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The objective was to determine the effect of dietary intake on follicle and oocyte morphology in unstimulated and superovulated ewes. Fifty-four ewes were fed grass meal at 0.5, 1.0 or 2.0 times maintenance energy requirements (M) for 32 days. Oestrous cycles were synchronized using progestagen pessaries and either unstimulated or superovulated with 200 mg pig FSH. The ewes were killed and ovaries were collected either 36 or 12 h before the anticipated LH surge. Serum progesterone concentrations in ewes on day 10 after withdrawal of the pessary were lower in ewes fed 2.0M than in ewes fed 0.5M or 1.0M (P < 0.05). LH pulse frequency tended to be higher in ewes fed 2M than 1M (1.0 +/- 0.3 versus 0.3 +/- 0.2 pulses per 8 h) on day 6 after removal of the pessary but the effect was not significant. In unstimulated ewes, more follicles (>/= 3 mm) were observed when the animals were killed in ewes fed 2.0M (3.5 +/- 0.3) than in ewes fed 0.5M (2.4 +/- 0.3) or 1.0M (2.4 +/- 0.5; P < 0. 05). Fewer follicles were observed in superovulated ewes on 0.5M (7. 5 +/- 1.2) than in ewes on 1.0M (12.0 +/- 0.5) or 2.0M (12.3 +/- 1. 4; P < 0.05). Follicular fluid progesterone concentrations were higher in ewes fed 0.5M compared with those fed 1M or 2M (P < 0.05). Insulin-like growth factor (IGF)-I concentrations were higher in follicular fluid from ewes on 1M compared with either those on 0.5M or 2M (P < 0.05), whereas IGF-II concentrations were lower in follicular fluid from ewes on 2M compared with those on 1M or 0.5M (P < 0.05). Superovulation increased follicular fluid progesterone, oestradiol, IGF-I and IGF-II concentrations (P < 0.01). Concentrations of the 34, 22 and 20 kDa IGF binding proteins were lower in follicles from superovulated ewes compared with unstimulated ewes (P < 0.05). Oocytes from superovulated ewes showed abnormalities such as premature activation of cumulus expansion and vacuolation of the nucleolus and increased frequency of detachment of interchromatin-like granules from the nucleolar remnant. Collectively, these results indicate that both high and low dietary intakes can alter systemic and follicular fluid hormone concentrations. Relative to dietary effects, the effects of superovulation were greater and involved substantial increases in follicular fluid hormone concentrations and abnormal oocyte morphology.

Prolonged postpartum anoestrus in beef cows is due to failure of early dominant follicles to ovulate. It is hypothesized that this failure to ovulate is due to inadequate LH pulse frequency. The objective of this study was to determine whether administration of hourly LH pulses would cause the first dominant follicle to ovulate. In Expt 1, 16 cows received either saline (n = 8) or porcine LH (pLH; 50 micrograms h-1; n = 8) as hourly pulses for 3-5 days from the second day of dominance of the first dominant follicle (day 0). In Expt 2, 21 cows received either saline (n = 7), or 50 micrograms pLH (n = 7) or 100 micrograms pLH (n = 7) as hourly pulses for 3 days. Appropriate ovarian scanning and assays of blood samples were carried out. In Expt 1, the number of dominant follicles that underwent atresia was not affected by increasing the number of LH pulses, but the duration of dominance (days) of the first and second dominant follicles and maximum size (mm) of the second dominant follicle were increased (P < 0.05). Oestradiol concentrations were higher (P < 0.05) in cows given hourly pLH pulses (3.1 +/- 1.2 pg ml-1) compared with controls (1.2 +/- 0.2 pg ml-1). Four of eight treated cows had an anovulatory LH surge. The number of follicle waves to first ovulation was not different (P < 0.05) between control (4.6 +/- 0.9) and pLH treated cows (3.9 +/- 0.5). In Expt 2, four of seven cows given pulses of 100 micrograms pLH h-1 ovulated the first dominant follicle, and the interval from calving to first ovulation was decreased (P < 0.05). In the remaining three cows, the duration of dominance of the first dominant follicle was increased (P < 0.005), the maximum size of the first dominant follicle was greater (P < 0.05), and the interval (days) from the start of infusion to new wave emergence was greater (P < 0.05) compared with cows that failed to ovulate in either the 50 micrograms pLH h-1 or control treatments. In conclusion, hourly pulses of pLH from day 1 after dominance of the first dominant follicle in postpartum beef cows can either prolong dominance or induce it to ovulate. This finding supports the hypothesis that LH pulse frequency is a key determinant of the fate of the dominant follicle in the early postpartum period.

