Relationship of Fertility to Patterns of Ovarian Follicular Development and Associated Hormonal Profiles in Dairy Cows and Heifers

Ovarian follicular development, hormonal patterns, and fertility were compared for growing and persistent follicles in 98 lactating dairy cows and in 89 heifers. Pregnancy rates were greater in animals that ovulated the first-wave dominant follicle while it was growing (GF) vs persistent (PF; for cows 54.2 vs 14.0%, P < .001; for heifers 62.0 vs 35.9%, P < .05). Follicles were larger in cows than in heifers (P < .05). Preovulatory growth rate (mm/d) for PF in cows was parallel to that of GF in both groups; in heifers, PF grew more slowly. At estrus, PF were larger than GF in cows and overall (P < .001), but not in heifers. Estradiol in plasma was greater (P < .05) in animals with PF than in those with GF before estrus (for 6 d in heifers, 8 d in cows). During d -6 through -2, progesterone in plasma tended to be lower (P = .12) in cows with PF than in heifers with PF. Pulse frequency of LH in plasma increased on d 7 in animals with GF and more frequent LH pulses continued through d 13 and 14 in animals with PF. After AI, progesterone in plasma did not differ between GF and PF, in either cows or heifers. However, among cows with GF, progesterone was greater (P < .01) by d 6 to 7 after estrus in pregnant than in nonpregnant cows. In summary, fertility was lower in animals that ovulated a persistent rather than a growing follicle, especially in lactating cows. Lower fertility in animals with PF was associated with prolonged increases in concentrations of LH and estradiol in plasma before estrus and ovulation.