Oestrous Ewes Research Articles

Ram-induced reproduction in seasonally anovular Corriedale ewes: MAP doses for oestrous induction, ram percentages and post-mating progestagen supplementation

AbstractExploiting the ‘ram effect’ is an inexpensive alternative for out-of-season breeding in moderately seasonal breeds. For maximum efficacy in Corriedale sheep, oestrous ewes have to be introduced together with the teaser rams. Successful applications depend upon timely manipulation of the animals to induce oestrus in most ewes and to minimize the likelihood of successfully induced non-pregnant ewes returning to anoestrus during the mating period.In the first of two experiments, the effects of two alternative ram: ewe ratios (1:6 or 1:12) and five different doses (0, 15, 30, 45 or 60 mg) of medroxy-progesterone acetate (MAP) applied in intravaginal sponges for 9 days were assessed on seasonally anovular adult Corriedale ewes. Control ewes (0 MAP) did not receive sponges, but were injected with 20 mg progesterone at ram introduction. A second experiment tested the efficacy of post-oestrus intravaginally applied MAP (30 mg; 7-day treatment starting on days 3 to 6 after oestrus) for improving reproductive variables of successfully induced ewes exposed to entire rams.Proportions of ewes ovulating and ovulation rates (assessed through laparoscopy) did not differ significantly (P > 0·05) in ewes treated with various MAP doses (213/220 = 96·8% and 1·26 (s.e. 0·031) respectively) or injected with progesterone (56/58 = 96·6% and 1·21 (s.e. 0·058) respectively). The MAP content of the sponges did not affect (V > 0·05) the proportion of ewes ovulating (269/278), marked by the rams (197/213), returning to oestrus (81/197) or lambing among those not returning to first oestrus (87/119). More ewes were marked in the groups exposed to a higher ram percentage (79·7 to 70·6%; P < 0·001) but no other reproductive variable was affected by the ram: ewe ratio at ram introduction (P > 0·05). In the second experiment, post oestrus progestagen supplementation reduced the proportion of ewes returning to first oestrus from 27% to 16% (P < 0·05) but failed to improve lambing rate or the number of lambs born per ewe lambing. Thus, MAP doses as low as 0·25 of the commercial formulation (60 mg) induced oestrus in seasonally anovulatory Corriedale ewes exposed to rams and oestrous ewes. Increasing the ram: ewe ratio augmented the proportion of marked ewes but did not affect any other reproductive variable. Supplementing MAP after oestrus did not improve reproductive rate in Corriedale ewes induced to ovulate during the seasonal anoestrus.

Ovulation rate in ewes after single oral glucogenic dosage during a ram-induced follicular phase

A 2-factor factorial array with three replicates (N = 280) was used to simultaneously assess the effects on ovulation rate of two alternative doses of medroxy-progesterone acetate (MPA) (10 or 60 mg), applied during a 6-day priming period, and the effect of a single dosage of a glucogenic formulation, administered immediately before ram exposure to groups of adult seasonally anovular Corriedale ewes. The glucogenic formulation contained 1,2,3-propanetriol (glycerol; 70% vv), 1,2-propanediol (propylene glycol; 20% vv) and distilled water (10% vv). At sponge withdrawal, a single oral dose of 100 ml of this formulation or the same volume of distilled water was administered to treated and control groups, respectively, and ewes were immediately exposed to rams and hormonally-induced oestrous ewes. Data from an ancillary experiment (n = 10) showed significantly (P < 0.005) above normal plasma glucose levels in treated animals at 3 and 6 h after dosage. A significant interaction (P = 0.0006) between MPA priming doses and glucogenic supplementation was detected. Supplemented ewes, among those exposed to the lower dose of MPA, exhibited a higher (P = 0.0098) mean ovulation rate (1.56 ± 0.076) than ewes that did not receive glucogenic treatment (1.31 ± 0.060). In contrast, ovulation rate was significantly decreased (P = 0.021) from 1.30 ± 0.058 to 1.13 ± 0.042 after glucogenic treatment in ewes that were primed with sponges containing 60 mg of MPA. Ewes exposed to 60 mg of MPA were marked by the rams at a significantly later (P < 0.00001) mean time (54.8 ± 1.44 h) than ewes receiving 10 mg sponges (43.6 ± 1.08 h). These results reveal the potential for modifying ovulation rate through short-term glucogenic manipulations, at least during the compressed follicular phase typical of ram-induced ovulations.

