title: Resumption of follicular activity in the early post-partum period of dairy cows.
abstract: Lactating Friesian dairy cows (2nd-4th parity) which calved in spring (N = 7) or autumn (N = 15) were used. Their ovaries were examined by ultrasound scanning and blood samples were obtained daily for progesterone and oestradiol concentrations from the 5th day after calving until the first post-partum ovulation occurred. Five autumn-calving cows selected at random were bled every 15 min over a 6-h period on 1 day each week for 4 weeks after calving to assess the patterns of LH secretion. Follicular development during the post-partum anoestrous period was characterized by the growth and regression of small (less than or equal to 4 mm) and medium-sized (5-9 mm) follicles, until a dominant follicle (greater than 10 mm) was detected. The first detected dominant follicle ovulated in 14 cows, became cystic in 4 cows (all in autumn), and failed to ovulate in 1 cow. It was not possible to detect a dominant follicle in 3 cows due to scanning difficulties. The post-partum interval to detection of the first dominant follicle (mean +/- s.d.) was shorter (P less than 0.05) in autumn (6.8 +/- 1.8 days) than in spring (20 +/- 10.1 days). However, there was no significant difference between the respective intervals to first ovulation (autumn 27.4 +/- 25.9 and spring 27.3 +/- 18.9 days). Autumn-calved cows which had cysts had longer (P less than 0.001) intervals to first ovulation (58.2 +/- 23.5 days) than did normal cows (12.0 +/- 2.5 days). All cows with cysts had twin ovulations at their first post-partum ovulation. A pulsatile pattern of LH secretion was detected in the first week post-partum and LH pulse frequency was 2-3 per 6-h period in Weeks 1 and 2 post partum and increased to 5-7 pulses per 6-h period in the presence of a dominant or cystic follicle. Concentrations of progesterone in plasma during post-partum anoestrus were usually low (less than 0.2 ng/ml); oestradiol concentrations were also low (less than 5 pg/ml), but higher values (5-110 pg/ml) were observed in cows that had a dominant or a cystic follicle.
authors.affiliation: Faculty of Veterinary Medicine, University College Dublin, Ireland.
authors.forename: J D
authors.initials: JD
authors.lastname: Savio
authors.forename: M P
authors.initials: MP
authors.lastname: Boland
authors.forename: N
authors.initials: N
authors.lastname: Hynes
authors.forename: J F
authors.initials: JF
authors.lastname: Roche
mesh_terms: D000818:Animals; D002417:Cattle; D004958:Estradiol / Q000097:blood; D005260:Female; D007774:Lactation / Q000502:physiology*; D007986:Luteinizing Hormone / Q000097:blood; D006080:Ovarian Follicle / Q000033:anatomy & histology / Q000502:physiology*; D010060:Ovulation / Q000502:physiology; D049590:Postpartum Period / Q000502:physiology*; D011247:Pregnancy; D011374:Progesterone / Q000097:blood; D014463:Ultrasonography
chemical_list: D011374:Progesterone; D004958:Estradiol; D007986:Luteinizing Hormone