Intrauterine insemination by laparoscopy is required to achieve acceptable lambing rates in ewes when using frozen semen but the procedure has evoked welfare concerns. Oxytocin has been used to dilate the cervix as a means of accessing the uterus during conventional cervical insemination, but its effect on fertility is not well documented. Three hundred crossbred ewes were synchronised in estrus and randomly allocated to one of three insemination procedures using frozen/thawed semen containing 400×106/ml progressively motile sperm: single cervical (0.2 ml), multiple cervical (4×0.05 ml) or laparoscopic (0.05 ml per uterine horn). The effects of each insemination procedure on lambing rate (percentage of treated ewes lambing) and litter size (lambs per ewe lambing) were tested with and without oxytocin (10 IU given i.m.) prior to fixed-time insemination. Oxytocin did not permit complete cervical penetration in any ewes and neither lambing rate nor litter size was influenced by the number of inseminations. Lambing percentages were 69 and 42 (P<0.01) for the laparoscopic and cervical insemination methods, respectively, and oxytocin reduced these to 58 (NS) and 10 (P<0.001) percent, respectively. Corresponding litter sizes for ewes not receiving oxytocin were 1.91 and 1.51 and for those receiving oxytocin, 1.83 and 1.41 (laparoscopic versus cervical, P<0.02). Thus, in the absence of complete cervical penetration at insemination, 10 IU oxytocin decreased the number of ewes lambing but had no effect on their litter size.

Using primiparous autumn-lambing ewes, this study investigated nutritional effects on (i) pulsatile LH secretion, (ii) responsiveness of the pituitary-ovarian axis to exogenous GnRH, and (iii) oestrus and ovarian cyclicity during the early post-partum period. At lambing (25 October +/- 0.3 days), 32 primiparous ewes rearing 2.1 +/- 0.04 lambs were equally allocated to four dietary treatments in a 2 x 2 factorial designed experiment. Diets comprised ad libitum hay and 1.5 kg per ewe per day of one of four concentrates (similar to12.5 MJ metabolizable energy per kg dry matter) containing either fibrous (F) or starchy (S) ingredients with (P) or without (O) the inclusion of 120 g/kg fish meal. Throughout the study (lambing to 17 December) ewe body condition score was assessed and ewes and their lambs were weighed at weekly intervals. Blood samples were obtained from all ewes to measure circulating concentrations of progesterone and oestrous behaviour was monitored using vasectomized rams. On day 12 post partum, blood samples were obtained from all ewes at 2-h intervals (09: 00 to 17: 00 h) to measure concentrations of insulin and urea nitrogen, and at 15-min intervals (09: 00 to 21: 00 h) to measure pulsatile LH secretion. All ewes received 25 i. v. injections of GnRH (250 ng GnRH in 2 ml 0.9% saline) at 2-h intervals commencing 4 h before the end of the 15-min blood sampling period and their ovaries were examined via laparoscopy on day 17 post partum. There was no effect of dietary treatment on ewe live weight or body condition score throughout the study but inclusion of fish meal in the ewe diet increased lamb growth (FP/SP 255 (s.e. 8.9) v. FO/SO 234 (s.e. 8.2) g/day, P < 0.05). Circulating concentrations of insulin on day 12 post partum were lower in ewes given the fibrous compared with the starchy diets (P < 0.05) while dietary inclusion of fish meal increased (P < 0.001) urea nitrogen. Pulsatile LH secretion on day 12 post partum was not affected by dietary treatment. For ewes on diets FP, FO, SP and SO, the numbers that experienced an LH surge during the period of GnRH administration were 1, 2, 1 and 0, and that ovulated by day 17 post partum were 3, 5, 0 and 5 (FP/SP v. FO/SO, P < 0.05) respectively. Dietary treatment did not affect the intervals from parturition to the onset of ovarian cyclicity or oestrus (overall means were 23 (s.e. 1.0) days and 38 (s.e. 1.6) days respectively) but ewes on the fibrous compared with the starchy diet had a higher (P < 0.05) incidence of short (<= 10 days) first ovarian cycles. Results of this study, which involved young growing animals, demonstrate that (i) inclusion of fish meal in the ewe diet influenced the sensitivity of the pituitary-ovarian axis to exogenous GnRH, and (ii) a fibrous compared with a starchy diet was associated with an increased incidence of premature luteal regression.