This study investigated the effects of quantity and type of diet fed to superovulated donor heifers on molecular and metabolic indices of embryonic development. These effects included the relative abundances of mRNAs for the alpha 1 subunit of Na/K-ATPase and the antioxidant enzyme Cu/Zn-SOD, as well as pyruvate utilization in bovine morulae and blastocysts developed in vivo. Heifers were fed a daily ration of either grass silage and a citrus-beet pulp-based concentrate or grass silage and a barley-based concentrate for 116 days, both at 3 kg per day or ad libitum. In embryos derived from heifers fed the pulp-based diets, the relative abundances of the transcripts were not affected by either day of collection or quantity of diet. In embryos derived from heifers fed the barley-based diets, the relative abundances of the Na/K-ATPase transcripts were also not changed by these main effects, while the relative abundances of the Cu/Zn-SOD transcripts were affected by day of collection and by the quantity of diet. Pyruvate metabolism was affected by day of collection, and was significantly increased in day 8 embryos compared with day 7 and day 6 embryos. Diet quantity did not affect pyruvate utilization, whereas diet type did increase pyruvate metabolism in the barley group when compared with the pulp group. The results of this study show for the first time that molecular and metabolic variations may exist in embryos derived in vivo and developed in donor heifers on nutritional regimens differing in type and quantity. Differences in embryos collected on different developmental days may be attributed to varying cell numbers. Alterations in the relative abundances of the Cu/Zn-SOD transcripts and pyruvate metabolism caused by the quantity of diet fed to the donor animal were likely to have been due to alterations in metabolic end products that accumulate in reproductive tract fluids, whereas differences in embryonic metabolism caused by type of diet are related to the composition of the diet. These findings characterize embryos produced in vivo at the molecular level, indicating that the molecular markers used in the present study can differentiate between populations of embryos produced under different nutritional regimens and determine conditions conductive to the production of good quality embryos.

In vitro produced bovine zygotes show substantial variation in the time required to complete the first cell cycle and in their in vitro development potential. A number of reports have highlighted the fact that the fastest developing embryos in vitro are most likely to be comparable with their in vivo counterparts. At 24 h after IVF, presumptive zygotes were cultured in droplets of synthetic oviduct fluid medium. Droplets were examined at regular intervals and all cleaved embryos at each time point were transferred into new droplets and cultured separately for the duration of the experiment. All uncleaved zygotes were returned to the incubator and re-examined at the successive time points until 48 h after insemination, at which time the remaining uncleaved oocytes were retained as a group. A representative number of day 7 blastocysts from zygotes that had cleaved by 30 or 36 h were transferred to synchronized recipients and pregnancy was diagnosed by ultrasonography at day 35. Glucose and glutamine metabolism was examined in zygotes and blastocysts and compared retrospectively with time of first cleavage. A representative number of blastocysts from each of the cleavage groups was sexed using PCR. Data were analysed by chi-squared and regression analysis. Development to the blastocyst stage decreased as the time from insemination to first cleavage increased (r = 0.97, P < 0.03). There was no difference in blastocyst hatching, number of blastocyst cells or pregnancy rate between the 30 and 36 h groups. The overall sex ratio was 62% males (n = 258, P < 0.0001) and was not different in the 30 and 36 h groups (61%, n = 155 versus 63%, n = 95, respectively). These results indicate that although time of first cleavage has a major influence on the probability of an embryo developing to the blastocyst stage, once that stage is attained, subsequent developmental characteristics are unrelated to the time of first cleavage.

