Dietary restriction in sheep: Uterine functionality in ewes with different body reserves during early gestation

The aim of this study was to characterize insulin, leptin and IGF-1 profiles after undernutrition in pregnant ewes with different initial body condition (iBCS) and to investigate embryo quality, uterine gene expression and presence and location of proteins during early gestation (day 5). Thirty-six Rasa Aragonesa ewes were divided into 2 groups with different BCS: BCS> 2.75 (high, H, n = 19) and BCS <2.25 (low, L, n = 17) and they were randomly assigned to two nutritional treatments: 1.5 maintenance (M) (control, C) or 0.5 (M) (undernourishment, U) times the daily maintenance requirements establishing four groups: high-iBCS control (HC, n = 9), high-iBCS undernourished (HU, n = 10), low-iBCS control (LC, n = 9) and low-iBCS undernourished (LU, n = 8). High-iBCS ewes presented higher concentration of IGF-1, reflecting a better metabolic status in these animals. There was a greater proportion of high-iBCS ewes presenting more than one CL (P < 0.05), and associated greater P4 plasma concentration, number of recovered embryo and a tendency for higher embryo viability rate (P = 0.13). In uterus, undernourished ewes tended to present lower P4 (P = 0.09) and higher E2 concentration (P = 0.10). Inmunostaining of uterine progesterone and estrogen receptors (PR and ERα) was not affected by iBCS and nutritional treatment. Ewes with low-iBCS tended to have more INSR mRNA, and undernourished ewes tended to have more IGFBP2 mRNA expression (P < 0.08). An interesting finding was that the uterine response to undernutrition was dependent on iBCS: a higher expression of GHR (P < 0.05) and a tendency in IGFBP5 (P = 0.09) mRNA was found in undernourished than control ewes but only in the high-iBCS group. In summary, the present study demonstrates that the endocrine response and the uterine gene expression to undernutrition depend on the initial body energy reserves (iBCS) and appears to be associated with a differential embryo quality.

193 Melatonin implants in spring improve embryo production of aged ewes after superovulation regardless of endometrial progesterone receptor expression

Twenty-three Rasa Aragonesa aged ewes (average age: 10.3±0.3 years) were used to determine the effect of melatonin on ovulatory response, embryo production, and endometrial expression of progesterone receptors (PR) after superovulation. Ewes were treated (M, n=13) or not (control, C, n=10) with melatonin implants in March (Day 0, Northern Hemisphere autumn), and received intravaginal progestogen sponges for 14 days on Day 77. Superovulatory treatments consisted of 8 doses in decreasing concentrations (2 mL×2 and 1 mL×6) of 176 NIH-FSH-S1 units of NIADDK-oFSH-17 (Ovagen, ICPbio Reproduction, Auckland, New Zealand) administered twice daily starting 72h before sponge removal. Seven days after oestrus, embryos were recovered by laparotomy, ewes were killed, and uterine horns were processed to study PR expression by immunohistochemistry. The amount of PR was estimated subjectively by 2 independent observers in 5 endometrial compartments: luminal epithelium (LE), superficial (sGE) and deep (dGE) glandular epithelia, and superficial (sS) and deep (dS) stroma. The extent of staining was expressed on a scale from 0 to 100. Data were analysed with a 2×2 factorial ANOVA. Melatonin implants improved fertilization (92v. 57%, for M and C groups, respectively; P&lt;0.01), blastocyst (47v. 9%; P&lt;0.01), viability (88v. 31%; P&lt;0.0001), and freezability (69v. 21%; P&lt;0.001) rates. Specifically, melatonin induced a significant reduction of the number of non-viable (degenerate and retarded) embryos (0.3v. 1.5; P&lt;0.05) and increased blastocysts (2.8v. 0.8; P&lt;0.05) per ewe. Melatonin treatment decreased PR staining intensity (47v. 55%; P&lt;0.05), but this effect was not observed when the individual cell types were compared (Table 1). Because the number of corpora lutea (CL) was responsible for different PR expression in both groups (P&lt;0.0001), animals were divided into 2 ovulation rate categories: &lt;10 CL and ≥10 CL, with lesser PR expression in the ≥10 CL group (P&lt;0.0001); this lower PR immunostaining in ≥10 CL is consistent with progesterone down-regulation of its own receptor. An interaction among number of CL and treatment was found for embryo quality (P&lt;0.05); thus, the positive effect of melatonin on this parameter was particularly effective in the low-ovulation-rate group. These results demonstrate that melatonin treatment in the autumn improves embryo quality in aged ewes, and that this effect is not explained by a differential endometrial sensitivity to progesterone. Table 1.Embryo production (mean±s.e.m.) in melatonin-treated (M) and control (C) ewes after superovulation in autumn, and staining intensity of progesterone receptors in the endometrium (CL=corpora lutea)

125 Presence of melatonin receptors in ovine blastocysts

Melatonin increases in vivo embryo viability in sheep and improves the blastocyst rate on in vitro sheep embryo culture. To determine whether this melatonin effect is receptor-mediated, we evaluated the presence of melatonin receptors MT1 and MT2 on in vitro-obtained sheep embryos by means of RT-PCR and indirect immunofluorescence (IIF). For in vitro embryo production, oocytes were collected from ovaries of adult ewes and matured with TCM-199; 10% oestrus sheep serum; FSH and LH, 10μg mL−1 each; cysteamine, 100 μM; sodium pyruvate, 0.3 mM; penicillin G, 100IU mL−1; and streptomycin sulfate, 100μg mL−1 for 24h at 39°C and 5% CO2. Matured oocytes were transferred to a fertilization medium (SOF without glucose, with 2% oestrus sheep serum; heparin, 10μg mL−1; and hypotaurine, 1μg mL−1) and fertilized with swim-up selected spermatozoa at a final concentration of 106 cells mL−1. After 36h, the cleaved embryos were incubated in culture medium (SOF with amino acids, 0.4% BSA; l-glutamine, 1 mM; penicillin G, 100IU mL−1; and streptomycin sulfate, 100μg mL−1) for 8 days at 39°C with 5% CO2, 5% O2, and 90% N2. In vitro fertilization was repeated 3 times. Day 8 hatched blastocysts were selected for RT-PCR or IIF. For RT-PCR assays, RNA from 5 to 10 blastocysts was extracted and reverse transcribed with SuperScript™ III CellsDirect™ cDNA Synthesis Kit (Thermo Fisher Scientific Inc., Waltham, MA, USA). The PCR amplification was carried out in a Step One Plus Real-Time PCR System (Applied Biosystems, Foster City, CA, USA). The PCR mix contained 2μL of embryo cDNA, iTaq Universal SYBR Green Supermix (Bio-Rad Laboratories Inc., Waltham, MA, USA) and 200nM of the MT1 (forward: 5′-CTCCATCCTCATCTTCACCATC-3′, reverse: 5′-GGCTCACCACAAACACATTC-3′, 113bp) or MT2 (forward: 5′-GCTGAGAGAATGGAGCGATATG-3′, reverse: 5′-GTCCACAGTGAGAAGCCATC-3′, 81bp) primers. The RT-PCR products were visualised under ultraviolet light on 2% agarose gel in a TBE buffer (Tris, 0.9 M; boric acid, 0.9 M; and EDTA, 20mM) with 0.5μL mL−1 ethidium bromide. Ovine testis was used as positive control. For IIF, 5 blastocysts were fixed with 4% paraformaldehyde, permeabilized with 0.5% Triton X-100 and blocked with 5% BSA in PBS for 2h at RT. Embryos were incubated overnight at 4°C with MTNR1A mouse polyclonal antibody (Abnova, Taipei City, Taiwan) for MT1, and rabbit melatonin receptor 1B antibody (Acris Antibodies, Atlanta, GA, USA) for MT2, both diluted 1/50 in PBS with 1% BSA. Secondary antibodies were Alexa Fluor 594 chicken anti-mouse (Invitrogen, Carlsbad, CA, USA) for MT1 and Alexa Fluor 488 chicken anti-rabbit for MT2, diluted 1/800 in PBS containing 1% BSA. Embryos were mounted in slides and visualised on a Nikon Eclipse E-400 microscope (Nikon, Tokyo, Japan). The RT-PCR revealed a single band of 113bp for MT1 and another one of 81bp for MT2 in both the embryo samples and the positive control, which confirmed the gene expression of melatonin receptors in the ovine embryo. The IIF located the MT1 receptor around the nucleus of the trophoblastic cells, whereas MT2 was over the nucleus in the same cells. These results indicate the presence of melatonin receptors in sheep blastocyst, which could mediate the positive effects of this hormone on embryo viability.