Using autumn-lambing ewes, this study investigated (i) the effects of diet on gonadotrophin secretion and responsiveness of the hypothalamic-pituitary-ovarian axis to exogenous GnRH during the early post-partum period; and (ii) whether ovulation prior to completion of uterine involution results in an increased incidence of aberrant ovarian cycles. Thirty-two ewes rearing 1.9±0.12 lambs were equally allocated to two dietary treatments at lambing (22 October ±0.2 day). Diets comprised ad libitum hay and 1.5 kg per ewe per day of one of two concentrates (11.5 MJ ME, 195 g CP per kg) containing 300 g kg−1 cracked maize grain (M) or 300 g kg−1 sugar beet pellets (S). Half of the ewes on each diet (G) received 25 i.v. injections of 250 ng GnRH in 2 ml 0.9% saline at 2 h intervals from days 12–14 post-partum while remaining ewes (N) were monitored for the resumption of spontaneous ovarian cyclicity. Blood samples were obtained from all ewes throughout the study (lambing to 18 December) for measurement of circulating hormone concentrations and the uteri and ovaries of all ewes were examined via laparoscopy on day 21 post-partum. There were no effects of dietary treatment on ewe daily live weight loss, lamb daily live weight gain or the immediate post-partum increase in circulating FSH concentrations. Diet did not affect insulin concentrations or LH pulse frequency on day 12 post-partum but LH pulse amplitude was lower in ewes fed concentrate M compared to concentrate S (1.4±0.10 versus 1.7±0.12 ng ml−1, respectively, P<0.05) and this was associated with an increased interval to the resumption of spontaneous ovarian cycles (35±3.1 versus 26±2.1 day, respectively, P<0.05). Administration of exogenous GnRH increased (P<0.05) the proportion of ewes on both diets that ovulated within 20 days of parturition and advanced the onset of ovarian cyclicity in ewes fed concentrate M by 9.5 days (significance of interaction, P<0.05). Four ewes, all of which ovulated before day 22 post-partum, had extended luteal activity while in remaining ewes, duration of the first luteal phase was inversely related to the time of first ovulation (r2=0.16, P<0.05). Results demonstrate that (i) the onset of ovarian cyclicity is influenced by diet and can be advanced by administration of exogenous GnRH; and (ii) ovulation during the early post-partum period is associated with an increased incidence of extended luteal activity.