The aim of the present study was to characterize in detail the cytoplasmic and nuclear morphology of cattle oocytes recovered from follicles that are dominant for more than 9 days (with low fertility after ovulation), and to relate morphological changes to intrafollicular markers of follicle health. Beef heifers received prostaglandin F2 alpha and a synthetic progestagen (3 mg Norgestomet) for 2 or 10 days on the first day of dominance of the second dominant follicle (DF2) of the oestrous cycle, to give a 4 day (n = 19; N2) or 12 day (n = 21; N10) duration of dominance of the dominant follicle at ovariectomy 18 h after implant removal and before the predicted gonadotrophin surge. Ultrasound scanning determined emergence of a new wave of follicles in five N10 heifers the day before (n = 1) or day of ovariectomy (n = 4) (N10-NonDom). Dominant follicles from the remaining N10 heifers (N10-Dom) were larger (P < 0.05) on the day of ovariectomy (17.8 +/- 0.6 mm) than those from N2 heifers (13.6 +/- 0.4 mm). The oestradiol:progesterone ratio of follicular fluid from N10-Dom heifers was reduced (21.7 +/- 3.1 versus 34.1 +/- 4.4; P < 0.05), while inhibin A (as measured by immunoradiometric assay) was increased (12.7 +/- 1.0 versus 9.0 +/- 0.7 micrograms ml-1; P < 0.05) compared with N2 heifers. Eleven of twelve N2 oocytes demonstrated nuclear activation without germinal vesicle breakdown, while seven of eight N10-Dom oocytes had undergone germinal vesicle breakdown and had progressed to metaphase I (6/8) or II (1/8). In contrast to N2 oocytes, N10-Dom oocytes showed a larger perivitelline space containing more cumulus cell process endings, vacuoles, irregular vesicles, and more mitochrondia and lipid droplets throughout the ooplasm, yet the degree of cumulus cell expansion and atresia was similar. Thus, final oocyte maturation leading to metaphase I is initiated in most dominant follicles with a dominance period of > 9 days before the gonadotrophin surge and is associated with a reduction in dominant follicle health. However, ovulatory ability is maintained and will lead to the ovulation of aged oocytes, markedly reducing subsequent pregnancy rates.

The effects of inhibin immunization on inhibin antibody titres, semen characteristics, scrotal size, fertility, FSH, LH and testosterone concentrations were determined by immunizing adult rams against bovine inhibin alpha 1-26-Gly-Tyr conjugated to human serum albumin (n = 16) in non-ulcerative Freund's adjuvant and DEAE:dextran (1:1) or adjuvant alone (n = 16) on days 0 (29 June), 30, 60, 191, 303 and 394. Blood samples were collected and bovine inhibin alpha 1-26-Gly-Tyr antibody titres and serum testosterone concentrations were determined. Each month, between days 174 and 417, semen was collected every 30 min to a maximum of 15 ejaculates over 7 h and scrotal circumference was measured. Ram fertility was recorded during natural service. FSH, LH and testosterone concentrations and GnRH-induced FSH and LH release were measured in a subgroup of immunized (n = 5) and control (n = 5) rams at frequent intervals. Antibody titres were variable among immunized rams (0-46% 125I-labelled bovine inhibin alpha 1-26-Gly-Tyr at 1:1600 serum dilution) but mean titres were consistently higher than in control rams (P < or = 0.001). Immunization did not alter the semen volume, output or quality of spermatozoa or ram fertility, but increased the mean scrotal circumference (37.6 +/- 0.8 cm versus 34.4 +/- 0.7 cm, P < 0.001). Mean FSH concentrations were higher in immunized rams during two intensive blood sampling periods (in June and August) (5.8 +/- 0.7 ng ml-1 versus 3.0 +/- 0.3 ng ml-1, P < 0.001 in June; and 4.8 +/- 0.9 ng ml-1 versus 2.0 +/- 0.3 ng ml-1, P < 0.02 in August), and were correlated with antibody titres (r2 = 0.3, P < 0.05 in June; and r2 = 0.8, P < 0.001 in August). Discrete FSH pulses were not detected. Immunization did not alter mean or basal testosterone or LH concentrations, or LH pulse frequency; LH pulse amplitude was increased (1.6 +/- 0.2 ng ml-1 versus 0.8 +/- 0.2 ng ml-1, P < 0.02) and was correlated with antibody titres (r2 = 0.6, P < 0.01). Immunization enhanced GnRH-induced FSH (P < 0.05) but not LH release. In conclusion, immunization of adult rams against bovine inhibin alpha 1-26 Gly-Tyr increased scrotal circumference, mean FSH concentrations and LH pulse amplitude, without altering semen characteristics, fertility, mean LH concentrations, LH pulse frequency or mean testosterone concentrations.