Ram Sperm Selection by a Dextran/Swim-Up Procedure Increases Fertilization Rates Following Intrauterine Insemination in Superovulated Ewes

The objective of this study was to compare the efficacy of 2 dextran/swim-up media to increase the sperm quality parameters and the maintenance of these parameters at 15 degrees C and 30 degrees C over 6 hours. Additionally, this study examined whether differences in sperm quality reflect different reproductive efficiencies following intrauterine insemination in superovulated ewes. The study involved 2 selected samples (SS) obtained by dextran/swim-up, performed either with (SS+) or without (SS-) capacitating compounds, and a control sample consisting of raw semen diluted in the same medium. The efficacies of the swim-up sperm selection procedures were similar in both media, and no significant differences were found among the evaluated parameters. Conversely, we found important differences between selected and control samples. Sperm motility, viability (as assessed by carboxifluorescein diacetate/propidium iodide [PI] staining), and mitochondrial activity (as assessed by rhodamine 123/PI) were significantly higher in the selected samples than in the control. Additionally, following incubation at 15 degrees C, the preservation of sperm quality was significantly better in the selected samples than in the control samples. After 6 hours of incubation at 15 degrees C, selected samples had a motility value of 46%, which was significantly (P < .001) higher than the value observed in control samples (27%). The percentage of viable cells observed after 6 hours of incubation at 15 degrees C was significantly (P < .0001) higher in selected samples than in the control samples. Furthermore, after 2 hours of incubation at 30 degrees C, swim-up samples had viability values that were significantly (P < .0001) higher than those of the control samples. SS+ and SS- samples did not differ significantly in spermatozoa yield, sperm quality, or survival. Differences between selected samples and controls were reflected in the fertilization rate obtained following intrauterine insemination in superovulated ewes that experienced a 52-hour interval between progestagen removal and artificial insemination. A restricted criterion for fertilization rate evaluation was established, and only the percentage of embryos recovered from the uterine horns 6 days after insemination was considered with respect to the total number of corpora lutea counted in the ovaries. The fertilization rate of SS- samples (50%) was significantly higher (P > .001) than those of the SS+ (2%) and control samples (5%).

Hormonal control of reproduction in small ruminants

Reproduction of small ruminants can be controlled by several methods developed in recent decades. Some of these involve administration of hormones that modify the physiological chain of events involved in the sexual cycle. Methods which utilise progesterone or its analogues are based on their effects in the luteal phase of the cycle, simulating the action of natural progesterone produced by the corpus luteum after ovulation, which is responsible for controlling LH secretion from the pituitary. Use of prostaglandins is an alternative method for controlling reproduction by eliminating the corpus luteum and inducing a subsequent follicular phase with ovulation. Finally, the discovery of the properties of melatonin in photoperiod-dependent breeding animals opened up a new methodology to control reproduction in these species, inducing changes in the perception of photoperiod and the annual pattern of reproduction. Use of hormones to induce oestrus has allowed increased use of artificial insemination in small ruminants, a very useful management tool, considering the difficulty of detecting oestrus in these species. At commercial level, synchronisation of oestrus allows control of lambing and kidding, with subsequent synchronisation of weaning of young animals for slaughter. Also, it allows more efficient use of labour and animal facilities. Multiple ovulation and embryo transfer programmes are also possible with the use of oestrus synchronisation and artificial insemination. Finally, hormonal treatments have also been used to induce puberty in ewe-lambs and doelings.

Use of laparoscopic intrauterine insemination associated with a simplified superovulation treatment for in vivo embryo production in sheep: a preliminary report

This study evaluated the reproductive performance of sheep that were subjected to superovulatory treatment and intrauterine insemination with two different doses of semen. The main objective was to determine whether intrauterine insemination is associated with higher rates of embryo recovery than existing procedures. In the first experiment 30 Ojalada de Soria ewes were used at the end of their productive life and nine younger ewes of the same breed were used in Experiment 2. Synchronisation of oestrus was conducted with intravaginal sponges and the superovulation treatment consisted of an intramuscular injection of 210 IU pFSH and 500 IU eCG administered 24 h before sponge removal. After 48 h of sponge withdrawal, ewes were inseminated by laparoscopy. They were divided into two groups: low dose group (LD, 25 × 106 sperm; n = 14 Expt 1 and n = 5 Expt 2) and high dose group (HD, 100 × 106 sperm; n = 14 Expt 1 and n = 4 Expt 2). Embryos were recovered 7 days after the onset of oestrus by laparotomy and uterine flushing. Two blood samples were collected in order to analyse cortisol, at sponge insertion and the day the embryos were recovered. The same protocol was repeated twice in Experiment 1, with an interval of 2 months between two consecutive treatments. Results show a significant effect of the number of recovery on ovulation rate (21.7 ± 2.2 v. 11.8 ± 1.1 corpora lutea for first and second recoveries, respectively), and number of structures recovered (11.4 ± 1.6 v. 5.2 ± 1.1, P < 0.01). Differences of embryo performance in the second recovery compared with the first one were more evident in the LD group compared with the HD group. In Experiment 2, results reflected a significant superiority of the HD group compared with the LD group, especially rate of fertilisation, which was 25% higher. Sheep producing non-fertilised embryos had higher cortisol levels at the time of flushing than those with embryos (P < 0.01). It is concluded that the use of simplified and consecutive superovulatory treatments associated with intrauterine insemination is a potential means of obtaining embryos, although the response seems to depend on donor sheep age. The use of a higher number of sperm cells per millilitre results in better outcomes in terms of embryos produced.