The aim of this study was to determine whether there are seasonal shifts in ovulatory response, and in the viability of ova recovered from superovulated ewes. Fifty mature ewes underwent a standard oestrous synchronisation (CIDR), superovulation (oFSH) and artificial insemination procedure during October (peak breeding season) and April (transition to anoestrus). In each month peripheral LH and progesterone concentrations were measured around the time of ovulation and embryos were recovered, graded and cryopreserved on day 6 after insemination. During the subsequent breeding season, grade 1 and 2 morulae and unexpanded blastocysts were thawed and transferred singly to synchronous recipients (October, n=40; April, n=40) or cultured in vitro for 18–20h (October, n=107; April, n=98). Following culture, viable embryos were stained to count cell nuclei or assayed to measure their capacity for glucose metabolism ([3H]glucose) and protein synthesis ([35S]methionine). Peak LH concentrations were higher in October than in April (38.2±3.26ngml−1 versus 25.7±1.99ngml−1, respectively; P<0.01) and the pre-ovulatory LH surge was advanced by ∼3h (P<0.05). Progesterone concentrations at CIDR withdrawal were lower in October than in April (3.1±0.16ngml−1 versus 4.3±0.19ngml−1, respectively; P<0.001) but were not different at embryo recovery. Season did not affect the numbers of corpora lutea per ewe or the numbers of ova recovered but the proportion of recovered ova that was unfertilised/degenerate was lower in October than in April (0.43 versus 0.58, respectively; P<0.001). For embryos containing more than 16 cells, there was no effect of season on the median stage of development or morphological grade. The proportions of October and April embryos that established pregnancy following transfer to recipient ewes were 0.78 and 0.70 (not significantly different), and that were viable after in vitro culture were 0.66 and 0.37 (P<0.05), respectively. Season did not affect the number of nuclei per viable embryo or the capacity for protein synthesis but the glucose uptake of October embryos was approximately double that of April embryos (3163±293.4dpm versus 1550±358.9dpm, respectively; P<0.05). Results indicate that during the late compared to peak breeding season, there is an increased incidence of fertilisation failure as a possible consequence of seasonal shifts in LH secretion and (or) associated effects on follicular function. Frozen–thawed embryos produced at contrasting stages of the breeding season are equally viable in vivo but those produced during the late, as opposed to the peak breeding season have lower viability following in vitro culture.

The effects of different energy Sources in the lactation diet on sow and piglet performance were assessed in association with effects on the metabolic state of the sow around peak lactation. Either maize starch (S) or soya-bean oil (F) was added to a basal diet to provide 0.34 of total digestible energy (DE) intake, such that the experimental diets provided the same daily intakes of DE and crude protein. Twenty-four multiparous sows were allocated between two groups at farrowing, each given one of the two dietary treatments for a lactation period of 28 days. Sow weight and backfat (P-2) as well as individual piglet weights were measured on a weekly basis. Litter sizes were standardized to 10 piglets. Milk samples were collected from sows on days 8, 12, 17, 21 and 25 of lactation to measure milk composition and prolactin concentrations. Blood samples were taken via an ear vein catheter from a subsample (7 S, 6 F) of sows on day 14 of lactation; two pre- and seven post-feeding samples were taken at 60-min intervals to measure plasma prolactin, insulin, glycerol, triglyceride, non-esterified fatty acid, urea, beta-hydroxybutyrate and glucose concentrations. There was no effect of energy source on sow weight or P2 loss or on subsequent weaning-to-oestrus interval. Sows offered starch weaned more piglets than sows offered soya-bean oil (9.4 v. 8.4. P < 0.05). Litter weight gains were higher for S than F sows in week 3 of lactation (2.2 v. 1.7 kg/day, P < 0.05), irrespective of litter size. Significantly increased plasma urea and beta-hydroxybutyrate concentrations and lower post-prandial increases in plasma glucose and insulin concentrations were observed in F sows around peak lactation. Neither milk nor plasma prolactin concentrations were significantly affected by dietary treatments. The metabolic indices indicated that the F diet was more limiting in dietary glucose availability, which was associated with impaired milk yield as indicated by poorer litter performance. In conclusion, this study suggests that starch is superior to fat as an energy source in sow lactation diets, particularly in the later stages of lactation.