After luteolysis, subluteal concentrations of progesterone or treatment with a synthetic progestagen result in an extended period of dominance (persistence) of the dominant follicle in cattle. Two experiments studied (1) the relationship between the duration of dominance of the ovulatory follicle and pregnancy rate and (2) the ability of a persistent dominant follicle to ovulate and form a normal functioning corpus luteum. In Expt 1, beef heifers were either untreated (n = 30) or given a synthetic progestagen implant (3 mg norgestomet) for 12 days starting on day 16 of their cycle (n = 32). The mean duration of dominance of the ovulatory follicle differed (P < 0.05) between treated and control heifers (10.8 +/- 1.2 and 3.3 +/- 0.8 days, respectively) and 20 of 26 control and 7 of 30 treated heifers were diagnosed pregnant 28 days after artificial insemination (P < 0.01). In Expt 2, on the first day of dominance of the second dominant follicle, heifers received either a PGF2 alpha analogue alone (controls; n = 18), or prostaglandin and a norgestomet implant for 6 (T6; n = 19) or 10 days (T10; n = 20). Increases in the duration of dominance of the second dominant follicle (controls, 4.1 +/- 0.2 days; T6, 8.6 +/- 0.2 days; T10, 12.1 +/- 0.2 days; P < 0.05) resulted in a decrease in pregnancy rate (controls, 14 of 16; T6, 11 of 19; T10, 0 of 13; P < or = 0.05). Progesterone concentrations on days 7 and 12 and the area of luteal tissue on day 12 after artificial insemination were not different (P > 0.05) between treatments.(ABSTRACT TRUNCATED AT 250 WORDS)

This study examined the correlation between measurement of follicle growth by ultrasound, and measurement of intrafollicular ratios of oestradiol and progesterone concentrations and the serum concentrations of FSH during selection, dominance and atresia or ovulation of dominant follicles in heifers. Heifers were ovariectomized on days 0 (before LH surge), 1 (after LH surge, preovulation), 1 (postovulation), 3, 6 and 12 of the oestrous cycle. Blood samples were collected at 4-6 h intervals. After ovariectomy all follicles > or = 5 mm were measured and follicular fluid was aspirated. Follicles were classified by size according to ultrasound (F1, largest; F2, second largest; F3, all remaining follicles > or = 5 mm) and by the ratio of oestradiol:progesterone concentrations. During the follicular phase, a single dominant oestrogen-active follicle increased in diameter while serum concentrations of LH increased and FSH decreased (P < 0.05). On day 1 (after LH surge, preovulation), serum LH and FSH decreased to pre-surge concentrations (P < 0.0001), while follicle size and intrafollicular progesterone concentration increased and oestradiol concentration decreased (P < 0.05). A dominant nonovulatory follicle, classified as oestrogen-active on days 1, 3 and 6 and oestrogen-inactive on day 12, increased in size from day 1 to day 7 and lost dominance during days 10-12, coincident with the growth of multiple oestrogen-active follicles. The serum FSH concentration increased transiently (P < 0.05) before each new wave of dominant follicular growth. The overall correlation of ultrasound measurements of follicle diameter with measures of follicle size after ovariectomy was high.(ABSTRACT TRUNCATED AT 250 WORDS)

