Sexual behavior of stallions during in-hand natural service and semen collection: an observation in French studs.

The sexual behavior of 42 stallions from French national and private studs was examined in two contexts: semen collection for artificial insemination (AI) and in-hand natural service (NS). Each stallion was observed twice in the same context. Erection and ejaculation latencies, the number of mounts leading to ejaculation, dismount latency and total breeding time were measured and compared between AI and NS. Mount without erection was rare (6/83 observations). Erection latency was 89+/-11s, and was not different between NS (62+/-22s) and AI (100+/-13s, P=0.128). Stallions ejaculated after either one mount (62/83 observations), or two (11/83 observations) or three mounts (10/83 observations). Ejaculation latency was 85+/-15s (84+/-19 in AI and 86+/-28 in NS). If 1st mount did not lead to ejaculation, then ejaculation latency increased several fold following the 2nd mount during both AI and NS. The results provide reference measures for semen collection in French studs. Difference in erection latency between AI and NS, although not statistically significant, may reflect different contributions of excitatory inputs from the brain and the genital area to the activation of spinal networks controlling erection. In contrast, lack of difference in ejaculation latency between AI and NS suggests that the spinal network that controls ejaculation follows a more rigid motor pattern.     

Impotence and abnormal sexual behavior in the stallion

Clinical observations have been made on stallions exhibiting impotence and other abnormal forms of sexual behavior. Procedures for diagnosing and retraining consisted of presenting the patient to one or more estrcus mares and observing his sexual behavior. Following sufficient observations, patients were classified into one or more of the following categories: (a) failure to obtain or maintain an erection; (b) incomplete intromission, or lack of pelvic thrusts after intromission; (c) dismounting at onset of ejaculation; (d) failure to ejaculate despite a complete, prolonged erection and repeated intromissions; and (e) ejaculate normally for several ejaculates, then cannot ejaculate without sexual rest, although libido remains high.To successfully diagnose and treat patients with abnormal sexual behavior the following are needed: (a) a variety of mares in estrus; (b) other stallions to provide a competitive environment; (c) a phantom; (d) an artificial vagina and laboratory equipment for seminal evaluation; and (e) extreme patience.Selected clinical cases are presented, including history, diagnosis and treatment with recommendations in relation to reproductive management. Some of the more important observations were: (a) impotence was often diagnosed as aspermatogenesis, due to failure of the impotent stallion to ejaculate; (b) erection was not always essential for ejaculation; (c) pain from injury or disease was often the etiology of abnormal sexual behavior; (d) in excess of 125 ml of semen were collected from a stallion without the occurrence of complete ejaculation; (e) the presence of gelatinous material (gel) in the semen did not necessarily mean complete ejaculation occurred; (f) occasionally seminal emissions from some stallions contained spermatozoa, usually nonmotile, with a large proportion of morphologically abnormal forms, without complete ejaculation.It was concluded that the most common cause of abnormal sexual behavior was mismanagement, such as excessive use, abusive training procedures, injuries during breeding, etc. The majority of the stallions responded well to retraining and recovery was essentially complete without the use of drugs.     

Imipramine and xylazine-induced ex copula ejaculation in stallions

This study is a part of our ongoing work toward developing pharmacological methods for enhancing and inducing ejaculation in stallions with ejaculatory dysfunction. We evaluated a combination treatment of imipramine hydrochloride followed 10 minutes later by xylazine hydrochloride for the induction of ex copula ejaculation. Eight pony stallions each underwent 6 treatment trials conducted at 4-day intervals. The trials were conducted in the animals' stalls, where they were observed for 90 minutes following treatment. To evaluate the effect of pretreatment sexual stimulation on the rate of ejaculation for each of the 8 stallions, 3 of the 6 trials were preceded by exposure to a restrained ovariectomized pony mare. For 7 of the 8 stallions, 1 to 4 of the 6 trials resulted in induced ejaculation, for a total of 16 ejaculations in the 48 trials. Six of the ejaculations occurred with imipramine treatment alone, before the administration of xylazine. All ejaculations were associated with erection and masturbation. Six of 24 trials (25%) preceded by sexual stimulation resulted in ejaculation, while 10 of 24 trials (42%) without sexual prestimulation resulted in ejaculation. These proportions were not different (P = 0.11). Induced ejaculates were collected into a plastic bag positioned over the prepuce by a girth strap for the comparison of semen characteristics with 2 base line ejaculates obtained in copula from these stallions during the week preceding the series of induced ejaculation trials (with similar 4-day intervals from previous ejaculation). The induced ejaculates were of lower total volume, higher concentration, lower gel volume, higher total numbers of spermatozoa, and lower pH (P < 0.05) than the base line in copula ejaculates. Together, these semen characteristics suggest increased emission of the sperm-rich fraction and reduced emission of accessory gland fluids, probably resulting from imipramine treatment.     