The roe deer blastocyst is in diapause between August and December, after which time it expands and elongates rapidly before implantation. Blood samples were taken from 30 animals to define temporal changes in reproductively important hormones to investigate the physiological cues present at embryo reactivation. In 15 of these animals, changes in uterine and conceptus protein synthesis and secretion, and luteal progesterone release during diapause and reactivation, were assessed after culture of these tissues in vitro. Oestradiol concentrations remained low during diapause (1.07 +/- 0.4 pg ml(-1)) and expansion (1.2 +/- 0.4 pg ml(-1)) but increased by 30 times at trophoblast elongation (49.17 +/- 0.37 pg ml(-1)). Prolactin remained at basal concentrations (4.69 +/- 0.86 ng ml(-1)) and increased after implantation (12.34 +/- 2.71 ng ml(-1)). Peripheral progesterone concentrations and luteal progesterone release remained constant throughout diapause, reactivation and implantation (peripheral progesterone: 3.82 +/- 1.97 ng ml(-1); luteal progesterone: 6.72 +/- 0.81 ng mg(-1) protein). Incorporation of a radiolabel into conceptus secretory proteins increased by four times at expansion compared with diapause, whereas incorporation into endometrial secretions remained constant. At elongation, incorporation into endometrial secretions increased two times and conceptus secretions increased 32 times. Two-dimensional electrophoresis and fluorography showed that the profile of endometrial secretory proteins was constant until implantation when qualitative changes were evident. Although a role for an endocrine maternal trigger of reactivation from diapause cannot be dismissed, these data provide no supporting evidence and indicate that the conceptus itself may drive reactivation.

The extent to which young sows, which still have a strong drive to continue maternal growth, partition nutrients from body reserves towards milk production, may be influenced by their genetic growth target. Modern genotype sows, with a high mature body protein mass, are thus particularly challenged. It has been suggested that to optimise their metabolic state for expressing lactational potential they will have to achieve a satisfactory proportion of their mature body protein mass before farrowing. This could be constrained by current feeding and breeding regimes. To test this hypothesis, gilts of genotypes differing in their body protein:lipid content were given the choice between a low and a high protein diet during rearing and pregnancy, and their intake, subsequent performance and metabolic state in lactation were measured.

In vitro blastocyst production was determined for oocytes recovered postmortem from 48 beef x dairy heifers offered low (Low NH3) or high (High NH3) plasma ammonia-generating diets during the period of late antral follicle development. Following the establishment of a reference estrus (d 0), the experimental diets were offered for an 18-d period starting on d 3 and during which a second estrus was induced (d 16) 4 d before the animals were slaughtered. Blood samples collected at varying intervals were analyzed for ammonia, urea, progesterone, and LH. Ovarian folliculogenesis was monitored daily by transrectal ultrasonography. Ovaries were collected at slaughter and cumulus-oocyte complexes were aspirated from small (1 to 4 mm) and medium-sized (> 4 to 8 mm) sized follicles. In vitro-matured and -fertilized putative d-1 zygotes were cultured for a further 7 d in vitro and embryo development and metabolism were assessed. Relative to the low-NH3-generating diet, the high-NH3-generating diet increased peak postprandial levels of plasma ammonia (326.1 +/- 43.3 vs 52.1 +/- 7.4 micromol/L; P < .001), mean levels of plasma urea (7.0 vs 5.7 mmol/L; SED = .2; P < .001), peak levels of plasma progesterone prior to induced luteolysis (8.9 +/- .4 vs 6.8 +/- .3 microg/L; P < .001), and follicular fluid levels of ammonia (267 +/- 18 vs 205 +/- 20 nmol/mL; P < .05) and progesterone (351 +/- 69 vs 199 +/- 26 ng/mL; P < .05). The timing and level of the preovulatory LH surge was not affected by dietary treatment. Of oocytes cultured, cleavage (47.4 vs 62.4%; P = .02) and blastocyst production (10.9 vs 20.6%; P = .06) rates were reduced when the oocytes were derived from heifers offered the high- rather than the low-NH3-generating diets. There were interactions between dietary treatment and follicle size class, which indicated that fewer blastocysts were produced from cleaved oocytes derived from medium-sized follicles of heifers offered the high-NH3 treatment but that de novo protein synthesis was increased in such embryos. In conclusion, exposure to high levels of ammonia and(or) urea in vivo can significantly compromise the subsequent capacity of oocytes to develop to blastocysts in vitro, and oocytes recovered from medium-sized follicles are particularly sensitive to this effect.

