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J. D. Savio, M. P. Boland and J. F. Roche

Summary. The resumption of ovarian activity after normal calvings was studied in 18 lactating Friesian cows. Since, in 17 cows, first post-partum ovulation occurred without overt oestrous behaviour being detected, the resultant cycles were called 'ovarian cycles'. The mean (± s.d.) length of the ovarian cycles was 21·0 ± 8·7 days. The duration of cycles tended to be normal (18–24 days) or long (≥25 days) when the ovulatory dominant follicles were identified before Day 10 post partum; they were consistently short (9–13 days) when dominant follicles identified after Day 20 post partum ovulated. When such follicles were detected between Days 10 and 20 post partum, long, normal and short ovarian cycles were detected. The number of waves of follicular growth with associated dominant follicles observed during the ovarian cycles tended to be related to cycle length; short cycles had 1 dominant follicle, normal cycles predominantly 2, and long cycles mostly 3 dominant follicles. The mean (± s.d.) duration of 13 oestrous cycles studied was 23·1 ± 2·1 days. Of these cycles, 7 had 3 and 6 had 2 dominant follicles. The oestrous cycles with 3 dominant follicles had a mean (± s.d.) duration of 24·0 ± 1·2 days and the respective dominant non-ovulatory follicles reached maximum sizes on Days 8 and 18, respectively; oestrous cycles with 2 dominant follicles were 22·2 ± 2·6 days in duration, and the dominant non-ovulatory follicle reached maximum size by Day 8. Ovarian follicular development during the first 45 days of pregnancy was characterized by the growth and regression of successive dominant follicles, each lasting 10–10 days. These results show that the first ovarian cycle was predominantly short when the ovulatory dominant follicle was first detected after Day 20 post partum.

Keywords: dairy cow; dominant follicle; post partum; ovarian activity; ultrasound

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J. D. Savio, W. W. Thatcher, L. Badinga, R. L. de la Sota and D. Wolfenson

The effect of progestin and luteinizing hormone (LH) pulse frequency on dynamics of dominant follicle growth during the first follicular wave after oestrus was examined in non-lactating Holstein cows by ultrasonography. On day 8 of the cycle, cows (n = 8) received a luteolytic dose of prostaglandin F (PGF; 25 mg) and an ear implant of Norgestomet (6 mg). On day 18, cows were assigned to a crossover design in which the implants were retained (T1) or replaced with a new implant (T2). All implants were removed on day 23. After oestrus, cows underwent a normal intervening oestrous cycle. On day 8 of the third cycle, T1 and T2 were reversed among cows. Ultrasonography and blood sampling were performed on alternate days throughout the experiment. On days 10 and 19 of the third cycle, blood was sampled every 15 min for 8 h in concert with an additional control group (n = 3) sampled on day 10 of the cycle. Progesterone concentration on day 8 before PGF was 6.5 ± 0.5 ng ml−1. Dominance of the first wave dominant follicle was extended beyond day 18 in 15 of 16 cows for T1 and T2 periods. The original dominant follicle ovulated in five of eight T1 and none of eight T2 periods (P < 0.01). New dominant follicles were detected on day 24 ± 1 in T1 (n = 3) and on day 20.6 ± 1 in T2 (n = 8; P < 0.01) cows. Growth rate of the dominant follicle from day 8 (15.8 ± 0.4 mm) to day 18 (22.9 ± 0.6 mm) was 0.7 mm day−1 (n = 15). Preovulatory sizes for the initial and new dominant follicles were 26.8 ± 1 mm (n = 5) and 15.3 ± 0.8 mm (n = 11), respectively (P < 0.01). Intervening oestrous cycles comprised three (n = 5) and two (n = 3) follicular waves. An interaction of treatment by day (P < 0.01) for LH pulses in 8 h was detected (pulses on days 10 and 19 for T1 (5.2 ± 0.5 and 7 ± 0.7) versus T2 (5.7 ±0.5 and 3 ±0.4)). A mean of 0.7 ± 0.3 LH pulses in 8 h was detected on day 10 for control cows (n = 3). Increased LH support appears to maintain a dominant follicle, whereas high progesterone concentrations decrease LH pulse frequency leading to turnover of the dominant follicle in cattle.