Estrus Diagnosis in Ewes by Using a Plasma/ Serum Progesterone Enzyme Immunoassay (EIA) Kit

A quantitative Enzyme Immunoassay (EIA) Kit (Ovucheck Plasma/Serum Proges-terone EIA Kit, Cambridge Life Science LTD., U. K.) for bovine progesterone (P) was applied to detect estrus in ewes. Serum P concentrations were measured during the estrus cycle of nine ewes. Dilution-assay and recovery test of serum P were conducted. Measurement of P concen-trations of standard and ewe's serum samples showed parallelism, and nearly 100% of a known quantity were gained in recovery test. Intra-assay coefficients of variation (CVs) were from 4.7 to 16.4%, and interassay CVs were from 4.4 to 20.3%. Estrus was confirmed with mounting behavior by a ram. P concentrations in 92% of serum samples from ewes in estrus were less than 1ng/ml, while the concentrations in 88% of samples from ewes in non-estrus were more than 1 ng/ml. In conclusion, this EIA kit was practical for measurement of P concentrations in ewe's serum and useful for diagnosis of estrus in ewes.

Use of melengestrol acetate-based treatments to induce and synchronize estrus in seasonally anestrous ewes.

Ten experiments utilizing 1,659 ewes were conducted to determine the potential of melengestrol acetate (MGA)-based treatments in inducing and synchronizing estrous activity in ewes during the nonbreeding season. In May or June, ewes were given .25 mg of MGA.ewe-1.d-1 or control diet and(or) a subsequent i.m. injection of zeranol, estradiol-17 beta, or oil vehicle. Fertile rams were introduced, and estrous and(or) lambing responses were determined. In Exp. 1, more (P < .01) ewes given MGA for 14 d followed by 5 mg of zeranol (i.m.) were in estrus than controls. Melengestrol acetate and zeranol independently induced estrus in Exp. 2, with MGA-treated ewes exhibiting the greatest lambing response (P < .05). The optimum duration of feeding MGA was 8 d vs 11 or 14 d (Exp. 3). In Exp. 4, as the dose of zeranol increased, synchrony of estrus increased but lambing response decreased. A dose of 1.25 mg of zeranol represented a compromise in estrous and lambing response and was determined to be optimally effective when given 54 h after the last feeding of MGA (Exp. 5). Shortcomings in lambing responses were treated in Exp. 6 by supplementing ewes with MGA after breeding, which proved unsuccessful, and in Exp. 7 by substituting estradiol-17 beta for zeranol, which proved effective when given 54 h after the last feeding of MGA (Exp. 8). In Exp. 9, use of MGA + estradiol increased (P < .05) the estrous and subsequent lambing response of 30-d postpartum ewes temporarily weaned of their lambs. In contrast, lambing response of 90-d postpartum ewes treated with MGA + estradiol was not increased by temporary removal of lambs (Exp. 10). These data collectively support the hypothesis that treatment of ewes with MGA + estradiol is an effective and practical approach for inducing and synchronizing a fertile estrus in ewes during the non-breeding season.

Female to female stimulation of ovarian activity in the ewe

The ovulatory and oestrus responses of seasonally anovulatory ewes to the presence of ewes with synchronised oestrus was evaluated. The experiment was carried between 4 June and 1 July when the ewes were in seasonal anoestrus. Two hundred adult Suffolk and Dorset ewes were used. The animals were randomly divided into five groups balanced according to breed: Group I (treated) consisted of 25 ewes induced to cycle by the treatment for 10 days with vaginal sponges containing 40 mg of fluorogestone acetate and an injection of 200 IU of pregnant mares' serum gonadotropin (PMSG) at the time of sponge removal. Group II (mixed) consisted of 25 untreated ewes housed in the same pen as the treated ewes throughout the experiment. Groups III, IV and V each consisted of 50 untreated ewes located in adjacent pens progressively more distant from the pen which contained the treated animals. The ewes in Group III had contact with the treated animals through the fence, while those in Groups IV and V were separated from the treated ewes by one and two pens respectively. Day 0 of the experiment was defined as the day in which the sponges were removed from the treated ewes. Blood samples for progesterone determination were obtained from 25 animals from each group on days 6, 10 and 13. Oestrus was detected twice a day using vasectomised rams introduced to each pen for 15 min in the morning and 15 min in the evening. As expected, the proportion of ewes with luteal activity was higher (P < 0.01) in the treated group than in the other four groups on days 6, 10 and 13. By day 13 progesterone levels were elevated in 87.5%, 52%, 37.5%, 32% and 13% of the ewes sampled in Groups I, II, III, IV and V respectively. There was a direct relationship between the proportion of non-treated ewes with ovarian activity and the intensity of contact with the treated ewes, being maximal in the ewes that remained mixed with the synchronised animals, and lowest in the ewes located in the most distant pen. The proportion of ewes that showed oestrus during the first 14 days after sponge removal was significantly higher in the treated (92%) and mixed (40%) groups than in Groups III (10%), IV (8%) and V (4%). It is concluded that the presence of a large number of ewes in oestrus can stimulate ovarian activity in seasonally anoestrous ewes. This female to female stimulation could be mediated by olfactory, visual and/or auditory stimuli.