Superovulation in cattle normally involves the administration of gonadotrophins at specific times of the oestrous cycle, followed by the induction of luteolysis and insemination with high quality semen. The first aim of this experiment was to examine the effect of supplementary progesterone when used in conjunction with porcine FSH (pFSH) to induce superovulation in heifers. The methods compared were PGF2 alpha given at mid-cycle or a progesterone-releasing intravaginal device (PRID) inserted at different phases of the cycle. The second aim was to determine whether site of insemination or use of fresh or frozen semen affected embryo production. A factorial design was used involving 185 beef heifers. The main factors were (i) synchronization methods (PGF2 alpha or PRID); (ii) semen type (fresh or frozen); (iii) insemination regimens (involving two inseminations and variations in the sites) and number of straws used (one or two) at the second insemination. Eight injections of pFSH were given twice a day for 4 days starting either on days 9, 10 or 11 of the oestrous cycle or on the fourth day after insertion of a PRID. Heifers were checked for oestrus, inseminated twice and embryos were recovered on day 7 of the superovulated cycle. There was no difference between heifers given either PRID or PGF2 alpha in the oestrous response (93% versus 96%), number of ovulations (15.9 +/- 1.11 versus 13.4 +/- 1.06), large follicles (2.5 +/- 0.24 versus 2.3 +/- 0.23) or embryos recovered (9.1 +/- 0.77 versus 9.1 +/- 0.74).(ABSTRACT TRUNCATED AT 250 WORDS)

Four experiments were carried out to determine the effect of the presence of ewes and rams on the reproductive state of ewes. In Expt 1, the breeding season of ewes kept with a vasectomized ram ended later (April 18 +/- 8 days; mean +/- SEM) than that of ewes isolated from rams (6 March +/- 7 days; P < 0.01). In Expt 2, the end of the breeding season was later (5 May +/- 6 days; P < 0.05) and the onset of the next breeding season earlier (29 September +/- 2 days; P < 0.001) in ewes maintained with rams, compared with ewes isolated from rams (14 April +/- 7 days and 1 November +/- 2 days, respectively). There was no difference in the timing of, or variation in, reproductive transitions between ewes maintained either as individuals or in groups. In Expt 3, all ewes exposed to artificial short days from the date of the winter solstice and interrupted with 35 long days in spring resumed cyclicity (median date, 7 September; range, 59 days). Most ewes (seven of nine) exposed to short days from the date of the winter solstice and isolated from other ewes did not resume cyclicity in the following 11 months. In contrast, all ewes resumed cyclicity (median date, 19 October; range, 144 days) when exposed to short days but housed in social contact with other ewes that became reproductively active in early September; however, the onset of cyclicity was later than in ewes exposed to long days (P < 0.01).(ABSTRACT TRUNCATED AT 250 WORDS)

There is a low incidence of ovulation of the first dominant follicle that develops in the early postpartum period of beef suckler cows, which prolongs the interval from calving to first ovulation. The objective of this study was to determine whether a single injection of a GnRH analogue would ovulate the first postpartum dominant follicle. Limousin x Friesian beef suckler cows were assigned at parturition, over two years (16 cows in year 1; 19 cows in year 2), to one of three treatments: (1) untreated (control; n = 12), (2) GnRH analogue (20 micrograms buserelin i.m.) administered in the growing-plateau phase of the first postpartum dominant follicle (GnRH-G; n = 12) and (3) GnRH analogue administered in the declining phase of the first postpartum dominant follicle (GnRH-D; n = 11). From day 8 or 9 post partum, the ovaries of each cow were examined daily by ultrasound to determine the time of GnRH injection and ovulation. Blood samples were collected daily for progesterone measurement to confirm ovulation and in year 2 to determine the duration of the first oestrous cycle. The mean (+/- SEM) number of days from parturition to development of the first dominant follicle was 11.0 +/- 0.3, 10.3 +/- 0.5 and 10.1 +/- 0.7 for cows assigned to treatments 1-3, respectively (P > 0.05). The proportion of cows ovulating the first dominant follicle was higher (P < 0.05) following GnRH treatment (12 of 12 and 7 of 10; GnRH-G and GnRH-D, respectively) than with controls (2 of 12).(ABSTRACT TRUNCATED AT 250 WORDS)