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J. D. Savio, M. P. Boland, N. Hynes and J. F. Roche

Summary. 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 (⩽ 4 mm) and medium-sized (5–9 mm) follicles, until a dominant follicle (> 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 < 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 < 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 (< 0·2 ng/ml); oestradiol concentrations were also low (< 5 pg/ml), but higher values (5–110 pg/ml) were observed in cows that had a dominant or a cystic follicle.

Keywords: cow; follicle; oestrus; post partum; ultrasound

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J. D. Savio, L. Keenan, M. P. Boland and J. F. Roche

Summary. Ovarian follicular development was studied in 13 heifers by daily ultrasound examination during 2 complete and consecutive natural oestrous cycles. In 21 cycles (81%) 3 dominant follicles were identified, in 4 cycles (15%) 2 and in the remaining cycle 1 (4%). Consistently, the first dominant follicle was detected on average on Day 4, reached a maximum size on Day 6, went through a period of relative stability between Days 6 and 10, then began to decrease in size and was undetectable by Day 15. The second dominant follicle was detected by Day 12, reached maximum size on Day 16 (or 19 in the 4 cycles in which the 2nd dominant follicle was the ovulatory follicle) and was undetectable by Day 19. The 3rd (ovulatory) follicle was identified on average by Day 16 (range Days 10 to 19) and maximum size was reached on Day 21. The ovulatory follicles were larger (P < 0·05) than the previous ones and the stage of the cycle at which maximum size was reached was significantly different for each dominant follicle (P < 0·05). The analysis of the rates of growth and atresia suggest that the rate of growth is slowest during mid-cycle. The number of dominant follicles that developed in the ovary ipsilateral to the corpus luteum was greater (P < 0·05) than in the contralateral ovary.

Keywords: heifer; dominant follicle; growth; oestrous cycle; ultrasound

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J. D. Savio, W. W. Thatcher, G. R. Morris, K. Entwistle, M. Drost and M. R. Mattiacci

The effects of concentration of progesterone in plasma on development and fertility of the first wave dominant follicle were studied in cattle. To identify a source of exogenous progesterone that would permit extension of the first wave dominant follicle, nonlactating Holstein cows (n = 6) received on day 8 of two successive oestrous cycles an injection of PGF (25 mg) and a new (1.9 g of progesterone (Period 1)) or used (≈ 1.2 g of progesterone (Period 2)) CIDR-B device that was removed on day 17. Control cows (n = 6) received a new CIDR-B device on day 8 that was removed on day 17 and a PGF injection (25 mg) on day 17. Ultrasonography and collection of blood samples were performed on alternate days throughout the experiment. Plasma concentrations of progesterone and oestradiol were different between treatments (P < 0.0001 and P < 0.05, respectively). The dominant follicle was maintained until day 17 and ovulated upon removal of the intravaginal device in 1 of 6, 6 of 6 and 0 of 6 in new CIDR-B, used CIDR-B and control groups, respectively (P < 0.01). The preovulatory dominant follicles were 14.2 ± 1.6 mm, 20 ± 1.3 mm and 10 ± 1.3 mm, respectively (P < 0.001) on day 17. There were fewer 5–9 mm follicles in cows having a persistent dominant follicle (P < 0.01). The interval to onset of oestrus was negatively correlated with size of the dominant follicle on day 17 (P < 0.001). In Expt 2, the fertility of oocytes ovulated from new (PGF on day 7; T1; n = 91) and persistent dominant follicles (PGF on day 7 and a used CIDR-B device inserted on day 7 and withdrawn on day 16; T2; n = 91) was tested using Holstein heifers. Size of the dominant follicle and plasma concentrations of progesterone and oestradiol on days 7 (T1) and 16 (T2) were different between treatments: 11.3 ± 0.2 versus 16.2 ± 0.3 mm (P < 0.001); 4.2 ± 0.2 versus 2.9 ± 0.3 ng ml−1 (P < 0.01) and 3.5 ± 0.3 versus 11.7 ± 1.7 pg ml−1 (P < 0.01), respectively. Pregnancy rates at first artificial insemination were 64.8% (46 of 71) and 37.1% (26 of 70) for new and persistent dominant follicles, respectively (P < 0.01). Pregnancy rates at second service were 50% and 52.8%, respectively. Low plasma concentrations of progesterone, therefore, resulted in persistency of the dominant follicle and temporarily impaired fertility.