Repeated superovulation using a simplified FSH/eCG treatment for in vivo embryo production in sheep

This study investigated the efficacy of a simplified repeated superovulation treatment (eCG plus FSH in a single dose, rather than the usual protocol of six decreasing doses of FSH) in the in vivo embryo production in Ojalada donor ewes during the breeding season. In vitro viability after vitrification and warming of embryos recovered from both treatments was also assessed. In addition, the study examined the effects of the concentration of anti-eCG antibodies before each eCG/FSH treatment on in vivo embryo production. Thirty-eight females at the end of their reproductive lives were given the decreasing (n = 19) or simplified (n = 19) superovulatory treatment up to three times at intervals of ≥ 50 d. The onset of estrus was 5 h earlier (P < 0.05) among ewes that received the eCG/FSH protocol (25.2 ± 0.80 h) than it was among those that received the decreasing superovulatory treatment (30.1 ± 1.0 h), but the two treatments did not differ significantly in ovulation rates or the number and viability of embryos recovered. Both of the superovulatory protocols were significantly (P < 0.05 to P < 0.01) less effective after the first application. After three superovulatory treatments, the average number of viable embryos per ewe was 14.1 ± 2.3 and 13.7 ± 2.5 in the decreasing and simplified protocols, respectively. High anti-eCG antibody concentrations just before the superovulatory treatment with eCG/FSH were associated with a significant decrease (P < 0.05) in the rates of fertilization, viability, and freezability, especially in the second and third recoveries. Repeated superovulatory treatments with eCG/FSH can provide an efficient means of producing high quality embryos in the ewes of endangered breeds at the end of their reproductive lives, although further studies are needed to characterize the response associated with high concentrations of anti-eCG antibodies.

Effects of exogenous melatonin on in vivo embryo viability and oocyte competence of undernourished ewes after weaning during the seasonal anestrus

This study investigated the effects of exogenous melatonin on embryo viability and oocyte competence in post-partum undernourished ewes during the seasonal anestrus. At parturition (mid-Feb), 36 adult Rasa Aragonesa ewes were assigned to one of two groups: treated (+MEL) or not treated (-MEL) with a subcutaneous implant of melatonin (Melovine(R), CEVA) on the day of lambing. After 45 d of suckling, lambs were weaned, ewes were synchronized using intravaginal pessaries, and fed to provide 1.5x (Control, C) or 0.5x (Low, L) times daily maintenance requirements. Thus, ewes were divided into four groups: C-MEL, C+MEL, L-MEL, and L+MEL. At estrus (Day=0), ewes were mated. At Day 5 after estrus, embryos were recovered by mid-ventral laparotomy and classified based on their developmental stage and morphology. After embryo collection, ovaries were recovered and oocytes were classified and selected for use in in vitro fertilization (IVF). Neither diet nor melatonin treatment had a significant effect on ovulation rate and on the number of ova recovered per ewe. Melatonin treatment significantly improved the number of fertilized embryos/corpus luteum (CL) (-MEL: 0.35 +/- 0.1, +MEL: 0.62 +/- 0.1; P = 0.08), number of viable embryos/CL (-MEL: 0.23 +/- 0.1, +MEL: 0.62 +/- 0.1; P < 0.01), viability rate (-MEL: 46.6%, +MEL: 83.9%; P < 0.05), and pregnancy rate (-MEL: 26.3%, +MEL: 76.5%; P < 0.05). In particular, exogenous melatonin improved embryo viability in undernourished ewes (L-MEL: 40%, L+MEL: 100%, P < 0.01). Neither nutrition nor exogenous melatonin treatments significantly influenced the competence of oocytes during IVF. Treatment groups did not differ significantly in the number of healthy oocytes used for IVF, number of cleaved embryos, or number of blastocysts and, consequently, the groups had similar cleavage and blastocyst rates. In conclusion, melatonin treatments improved ovine embryo viability during anestrus, particularly in undernourished post-partum ewes, although the effects of melatonin did not appear to be mediated at the oocyte competence level.

Effects of annual rainfall and farm on lamb production after treatment with melatonin implants in Merino sheep: a 4-year study

AIM

To determine the effects of annual rainfall and farm on the efficacy of melatonin implants in improving lamb production in Merino sheep in Spain.

METHODS

A study was conducted on 3,871 Merino sheep on six farms over a 4-year period (2004-2007). Melatonin implants were inserted during the second half of February or early March (winter) (Melatonin group) or not (Control group). Multinomial logistic regression was used to determine the effects of melatonin, farm and year, and their interactions, on reproductive outcomes. Regression analysis was used to examine the relationship between annual rainfall and the percentage of ewes lambing, percentage of lambs born to ewes lambing, and overall lambing percentage, for each year and treatment group within farm.

RESULTS

Annual rainfall, farm and treatment with melatonin, and their interactions, had a significant effect on the reproductive performance of ewes (p<0.001). Treatment with melatonin increased the percentage of ewes lambing (Melatonin group = 77 (SEM 4)%, Control group = 44 (SEM 7)%; p<0.0001), and overall lambing percentage (Melatonin group = 109 (SEM 1)%, Control group = 59 (SEM 2)%; p<0.0001). Treatment differences were especially pronounced in 2005 and 2006, when annual rainfall was exceptionally low; ewes in the Control group had the lowest lambing rates those years. Lambing rates and overall lambing percentage were positively correlated (p<0.05) with the amount of annual rainfall but the correlation coefficients were higher in the Control than Melatonin group.

CONCLUSIONS

Melatonin implants are an effective means of improving lamb production of Merino ewes, especially in harsh environments where low annual rainfall limits the availability of food. When melatonin treatment was used, however, the responses of flocks on individual farms were difficult to predict because within a year, responses did not occur on all farms.

Undernutrition and exogenous melatonin can affect the in vitro developmental competence of ovine oocytes on a seasonal basis

This study evaluated the effects of exogenous melatonin and level of nutrition on oocyte competence, in vitro fertilization (IVF), and early embryonic development in sheep during seasonal anoestrus (SA) and the reproductive season (RS). Adult Rasa Aragonesa ewes were assigned randomly to one of four treatment groups in two experiments based on a 2 x 2 x 2 factorial design. Individuals were treated (+MEL) or not treated (-MEL) with a subcutaneous implant of melatonin for 42 days and then were fed 1.5 (Control, C) or 0.5 (Low, L) times the daily maintenance requirements for 20 days. Ewes were synchronized and mated at oestrus (Day = 0). On Day 5, ovaries were collected and oocytes were used for IVF. Season had a significant (p < 0.01) effect on the number of oocytes recovered (RS: 19.6 +/- 1.0; SA: 14.5 +/- 1.0) and the number of healthy oocytes (RS: 13.9 +/- 0.7; SA: 9.0 +/- 0.7). In the RS, neither nutrition nor melatonin had a significant effect on the evaluated oocytes quality parameters although melatonin implants appeared to reduce the number of unhealthy oocytes in the undernourished group (p < 0.05). During SA, in undernourished ewes exogenous melatonin tended to increase the number of healthy (L+MEL: 9.4 +/- 1.0, L-MEL: 7.6 +/- 1.4; p < 0.1), and significantly improved both cleaved oocytes (L+MEL: 7.0 +/- 0.7, L-MEL: 4.1 +/- 0.9; p < 0.05) and blastocyst rate (L+MEL: 37.2, L-MEL: 21.9%; p < 0.05). In conclusion, oocyte competence in ewes was affected by season, and melatonin implants appeared to improve developmental competence in the seasonal anoestrous period, particularly in experimentally undernourished ewes.

Early pregnancy alters the metabolic responses to restricted nutrition in sheep

This study investigated whether a 27-day period of nutrition at half-maintenance during early pregnancy (up to Day 14) could alter maternal endocrine responses. Forty-six ewes were fed all or half of their maintenance requirements and slaughtered on Day 14 of the oestrous cycle or pregnancy. We used real time RT-PCR to study gene expression of growth hormone receptor (GHR) and leptin in adipose tissue and GHR, GHR1A and of the insulin-like growth factor I (IGF-I) in the liver. Blood profiles of metabolites and metabolic hormones were also determined. Throughout the experiment, underfed animals presented lower body weight and body condition, greater plasma concentrations of non-esterified fatty acids (NEFA), and lower plasma concentrations of leptin, compared to adequately fed animals. Undernutrition affected the patterns of gene expression in adipose and hepatic tissues, and the responses differed between pregnant and non-pregnant ewes. In adequately fed ewes, pregnancy up-regulated leptin mRNA expression in adipose tissue, a response that was impaired in underfed ewes. The hepatic expression of IGF-I mRNA was increased by pregnancy in underfed animals while no effect was observed in adequately fed ewes. It remains to be determined whether the changes in the endocrine milieu are paralleled by modifications in uterine gene expression that could alter the environment of the embryo during early pregnancy.