Modulating reproductive activity in stallions: a review

Situations in which suppression or stimulation of reproductive activity in stallions has been attempted, or is desired, include resolution of the equine arteritis virus 'shedding' state, induction of testicular descent in inguinal cryptorchids, and the improvement of sperm production capacity and/or semen quality in sub-fertile stallions. However, the most common reason for wanting to modulate reproductive activity in a stallion is to alter the expression of sexual behaviour. In the case of intact stallions used for competitive or recreational purposes, the overt expression of sexual or aggressive behaviour can be distracting for both animal and owner and, in some cases, dangerous to all concerned. By the same token, a breeding stallion that displays little interest in mounting a mare/phantom, or is slow to achieve erection and/or ejaculation, can be extremely frustrating. This paper reviews the major pharmacological agents reported to usefully modify reproductive activity in stallions, and outlines their pros and cons when compared to training, management or surgical alternatives.     

PGF(2α), LH, testosterone, oestrone sulphate, and cortisol plasma concentrations around sexual stimulation in jackass

Many hormones are involved in the regulation of male reproductive functions, controlling sexual behavior, and influencing sexual arousal, the onset of erection and ejaculation, and the post-ejaculatory detumescence. The aims of this study were to analyze the plasma concentrations of 15-ketodihydro-PGF_2α (PGFM), LH, testosterone (T), oestrone sulphate (OS), and cortisol (C) in relation to sexual stimulation and to evaluate the possible correlations among circulating hormones and between hormones and semen characteristics in the donkey stallion. Thirteen sexually experienced Martina Franca jackass of proven fertility were enrolled and semen was collected through an artificial vagina. Plasma samples were collected at 12, 9, 6 and 3 min before oestrous jenny exposure, at the first erection in the mating arena in the presence of an oestrous jenny, during ejaculation, at dismounting, 3, 6, 9 and 12 min after ejaculation in box, and then every 10 min during the following 50 min. PGFM showed an increasing trend with significant differences between the pre-ejaculatory and post-ejaculatory period, suggesting a role of this hormone in the control of ejaculation. LH showed a significantly higher concentration at ejaculation compared to last samples, while T showed significantly higher levels at erection, ejaculation and dismounting, probably for its influence on these processes and on sexual behavior. Finally, OS did not show any difference in the period of observation, while C presented a significant increase only 22 minutes after erection. The only hormonal correlation found was a positive one between LH and T at erection and dismounting, while T and OS were positively correlated with total and progressive motility, respectively.     

Effect of semen collection practices on sperm characteristics before and after storage and on fertility of stallions

This study analyzed effects of different methods and intervals of semen collection on the quantity and quality of fresh, cool-stored, and frozen-thawed sperm and fertility of AI stallions. In Experiment 1, ejaculates were obtained from six stallions (72 ejaculates per stallion) using fractionated versus non-fractionated semen collection techniques. Initial sperm quality of the first three jets of the ejaculate was not different from that of total ejaculates. Centrifugation of sperm-rich fractions before freezing improved post-thaw motility and sperm membrane integrity when compared to non-centrifuged sperm-rich fractions or non-fractionated centrifuged ejaculates (P<0.05). In Experiment 2, semen from four stallions (60-70 ejaculates per stallion) was collected either once daily or two times 1h apart every 48 h. The first ejaculates of double collections had significantly higher sperm concentrations, percentages of progressively motile sperm (PMS) after storage for 24h at 5 degrees C and lower percentages of midpiece alterations than single daily ejaculates. Semen collected once daily showed significantly lower values of live sperm after freezing and thawing than the first ejaculate of two ejaculates collected 1h apart every 48 h. In Experiment 3, semen was collected from 36 stallions (> or =12 ejaculates per stallion) during the non-breeding season and the time to ejaculation and the number of mounts was recorded. When time to ejaculation and the number of mounts increased, volume and total sperm count (TSC) also increased (P<0.05), whereas a decrease was observed in sperm concentration, percentage of PMS after storage for 24 h at 5 degrees C, percentage of membrane-intact sperm in fresh semen (P<0.05) as well as motility and percentage of membrane-intact sperm of frozen-thawed sperm (P<0.05). In Experiment 4, AI data of 71 stallions were retrospectively analyzed for the effect of number of mounts per ejaculation and frequency, time interval of semen collections on pregnancy, and foaling rates (FRs) of mares. Semen volume increased, but sperm concentration and percentage of PMS after 24-h cool-storage decreased with increasing number of mounts on the phantom (P<0.05). A statistically significant inter-relationship was demonstrated between frequency and interval of semen collection and FR. Mares inseminated with stallions from which semen was collected frequently (> or =1 on an average per day) showed significantly higher FRs than mares inseminated with semen from stallions with a daily collection frequency of 0.5-1 or <0.5. FR of mares inseminated with stallions having 0.5-1 days between semen collections was significantly better than FR of mares that were inseminated with stallions having semen collection intervals of 1-1.5 days or >2.5 days.     

