Carrick & Shelton (1969) J.Endocrinol.  45; 99-109.))

Cows ovulate after the end of heat signs, while mares, sheep and goats ovulate toward or before the end of heat. Differences in the FSH/LH ratio among those animals might also explain the differences in estrus duration and time of ovulation in relation to the end of heat signs.  

Estrogens should be secreted  by granulosa cells of ovarian folicle(s) where theca produced androgens are converted by aromatase .

  Is this paradigm changed ?

I agree with the answer provided by Mr.  Ahmed Ali.