Effect of undernutrition on the uterine environment during maternal recognition of pregnancy in sheep

The effects of pregnancy and undernutrition on endometrial gene expression were investigated in ewes fed all or half their maintenance requirements and killed on Day 14 of pregnancy or of the oestrous cycle. The endometrial expression of progesterone, oestrogen, oxytocin and interferon receptors (PR, ERα, OXTR and IFNAR, respectively), cyclo-oxygenase (COX)-2, proliferating cell nuclear antigen (PCNA), insulin-like growth factors (IGF)-I and -II, and IGF-1 receptor (IGF-1R) was studied by immunohistochemistry or real-time reverse transcription–polymerase chain reaction. The luminal epithelium of cyclic control ewes was devoid of PR staining and had relatively high levels of ERα, OXTR, COX-2 and IFNAR2. The presence of a conceptus decreased the in vitro uterine secretion of prostaglandin (PG) F2α and the expression of IFNAR2 in most cell types, and increased the gene expression of IGF-I and IGF-II. Undernutrition tended to increase ERα protein and gene, but decreased in vitro uterine secretion of PGE2 and the gene expression of IFNAR2 in cyclic ewes. There was no effect of undernutrition on pregnancy rates or the number of conceptuses recovered. Consistent with this, undernutrition of pregnant ewes did not have any effect on uterine gene expression. Moreover, in cases where changes were observed in cyclic ewes, these changes were negated when a conceptus was present.

Changes in calmodulin immunocytochemical localization associated with capacitation and acrosomal exocytosis of ram spermatozoa

The aim of this study was to determine the localization of calmodulin (CaM) in ram sperm and the possible changes during in vitro capacitation (CA) and the ionophore-induced acrosome reaction (AR). Likewise, changes in intracellular calcium levels ([Ca(2+)](i)) were also analysed by using flow cytometry. CA was induced in vitro in a medium containing BSA, CaCl(2), NaHCO(3), and AR by the addition of the calcium ionophore A23187. The acrosomal status was assessed by the chlortetracycline-fluorescence (CTC) assay. Flow cytometry (FC) analyses were performed by loading samples with Fluo-3 AM, that emits fluorescence at a high [Ca(2+)](i), combined with propidium iodide (PI) that allowed us to discriminate sperm with/without an integral plasma membrane both with high/low [Ca(2+)](i). Immunocytochemistry localized CaM to the flagellum, and some sperm also contained CaM in the head (equatorial and post-acrosomal regions). CA and AR resulted in a slight increase in the post-acrosomal labelling. The treatment of sperm with increasing concentrations of two CaM antagonists, W7 and calmidazolium (CZ), accounted for an increase in capacitated and acrosome-reacted CTC-sperm patterns. CZ induced a significant reduction in the content of three protein tyrosine-phosphorylated bands of approximately of 30, 40 and 45kDa. However, W7 showed no significant effect at any of the studied concentrations. Neither of them significantly influenced protein serine and threonine phosphorylation. FC analysis revealed that the main subpopulation in the control samples contained 70% of the total sperm with integral plasma membrane and a medium [Ca(2+)](i). After CA, 67.1% of the sperm preserved an integral membrane with a higher [Ca(2+)](i). After AR, only 7.2% of the total sperm preserved intact membranes with a very high [Ca(2+)](i). These results imply that CaM appears to be involved in ram sperm capacitation, and both treatments increased its localization in the post-acrosomal region.

Effects of melatonin implants during non-breeding season on sperm motility and reproductive parameters in Rasa Aragonesa rams

The effect of melatonin implants administered during non-breeding season in Rasa Aragonesa rams on sperm motility parameters and other reproductive traits was assessed. In a first experiment, two Rasa Aragonesa rams were implanted (with melatonin group M), remaining other two males as control group (C). Semen of each group was collected from 1 May to 23 June, twice or three times a week, and motility parameters were assessed using a computer-assisted sperm analysis system. Melatonin increased the percentage of progressive motile spermatozoa, particularly during 46-75 days after melatonin implantation (p < 0.01). In experiment 2, M and C in vitro fertilization ability had been determined by zona-pellucida binding assays, using spermatozoa from experiment 1, obtained 60-70 days after melatonin was implanted. A significantly higher number of spermatozoa attached per oocyte was observed in frozen-thawed immature ovine oocytes incubated with sperm from M animals than in those incubated with sperm from the C group (p < 0.01). Finally, a field assay (experiment 3) was performed. In this case, five Rasa Aragonesa rams were implanted with melatonin and three remained as control group. Sperm doses from those animals were used for artificial insemination of 2608 Rasa Aragonesa ewes from 39 different farms at non-breeding season. Fertility, litter size and fecundity were studied. Semen from melatonin implanted rams seemed to increase both fertility and fecundity in ewes inseminated with spermatozoa obtained 46-60 days after implantation (p < 0.1). Thus, melatonin treatment in rams during non-breeding season modifies sperm motility parameters and seems to improve the fertilization parameters obtained.

Simplified superovulatory treatments in Corriedale ewes

Two experiments were designed to evaluate the possibility of simplifying superovulatory treatments in Corriedale ewes with use of ovine FSH (oFSH). Ewes received intravaginal progestogen sponges for 14 days. In Experiment 1, several simplified schedules were tested. Ewes were treated with 176 NIH-FSH-S1 units' oFSH given as a single injection in saline, along with 500 IU eCG 48 h before sponge removal (Group A1), in four equal doses (B1), or given as a single injection in a polyvinylpyrrolidone vehicle (C1) 24 h before sponge removal. In Experiment 2, the simplified protocol that exhibited the most desirable results in Experiment 1 (A2) was compared with the same protocol, but using less oFSH (132 units) (B2) and with the most conventional protocol (176 units of oFSH in eight decreasing doses; C2). Estrus was detected and ewes were naturally mated. The ovarian response and embryo production were assessed on Day 6 after estrus. LH was measured at 6h intervals from pessary withdrawal. The onset of estrus and the pre-ovulatory LH surge were advanced (P<0.05) in ewes treated with FSH and eCG. In Experiment 1, protocol A1 produced a greater percentage of superovulated ewes compared to C1 (100.0 compared with 58.3%; P<0.05), increased ovulation rate (13.8 corpora lutea compared with 6.2 and 4.7 for B1 and C1, respectively; P<0.05), and tended to increase the number of transferable embryos compared to B1 (P=0.08). In Experiment 2, percentages of superovulated ewes and ovulation rates were similar among groups; however, Group A2 tended to have more large follicles (P=0.07) than C2. The number of transferable embryos was similar among the three treatments. In conclusion, the reduced-dose oFSH given once along with eCG is the most appropriate superovulatory treatment because it combines simplicity and a lesser dose of gonadotropin, which also implies a reduction in cost, without reducing embryo production.