Two experiments were conducted in cyclic beef heifers to determine whether active immunization against bovine inhibin alpha 1-26 Gly-Tyr (bINH) affected follicular dynamics, hormone concentration or ovulation rate. In Expt 1, heifers (n = 9) were actively immunized against bINH conjugated to human alpha globulins (HAG) using bis-diazotized benzidine in non-ulcerative Freund's adjuvant (NUFA; primary on day 0; booster injections on days 53, 84 and 116 using conjugated bINH and on days 176 and 366 using unconjugated bINH; ten heifers were used as controls). Ovaries were examined daily using ultrasound scanning (days 70-155 and 384-391) and corresponding blood samples were collected for bINH antibody titre, luteinizing hormone (LH), follicle-stimulating hormone (FSH) and oestradiol determinations. Four treated and four control heifers were injected with 10 micrograms gonadotrophin-releasing hormone (GnRH) on day 386 (day 2 of the oestrous cycle). Although bINH-immunized heifers had variable antibody titres ranging from 4 to 50% I125-labelled bINH bound to serum diluted 1:2000, ovulation rate was unaffected. In oestrous cycles with three dominant follicles, the ovulatory follicles grew faster (2.5 +/- 0.2 versus 1.6 +/- 0.3 mm day-1; mean +/- SEM), had shorter durations of growth (5.7 +/- 0.8 versus 9.6 +/- 1.6 days) and duration of detection (7.5 +/- 0.8 versus 12.0 +/- 2.4 days) in immunized heifers. Mean concentrations of FSH, LH and oestradiol were unaltered in most cases during oestrous cycles in bINH-immunized compared with control heifers. There was no significant difference in the percentage increase in FSH or LH, after GnRH injection, between control and immunized heifers. As ovulation rate was unaltered in the first experiment, a second similar study was designed using a different immunization protocol. In Expt 2, heifers were immunized with bINH conjugated to human serum albumin using glutaraldehyde with the following doses: 0.0 (control; n = 7), 0.33 (n = 7), 1.0 (n = 8) and 3.0 (n = 7) mg. Three booster immunizations were given 33, 66 and 209 days after primary immunization. Immunization increased the number of oestrous cycles with multiple ovulations (42 of 132 (32%) oestrous cycles examined) compared with controls (1 of 30 (3.3%) oestrous cycles examined). Neither titre nor ovulation rate was affected by dose of bINH used. In summary, following bINH immunization, ovulation rate was not increased despite changes in follicular dynamics in Expt 1, but was increased in 32% of oestrous cycles in Expt 2.(ABSTRACT TRUNCATED AT 400 WORDS)