Interactive effects of light and temperature on aspects of seasonality were studied in female British Saanen dairy goats. Four groups of adult non-pregnant non-lactating goats (n = 5) were housed under the following conditions: controls (July-June): natural photoperiod and temperature; group 1 (July-December): long days (16 h light: 8 h dark) and natural temperature; group 2 (July-December): long days and average summer temperature (17.6 degrees C); group 3 (December-June): short days (8 h light: 16 h dark) and winter temperature (8.4 degrees C). Plasma prolactin and progesterone were measured once a week, circadian changes in prolactin and melatonin were determined in December and May, and coat development was assessed. Seasonal variation in prolactin was influenced by manipulation of both daylength and temperature. In group 1, prolactin concentrations decreased as the environmental temperature decreased, despite maintenance of long days. When light and temperature were maintained under summer (group 2) and winter (group 3) conditions, prolactin remained relatively constant, although at different high and low set points, respectively, but with indications of a seasonal rhythm. An asymptotic relationship between prolactin and temperature was maintained under all daylengths. The circadian pattern of melatonin was related to daylength and was not influenced significantly by temperature. Onset of oestrus was unaltered. In group 3 (maintained winter solstice light and temperature), anoestrus was delayed (P < 0.05) from a median control date of 17 March to a median date of 28 April. Winter coat development was delayed in group 1; group 2 showed premature moulting of the winter coat; and in group 3, development of the summer coat was delayed. The results imply that temperature modifies the influence of daylength on prolactin secretion and hair follicle growth by mechanisms that do not involve melatonin.

Supplements of dietary fat are highly effective in boosting energy intake at critical phases during the reproductive cycle. When fed to ruminants in the form of calcium salts of fatty acids, they have been shown to increase plasma cholesterol and progesterone levels (Spicer et al, 1993) which, in turn, could have beneficial effects on ovulation rate and embryo quality. In sheep, a likely reproductive state for a physiological response to a lipid supplement is during the superovulation of young animals in which the post-ovulatory steroidogenic capacity of the corpora lutea may be sub-optimal. The present study examined the effects of donor age and dietary fat on plasma progesterone concentration, and the yield and quality of embryos in superovulated Cheviot sheep.

The objective of this study was to determine the relative importance of seasonal changes in ovulation rate, fertilization rate and embryo survival as the cause of reduced lambing rates in ewes mated in February compared with those mated in November. The study was conducted at 57 degrees N using mature Mule ewes and Suffolk rams. Sixty ewes were allocated equally to five groups: unbred (UB) or mated at a natural oestrus during November (N) or February (F) by natural (N) or cervical artificial (A) insemination. Groups were maintained separately at pasture supplemented with hay. A raddled vasectomized or non-vasectomized ram was present with UB, NN and NA groups from 26 October 1995 to 1 January 1996 and with UB, FN and FA groups from 25 January 1996 to 31 March 1996. Ewes marked by the ram were recorded twice a day, and those in groups NN, NA, FN and FA were inseminated at their second behavioural oestrus. For all ewes, blood samples were obtained once a day from introduction of the vasectomized rams until 30 days after mating (groups NN, NA, FN and FA) or 20 days after the first oestrus (group UB), and ovulation rate was measured by laparoscopy 7 days after the first oestrus. For ewes in groups NN, NA, FN and FA, ovulation rate was measured again after the second oestrus and ova were recovered from six ewes per group for assessment of fertilization before autotransfer. Pregnancy and lambing rates were recorded at term. Mean (+/- SE) dates of the first recorded oestrus for ewes in groups NN, NA and UB, and FN, FA and UB were 4 +/- 1.1 November and 4 +/- 0.9 February, respectively, and intervals between the first and second oestrus were 16 +/- 0.2 and 17 +/- 0.3 days (P < 0.01), respectively. Ovulation rates were 2.6 +/- 0.08 and 2.0 +/- 0.05 (P < 0.001), and peripheral progesterone concentrations during the luteal phase were 8.5 +/- 0.25 and 7.6 +/- 0.31 ng ml-1 (P < 0.05), for November and February, respectively. The difference in peripheral progesterone concentration was not solely attributable to the difference in ovulation rate. There was no significant effect of month or method of insemination, or of embryo recovery and autotransfer procedures on pregnancy rates and the proportion of ewes that became pregnant were NN 0.92, NA 0.83, FN 0.67 and FA 0.75. For ewes undergoing embryo recovery and autotransfer, ova recovered per corpus luteum were 1.00, 0.93, 1.00 and 0.92, fertilized ova per ovum recovered were 0.69, 0.92, 1.00 and 0.83, and lambs born per corpus luteum were 0.62, 0.79, 0.78 and 0.58 for NN, NA, FN and FA groups, respectively. There were no significant seasonal effects on fertilization rate or embryo survival. It is concluded that a seasonal decline in ovulation rate is the primary cause of reduced lambing rates in ewes mated in February compared with those mated in November. Pregnancy rates were high after mating in both periods and were not enhanced by the use of cervical insemination.