Effect of exogenous melatonin and plane of nutrition after weaning on estrous activity, endocrine status and ovulation rate in Salz ewes lambing in the seasonal anestrus

Forty-nine Spanish Salz ewes lambing in the second fortnight of March (20 March ± 1.5 d) were used to determine the effects of exogenous melatonin and postweaning nutrition on endocrine status, date of first estrus and ovulation rate. Experimental design was a factorial defined by 2 postweaning planes of nutrition, 1.80 (high) and 1.35 (low) times the maintenance requirements, and treatment with a single 18-mg subcutaneous implant of melatonin (M) 32 d after lambing or no treatment control (C). Mean weaning to first estrus interval was shorter in treated than in control ewes (50.8 ± 4.2 vs 87.6 ± 6.3 d; P < 0.01). Considering both the treated and control animals together, the ratio between mean night and daytime plasma melatonin levels was significantly correlated with the implant insertion-first estrus interval on Day 5 (0.67; P < 0.01) and Day 35 (0.63; P < 0.05) after implantation. Melatonin implants induced a significant increase of mean LH concentrations at Days 14 and 33 after implantation (P < 0.01) without any significant influence of plane of nutrition. Ovulation rate was higher for treated than control ewes in the second estrus (P < 0.05). An interaction between plane of nutrition and exogenous melatonin on ovulation rate at the second cycle after weaning was detected (P < 0.01), being close to the significance in the first, fourth and fifth cycles (P < 0.1). These results suggest that exogenous melatonin in April may be an effective way of advancing the breeding season and enhancing ovulation rate associated with a low rather than a high plane of nutrition.

In vitro effects of different doses of FSH on oocyte maturation and embryo development

The purpose of this study was to assess the ovulatory response and embryo production after repeated superovulation of selected high-prolificacy Rasa Aragonesa ewes at the end of their reproductive life. A total of 211 superovulatory treatments were performed during the breeding seasons of 3 consecutive years. Ewes were given the same gonadotrophin treatment up to three times at intervals of at least 50 days. They were synchronized with intravaginal progestagen sponges and treated with ovine follicle stimulating hormone (oFSH) equivalent to a total dose of 176 NIH-FSH-S1 units in eight decreasing doses administered at 12-h intervals from 72 h before sponge removal. Embryos were recovered by laparotomy 7 days after the onset of oestrus. There was no effect of year on the superovulatory response as measured by the percentages of ewes in oestrus (80%) or ovulating (67%). An average of four freezable embryos (compacted morulae and blastocysts) were recovered at each treatment from the 141 ovulating ewes, with no significant differences amongst years, although the process seemed to be less efficient after the third treatment than after the first or second ones (2.4 vs. 4.1 (P<0.10) or 4.5 (P<0.05) freezable embryos, respectively). This was primarily attributable to a lower ovulation rate (three fewer corpora lutea; P<0.10). Results indicate that the methodology used in the present study could be an efficient and inexpensive way to obtain high-quality embryos from selected high-prolificacy animals before culling.

Characterization and localization of a putative oxytocin receptor in the cervix of the oestrous ewe.