Undernutrition reduces the oviductal mRNA expression of progesterone and oestrogen receptors in sheep

The effect of undernutrition on the oviductal mRNA expression of oestrogen and progesterone receptors (ERalpha and PR) determined by a solution hybridisation assay in sheep was investigated. Adult ewes were fed either 1.5 (C) or 0.5 (L) times their maintenance requirements and were slaughtered on day 5 or 14 of a synchronised oestrous cycle (day 0=oestrus). In the oviduct ipsilateral to the corpus luteum, Group L presented lesser concentrations of ERalpha mRNA than Group C on day 5 (P<0.05), and lesser PR mRNA concentrations on both days (P<0.05). No effect of undernutrition was observed in the contralateral oviduct, and there was no difference in transcripts concentrations between days 5 and 14. The lesser sensitivity of the oviduct to ovarian steroids found in undernourished ewes could compromise the embryo environment and partly explain the retarded development reported in embryos collected from nutritionally restricted ewes.

Development of a Simple Enzyme Immunoassay for the Determination of Ovine Luteinizing Hormone

The present study describes the development and validation of a simple sensitive and specific sandwich enzyme immunoassay (EIA) for the quantification of ovine luteinizing hormone (LH) in plasma. Microtitre plates were coated with the capture antibody 518b7 anti-bovine LH. A second peroxidase-labelled anti-ovine LH antibody was used as tracer. A simple 3-step procedure was used for the sample analysis; (1) incubation of standards and samples with the pre-coated antibody plates for 2 h at 37 degrees C; (2) incubation with the peroxidase-labelled antibody for 1 h at room temperature; and (3) colour development with TMB substrate. A linear dose-response curve was obtained in the range 0-10 ng/ml (r2 > 0.99). The detection limit was 0.05 ng/ml, and the intra-assay and inter-assay coefficients of variation were 7% and 11.7%, respectively. The theoretical stability of microplates and reagents was calculated, this being greater than one year. Low or undetectable cross-reactivities were recorded for follicle-stimulating hormone, bovine thyroid-stimulating hormone, equine chorionic gonadotrophin and a gonadotrophin-releasing hormone (GnRH) analogue. The EIA was biologically validated by the determination of plasma LH concentrations of nine Rasa Aragonesa ovariectomized and estradiol-implanted ewes after a double GnRH challenge. In conclusion, this enzyme immunoassay provides an efficient, simple and sensitive method for the routine analysis of ovine LH.

Effects of ageing and exogenous melatonin on pituitary responsiveness to GnRH in ewes during anestrus and the reproductive season

The study examined the effect of melatonin implants on in vivo pituitary responsiveness to GnRH in control, fully productive (5.7+/-0.4 years old, n=17) and aged (10.7+/-0.3 years old, n=14) ovariectomized, estradiol-treated Rasa Aragonesa ewes. On 27 February, eight ewes in each age group received a single implant containing 18 mg melatonin. On 10 April, blood samples to be assayed for LH were collected at 10-min intervals over 4h (starting at 09:00 and 22:00 h). After samples 6 and 18 were collected, ewes received a single i.v. injection of GnRH (20 ng/kg liveweight). The pituitary response to GnRH was assessed using the difference between plasma LH concentrations before and after (highest value) each injection (DLH1, DLH2)), and the area under the LH response curve for 1h after each GnRH injection (AUC1, AUC2). On 23 September, the previously implanted ewes received a new melatonin implant and, on 17 November, all of the ewes were subjected to the same diurnal and nocturnal sampling protocols, again. Generally, non-implanted aged ewes exhibited a lower pituitary response to GnRH than did non-implanted control ewes, particularly in November and after the first injection (P<0.05 for DLH1 and AUC1 in both the diurnal and nocturnal tests). The response was significantly affected by the interaction of age and melatonin treatment, particularly in the diurnal tests (P<0.1 for DLH1 and AUC1, and P<0.05 for AUC2 in April; P<0.05 for DLH1, AUC1 and AUC2 in November), which indicated that exogenous melatonin increased LH levels after GnRH injections in aged ewes compared to non-implanted ewes, this effect being the opposite in control females. Thus, melatonin can restore in ewes the functionality of the neuroendocrine system, after it has been reduced by senescence.

Monthly variations in ovine seminal plasma proteins analyzed by two-dimensional polyacrylamide gel electrophoresis

This study was conducted to evaluate monthly changes in the ram seminal plasma protein profile using two-dimensional polyacrylamide gel electrophoresis (2D-PAGE) with a polyacrylamide linear gradient gel. Likewise, comparative analyses of the protein composition of ovine seminal plasma (SP) from ejaculates obtained along the year, and its relationship with sperm motility, viability and concentration of ejaculate were carried out. Western-blot analysis was performed to specifically detect P14, a ram SP protein postulated to be involved in sperm capacitation and gamete interaction [Barrios B, Fernández-Juan M, Muiño-Blanco T, Cebrián-Pérez JA. Immunocytochemical localization and biochemical characterization of two seminal plasma proteins which protect ram spermatozoa against cold-shock. J Androl 2005;26:539-49], and its variations along the year have also been established. The experiment was carried out from May 2003 to April 2004, with nine Rasa Aragonesa rams. Ejaculates obtained every 2 days were pooled and used for each assay, to avoid individual differences, and three two-dimensional SDS-PAGE gels were run for each month. The high resolution of the gradient gel allowed the image analysis software to detect around 252 protein spots, with pIs ranging from 4.2 to 7.6, and molecular weight (M(r)) from 12.5 to 83.9 kDa. Four protein spots (1, 2, 3 and 4) of low M(r) (15.1, 15.7, 15.9 and 21.0 kDa) and acidic pI (5.9, 5.3, 5.7 and 6.6), respectively, had the highest relative intensity in the SP map (11.2, 9.3, 4.7 and 7.7%, respectively). Spot 3 was more abundant (P<0.05) from May to December, and negatively correlated (P<0.05, r=-0.34) with sperm viability and concentration (P<0.05, r=0.36). Another 12 protein spots also had significant quantitative differences (P<0.05) along the year, and 17 protein spots, which correlated with some seminal quality parameter, did not show quantitative monthly changes. Western-blot analysis indicated that spots 1 and 2 reacted with the anti-P14 antibody, raised against the P14 band (approximate M(r) 14 kDa) of ram SP. This indicates that spots 1 and 2 are similar to RSP15 [Bergeron A, Villemure M, Lazure C, Manjunath P. Isolation and characterization of the major proteins of ram seminal plasma. Mol Reprod Dev 2005;71:461-70], bovine PDC-109 [Esch FS, Ling NC, Bohlen P, Ying S, Guillemin R. Primary structure of PDC-109, a major protein constituent of bovine seminal plasma. Biochem Biophys Res Commun 1983;113:861-7] (also called BSP A1/A2 [Manjunath P, Sairam MR. Purification and biochemical characterization of three major acidic proteins (BSP-A1, BSP-A2 and BSP-A3) from bovine seminal plasma. Biochem J 1987;241:685-92]) and goat GSP-14/15 kDa [Villemure M, Lazure C, Manjunath P. Isolation and characterization of gelatine-binding proteins from goat seminal plasma. Reprod Biol Endocrinol 2003;1:39], based on our previous results on the P14 amino acid sequence [Barrios B, Fernández-Juan M, Muiño-Blanco T, Cebrián-Pérez JA. Immunocytochemical localization and biochemical characterization of two seminal plasma proteins which protect ram spermatozoa against cold-shock. J Androl 2005;26:539-49].

