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B. J. McLeod and J. Craigon

Summary. Time series analysis was used to detect LH and FSH episodes in untreated seasonally anoestrous ewes and prepubertal heifers, and in these animals when treated with low doses of GnRH. For comparison, these profiles were also assessed for episodic secretion by subjective, visual appraisal methods and by cycle detection—an objective threshold method. In untreated animals, time series analysis detected recurring events in the LH and FSH profiles, the period lengths of which varied between individual animals. When GnRH was injected at 2-h intervals, cycles in LH secretion with period lengths of 120 min were recorded in all animals, of 60 min in all ewes and 11/12 heifers, and of 40·5 min in 22/24 ewes and 10/12 heifers. The cycles with period lengths of 60 and 40·5 min are probably artefacts of this method of analysis. No consistent cycles in FSH release were detected in GnRH-injected anoestrous ewes, but 120-min cycles were recorded in 8/12 GnRH-injected heifers. When GnRH was administered to seasonally anoestrous ewes by continuous infusion, recurring cycles in both LH and FSH secretion were evident. However, there was no consistency in their period lengths and the mean number and frequency of cycles were similar to pretreatment values. The number of episodes detected by visual appraisal was influenced by the choice of episode definition. Both methods identified LH, but not FSH, episodes in response to each injection in all GnRH-injected animals. Cycle detection, which does not identify individual episodes, recorded LH and FSH episode frequencies similar to those detected by the more stringent method of visual appraisal.

Time series analysis detected an FSH response to GnRH injections in prepubertal heifers that was not identified by the other methods of analysis. However, because of the asymmetric nature of LH episodes, it also detected cycles in LH profiles that were probably spurious. Subjective decisions influenced the frequencies of LH and FSH episodes recorded by visual appraisal, and the variation in episode amplitude in these profiles made cycle detection inappropriate. Each of these methods can contribute to the interpretation of hormone profiles, but their constraints and limitations must be recognized.

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B. J. McLeod and W. Haresign

Summary. Ovulation was induced in seasonally anoestrous ewes by repeated 2-h injections of 250 ng Gn-RH, after 12 days (Group 1, N = 7; Group 2, N = 8), 2 days (Group 3, N = 8) or no (Group 4, N = 7) progesterone pretreatment. A preovulatory LH peak occurred spontaneously at a mean ( ±s.e.m.) time of 43·1 ± 2·0 h, 38·5 ± 3·1 h and 26·8 ± 1·7 h after the start of Gn-RH treatment in Groups 1, 3 and 4 respectively, and was artificially induced in ewes in Group 2, after 24 h of treatment, by a single i.v. injection of 150 μg Gn-RH. Normal luteal function occurred in all progesterone-pretreated ewes, but in only 1/7 animals not treated with progesterone. These results demonstrate that, although normal luteal function in progesterone-primed ewes induced to ovulate with repeated injections of low doses of Gn-RH is associated with a delayed preovulatory LH peak, it is not this extended period of follicle development which is responsible for functional competence of the resultant corpus luteum. Since as little as 2 days of exposure to elevated plasma progesterone concentrations is effective, it is suggested that progesterone may act directly on the preovulatory follice.

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B. J. McLeod and A. S. McNeilly