Alkaline phosphatase in stallion semen: characterization and clinical applications

Significant amounts of alkaline phosphatase (AP) activity have been found in semen plasma from numerous species. In species in which the majority of semen plasma AP (SPAP) activity originates from the epididymis and testicle, SPAP activity can be used clinically as a marker to differentiate testicular origin azoospermia or oligospermia from ejaculatory failure. Information on SPAP activity in stallions to date has been limited. In this study, a standard clinical chemistry analyzer was used to determine AP activity in pre-ejaculatory fluid and ejaculates from groups of normal stallions. Additionally, accessory glands, epididymides, testicles and other components of the urogenital tract of normal stallions were assayed to determine which tissues contain SPAP activity. The results indicated that levels of AP activity are low in pre-ejaculatory fluid, but significantly higher in ejaculatory fluid from normal stallions. Spermatozoa were not a significant source of SPAP activity. High levels of SPAP activity were found in the testes and epididymides. These findings suggest that SPAP activity is a candidate for a sperm-independent marker for ejaculation in the stallion. Finally, AP activity was determined in ejaculatory fluid from a stallion with bilaterally blocked ampullae, both before and after relief of the blockage. While the blockage was present, AP activity in ejaculatory fluid was low. However, following relief of the blockage, AP activity in ejaculatory fluid rose dramatically, thus suggesting that AP activity will be useful as an inexpensive, simple clinical assay for differentiating ejaculatory failure or excurrent duct blockages from testicular origin azoospermia and oligospermia.     

Age and seasonal effects on sexual behaviour of stallions at rest

Sexual reactions were studied in stallions kept under uniform stable conditions and having no contact with mares. The stallions were observed continuously for 7 days during the short photoperiod and for 7 days, 6 months later, when the photoperiod was long.The monotonous life and environment of the stable appear to be the main causes of the frequent occurrence of erection and masturbation.Full erection was observed on average 4 times per day per stallion and masturbation attempts on average 4.4 times per day, while the total time of erection per stallion was an average of 38 min per day during the short photoperiod and 45 min during the long photoperiod. Two periods of the day, in the morning and in the evening, were characterized by an increased amount of sexual activity. Full masturbation, ending with ejaculation was observed sporadically, and only in some of the stallions. It was found that erection time tended to be longer during the long-day period, P <0.10.     

Influence of exogenous testosterone on sperm production, seminal quality and libido of stallions.

The effect of exogenous testosterone on sperm production, seminal quality and libido was studied in 24 stallions. Based on pretreatment data, a stallion was assigned to 1 of 3 groups each containing 8 animals. One member of each group received 0 (Group 1), 50 (Group 2), or 200 micrograms (Group 3) testosterone propionate per kg body weight every 2 days for 88 days. The lower dose of testosterone had no significant effect on most of the parameters studied: the higher dose depressed total scrotal width at Day 90 post-treatment (P less than 0.01), total spermatozoa ejaculated between Days 60 and 90 (P less than 0.01) and 96 progressively motile spermatozoa between Days 60 and 90 (P less than 0.10). One half of the stallions from each treatment were castrated on Day 90. In the operated stallions, the mean number of spermatids per g testicular parenchyma in the controls (Group 1) was significantly (P less than 0.05) higher than that in Group 3 whereas the difference between the number of spermatids/testis in the same stallions of these two groups was significant only at P less than 0.1. Testosterone propionate treatment did not influence time to erection, interval from first mount to ejaculation or number of mounts per ejaculation. The treatment of normal, intact stallions with testosterone propionate did not enhance libido and caused a severe depression of reproductive capacity.     