The effect of melatonin treatment on the ovarian response of ewes to the ram effect

To determine the ovarian response to the ram effect after treatment with melatonin, on 8 March, 71 Rasa Aragonesa ewes were randomly assigned to either the treatment group and given an 18mg melatonin implant or the untreated group. On 19 April (day 0), rams were introduced into the flock. Melatonin treatment produced a significantly higher percentage of cyclic ewes at ram introduction (P<0.05). Melatonin-treated ewes had their first oestrus after ram introduction significantly earlier than did untreated ewes (P<0.0001), and the groups differed in the distribution of their ovarian response. Most (80%) of the treated ewes exhibited a silent ovulation followed by a cycle of normal duration, whereas about half (52%) of the untreated ewes exhibited a silent ovulation, a short cycle, and another silent ovulation followed by a cycle of normal duration (P<0.05). At ram introduction, melatonin-treated ewes, cyclic and non-cyclic, had higher mean plasma progesterone concentrations than did untreated ewes. The proportion of ewes that mated within the first 17 days of the mating period was significantly higher among the treated ewes than in the untreated ewes (P<0.0001). Furthermore, at lambing, 39% of the melatonin-treated ewes lambed within the first 17 days of the lambing period, while none of the untreated ewes lambed in that period. The untreated group exhibited peaks in mating between days 18 and 21, and particularly, between days 22 and 25, when the majority of ewes lambed; peaks did not occur in the treatment group. Treated and untreated ewes did not differ significantly in fertility, litter size and fecundity. In conclusion, melatonin treatment modifies the ovarian response to the ram effect in ewes, which leads to modifications in mating patterns, and consequently, the lambing curve.

The effect of melatonin implants during the seasonal anestrus on embryo production after superovulation in aged high-prolificacy Rasa Aragonesa ewes

The aim of this study was to assess the effect of melatonin implants administered in March on the ovarian cyclicity, ovulatory response and embryo production after repeated superovulation of selected high-prolificacy Rasa Aragonesa aged ewes. During the seasonal anestrus of two consecutive years, 113 superovulatory treatments have been performed. Ewes were treated (M) or not (C) with melatonin implants in March (day 0). All of them received intravaginal progestogen sponges on day 24 (recovery 1) and 80 (recovery 2) after melatonin implants insertion in year 1, and on day 28 and 77 in year 2. The intravaginal sponges were removed after 14 days. Superovulatory treatments consisted of eight doses in decreasing concentrations (2 mL x 2 and 1 mL x 6) of oFSH (Ovagen) administered twice daily starting 72 h before sponge removal. Seven days after the onset of estrus, embryos were recovered by laparotomy. Melatonin increased cyclicity only in recovery 2 year 2 (83% versus 42%; P < 0.05) but not in the other experimental periods. Among the 78% (88) ewes that ovulated and produced functional corpora lutea, melatonin implants tended to improve embryo viability in recovery 2 by increasing the number of blastocysts per superovulatory treatment (2.4 +/- 0.6 versus 1.1 +/- 0.4; P = 0.09), the rate of viability (67 +/- 9% versus 43 +/- 9%; P < 0.05), and freezability (55 +/- 9% versus 33 +/- 8%; P < 0.05). More specifically, melatonin induced a significant reduction of the number and rate of non-viable (degenerate and retarded) embryos in recovery 2 (0.4+/-0.1 embryos versus 1.3 +/- 0.3 embryos and 4 +/- 1% versus 22 +/- 6%, respectively; P < 0.05). Our results demonstrate that melatonin implants in March can improve at medium term (3 months after implantation) the viability of embryos collected from selected high-prolificacy Rasa Aragonesa aged ewes after superovulation.

Effect of undernutrition on uterine progesterone and oestrogen receptors and on endocrine profiles during the ovine oestrous cycle

In the present study, it was investigated whether undernutrition affected the binding capacity, immunoreactivity and mRNA expression for uterine oestrogen and progesterone receptors (ER and PR, respectively) in sheep, as well as whether the responses were associated with changes in plasma concentrations of progesterone (P4), oestradiol (E2), glucose, fatty acids, insulin, leptin and insulin-like growth factor (IGF)-I during the oestrous cycle. Twenty ewes were fed either 1.5 (C) or 0.5 (L) times their maintenance requirements and were killed on Day 5 or 14 of the cycle (Day 0 = oestrus). Compared with Group C, Group L had higher concentrations of non-esterified fatty acids and lower concentrations of insulin, leptin and IGF-I. Group L also had higher plasma concentrations of P4 during the final days of the luteal phase. At oestrus in both treatment groups, there were peaks in the concentrations of glucose, insulin and IGF-I. For ER and PR, transcript expression, binding capacity and immunoreactivity were higher on Day 5 than on Day 14 of the cycle. The binding capacities for ER and PR were lower in Group L than in Group C on Day 5. Group C showed more immunoreactive staining for ER than did Group L in two of five cell types, whereas no effect of treatment was observed for PR immunoreactivity. There was more PR mRNA in the uterine horn contralateral to the corpus luteum in Group C than in Group L ewes. We conclude that undernutrition impairs steroid receptor expression and binding capacity. This may alter the uterine environment and help explain the reductions in embryo survival.

Sperm survival and heterogeneity are correlated with fertility after intrauterine insemination in superovulated ewes

Efficient animal production involves accurate estimations of fertilizing ability. One key factor is the plasma membrane of the sperm cell, which is actively involved in the cascade of events before oocyte fusion. Many methods are used to analyze the characteristics of this membrane, including partition in aqueous two-phase systems which is an efficient method to analyze sperm surface changes accounting for loss of viability and different functional states. Centrifugal countercurrent distribution (CCCD) analysis can also be used in an aqueous two-phase system to determine the relationship between sperm parameters and in vivo fertility in ewes. In a previous work, we found a significant correlation between two post-CCCD parameters (heterogeneity and recovered viability) and field fertility when the same sample was used after cervical AI. The present study was intended to find out whether the control of several external factors that affect reproductive efficiency is able to increase the correlation coefficient between post-CCCD parameters and fertility. Thus, 90 Rasa aragonesa ewes were controlled on the same farm and received intrauterine inseminations using the same technical equipment. The fertilizing ability of the raw semen and sperm samples selected by a dextran/swim-up process was compared using a low number of spermatozoa per insemination (7 x 10(7)) to enhance possible fertility differences. A new post-CCCD parameter was considered; the loss of viability (LV) occurred during the CCCD process. This variable denotes the sperm surviving ability and corresponds to the difference between the total number of viable cells loaded and recovered after the CCCD run. The mean fertility of eight sperm control samples was 60% (range: 25-76%), and there was no significant correlation between standard parameters and in vivo fertility. LV ranged from 2 to 69% (average 27%) and was negatively correlated with fertility (r = -0.914, P < 0.01). Ejaculate heterogeneity (H) ranged from 20 to 47% and was positively, but not significantly, correlated with fertility (r = 0.391). A predictive equation for fertility was deduced by multiple analysis with a very high correlation coefficient (r = 0.967), and level of significance (P < 0.005): predictive fertility PF = 52.546 - 0.594 LV + 0.665 H. The mean fertility of 13 swim-up selected samples was 63% (range: 25-86%). Again, only parameters derived from the CCCD analysis were highly correlated with fertility, especially LV and H (P < 0.05).