Summary. The specific requirement for FSH in the final stages of preovulatory follicle development was assessed in seasonally anoestrous ewes given 2-h injections of GnRH (250 ng/injection), with (N = 10) or without (N = 10) concurrent treatment with bovine follicular fluid (bFF: 2 ml given i.v. at 8-h intervals). Treatment with bFF significantly (P < 0·01) suppressed plasma FSH concentrations, but, at least for the first 30 h of treatment, did not influence the magnitude of GnRH-induced LH episodes (mean max. conc. 3·00 ± 0·39 and 3·63 ± 0·51 ng/ml for bFF-treated and control ewes, respectively). Of 10 animals treated with GnRH for 72 h, 5/5 control ewes showed oestrus and ovulated whereas 0/5 bFF-treated ewes showed oestrus or ovulated in response to GnRH treatment. There was, however, a transient (13·2 ± 1·0 h) increase in plasma LH concentrations in the ewes given bFF (mean max. conc. 4·64 ± 1·57 ng/ml), which was coincident with the preovulatory LH surge recorded in animals given GnRH alone. In 10 GnRH-treated ewes slaughtered after 32 h of treatment, the mean diameter of the largest antral follicle was significantly (P < 0·001) greater in control ewes (5·92 ± 0·17 mm) than in animals that were also given bFF (3·94 ± 0·14 mm). In addition, the incidence of atresia in the 3 largest antral follicles present at this time was greater in bFF-treated ewes. These results show that, when plasma FSH concentrations are suppressed by administration of bFF, although the magnitude of GnRH-induced LH episodes is unchanged, preovulatory follicular development is impaired and ovulation does not occur. This may be indicative of a specific requirement for FSH in the final stages of preovulatory follicle development, or due to direct inhibitory effects of bovine follicular fluid.

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G. E. Lamming and B. J. McLeod

Summary. Plasma LH concentrations were monitored in 6 Hereford × Friesian suckled cows at about 80 days post partum, before and during a 14-day period of continuous s.c. infusion of GnRH (20 μg/h). Blood samples were collected at 10-min intervals on Days −2, −1, 1, 2, 3, 4, 7, 10, 13 and 14 (Day 1 = start of infusion). Plasma LH concentrations rose from mean pretreatment levels of 1·3 ± 0·20 ng/ml to a maximum of 17·1 ± 3·09 ng/ml within the first 8 h of GnRH infusion, but returned to pretreatment levels by Day 2 or 3. In 4/6 animals, the initial increase was of a magnitude characteristic of the preovulatory LH surge. In all animals, an i.v. injection of 10 μg GnRH, given before the start and again on the 14th day of continuous infusion, induced an increase in LH concentrations but the increase to the second injection was significantly (P < 0·01) less (mean max. conc. 6·4 ± 0·76 and 2·3 ± 0·19 ng/ml). Mean LH concentrations (1·0 ± 0·08, 1·1 ± 0·08 and 0·9 ± 0·06 ng/ml) and LH episode frequencies (3·3, 4·3 and 3·2 episodes/6 h) did not differ significantly on Days −2,7 and 13. However, the mean amplitude of LH episodes was significantly lower (P < 0·05) on Day 13 (1·3 ± 0·10 ng/ml) than on Day −2 (1·8 ± 0·16 ng/ml). Therefore, although the elevation in plasma LH concentrations that occurs in response to continuous administration of GnRH is short-lived and LH levels return to pre-infusion values within 48 h of the start of infusion, these results show that the pituitary is still capable of responding to exogenous GnRH, although the LH response to an i.v. bolus injection of GnRH is reduced. In addition, this change in pituitary sensitivity is not fully reflected in endogenous patterns of episodic LH secretion.

Keywords: GnRH infusion; pituitary sensitivity; LH; cows

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A. S. I. Loudon, B. J. McLeod, and J. D. Curlewis

Summary. Changes in the secretion of LH during the oestrous cycle were studied in 5 tame Père David's deer in which ovulation was synchronized with progesterone implants and prostaglandin injections. Plasma LH concentrations were measured in samples collected at 15-min intervals for a 36-h period, starting 16 h after the removal of the progesterone implants (follicular phase), and for a further 10-h period 10 days after the removal of the progesterone implants (luteal phase). In all animals, there was a preovulatory surge of LH and behavioural oestrus which occurred at a mean time of 59·6 h (± 3·25) and 69 h respectively following implant removal. LH pulse frequency was significantly higher during the follicular phase (0·59 ± 0·03 pulses/h) than the luteal phase (0·24 ± 0·2 pulses/h), thus confirming in deer findings from research on domesticated ruminants. There were no significant differences between the follicular and luteal phases in mean plasma LH concentrations (0·57 ± 0·09 and 0·74 ± 0·13 ng/ml) or mean pulse amplitude (0·99 ± 0·14 and 1·05 ± 0·21 ng/ml) for the follicular and luteal phase respectively. The long interval from the removal of progesterone to the onset of the LH surge and the absence of a significant difference in mean LH concentration or pulse amplitude in the follicular and luteal phases resemble published data for cattle but differ from sheep in which there is a short interval from luteal regression to the onset of the surge and a marked increase in LH pulse amplitude during the luteal phase.