Xylazine-induced ex copula ejaculation in stallions

This study is a part of ongoing work toward developing pharmacological methods of enhancing and inducing ejaculation in stallions with ejaculatory dysfunction. We evaluated ex copula ejaculatory response to treatment with the alpha-adrenergic agonist xylazine hydrochloride, with and without preliminary sexual stimulation. Twenty-eight mature stallions each reveived, in random order, one xylazine trial (0.3 mg/lb, i.v.) without preliminary sexual stimulation, one xylazine trial with 5 to 10 min of sexual prestimulation, and one control trial (equivalent volume sterile water injection). Trials were conducted in the animal stalls. Ejaculation occurred in 15 of 56 (27%) xylazine trials. No ejaculations occurred in the sterile water control trials. In trials with sexual prestimulation, ejaculation occurred in 39% compared with 14% in trials without prestimulation. This difference was significant (P < 0.05). Xylazine-induced ejaculates were collected into a plastic bag attached to a girth and were similar to those obtained by artificial vagina. Nine of the 15 ejaculations occurred within 2 min of injection.     

Hormonal and social factors affecting evoked sexual behavior in Rhesus monkeys

Male rhesus monkey sexual behavior occurring spontaneously or evoked by remotely-controlled hypothalamic stimulation was studied in dominant and subdominant males with both dominant and subdominant, estrogen-treated or untreated, ovariectomized females. The behavior was quantified in terms of number and duration of ejaculatory sequences, number of thrusts, and number of mounts per sequence. Little or no spontaneous sexual behavior was observed with an untreated ovariectomized female. However, evoked sexual behavior with the exception of evoked ejaculation could be obtained whether the females were treated or untreated. Spontaneous and evoked sexual behavior was directed towards both dominant and subdominant females. The female chosen by the male was in part determined by the dominance status of the female. Evoked sexual behavior differed from spontaneous behavior in terms of an increased number of thrusts per mount, an increased number of ejaculations per session, and a decrease in latency between ejaculatory sequences.     

Influence of exogenous GnRH on sexual behavior and frozen/thawed semen viability in stallions during the non-breeding season

Twelve fertile stallions were divided into two groups, either receiving gonadotropin-releasing hormone (GnRH) (n = 6) or Placebo (n = 6). Based on the history of frozen/thawed semen characteristics three stallions within each group were assigned as being "good freezers" [GnRH (+); Placebo (+)] and three stallions were assigned as being "poor freezers" [GnRH (-); Placebo (-)]. The study was performed as a "blinded" investigation and stallions were treated twice daily by an intramuscular injection of 1 ml GnRH (Buserelin), 50 microg) or Placebo. The experiment was divided into three time periods. Period A (pre-treatment) was performed between 16 November and 20 December; Period B (treatment) was performed during 6 weeks between 21 December and 31 January; and Period C (post-treatment) was performed between 1 February and 12 February. Semen was collected every Monday, Wednesday, Friday, and analysed for motion characteristics by the use of a computerized semen analyser, and sperm morphology immediately after collection. The spermatozoa were cryopreserved, stored in liquid nitrogen, and evaluated for motility (computer assisted semen analysis), membrane integrity (carboxyfluoresceine diacetate (CFDA) combined with propidium-iodide (PI), CFDA/PI), viability and sperm morphology (Eosine-Nigrosine, EN), and osmotic reactivity (hypo-osmotic swelling test, HOS) following thawing in a water bath. The viability of spermatozoa was expressed as the difference between pre-freeze and post-thaw values. A libido score of 1-4, the number of mounts on the phantom before ejaculation, and ejaculation latency were used to evaluate the stallions sexual behavior. Effect of treatment was analysed by comparing time intervals within groups as well as comparing groups within time intervals using SAS statistics software. GnRH treatment decreased the number of mounts before ejaculation (GnRH (total): 2.5 +/- 1.14 versus 1.8 +/- 1.06, P < 0.05), and shortened ejaculation latency. Cessation of treatment increased ejaculation latency in the GnRH group (4.7 +/- 4.98 min versus 7.2+/-7.88min, P<0.05). With the exception of libido score all parameters of sexual behavior were superior in the GnRH (+) group compared to the Placebo (-) group during the treatment period (P < 0.05). GnRH administration increased progressive motility (GnRH (+): 30.7 +/- 10.74% versus 38.4 +/- 15.1%, P < 0.05; GnRH (total): 24.9 +/- 11.80% versus 31.9 +/- 14.68%, P < 0.05), membrane intact spermatozoa CFDA/PI (GnRH (-): 16.8 +/- 7.17% versus 26.2 +/- 7.02%, P < 0.05; GnRH (total): 23.1 +/- 12.33% versus 29.5 +/- 10.77%, P < 0.05) and HOS positive spermatozoa (GnRH (+): 33.2 +/- 11.29% versus 42.2 +/- 10.36%, P < 0.05; GnRH (total): 32.9 +/- 10.23% versus 40.1 +/- 10.30%, P < 0.05) of frozen/thawed spermatozoa. Following cessation of treatment, the viability of frozen/thawed spermatozoa decreased. GnRH treated stallions had lower losses of live stained spermatozoa (EN) compared to the Placebo group (GnRH (total): 17.6 +/- 4.77 versus Placebo (total): 27.2 +/- 5.44, P < 0.05). This was particularly observed in the "poor freezer" group (GnRH (-): 16.6 +/- 4.35 versus Placebo (-): 31.3 +/- 5.87; P < 0.05). In conclusion, exogenous GnRH was shown to improve sexual behavior and increase the quality of frozen/thawed spermatozoa in fertile stallions during the non-breeding season. Nevertheless, it seems that, although significance was achieved relative to improvement to post-thaw sperm quality, that the "real" change in sperm quality seems negligible in fertile stallions. The mechanism of GnRH effect was not determined but this study may support the possibility of a direct gonadal or epididymal effect of exogenous GnRH in the stallion.     