Effect of plane of nutrition on endometrial sex steroid receptor expression in ewes

The effect of plane of nutrition on progesterone receptor (PR) and estrogen receptor alpha (ERalpha) expression in ovine endometrium was investigated. Rasa Aragonesa ewes (n=26) were fed diets to provide either 1.5 (Group C) or 0.5 (Group L) times the daily maintenance requirement and were slaughtered at Days 5 or 10 of the estrous cycle (Day 0=estrus). PR and ERalpha immunoreactivity were analyzed in eight endometrial cell compartments, defined by cell type and location. Group L had less PR immunostaining on Day 5 (P<0.05), which is consistent with lesser endometrial content of progesterone found in such animals. Most cell types of Group C had down regulation of PR at Day 10, but in Group L, this pattern was observed only in three cell compartments. The lesser PR contents found at Day 5 in Group L ewes may explain the lack of inhibition of PR. No effect of treatment or day of the estrous cycle was observed in ERalpha. Results indicate that endometrial PR is affected in a cell type, in specific manner, by plane of nutrition.

Regulation of LH secretion during seasonal anestrus by dopaminergic pathways in Rasa Aragonesa ewes treated or not with melatonin

The involvement of the dopaminergic system in the steroid-dependent inhibition of luteinizing hormone (LH) secretion during anestrus in ovariectomized, estradiol-implanted adult Rasa Aragonesa ewes was investigated in both ewes treated with melatonin on 8 March (n = 10) and in control (n = 8) ewes. Melatonin implants did not significantly increase LH secretion. However, treatment with pimozide induced a significant increase (P < 0.05) in LH pulse frequency in both groups during early anestrus. We conclude that, in the absence of males, the dopaminergic system is clearly involved in the inhibition of LH secretion during anestrus in both melatonin-treated and control ewes. Key words: Sheep, melatonin, pimozide

The effect of melatonin implants on the response to the male effect and on the subsequent cyclicity of Rasa Aragonesa ewes implanted in April

Rasa Aragonesa ewes were used to evalutate whether treatment with melatonin implants in spring could modify: (i) the response to the male effect in terms of oestrous behaviour and ovulation rate; and (ii) the maintenance of sexual activity and ovulation rate at medium term, i.e. over the next 306 days. On 12 April, 42 ewes were divided into two groups, with (M; n = 21) or without (C; n = 21) a subcutaneous implant containing 18 mg melatonin. On 17 May (day 0), three aproned rams were introduced to each group to induce a ram effect. Ewes were observed for oestrus daily. The rams were removed 40 days later after which one aproned ram was introduced daily. Oestrous detection continued until 28 February, 306 days after the first male-female contact. The ovulation rate was determined by endoscopy in the first three cycles after ram introduction and in September-October and January. Progesterone was assayed from blood samples taken on 6 May, 10 and from day 0 to day 22 after ram introduction. Luteal activity before ram introduction was seen in 33% (M) and 29 (C)% of the ewes, respectively. Significantly more M ewes showed oestrous behaviour during the first 40 days after ram introduction (M: 100%; C: 62%; P < 0.01). Similar differences were observed for ewes anovulatory at ram introduction (M: 100%, C: 47%; P < 0.01). These differences were maintained over the three oestrous cycles in both groups. Treatment with melatonin implants was without detrimental effect on cyclic functions in the following breeding season, after seasonal anoestrus. Melatonin treatment significantly increased (P < 0.05) the mean ovulation rate of the first (1.62 +/- 0.11 versus 1.31 +/- 0.13), second (1.78 +/- 0.15 versus 1.36 +/- 0.15) and third cycles (M: 1.73 +/- 0.12 versus C: 1.27 +/- 0.14). There was a significant interaction between the effects of cyclicity at day 0 and melatonin treatment on the ovulation rate in the first cycle (P < 0.05). The mean ovulation rates of both groups were similar at the beginning (September) and middle (January) of the subsequent breeding season. Overall, the results confirmed that melatonin implants, combined with the ram effect, improved the reproductive parameters of reduced-seasonality ewes during spring mating, without impairing sexual activity or ovulation rate during the subsequent breeding season.

The effect of melatonin on the secretion of progesterone in sheep and on the development of ovine embryos in vitro

Two experiments were carried out in order to determine whether melatonin can improve secretion of progesterone in vivo, and its effect on embryonic development in vitro. In the first experiment, blood samples were collected from 5 ewes at 15 min intervals for 2 h at 7 and 10 days after withdrawal of progestagen pessaries. The first hour constituted a control period, which ended with an intravenous administration of 3 microg/(kg bw)(0.75) melatonin. All the ewes on day 7 and three of the ewes on day 10 showed a progesterone response to melatonin challenge, defined as an increase in the plasma progesterone concentration in at least two consecutive samples during the post-treatment period above the mean+2SD of the values in the pre-treatment period. A paired t-test revealed a significant effect of melatonin on the overall plasma progesterone concentrations before and after the challenge, both on day 7 (pre, 0.61 +/- 0.11; post, 0.73 +/- 0.13 ng/ml; p<0.01) and day 10 (pre, 1.16 +/- 0.19; post, 1.30 +/- 0.20 ng/ml; p<0.05). Ninety-one thawed embryos (46 morulae and 45 blastocysts) were used in the second experiment, being cultured with or without 1 microg/ml melatonin. If the embryos were blastocysts when the culture started. melatonin increased the percentage that had hatched after 24 h of culture (p<0.01), and there was a lower percentage of degenerated embryos at the end of the incubation period (p<0.05). It may be concluded that melatonin treatment in sheep can increase both fertility and prolificacy by improving luteal function and embryonic survival.

Variation in the ability of melatonin implants inserted at two different times after the winter solstice to restore reproductive activity in reduced seasonality ewes

The purpose of the present study was to assess the effects on reproductive activity of melatonin implants inserted immediately after the winter solstice compared with the classical implantation around the spring equinox. The experiment was conducted at latitude 41˚ N in the absence of rams. Twenty-one ovariectomised, oestradioltreated Rasa Aragonesa ewes received (M1, n = 7, 15 January; M2, n = 7, 15 March) or not (C, n = 7) a single implant containing 18 mg melatonin. Blood samples were collected twice weekly from 15 January (M1) and from 15 March (M2, C), and assayed for luteinizing hormone. Six M1 ewes resumed their reproductive activity by 20 April, 95 days after implant insertion, although the reproductive season induced only lasted for 45 days. Melatonin implants inserted on 15 March did not induce a resumption of reproductive activity (0 ewes; P < 0.05). It is concluded that, in the absence of males, the response of Mediterranean ewes to melatonin implants is better when implantation takes place immediately after the winter solstice than around the spring equinox. Two subsequent field experiments with the same breed and year were carried out. Animals were implanted (M) or not (C) with melatonin on 29 December (M, n = 156; C, n = 159) and on 20 March (M, n = 150; C, n = 128). Results confirmed the efficacy of the treatment with melatonin immediately after the winter solstice in ewes with a short seasonal anoestrous period. Implants induced a mean productivity increase of 0.30 (December) and 0.36 (March) lambs per treated ewe compared with those in the control groups.