Keywords: deer; LH; oestrous cycle; pulsatile secretion

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J. D. Curlewis, B. J. McLeod, and A. S. I. Loudon

Summary. The pattern of LH secretion and response to exogenous GnRH was determined on 5 occasions during seasonal anoestrus of the Père David's deer hind. LH pulse frequency was low (3·3 ± 0·6 pulses/18 h) in early anoestrus (February), increased significantly in mid-anoestrus (April; 8·4 ± 1·4 pulses/18 h) and thereafter declined slightly in late anoestrus (June; 6·3 ± 0·25 pulses/18 h). Mean LH concentrations also showed significant changes during anoestrus with higher levels in mid-anoestrus (April; 0·85 ± 0·12 ng/ml) when compared with other times (0·53 ± 0·05, 0·60 ± 0·10, 0·68 ± 0·06 and 0·71 ± 0·05 ng/ml for February, March, May and June, respectively). LH pulse amplitude showed no significant changes during the study. The LH response to intravenous injections of 2 μg GnRH was lowest in early anoestrus (February), increased significantly in mid-anoestrus (April) and remained high through late anoestrus. The response during the luteal phase was similar to that seen during late anoestrus. These results indicate that seasonal anoestrus in the Père David's deer hind is not a uniform state but is characterized by an early period of 'deep' anoestrus.

Keywords: LH; deer; GnRH; seasonal anoestrus; breeding season

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B. J. McLeod, W. Haresign, and G. E. Lamming

Summary. Four groups, each of 5 seasonally anoestrous ewes, were treated i.v with small doses (75, 125, 250 or 500 ng) of Gn-RH at 2-h intervals for 48 h. A further 15 ewes received 14 days pretreatment with progesterone and then the 250 ng Gn-RH treatment. Gn-RH injections induced an episodic pattern of LH secretion which differed significantly for the doses of Gn-RH used. A preovulatory LH surge occurred in all but 1 of the ewes during the period of Gn-RH treatment. Ovulation occurred in all 15 ewes pretreated with progesterone and in 19/20 ewes treated with Gn-RH alone. Although normal luteal function occurred in all ewes pretreated with progesterone, it was present in only 5 of the 20 ewes treated with Gn-RH alone. Oestrus, as shown by mating, occurred at a mean time of 34·7 ± 2·6 h after the start of Gn-RH treatment only in those ewes receiving progesterone pretreatment. These results indicate that progesterone pretreatment has a marked effect on the ability of small doses of Gn-RH to induce ovulation and normal luteal function in seasonally anoestrous ewes.

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B. J. McLeod, W. Haresign, and G. E. Lamming

Summary. Seasonally anoestrous ewes were injected i.v. with 250, 500 or 1000 ng Gn-RH at 2-h intervals for 8 days (2 sheep/treatment). Each injection of 250 or 500 ng Gn-RH resulted in a transient rise in plasma LH concentrations. Treatment with 1000 ng Gn-RH per injection resulted in a more sustained rise in plasma LH concentrations in 1 of 2 sheep during the early part of the treatment period. A preovulatory-type LH peak occurred 17–48 h after the start of treatment in all ewes, with a second preovulatory-type peak 106–133 h later in those ewes receiving 500 or 1000 ng Gn-RH per injection. Ovulation, with subsequent normal luteal function, occurred in all sheep. However, the rise in plasma progesterone concentrations appeared to be delayed in those ewes treated with 500 or 1000 ng Gn-RH compared to ewes treated with 250 ng Gn-RH. These data suggest that the absence of ovulation during seasonal anoestrus is due to an inadequate pattern of episodic LH secretion.