Sexual behavior and ejaculate characteristics in Pêga donkeys (Equus asinus) mounting estrous horse mares (Equus caballus)

The objectives were to (i) characterize sexual behavior of donkey stallions (jacks; Equus asinus) during on-farm semen collection using estrous horse mares (mares; Equus caballus); (ii) compare behavior of young (less experienced) versus older (more experienced) jacks; (iii) determine whether semen suitable for artificial insemination (AI) could be collected using mares; and (iv) determine the suitability of using mares in field collection of semen from jacks. Six Pêga jacks (3.5 to 16 yr old), previously conditioned to breed mares, were used. Mount mares were confirmed in estrus by a teaser horse stallion (stallion) and a jack. Semen was collected with an artificial vagina, at intervals of 48 to 72 h (180 collections). The mean ± SD (young [3.5 yr] vs. old [14 to 16 yr]) were Flehmen response frequency, 7.4 ± 5.8 (8.1 ± 3.0 vs. 7.0 ± 2.0); number of mounts without erection, 1.1 ± 1.3 (2.1 ± 1.4 vs. 1.2 ± 0.4, P < 0.05); latency from first exposure to mare to full erection on the ejaculatory mount, 18.3 ± 17.7 min (25.3 ± 21.3 vs. 12.2 ± 6.2, P < 0.05); latency from erection to insertion, 5.1 ± 3.5 sec (5.3 ± 3.8 vs. 4.8 ± 3.2); and duration of copulation from insertion to dismount after ejaculation, 25.4 ± 7.8 sec (22.1 ± 2.9 vs. 28.1 ± 9.3). In all jacks, sexual behavior was generally normal, with the notable absence of open mouth behavior. Mare estrous behavior was markedly less intense than that in the presence of a stallion and usually absent. Semen characteristics were gel free volume, 47.3 ± 28.7 mL; gel volume, 71.8 ± 54.8 mL; total motility, 84.3 ± 6.0%; progressive motility, 74.3 ± 74.5%; sperm vigor, 3.9 ± 0.5 (scale 1 to 5); sperm concentration, 253 × 10⁶ cells/mL; and total number of sperm, 10.3 × 10⁹ cells. Copulation duration was significantly correlated with gel free volume (r = 0.9) and gel volume (r = 0.7). We concluded that (i) the sexual behavior of jacks during semen collection using mares was similar to that reported for natural mating to jennies, (ii) precopulatory and copulatory behavior for the young (less experienced) jacks and older (more experienced) jacks were generally similar (except number of mounts without erection and latency to full erection); (iii) semen obtained using mares as stimulus and mount females was similar to that reported with estrous jennies; and (iv) semen collection from previously conditioned jacks, using estrous mares, was appropriate for field collection of semen.     

Oral imipramine and intravenous xylazine for pharmacologically-induced ex copula ejaculation in stallions.

