164 J. Taponen et al. Animal Reproduction Science 64 2000 161–169
the corpus luteum CL and of possible secondary corpora lutea, and to determine the day of ovulation and diameter of the ovulatory follicle as described by Assey et al. 1993. All
examinations were carried out by the same operator. The ovaries were scanned several times in lateromedial and dorsoventral planes to de-
termine the largest cross-section of follicles andor a CL. By freezing the image, the largest and the smallest diameters were measured and recorded, with the average diam-
eter calculated later. The central cavities of CLs were measured and recorded in the same way.
All follicles equal to or larger than 8 mm were measured. Follicles smaller than 8 mm were only counted and divided according to their size into groups of small less than
5 mm and medium 5–8 mm follicles. Day of ovulation day 0 was determined to be the last day when the follicle was intact according to ultrasound scanning in the morn-
ing before the subsequent examination the next morning when the follicle had disap- peared.
2.4. Hormone determinations The concentration of progesterone in the serum was measured in all samples by radioim-
munoassay by use of a commercial kit Coat-A-Count® Progesterone, Diagnostic Products Corporation, Los Angeles, USA. The intra-assay coefficient of variation for progesterone
was 6.31 when calculated from duplicates of measurements between 1.0 and 20.0 nmoll n = 380. The inter-assay coefficient of variation was 6.74 81.9 nmoll, n = 8. The
detection limit of the assay was 0.3 nmoll.
2.5. Statistical analysis Data were analysed using the statistical analysis system software SAS, 1987. Pro-
gesterone concentrations were analysed by repeated measures analysis of variance, with manipulation and day as the within-subject factors. Significance of day effects and day
by manipulation interaction effects was evaluated by use of Greenhouse–Geisser-adjusted P
-values. Effects of manipulations on interoestrous intervals and on size of CLs were anal- ysed by repeated measures analysis of variance, with manipulation as the within-subject
factor. Differences between animals in interoestrous intervals were tested by one-way anal- ysis of variance. Differences were considered significant at P 0.05.
3. Results
3.1. Follicles The diameter of the ovulatory follicle mean ± S.E.M. on the day of ovulation 0–24 h
before ovulation was 15.3±0.9, 15.3±0.6 and 15.6±1.0 mm in T1, T2 and C, respectively with an average over all manipulations at 15.4 ± 0.4 mm. No double ovulations were
detected.
J. Taponen et al. Animal Reproduction Science 64 2000 161–169 165
On day 1 0–24 h after ovulation, follicles larger than 8 mm were found in four cases, two times in T1, once in T2 and once in C. GnRH treatment did not induce ovulation of
larger or smaller follicles. Thus, no accessory corpora lutea were found later. 3.2. Corpus luteum
The size of CL was analysed on days 11 or 12 and 14 or 15 after ovulation. Only the diameter of CL was included in the analysis. In T1, T2 and C, on day 11 or 12, the diameters
mean ± S.E.M. were 22.2 ± 0.7, 22.7 ± 1.1 and 22.7 ± 1.1 mm, respectively; and on day 14 or 15, 21.2 ± 0.7, 22.1 ± 1.0 and 22.6 ± 0.7 mm, respectively. In T1, on day 14 or 15,
CL was 1.3 ± 0.3 mm smaller than in C P 0.01, but no significant differences were found on day 11 or 12. Neither were there any differences found between T2 and C.
3.3. Progesterone The P
4
curves of T1, T2 and C from days 1–15 are shown in Fig. 1. A significant effect of day was observed on P
4
concentration in all manipulations P 0.001. P
4
had begun to rise on day 3. The rise continued steadily until day 11. The level remained thereafter unchanged.
The mean estimated daily rise in P
4
concentration from days 2 to 11 was 1.8 ± 0.1 nmoll mean ± S.E.M.. In T1, T2, and C, the rises were 1.9 ± 0.2, 1.8 ± 0.1 and 1.7 ± 0.1 nmoll,
Fig. 1. Mean ±S.E.M. P
4
concentration during 15 days after ovulation, when GnRH was given 0–24 h T1 or 24–48 h T2 after ovulation, or with no GnRH C administered.
166 J. Taponen et al. Animal Reproduction Science 64 2000 161–169
Fig. 2. Mean ±S.E.M. P
4
concentration during 8 days before next ovulation, when GnRH was given 0–24 h T1 or 24–48 h T2 after preceding ovulation, or with no GnRH C administered.
respectively. There were no significant differences in levels or profiles of P
4
curves between GnRH treatments and control manipulation.
In C, P
4
concentration rose continuously from days 2 to 11, but a slight decline in P
4
concentration was noticed in GnRH treatments between days 7 and 8 after ovulation in T1 and between days 8 and 9 in T2. In both treatment groups T1 and T2, the decline
occurred between days 6 and 7 after the GnRH injection Fig. 1. In individual animals, this decline occurred in 89 animals in T1 and T2, and in 29 in C between days 5 and 9 after
ovulation. The decline occurred in six cases between days 7 and 8 in T1; in T2 there was more inconsistency.
P
4
curves of T1, T2 and C during the last 8 days before the next ovulation are shown in Fig. 2. A significant decline in P
4
concentration was detected between days −4 and −3 P 0.01 in T1, T2 and C. There were no significant differences in the levels or profiles
of P
4
curves during these days between GnRH treatments and control manipulation. 3.4. Length of the oestrous cycle
The length of the oestrous cycle mean ± S.E.M. in T1, T2 and C was 21.9 ± 0.6, 22.3 ± 0.7 and 21.6 ± 0.6 days, respectively. GnRH treatment given on days 1 or 2 after
ovulation did not have any significant effects on inter-oestrous intervals. Instead, the animal effect was significant on the mean length of the oestrous cycle P 0.01.
J. Taponen et al. Animal Reproduction Science 64 2000 161–169 167
4. Discussion