Photoperiod may regulate seasonal reproduction either by providing the primary driving force for the reproductive transitions or by synchronizing an endogenous reproductive rhythm. This study evaluated whether breed differences in timing of the reproductive seasons of Finnish Landrace (Finn) and Galway ewes are due to differences in photoperiodic drive of the reproductive transitions or to differences in photoperiodic synchronization of the endogenous rhythm of reproductive activity. The importance of decreasing photoperiod after the summer solstice in determining the onset and duration of the breeding season was tested by housing ewes from the summer solstice in either a simulated natural photoperiod or a fixed summer-solstice photoperiod (18 h light:6 h dark; summer-solstice hold). Onset of the breeding season within each breed did not differ between these photoperiodic treatments, but Galway ewes began and ended their breeding season earlier than Finn ewes. The duration of the breeding season was shorter in Galway ewes on summer-solstice hold than on simulated natural photoperiod; duration did not differ between photoperiodic treatments in Finn ewes. The requirement for increasing photoperiod after the winter solstice for initiation of anoestrus was tested by exposing ewes from the winter solstice to either a simulated natural photoperiod or a winter-solstice hold photoperiod (8.5 h light:15.5 h dark). Onset of anoestrus within each breed did not differ between these photoperiodic treatments, but the time of this transition differed between breeds. These observations suggest that genetic differences in timing of the breeding season in Galway and Finn ewes do not reflect differences in the extent to which photoperiod drives the reproductive transitions, because neither breed requires shortening days to enter the breeding season or lengthening days to end it at appropriate times. These findings are consistent with the hypothesis that photoperiod synchronizes an endogenous rhythm of reproductive activity in both breeds and that genetic differences in timing of the breeding season reflect differences in photoperiodic synchronization of this rhythm.

Friesian x Hereford heifers (n = 19; mean +/- s.e.m. body weight (BW) = 375 +/- 5 kg) were used in a randomized incomplete block design. Heifers were fed 0.7 (n = 7; L), 1.1 (n = 7; M) or 1.8% (n = 5; G) of BW in dry matter (DM)/day for 10 weeks. Ovaries were examined by ultrasound, for one oestrous cycle, from week 5 of treatment. Maximum diameter of dominant follicles was smaller (P less than 0.05) in L (11.8 +/- 0.1 mm) than in M (13.7 +/- 0.2 mm) or G (13.2 +/- 0.3 mm) heifers. Growth rate (mm/day) of dominant follicles during the oestrous cycle was not affected (P greater than 0.05) by dietary intake. Persistence of dominant follicles was shorter (P less than 0.05) in L (9.8 +/- 0.2 days) than in M (11.9 +/- 0.3 days) or G (12.7 +/- 0.4 days) heifers. Three dominant follicles were identified during the oestrous cycle of 5 of 7 L, 3 of 7 M and 1 of 5 G heifers (P less than 0.10); 2 dominant follicles were identified in the remaining heifers (n = 2 of 7, 4 of 7 and 4 of 5, respectively). Length of the luteal phase and luteal-phase concentrations of progesterone were not affected (P greater than 0.05) by treatment. Low dietary intake reduced the diameter and persistence of dominant follicles during the oestrous cycle of beef heifers and tended to increase the proportion of oestrous cycles with 3 dominant follicles.

The ovaries of 18 post-partum beef suckler cows were examined daily, using ultrasound, from Day 5 post partum until a normal oestrous cycle was completed. Periods of growth and regression of medium-sized (5-9 mm) follicles were identified before one medium follicle became dominant (single large follicle greater than or equal to 10 mm). The mean (+/- s.e.m.) number of days from parturition to detection of the first post-partum dominant follicle was 10.2 +/- 0.5. The first post-partum dominant follicle ovulated in 2/18 (11%) cows. The interval from calving to first ovulation (mean +/- s.e.m. = 35.9 +/- 3.3 days) was characterized by the growth and regression of a variable number (mean = 3.2 +/- 0.2; range 1-6) of dominant follicles. The maximum diameter of the dominant follicle increased as the cows approached first ovulation (P less than 0.05). Behavioural oestrus was not detected in 16/18 (89%) cows at first ovulation. Following first ovulation, the length of the subsequent cycle was short (mean = 9.7 +/- 0.5 days; range 8-15 days) in 14/18 (78%) cows and was characterized by the development and ovulation of a single dominant follicle. During oestrous cycles of normal length (mean = 20.6 +/- 0.5 days; range 18-23 days) one (N = 2), two (N = 7) or three (N = 8) dominant follicles were identified. The growth rate, maximum diameter or persistence of non-ovulatory dominant follicles before first ovulation or during oestrous cycles were not different (P greater than 0.05). These data show that, in beef suckler cows, follicular development and formation of a dominant follicle occur early after parturition and the incidence of ovulation of the first dominant follicle is low. The number of dominant follicles that develop before first ovulation is variable; first ovulation is rarely associated with oestrus and short cycles are common after first ovulation. It is concluded that prolonged anoestrus in post-partum beef suckler cows is due to lack of ovulation of a dominant follicle rather than delayed development of dominant follicles.