Starch and fat are the two major energy sources available for sow lactation diets. Fat is more energy dense and can be used to maximise energy intakes, particularly in sows with low appetite. However, the quantity of milk produced in sows has been associated with milk lactose production and the main precursor for lactose is glucose, for which dietary starch is the major source. It is therefore important to know the consequences of using a glucose deficient energy source, such as fat, compared to starch in lactation diets. The following experiment was designed to assess energy sources in lactation diets at an isocaloric level in determining sow and piglet performance, in association with the effects of dietary glucose availability on the metabolic state of the sow around peak lactation.

Effective oestrous synchronisation for sheep AI programmes is characterised by low progesterone concentrations at the time of insemination. In a large scale study of over 2,000 Suffolk ewes inseminated in early August Dingwallet al(1996), found that a significant proportion (0.055) had elevated progesterone concentrations at the time of insemination. McKelveyet al(1997) showed that aberrant luteal activity occurs in some Suffolk ewes in deep anoestrus and speculated that this phenomenon was due to spontaneous ovulations following the preceding lambing. The present study involved the monitoring of circulating progesterone concentrations in Suffolk ewes lambing in early January with the aim of establishing the incidence and nature of ovarian luteal activity post lambing.

The objective was to determine the effect of age and dietary protein content on post-partum oestrous and ovarian cyclicity in autumn-lambing ewes. Twenty-four multiparous (age 4.5 (s.e. 0.61) years) and 24 primiparous (age 1.5 years) ewes which lambed on 28 October (s.e. 0.2) and were rearing 2.0 and 2.7 (s.e. 0.13) lambs, respectively, were equally allocated to two dietary treatments in a 2 X 2 factorial design. Diets comprised ad libitum hay supplemented with concentrate (12.5 MJ metabolizable energy per kg dry matter (DM) and either 210 or 140 g crude protein per kg DM), offered at a daily allowance of 1.2 kg per ewe from lambing to weaning (18 December) and 0.4 kg per ewe thereafter. Throughout the study (3 November to 24 May) eves were group-housed in straw-bedded pens under natural photoperiod at 57 degrees N and their live weights and body condition scores were assessed at 2-week intervals. A raddled vasectomized ram was continually present with each group and ewes marked by the ram were recorded thrice weekly. Blood samples were obtained thrice weekly for measurement of peripheral progesterone concentrations and ovulation rate was determined by laparoscopy during January and March. There was no significant effect of dietary protein content on any of the variables measured. For multiparous and primiparous ewes, mean live weights and body condition scares at lambing were 79.5 (s.e. 1.41) v. 58.4 (s.e. 1.54) kg (P < 0.001) and 2.5 (s.e. 0.05) v. 2.2 (s.e. 0.05) (P < 0.001) and daily live-weight losses over the suckling period were 153 (s.e. 19.3) v. 85 (s.e. 21.2) g/day (P < 0.05). Intervals from parturition to first overt oestrus were 39 (s.e. 3.2) v. 33 (s.e. 2.3) days and to the onset of ovarian cyclicity were 29 (s.e. 4.9) v. 25 (s.e. 1.5) days. Durations of ovarian cyclicity were 133 (s.e. 27.1) and 110 (s.e. 5.7) days (P < 0.01) during which 7.6 (s.e. 0.32) and 6.5 (s.e. 0.34) (P < 0.05) ovarian cycles were recorded respectively. Fifteen aves had initial short cycles (less than or equal to 10 days), six had prolonged cycles (greater than or equal to 22 days) and 11 had extended inter-luteal phase intervals (greater than or equal to 8 days). All ewes had recent ovulations at the January laparoscopy but only 19 multiparous and nine primiparous ewes had ovulations in March. Mean ovulation rates were: January 2 2 (s.e. 0.14) and 1.4 (s.e. 0.13) (P < 0.001), and March 1.6 (s.e. 0.23) and 1.2 (s.e. 0.15) for multiparous and primiparous ewes, respectively. It is concluded that, for aves lambing at their normal time of mating, (i) the strong seasonal drive for reproduction results in the resumption of oestrous and ovarian cyclicity during the early post-partum period; (ii) initial luteal phases may be of short or extended duration; (iii) there is no effect of age or dietary protein content, within the range studied, on the onset of ovarian cyclicity; and (iv) multiparous ewes experience a greater number of ovarian cycles and achieve higher ovulation rates than primiparous ewes.

The metabolic status and reproductive performance of four pure breeds of beef cow (small size and low milk potential, Aberdeen Angus; small size and high milk potential, Welsh Black; large size and low milk potential, Charolais; and large size and high milk potential, Simmental) were monitored during their first two parities. Heifers from each breed were allocated to one of two levels of annual energy intake relative to metabolic body weight (M-0.75) (mean daily intakes equivalent to 705 and 820 kJ/kg M-0.75) in a factorial design. In the 1st year 64 heifers (eight per treatment) which had calved as a consequence of first or second service were selected for the experiment. In the 2nd year 40 of these animals (five per treatment) which held to first or second service remained on experiment. Animals were housed all year round and given diets designed to represent energy intakes while grazing during the summer and conserved feeding during the winter. Pregnancy was established in late July of each year using a combination of oestrous synchronization and artificial insemination. Blood samples were collected at monthly intervals from weaning in November until calving in A May; three times weekly from calving until oestrous synchronization (11 weeks later); and fortnightly thereafter until weaning.For the annual levels of dietary energy intake offered, two breeds (Welsh Black and Charolais) exhibited relatively high growth rates and had the longest post-partum anovulatory periods; al and Charolais cotes also had the poorest conception rates of all breeds. Relatively lean cows at calving (body condition score less than or equal to 2.5 units) were sensitive, in terms of the duration of the anovulatory period, to live-weight loss during the early post-partum period, particularly when blood glucose levels were low, whereas relatively fat cows at calving (body condition score >2.5 units) were not. The data suggest: (i) that mechanisms controlling the anabolic processes governing maternal growth are antagonistic towards those that control rc production; and (ii) the catabolism of lean tissue rather than fat tissue during the early post-partum period is also antagonistic towards the mechanisms that govern reproductive function in cows.

