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J. F. Quirke and J. P. Hanrahan

Conception and lambing rates are lower in ewe lambs than in yearlings or adult ewes (Gordon, 1967; Forrest & Bichard, 1974). The causes of reproductive failure in ewe lambs, however, have not been determined. High ovum cleavage rates (80%) and low implantation rates (<40%) have been observed in Galway ewe lambs after various progestagen–PMSG treatments (J. F. Quirke, unpublished observation). It is possible that the ova produced by ewe lambs do not have the same potential for development as those from older ewes or that conditions in the reproductive tract of the ewe lamb are less favourable for survival. This report deals with the survival of cleaved ova from ewe lambs and adult ewes following transfer to the uteri of adult ewes.

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J. F. Quirke and J. P. Hanrahan

Summary. Fertilized eggs, obtained from mature donor ewes, were transferred into the uteri of adult ewes and ewe lambs (1 or 2 eggs per recipient). The survival rate to term of the transferred eggs was similar in the two classes of recipients. The percentage of adult ewe and ewe lamb recipients which gave birth to twins was 45·3 and 41·1 respectively. Gestation length was shorter (P < 0·01) and lamb birth weight lower (P < 0·01) for ewe lamb recipients. The results indicate that the generally lower lambing rate of ewe lambs compared to adults is unlikely to be due to unfavourable uterine conditions.

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J. F. QUIRKE and J. P. HANRAHAN

The Agricultural Institute, Ballinrobe, Co. Mayo, Ireland

(Received 5th October 1974)

An experiment was conducted to determine whether gonadotrophin-releasing hormone (Gn-RH) or HCG would reduce the proportion of unruptured follicles in the Galway ewe following a high superovulating dose of PMSG given in conjunction with a progestagen to synchronize oestrus.

Forty-four Galway ewes aged 1½ to 5 years (average wt 64·7 kg) were treated with intravaginal pessaries impregnated with 30 mg 'cronolone' (Synchromate: G. D. Searle) for 14 days in early October 1973. All ewes were given 2000 i.u. PMSG (Folligon: Intervet) intramuscularly in 5 ml water at the time of withdrawal of the pessaries and were placed with raddled fertile rams. At 24 hr after removal of the pessary, the ewes were assigned to three groups and were treated as follows: Group 1—50 μg Gn-RH intramuscularly in 1 ml water; Group 2—750 i.u. HCG intramuscularly in 1 ml water

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J. P. HANRAHAN and J. F. QUIRKE

Summary.

The duration of oestrus and the time interval from removal of progestagen-impregnated pessaries to the onset and end of oestrus were examined in Texel, Finnish Landrace, Galway and Fingalway (Finnish Landrace × Galway) ewes. The differences among the breeds in the relationship between these variables and ovulation rate at the controlled oestrus were also investigated. Breed differences were significant for all traits except the interval from pessary withdrawal to the onset of oestrus. The relationship between ovulation rate and both the interval from pessary withdrawal to the onset of oestrus and the duration of oestrus differed significantly among the breeds. The repeatability of the duration of oestrus was significant for Texel and Rambouillet ewes (mean = 0·5) and for pooled data from ewe lambs of various breeds. It was concluded that, in view of the breed differences in the relationship between ovulation rate and duration of oestrus and other traits, generalizations should not be made from among-breed to withinbreed relationships. The high repeatability for the duration of oestrus may mean substantial heritabilities for the physiological determinants of oestrus duration.

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J. P. Hanrahan, J. F. Quirke and J. P. Gosling

Summary. Plasma LH was measured at 4 and 8 weeks of age in purebred lambs born to Finnish Landrace, Galway, Fingalway and High Fertility ewes. The average litter sizes for these breeds vary from 1·4 to 2·5. Lambs born after the transfer of fertilized eggs (all Fingalway) to Finnish Landrace, Galway and Fingalway ewes were also studied. There was evidence for a significant positive effect of selection for litter size within the Galway breed on plasma LH at 8 weeks of age. Finnish Landrace lambs had significantly higher levels of plasma LH at 8 weeks of age than did Galway Control lambs. These two groups did not differ with respect to plasma LH at 4 weeks of age. Non-additive genetic effects were significant at 4 weeks of age. The ranking of genetic groups on plasma LH was not consistent with their ranking for litter size. There was no evidence for a maternal effect associated with breed of dam on plasma LH and the effects of litter size were generally insignificant. Female lambs had significantly higher levels of LH at 4 weeks of age but there was no sex difference at 8 weeks because LH levels in males had increased. The correlation between the level of plasma LH at 4 and 8 weeks of age was −0·04. It is concluded that plasma LH is unlikely to prove a practical aid to selection for increased fecundity in sheep.

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J. F. Quirke, J. P. Hanrahan and J. P. Gosling

Summary. The mean duration of oestrus, ovulation rate, duration of the preovulatory LH discharge, time interval between sponge removal and beginning of the LH discharge, total LH discharged, maximum LH value observed and the concentration of progesterone in the peripheral plasma during the luteal phase of the oestrous cycle was similar in Galway adult ewes and 8-month-old ewe lambs after treatment with intravaginal sponges containing 30 mg cronolone for 12 days and injection of 500 i.u. PMSG. The interval between sponge removal and the onset of oestrus was shorter for adults than for ewe lambs; the interval between the onset of oestrus and the beginning of the LH discharge was longer in adults. During the period 12–36 h after sponge removal the mean plasma total oestrogen concentration was significantly higher in lambs than in adults. In a separate study of the time of ovulation in Galway ewe lambs given the same progestagen-PMSG treatment, ovulation did not occur in any lamb before 17 h after the onset of oestrus and the majority ovulated close to the end of oestrus.