The purpose of the present study was to investigate the presence of high-affinity oxytocin-binding sites (putative oxytocin receptors) in the cervix of the non-pregnant ewe. [3H]Oxytocin binding to the peripheral layers of cervical tissue (comprising the serosal layer and the least dense collagenous and muscular layers) and the remaining dense collagenous cervical tissue were studied separately. [3H]Oxytocin-binding sites were detected in membrane fractions prepared from both of these regions, but binding to the peripheral cervix was variable and binding site concentrations were low, hence these were not characterized further. A high-affinity oxytocin-binding site, having a dissociation constant of 1.8 nmol/l, was characterized in the dense collagenous regions of the cervix of ewes killed during the oestrous period. Similar dissociation constants were determined for [Arg8]-vasopressin and the oxytocin-specific agonist [Thr4, Gly7]-oxytocin in competition studies. [3H]Oxytocin binding to peripheral cervical tissue and to the dense collagenous cervix was generally low or undetectable during the luteal phase, but increased in both tissues around the time of luteolysis. Although specific binding to both tissues was variable during the oestrous period, it was higher at this time than during the luteal phase. [3H]Oxytocin-binding site concentrations were also found to be higher within the inner dense collagenous cervix of oestrous ewes than of pregnant, ovariectomized or anoestrous animals.(ABSTRACT TRUNCATED AT 250 WORDS)

Detection of oestrous-related odour in ewe urine by rams

The ability of rams to discriminate between urine odour of oestrous ewes and urine odours from ewes at other days of the oestrous cycle was determined using operant conditioning techniques. Rams could discriminate between the odour of urine of oestrous ewes and the odours of urine from ewes at day 6 to day 1 before oestrus and from ewes at day 4 to day 10 after oestrus. Rams did not discriminate between odours of urine samples from different ewes in oestrus, or between urine odour of oestrous ewes (day 0) and urine odours from ewes at day 1 to day 3 after oestrus. These results support the hypothesis that ewes in oestrus produce an odour in urine that is detectable by rams.

The effect of bovine viral diarrhoea virus (BVDV) during follicular development on the superovulatory response of cattle

The purpose of the present study was to investigate the effects of three gonadotrophin treatments on follicular development and ovulation rate in Chall ewes. Thirty-three non-cycling, multiparous fat-tailed Iranian Chall ewes, weighing 62.5 ± 2.5 kg, were used in the trial. The ewes were allocated randomly to 1 of 3 groups (n = 11/group). Estrus was synchronized using CIDR's, inserted for 14 days with the following superovulation treatments being used: in group eCG/d14 the ewes received 1500 IU eCG on the day of CIDR removal (day 14); in group eCG/d12, 1500 IU eCG was administered 48 h prior to CIDR removal (day 12); in group eCG/d12 + FSH ewes were injected with 350 U eCG, 48 h prior to CIDR removal (day 12), followed by 12 ml FSH-P in six doses of 2.75, 2.75; 2.25, 2.25; 1, 1 ml over a 4 day period at 12 h intervals. Vasectomized rams were used to detect estrus in the ewes from 24 h after CIDR removal. Ovarian follicular activity was monitored daily with the aid of transrectal ultrasonograpy – from the day of superovulatory stimulation, until the day of estrus. Ewes in estrus were mated twice daily (morning and evening). The number of CLs was recorded using ultrasonography and laparoscopy, 7 days after mating. The number of large ovarian follicles at estrus was positively related to the number of small follicles at day 12 (P < 0.05, r = 0.56) in the eCG/d12 + FSH group of ewes. The number of large follicles at estrus and CLs 7 days later were higher in the eCG/d12 + FSH group, followed by the eCG/d14 group and the eCG/d12 group. It could be concluded that Chall ewes could be superovulated with eCG or with a combination of eCG and FSH. Of the three protocols tested, the eCG/d12 + FSH showed superiority in terms of the number of large follicles at estrus and CLs 7 days later.

Effects of hormonal treatment and interval between treatment on follicle development in calves