Cellular differentiation induces various morphological changes, including elongation, in mitochondria. Preimplantation embryos have round-shaped mitochondria, characteristic of undifferentiated cells. However, there is controversy regarding the precise mitochondrial morphology in blastocyst embryos, which are generated from two cell lineages: undifferentiated inner cell mass (ICM) and differentiated trophectoderm (TE). This study attempted to precisely determine mitochondrial morphology in these two blastocyst regions. Transmission electron microscopy analyses were conducted using more than 1000 mitochondria from blastocyst embryos. No significant differences were observed in the configuration of mitochondrial cristae and frequencies of hooded mitochondria, which are specific to embryos of livestock animals, between the ICM and TE. To accurately compare mitochondrial roundness between the ICM and TE, oblateness was calculated based on both the major and minor axes. Average oblateness was significantly greater in the TE than in the ICM (P < 0.01). These results indicate tissue-specific mitochondrial maturation with complete elongation in the TE at the blastocyst stage. Since mitochondrial elongation is closely associated with cellular metabolism and differentiation, the present study provides new insights for better understanding of early embryonic development in cattle.

The mammalian placenta is an active endocrine organ capable of synthesising and secreting a wide range of hormones and proteins. Pregnancy-associated glycoprotein (PAG) is one of these. It is produced by the binucleate cells of the placenta and becomes detectable in the maternal circulation soon after implantation (Zoli et al., 1992a). PAG occurs in cattle (bPAG), goats and sheep (oPAG), and has been used for early pregnancy diagnosis and the detection of embryonic death (Ranilla et al., 1994).In the postpartum cow bPAG has a slow disappearance rate and is detectable in maternal serum until 100 days after calving (Zoli et al., 1992b). The present work was carried out to determine the rate of decline of oPAG in postpartum ewes and to test if the disappearance rate differed with litter size, age and diet.

To avoid winter scarcity of fresh goat milk, simple methods of advancing the season of kidding would be commercially valuable. A combination of long-day light treatment followed by melatonin is successful but other aspects of seasonality including coat growth are also reset. To investigate whether effects on breeding season and coat growth can be dissociated, British Saanen dairy goats (no. = 30) were randomly allocated to one of six groups. Control gents were untreated. Goats in the other five groups received 2 months of treatment with 20 h light : 4 h darkness (20L : 4D) and were then given 3 mg melatonin orally at 16.00 h for 2 months. The treatments started on 11 January (group 1), 29 March (group 2) 14 June (group 3), 30 August (group 4) and 8 November (group 5). Weekly blood samples were taken for the measurement of progesterone to monitor ovarian activity and prolactin. Side patches (10 cm x10 cm) were clipped monthly from alternate sides and weighed to measure coat growth. The onset of ovarian activity was advanced from a median date of 15 November in controls to 24 May in group 1 (P < 0.01), 16 August in group 2 (P < 0.05) and 18 October in group 3 (P < 0.05). Groups 4 and 5 showed no significant change in the onset of oestrus (median onset dates 8 November and 1 November, respectively). Group 1 goats came into season again with controls in November. In all except group 5, treatment interacted with time to affect significantly the growth of the coat. The pattern of coat growth was most altered IP < 0.001) in groups I and 2. This teas associated with effects on plasma prolactin concentrations of light stimulation and melatonin suppression. Group I gents resynchronized with control goats to show a coat of normal weight in the winter following treatment. Division of milking goat herds into spring and autumn kidding groups is, therefore, a practical possibility, but effects on overall milk yield require study.

The success of sheep breeding programmes involving sire reference schemes depends on effective oestrous synchronisation programmes that provide optimum pregnancy rates following fixed-time insemination (McKelvey & Simm, 1995). Effective oestrous synchronisation is characterised by low progesterone concentrations at the time of insemination. However in pedigree Suffolk ewes inseminated at a synchronised oestrus in early August, Dingwall et al (1995) reported that a significant number of ewes in some flocks had elevated progesterone concentrations at the time of insemination and, as a consequence, flock fertility was adversely affected. It is hypothesised that high progesterone reflects aberrant luteal activity arising from spontaneous ovulations following the preceding lambing. The present study sought to identify the incidence of aberrant luteal activity in Suffolk ewes during seasonal anoestrus and to study the effect on conception of interventional treatment of these animals prior to artificial insemination.