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B. J. McLeod, W. Haresign, and G. E. Lamming

Summary. Two groups of 12 seasonally anoestrous ewes were infused with Gn-RH at the rate of 125 or 250 ng/h for 48 h. Four control ewes were infused with the saline vehicle alone. Mean LH concentrations increased significantly in response to Gn-RH infusion and were significantly higher (P < 0·05) in ewes receiving 250 ng Gn-RH/h. LH concentrations remained unchanged in the control ewes. Oestrus was detected in 22/24 Gn-RH-treated ewes and occurred at a mean time of 37·0 ± 1·2 h after the start of infusion. Ovulation occurred in all but one of the 24 Gn-RH-treated ewes with mean ovulation rates of 1·27 ± 0·14 (125 ng-Gn-RH/h) and 1·75 ± 0·22 (250 ng Gn-RH/h). These results demonstrate that a sustained elevation in mean circulating concentrations of LH induced by continuous administration of Gn-RH is sufficient to invoke the final phases of follicular development, and thereby ovulation, in the seasonally anoestrous ewe.

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B. J. McLeod, B. R. Brinklow, J. D. Curlewis, and A. S. I. Loudon

Summary. Père David's deer hinds were treated with GnRH, administered as intermittent i.v. injections (2·0 μg/injection at 2-h intervals) for 4 days, or as a continuous s.c. infusion (1·0 μg/h) for 14 days. These treatments were given early (February–March) and late (May–June) in the period of seasonal anoestrus. The administration of repeated injections of GnRH increased mean LH concentrations from pretreatment values of 0·54 ± 0·09 to 2·10 ± 0·25 ng/ml over the first 8 h of treatment in early anoestrus, and from 0·62 ± 0·11 to 2·73 ± 0·49 ng/ml in late anoestrus. The mean amplitude of GnRH-induced LH episodes was greater (P < 0·01) in late (4·03 ± 0·28 ng/ml) than in early (3·12 ± 0·26 ng/ml) anoestrus, but within each replicate (early or late anoestrus), neither mean LH episode amplitude nor mean plasma LH concentrations differed significantly between the four periods of intensive blood sampling. On the basis of their progesterone profiles, 6/12 hinds had ovulated in response to treatment with injections of GnRH (1/6 in early anoestrus and 5/6 in late anoestrus), and oestrus and a preovulatory LH surge were recorded in all of these animals. Oestrus and a preovulatory LH surge were also recorded in one other animal treated in early anoestrus in which progesterone concentrations remained low. The mean times of onset of oestrus (91·0 ± 1·00 and 62·4 ± 0·98 h) and of the preovulatory LH surge (85·8 ± 3·76 and 59·4 ± 0·25 h) both occurred significantly earlier (P < 0·001) in animals treated in late anoestrus.

Continuous infusion of GnRH to seasonally anoestrous hinds resulted in an increase in mean plasma LH concentrations, but this response did not differ significantly between early (2·15 ± 0·28 ng/ml) and late (2·48 ± 0·26 ng/ml) anoestrus. Ovulation, based on progesterone profiles, occurred in 2/7 hinds in early anoestrus and in 4/6 hinds in late anoestrus. Oestrus was detected in all except one of these hinds. The mean time of onset of oestrus occurred earlier in animals treated in late anoestrus (66·2 ± 0·32 h and 46·7 ± 0·67 h, P < 0·01).

The administration of GnRH, given either intermittently or continuously, will induce ovulation in a proportion of seasonally anoestrous Père David's deer. However, more animals ovulate in response to this treatment in late than in early anoestrus (75% compared with 23%).

Keywords: deer; anoestrus; GnRH; injection; infusion; ovulation