In order to study the reproductive response to a synchronising hormonal treatment, oestrus, fertility and litter size were compared among 44 Queue Fine de l’Ouest (QFO) ewe lambs and 44 D’Man×QFO contemporaries run in a single flock under natural grazing conditions. Within breed, animals were divided into two groups (balanced for live weight) of 22 ewes, each induced to breed at 9 months of age after being treated with intravaginal progestagen and 200 or 400 IU PMSG, respectively, in groups 1 or 2. Throughout the 45 days mating period, ewes in oestrus were mated by Noire de Thibar rams. The hormonal treatment was effective in inducing oestrus in over 90% of the ewes. At the induced ovulation, the breed and the dose of PMSG did not affect either the number of animals exhibiting oestrous behaviour, or allowing mating. After the mating period, breed had a significant effect on fertility, with lambing rates of 93 and 66% for ewes of the D’Man×QFO and QFO breeds, respectively. Breed also significantly affected the proportions of females lambing when conception occurred at the induced oestrus. Though not significant, ewe lambs of both breeds receiving 400 IU PMSG produced 16% more lambs than those treated with the lower dose of 200 IU. With a dose of 200 IU PMSG, ewe lambs of the D’Man×QFO breed tended to yield a higher litter size than the QFO contemporaries (1.2±0.40 vs. 1.1±0.26). Globally, the results showed that attempts to breed from ewe lambs of the D’Man×QFO breed under the conditions described here are likely to lead to more satisfactory conception rates than in the case of the autochthonous QFO breed.

Actions of oxytocin and vasopressin on oestrogen-induced electromyographic activity recorded from the uterus and oviduct of anoestrous ewes

Oxytocin and the related peptide [Arg8]vasopressin (AVP) have previously been shown to bind with equally high affinity to oxytocin binding-sites (presumed oxytocin receptors) present within the uterus and oviduct of oestrous ewes. There is a possibility, therefore, that AVP mediates oxytocic actions through these binding sites. For the present study, ewes in seasonal anoestrus were treated with oestradiol-17 beta (50 micrograms subcutaneously, daily for 2-4 days). It was shown initially that this treatment stimulated the development of high-affinity oxytocin binding-sites (Kd 4.4 +/- 0.8 nmol L-1) which had similar affinity for AVP (Kd 4.2 +/- 0.9 nmol L-1) in the myometrium. The efficacy of oxytocin and AVP in vivo were compared by recording electromyographic (EMG) activity from the ampullary-isthmic junction of the left oviduct and the left uterine horn of four conscious ewes. Before oestradiol treatment there was no EMG response to oxytocin even at supraphysiological (1000 mU) doses. During oestradiol treatment, EMG activity was consistently increased in response to injections of 25 mU and 100 mU oxytocin via the jugular vein, but not to saline or 100 mU AVP. Higher doses of AVP were not investigated because of the possibility of cardiovascular side effects. A subsequent blood sampling experiment showed that maximal concentrations of oxytocin and AVP (achieved in peripheral plasma during the first 2 min following injection into the jugular vein) were of a similar order of magnitude after injection of equivalent doses of the two peptides. It is concluded that AVP probably does not mediate biological activity through the oxytocin receptor in non-pregnant ewes.(ABSTRACT TRUNCATED AT 250 WORDS)

Luteinizing hormone and testosterone response of sexually active and inactive rams.

The objective of this study was to identify rams exhibiting high (HP) and low (LP) levels of sexual performance and to determine whether their respective behavioral responses to ewes in estrus were related to changes in serum testosterone (T) and LH concentrations. Rams were selected on the basis of standardized serving capacity tests. Plasma T and LH concentrations in rams were measured in three experiments: 1) after 15 min of exposure to estrous ewes, 2) after an injection of 500 ng of LHRH, and 3) during an 11-h exposure to estrous ewes. During 15 min of exposure to ewes, HP rams were sexually active, whereas LP rams showed no sexual interest. Secretion of LH was similar (P greater than .05) between ram groups. Sexual arousal, copulation, and ejaculation of HP males were not related (P greater than .05) to LH secretion. Exposure to estrous ewes for 11 h, however, stimulated LH pulse frequency and elevated basal LH and T concentrations in HP but not LP rams (P less than .001). Luteinizing hormone secretion was positively correlated to the frequency of mounts (r = .19; P less than .01) and ejaculation (r = .17; P less than .03). Aggressive behavior of rams directed at ewes was negatively correlated to LH (r = -.22 P less than .003). Concentrations of LH and T after LHRH injection were similar between HP and LP rams (P greater than .05). These results show that the effects of the ewe on LH secretion of rams depend on length of the exposure period and sexual activity of the male.