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J. P. Hanrahan, J. F. Quirke and J. P. Gosling

Summary. Male lambs of the Finn, Fingalway and High Fertility breeds aged 4 or 8 weeks of age were injected i.m. with 5, 10, 50, or 100 μg GnRH. Plasma LH after GnRH injection increased with age and GnRH dose but there was no effect of breed. There was no interaction among the three factors studied. In a second experiment the response of male and female lambs, aged 8 weeks, to 100 μg GnRH was investigated for 5 genetic groups (Finn, Galway Control, Galway Elite, Fingalway and High Fertility). Breed differences in plasma LH of male lambs were not found, which agreed with the result of the first experiment. Breed differences were observed for females, with the lowest values being observed for Finn and High Fertility lambs which represent the two most prolific breeds. This finding suggested breed differences in the development of the hypothalamic–pituitary–ovarian circuit. The difference between Galway Control and Galway Elite lambs was not significant (P > 0·10).

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J. F. Quirke, J. P. Hanrahan and J. P. Gosling

Summary. The concentrations of progesterone in the peripheral plasma throughout the oestrous cycle and the preovulatory LH discharge were examined in Finnish Landrace, Galway and Fingalway (Finnish Landrace × Galway) ewes. Progesterone levels were significantly higher in Finnish Landrace ewes during the luteal phase of the cycle (Days 10–13) than in Galways or Fingalways in which the concentrations were similar. Luteal-phase progesterone levels were almost 50% higher during December than during October in all three breeds. The relationship between the number of CL and plasma progesterone was not a simple linear function. All aspects of the preovulatory LH discharge were similar in the three breeds with the exception of the timing of the LH release in relation to the onset of oestrus. This occurred earliest in the Galway and latest in the Finnish Landrace while the Fingalway was intermediate.

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K. Reynaud, J. P. Hanrahan, A. Donovan and M. A. Driancourt

High prolificacy due to a gene that has a large effect on ovulation rate has been noted in Booroola and Inverdale ewes. High prolificacy in the Belclare breed (a composite developed from stocks selected for very large litter size or high ovulation rate) may be related to the segregation of two genes. The aims of this study were (i) to compare the morphological and functional features of ovulatory follicles from carriers (which could only be heterozygous for the genes of interest) and non-carriers, and (ii) to identify markers of the Belclare genes among secreted or cellular ovarian proteins. Belclare carrier ewes had more ovulatory follicles (4.9 ± 0.4) than did non-carrier ewes (2.0 ± 0.2) (P < 0.001). Ovulatory follicles from carriers were also smaller (4.4 ± 0.1 mm versus 5.7 ± 0.2 mm, P < 0.001) and contained a significantly reduced number of granulosa cells (P < 0.001). However, the proportion of proliferating granulosa cells in ovulatory follicles was similar in both groups. The in vitro secretion of steroids per follicle was only marginally lower in follicles from Belclare carriers compared with non-carriers. Furthermore, similar concentrations of steroidogenic enzymes were present in both groups, indicating that steroidogenic potential per granulosa cell is similar between carriers and non-carriers. Possible markers of the Belclare genes were identified among cellular proteins of follicular walls by two-dimensional PAGE and image analysis. Two spots at 78 and 49 kDa were always absent in samples from non-carriers. When secreted proteins in follicles from carriers were compared with those from non-carriers, two spots at 53 and 41 kDa were restricted to samples from carriers and three spots at 97, 91 and 45 kDa were unique to samples from non-carriers. Interestingly, the spot at 91 kDa is also affected by the Booroola gene.

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J. F. Quirke, J. J. Jennings, J. P. Hanrahan and J. P. Gosling

Summary. The influence of Gn-RH, hCG and a PMSG–hCG mixture (PG600) on the time of ovulation, ovulation rate and on the occurrence of oestrus in ewes treated with progestagen-impregnated sponges for 12 days was examined. The effects of Gn-RH analogues on plasma LH, oestrus, ovulation and conception rate were also investigated. Six separate experiments were carried out.

When 50 μg Gn-RH were given 24 h after sponge removal ovulation occurred in 44–46% of ewes within 24 h and in all ewes by 34 h. Gn-RH was a more potent ovulation synchronizer than hCG. Both hCG and PG600 reduced the incidence of overt oestrus. Gn-RH also had this effect in ewes treated during February and May but not in August and September.

Gn-RH analogues given 2 days before sponge removal significantly increased ovulation rate. The display of oestrus was not affected in ewes treated 2 days before sponge removal but was suppressed in 43–69% of ewes treated with an analogue at the time of sponge removal. Ovulation occurred in 50–62% of ewes within 30–35 h of injection of Gn-RH analogues, regardless of the time of their administration. The release of LH in response to one analogue was not influenced by the presence of the progestagen-impregnated sponge in the vagina. When given a Gn-RH analogue 2 days before sponge removal or at the time of sponge removal 63 and 62% of mated ewes became pregnant compared with 70% of control ewes.