Differences in reproductive performance, embryo development, interferon-tau secretion by the conceptus and luteal function in ewe lambs synchronized in oestrus before or after the spontaneous onset of luteal activity preceding puberty

In mid-September, 1 month before the insertion of intravaginal pessaries to induce sexual activity, blood samples were collected every 4 days from 16 ewe lambs aged 7 months, in order to determine the incidence of ovulations by measurement of plasma progesterone concentrations. It has been studied whether the response to a progestagen treatment of ewe lambs apparently close to puberty could be modified by the onset of the ovarian events preceding puberty. The effect of the presence or absence of ovulations prior to progestagen treatment on the potential reproductive performance (fertility, litter size and fecundity), embryo development [embryo quality and interferon-tau (IFNtau) secretion], luteal function (progesterone secretion in vitro) and endometrial progesterone content was studied in seven ovulating (Ov+) and nine nonovulating ewe lambs (Ov-) on day 14 after mating. The best potential reproductive results were obtained with Ov+ animals, although these differences could not be initially attributed to either different progesterone secretion in vitro or concentration of endometrial progesterone. Irrespective of the experimental groups, secretion of progesterone by luteal tissue from ewe lambs with normal embryos was significantly greater (p<0.05) than that of animals with abnormal embryos or with no embryos. Normal embryos secreted a higher amount of IFN-tau than those embryos classified as abnormal (p<0.07). In conclusion, ewe lambs which exhibit luteal activity before puberty have the highest levels of reproductive performances after a progestagen treatment. Corpora lutea from ewe lambs with normal embryos had higher rates of progesterone secretion in vitro and their embryos had a higher IFN-tau production by the embryos, indicating greater capacity for subsequent development.

Repeated surgical embryo recovery and embryo production in rabbits

The purpose of this study was to assess the embryo production after repeated surgical recovery of embryos in Gigante de España does. A total of 195 ovulatory treatments and embryo recoveries were performed from 1995 to 1999. Ovulation was induced by an intramuscular injection of 20 microg GnRH immediately after mating. Each doe was induced to ovulate up to four consecutive times at intervals of at least 50 days. Embryos were surgically collected from oviducts 68-69 h post-coitus. An average of 8.6 corpora lutea and 6.4 recovered embryos (90% of them classified as viable) were recorded from the 195 treatments. The process seemed to be less efficient in the fourth treatment, with a drop of more than two recovered and viable morulae with reference to the third (P<0.05 for both parameters) or the second recovery (P<0.1 and P<0.05, respectively). More than 20 recovered embryos and 18 viable embryos per donor doe were recorded considering the three first ovulatory treatments performed in 33% of the does (30/90). Results indicate that the methodology used in the present study could be an efficient way to maximize in vivo embryo production from rabbits.

A preliminary report on the effect of dietary energy on prostaglandin F2 alpha production in vitro, interferon-tau synthesis by the conceptus, endometrial progesterone concentration on days 9 and 15 of pregnancy and associated rates of embryo wastage in ewes

Two groups of ewes were fed to provide 1.70 x (high energy group; n = 15) or 0.56 x (low energy group; n = 15) energy requirements for maintenance of liveweight from 14 d before a synchronized mating in November until slaughter at 9 or 15 d after mating. We investigated the effects on interferon-tau (IFN tau) secretion by the conceptuses, prostaglandin F2 alpha (PG) production in vitro by endometrial tissue, and associated rates of embryo mortality, endometrial progesterone content and progesterone production by luteal tissue. No differences between groups in pregnancy rate were detected on Day 9 between the 2 groups. Proportionately (6/6 vs 2/5), there were more pregnant ewes in the high energy group on Day 15, although this difference did not reach significance (P = 0.06). The proportion of corpora lutea represented by embryos was significantly lower in undernourished ewes (P < 0.05). Secretion in vitro of PG was lower in the 2 pregnant ewes of the low energy group on Day 15, and it was accompanied by higher IFN tau secretion by conceptuses recovered from these ewes. However, the limited number of pregnant ewes recorded on Day 15 prevented any statistical comparison. Neither mean endometrial content of progesterone nor ovarian venous progesterone concentrations and production of progesterone by luteal were affected by nutrition. The provisional results of the present experiment indicate that undernutrition may induce a reduction in the rate of secretion of IFN tau and can therefore increase production of PG from the endometrium. This could initiate luteolysis. The lower pregnancy rates observed in underfed ewes could be mediated through this alteration in the signal of maternal recognition of pregnancy. However, these findings remain to be shown in further experiments including a larger number of animals, as they only represent data from 2 undernourished animals.

The effects on reproductive performance in the short and medium term of the combined use of exogenous melatonin and progestagen pessaries in ewes with a short seasonal anoestrous period

The effects on reproductive performance in the short and medium term of the combined use of exogenous melatonin and progestagen pessaries in ewes with a short seasonal anoestrous period.

Opioidergic and nutritional involvement in the control of luteinizing hormone secretion of postpartum Rasa Aragonesa ewes lambing in the mid-breeding season

The role of endogenous opioids and nutrition on the inhibition of luteinizing hormone (LH) secretion during the postpartum period was investigated in a Spanish breed of sheep lambing in the mid-late breeding season. Two groups of adult Rasa Aragonesa ewes housed in individual pens and lambing on 30 December were fed during the suckling period to provide maintenance requirements and the production of 1.1 (M; n = 8) or 0.55 (L; n = 8) kg of milk per day. On days 10, 20 and 30 after lambing, the effect of a treatment with the opiate receptor antagonist naloxone (1 mg/kg at four hourly intervals) on LH secretion was assessed in half of the ewes of each group, the remaining females receiving four saline injections. After weaning, animals were fed to provide requirements for maintenance of liveweight. Blood samples were collected twice a week from day 20 postpartum until the end of March, and assayed for progesterone and prolactin. Although underfed ewes showed significantly lower mean plasma concentrations during the control period on day 20 postpartum, nutrition did not seem to modify LH secretion before naloxone or saline injections. Moreover, no differences between nutritional groups in the response to naloxone injections on pattern of LH secretion were found. In fact, naloxone treatment induced an increase of mean LH concentrations on days 10, 20 and 30 postpartum (at least, P < 0.05), of LH pulse frequency on days 20 and 30 (P < 0.05), and of LH pulse amplitude on days 10 and 20 (P < 0.05). Underfed ewes during the postpartum period showed a slower decline in plasma prolactin levels, with significant differences on days 29, 36 and 39 after lambing (P < 0.05). Only 3 M ewes ovulated before the onset of the seasonal anoestrus period. It is concluded that endogenous opioids are involved in the inhibition of LH secretion during the early suckling period of a reduced seasonality breed of sheep without any influence of nutrition on the response to naloxone treatment; however, ewes underfed before weaning failed to reactivate their cyclicity prior to the onset of the seasonal anoestrus.

Effect of undernutrition on the distribution of progesterone in the uterus of ewes during the luteal phase of the estrous cycle

The effect of undernutrition on ovarian and uterine venous progesterone concentrations and endometrial progesterone content on Days 5 and 10 of the estrous cycle were studied. Forty ewes were synchronized using progestagen pessaries. At pessary withdrawal, the ewes were fed diets to provide either 1.5 or 0.5 times the daily maintenance requirement (Group H, n = 20 and Group L, n = 20, respectively). Ewes fed the low nutrition diet (Group L) had higher mean peripheral progesterone concentrations than those fed the high plane diet (Group H; P < 0.05) but lower endometrial progesterone content on Day 5 (P < 0.05). Neither ovarian nor uterine venous levels were affected by nutrition on either Day 5 or 10. Progesterone concentrations in blood samples collected ipsilateral to ovaries bearing a corpus luteum (CL) were higher than in the contralateral samples (P < 0.001). It is concluded that undernutrition can produce a reduction of endometrial content of progesterone the first week after mating. Since no differences in ovarian venous concentrations were observed, it remains to be shown whether this variation is due to other variables, such as the population of endometrial progesterone receptors or other nonhormonal factors.