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.

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 (greater than or equal to 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 10-12 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.

Cytogenetic examination was made of 103 13-14-day-old blastocysts and 116 24-32-day-old fetuses from untreated and androstenedione-7-HSA-immunized Merino ewes. There were no differences in the chromosome composition of blastocysts or fetuses from treated or untreated ewes and so the data were combined. At Days 13-14 a 1N/2N mosaic and a 2N - 1/2N/4N mosaic embryo were observed. In addition, 52 of the blastocysts were 2N/4N mosaics, with 8 of these also containing 8N cells, and one blastocyst was a 2N/8N mosaic. No aneuploid fetuses were observed, but 80 of the 116 fetuses contained polyploid cells, including 4N, 6N and 8N cells. The polyploid cells observed in the blastocysts and fetuses should not be considered as abnormal cells as they appear to be a normal part of the developmental processes leading to trophoblast formation and fetal differentiation.

Ewes were immunized against androstenedione (Fecundin) and assigned to be mated 14 days (179 ewes Group C) or 25 days (174 ewes Group B) after a booster immunization with Fecundin. The anti-androstenedione titres at these times were 6790 and 3240 respectively (P less than 0.01). The remaining 169 ewes were untreated controls (Group A). Ewes were mated to entire rams (12 rams to 180 ewes) at their second oestrus after synchronization of oestrus. Immunization against androstenedione caused a shortening of the time from sponge removal to mating (Day 0) and a decrease in the percentage of ewes mated by the rams. Also, ovulation rate was increased after immunization (P less than 0.01), being 1.42, 2.16 and 1.93 for Groups A, C and B respectively. Egg recovery rates on Day 2 were lower in immunized ewes and there was some indication that fertilization rates were lowered. On Day 13 after mating a higher proportion of blastocysts was recovered from ewes in Group A than from those in Groups B and C. Immunization resulted in lower fertilization rates and smaller blastocysts with lower mitotic indexes (P less than 0.01). At Days 24-32 of pregnancy fetal weight was lower in the immunized ewes. At all sampling stages, the proportion of ewes pregnant (fertility) was lowered in immunized ewes. The results of the present study show that significant reproductive wastage occurs in androstenedione-immunized Merino ewes, with lower rates of embryo recovery and delayed embryonic development being found in comparison to controls.(ABSTRACT TRUNCATED AT 250 WORDS)

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 less than 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 less than 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 less than 0.05) than in the contralateral ovary.

Chromosome counts were obtained from 73 out of 177 (41%) early cleavage-stage Merino embryos. A further 13 embryos were classified as probably diploid. Chromosome aberrations were found in 8 (11%) embryos, one of which was aneuploid and the remainder (9.6%) had euploid abnormalities. If the probable diploid embryos are included, the incidence of euploid aberrations falls to 8.1%. Of the abnormal embryos there was one aneuploid with 2N = 55, two haploids, four haploid/diploid mosaics and one zygote with 4 haploid metaphase plates. Two additional zygotes had 4 interphase pronuclei. Four of the euploid abnormalities were attributable to the entry of two or more spermatozoa and therefore polyspermy is the largest single factor leading to chromosomally aberrant embryos in this population of Merino ewes.

Chromosomal analysis was carried out on 48 Day 2-7 embryos collected from superovulated Merino ewes. Three embryos had abnormal chromosome complements (1 X 1N, 1 X 1N/2N, 1 X 3N), yielding an incidence of 6.25% abnormal embryos. It is concluded that superovulation does not cause an increase in the incidence of chromosomal abnormalities in embryos of Merino sheep.