Manipulation of reproductive activity in subtropical sheep

Prevailing sheep production systems in the region are based on continuous breeding throughout the year. Peak lambing, however, occurred in October–December and April–May. Twenty percent of ewes in the arid rangelands and 30% in the Nile Valley lambed twice a year. Breeding local ewes every 8 months increased number of lambs weaned per ewe annually by 54.2 and 41.9% in Ossimi and Rahmani breeds, respectively. Fertility and prolificacy were consistently better in fall (September) than in winter (January) and spring (May) matings. Ovulation rate (OR) was highest in September and January, while ova wastage was lowest in September and highest in January and May matings. Introduction of rams to ewes for one week prior to mating in spring increased (by 27%) the percentage of ewes that demonstrated oestrus and were mated. Applying artificial light in spring, to simulate autumn, increased percent of ewes in oestrus by 45% and of ewes ovulating by 30%. Continuous exposure to long days of July during the fall, decreased percentage of ewes in oestrus, especially in the more seasonal subtropical breeds. Melatonin treatment increased percentage of ewes ovulating and ovulations per ewe from 3.0 in controls to 4.1. Progesterone (PMSG) treatment and immunization against androstenedione significantly increased OR, but was not converted into increasing litter size, due to high ova wastage. Season of lambing had little effect on age at puberty of subtropical ewe lambs. Reducing age at puberty of subtropical breeds seems to be hindered by their low growth rate.

Enhancement of Teaser Ram Activity Using Exogenous Melatonin

Under Australasian conditions vasectomised (teaser) rams are widely and successfully used for the induction and synchronisation of oestrus in ewes. However under UK conditions success has been limited possibly as a consequence of the more marked seasonality exhibited by UK sheep stocks. The transitional phase of ewes in July at latitude 57°N may require a greater degree of stimulation than can be achieved using teaser rams at 2-4% of the flock. The rams may also be in sub-optimal breeding status resulting in lowering of their libido and hence stimulatory effect on the ewes.

Concentrations of insulin-like growth factor-I in serum of sheep with different ovulation rates: Changes during the estrous cycle

To determine if concentrations of IGF-I in serum are associated with the ovulation rate or if IGF-I concentrations change during an estrous cycle, blood was collected from ewes of three genotypes in two experiments. In Experiment 1, blood was collected once during the mid-luteal phase of an estrous cycle in nulliparous ewes. In Experiment 2, blood was collected every other day from Day 1 to 19 postestrus in primiparous ewes. Three genotypes of ewes were used in both experiments: Dorset × Rambouillet, Finn × Rambouillet and Booroola Merino × Rambouillet. Ovulation rates in Experiment 1 were 1.35, 1.88 and 2.50 for Dorset × Rambouillet (n=17), Finn × Rambouillet (n=49) and Booroola Merino × Rambouillet (n=28) ewes, respectively. IGF-I concentrations in serum were greater (P<0.05) in Finn × Rambouillet ewes than for Dorset × Rambouillet or Booroola Merino × Rambouillet ewes. In Experiment 2, ovulation rates were 1.57, 2.00 and 2.75 for Dorset × Rambouillet, Finn × Rambouillet and Booroola Merino × Rambouillet, respectively. IGF-I concentrations increased with age in Dorset × Rambouillet and Booroola Merino × Rambouillet ewes (but not Finn × Rambouillet ewes) such that they did not differ between crossbred ewe groups. IGF-I concentrations decreased between Days 1 and 5, then increased (P<0.05) between Days 8 and 17 postestrus suggesting that IGF-I concentrations increase during estrus in ewes.

Role of dihydrotestosterone in the control of sexual behaviour on castrated male sheep

Wethers (at least 2 1/2 years after castration) were implanted with testosterone propionate (TP), oestradiol dipropionate (ODP), dihydrotestosterone, or a combination of dihydrotestosterone and ODP Silastic capsules. Active immunization against both oestradiol and oestrone or oestradiol only was used to negate effects of oestrogens produced by aromatization of TP. On exposure to oestrous ewes, immunization of wethers implanted with TP significantly (P less than 0.01) reduced all components of mating behaviour (except sniffing and Flehmen) to levels seen in untreated controls. The results support the conclusion that dihydrotestosterone potentiates the action of oestrogens, particularly as regards Flehmen, and has no action on its own within the central nervous system, while oestrogens do not restore mating activity to the same level as that following treatment with testosterone.

Importance of behavioural stimuli in ram-induced ovulation in seasonally anovular Corriedale ewes

Three groups of about 65 seasonally anovular Corriedale ewes were penned and exposed to rams on November 4, 1989. A fourth group ( n=64) was maintained in a 3-ha paddock and also exposed to rams on the same date. The sexual behaviour exhibited by rams in contact with penned ewes was recorded during nine simultaneous observation sessions lasting 2 h each. Five days after ram introduction, incidence of ovulation and ovulation rate were higher ( P < 0.01) in adult than in 1.5-year-old ewes. Among penned adult ewes, a greater ( P < 0.05) incidence of ovulation was recorded in ewes maintained in contact with rams and oestrous ewes (95.8%) than in ewes exposed to either rams with or without recent experience with oestrous ewes (68.7 and 57.1%, respectively). The fourth group, exposed to rams in field conditions, exhibited a lower ( P < 0.05) incidence of ovulation (31.9%) than any other group. No differences among treatments were detected in 1.5-year-old ewes. The incidence of ovulation was associated ( r=0.99, P<0.05) with the sexual behaviour displayed by the rams. It was concluded that the sexual behaviour of the rams plays an important role in ram-induced ovulation and that the continuous presence of oestrous ewes is necessary for the maximum efficacy of the technique in Corriedale ewes.

Pulsatile release of oxytocin into the circulation of the ewe during oestrus, mating and the early luteal phase

Two experiments were designed to investigate release patterns of oxytocin into plasma during oestrus and the early luteal phase. In Exp. 1, blood samples were collected from 5 ewes every 30 min for 10 h during 6 days around oestrus and the early luteal phase. During oestrus concentrations of oxytocin were generally low (1.27 +/- 0.54 pg/ml; mean +/- s.d.) but with occasional pulses up to 6 pg/ml. By Day 5 mean basal concentrations had risen to 4.5 +/- 2.1 pg/ml with a fluctuating release pattern. In Exp. 2, a method was developed for continuous blood sampling from conscious, unrestrained ewes. On the predicted day of oestrus following an untreated oestrous cycle, 8-ml blood samples were collected every minute for two 35-min periods (8 ewes: 16 sampling periods). For 6 ewes a ram was introduced to the pen for part of this time, and resulting behaviour was recorded. Additional blood samples were assayed for LH and progesterone to determine the stage of the cycle. Overall mean oxytocin concentrations ranged from 1.5 +/- 0.53 to 6.8 +/- 5.25 pg/ml in different animals. Ewes which were both in oestrus and exposed to the ram showed a pulsatile oxytocin release pattern consisting of low baseline concentrations with short-duration pulses superimposed (duration 1-4 min; amplitude 2.5-31.7 pg/ml; frequency 3.18/h). Coitus was not temporally associated with pulsatile release. However, the importance of the presence of the ram was indicated by total separation of 2 oestrous ewes from the ram until after experimentation. In these animals only 1 pulse of oxytocin was detected in 2.7 h of sampling. It is concluded that, although mean oxytocin concentrations at oestrus were low, short duration pulses were released into the plasma at this time. This effect may be dependent on the presence of a ram.

Autoradiographical localization of oxytocin binding sites on ovine oviduct and uterus throughout the oestrous cycle.

A highly specific oxytocin receptor ligand, 125I-labelled d(CH2)5[Tyr(Me)2,Thr4,Tyr-NH9(2)] vasotocin (125I-OTA), was used to localize high affinity oxytocin receptors in ovine uterine and oviduct tissues throughout the oestrous cycle. The pattern of binding revealed by in vitro autoradiography correlated well with the results of the homogenate receptor assays using the same ligand and with previous binding assays using the tritiated ligand. At oestrus, specific 125I-OTA binding was evident on the luminal epithelium of the caruncular and intercaruncular regions, on the epithelial cells lining the secretory uterine glands and in the stroma underlying the caruncular epithelium. In the myometrium diffuse labelling was evident in the outer longitudinal smooth muscle layer. At Day 4 of the cycle, binding to the stroma was diffuse and virtually absent from the glandular epithelium. No specific binding was evident in either tissue at Day 12 of the luteal phase, but by Day 14, prior to the decrease in peripheral progesterone concentrations, binding was again apparent on the luminal epithelium only. Specific binding to the oviduct was localized to the smooth muscle layer of the isthmus region of oestrous ewes and was not detected at any other stage of the oestrous cycle. These studies extend our knowledge of the distribution of oxytocin binding sites in uterine and oviduct tissues throughout the oestrous cycle and suggest that oxytocin has an important role in stimulating oviduct and uterine motility at a time crucial to successful egg collection and/or sperm embryo transport.