This study is part of ongoing work toward developing pharmacological methods for enhancing and inducing ejaculation in stallions with ejaculatory dysfunction or disabilities that interfere with normal breeding behavior. The objective was to evaluate a treatment regimen involving oral imipramine followed by intravenous xylazine that, in uncontrolled field clinical trials, had shown promise for a higher rate of ejaculation and fewer side effects using a more easily obtained and administered form of imipramine. Eight stallions each underwent eight trials in which treatment consisted of imipramine hydrochloride (3mg/kg, orally in a small portion sweet feed) followed 2h later by xylazine hydrochloride (0.66 mg/kg, intravenously). Trials were conducted with the stallion in a stall. Semen was collected using a collection bag secured over the prepuce with a girth band. Overall, 44 of the 64 attempts (68%) resulted in ejaculation. Within-stallion ejaculation rate ranged from 3 of 8 to 7 of 8 attempts. Interval from xylazine treatment to ejaculation ranged from 1.2 to 14 min. As is typical for induced ejaculations in which imipramine is included in the treatment regimen, ejaculates were of low volume, high sperm concentration, and with a higher total number of sperm than for in copula ejaculates of these stallions. These results represent a modest improvement in rate of ejaculation over previous treatment regimens.     

Oxytocin, vasopressin, prostaglandin F2α, luteinizing hormone, testosterone, estrone sulfate, and cortisol plasma concentrations after sexual stimulation in stallions

This experiment was designed to determine the effects of sexual stimulation on plasma concentrations of oxytocin (OT), vasopressin (VP), 15-ketodihydro-PGF_2α (PG-metabolite), luteinizing hormone (LH), testosterone (T), estrone sulfate (ES), and cortisol (C) in stallions. Semen samples were collected from 14 light horse stallions (Equus caballus) of proven fertility using a Missouri model artificial vagina. Blood samples were collected at 15, 12, 9, 6, and 3 min before estrous mare exposure, at erection, at ejaculation, and at 3, 6, and 9 min after ejaculation. Afterwards, blood sampling was performed every 10 min for the following 60 min. Sexual activity determined an increase in plasma concentrations of OT, VP, C, PG-metabolite, and ES and caused no changes in LH and T concentrations. The finding of a negative correlation between C and VP at erection, and between C and T before erection and at the time of erection, could be explained by a possible inhibitory role exerted by C in the mechanism of sexual arousal described for men.     

Existence of an ejaculatory-like reaction in ewes ovariectomized and treated with androgens in adulthood

The complete behavioral repertoire of male sexual activity can be observed during daily androgen treatment (testosterone propionate, 15 mg/day) of normal ewes ovariectomized as adults. This includes the ejaculatory pattern (deep thrust accompanied by a rapid backwards movement of the head) which is followed by a dramatic decrease in the frequency of sexual interactions, similar to the male's postejaculatory reduction of activity. However, the sexual performances of the genetic females remain lower than those of normal males in ejaculation latency, postejaculation latency, and mount/ejaculation ratio.     

A contextual definition of male sexual arousal

Sexual arousal is a construct without a widely shared definition. Historically, sexual arousal has usually referred to a central physiological state, but there has been much less agreement on its relation to motivation, emotion, and - for males - penile erection and ejaculation. Many behavioral and physiological measures have been used as operational definitions of sexual arousal, but the relation of the measure to arousal is often assumed rather than tested. For men, penile erection in the presence of erotic stimuli has been considered the most reliable and valid indicator of sexual arousal. The adoption of analogous criteria is recommended for research on other male mammals in order to establish a minimal basis for inferring that they are sexually aroused. That is, sexual arousal should be inferred only when penile erection is observed in a sexual context. A sexual context is provisionally defined as an environment that tends in most reproductively active males of the species to provoke further sexual stimulation, e.g., copulation or self-stimulation to ejaculation. Erection occurring outside of a sexual context, as during REM sleep or from injection of drugs, is not grounds for inferring arousal. Conversely, males engaging in behavior directed toward estrous females may be sexually motivated, but in the absence of erection, the males should not be assumed to be sexually aroused. Implications of other erection-context interactions are also considered. Adoption of these more conservative criteria for inferring sexual arousal may promote greater precision in identifying the physiological systems mediating this hypothetical construct.     

Administration of oxytocin immediately after insemination does not improve pregnancy rates in mares bred by fertile or subfertile stallions

It is probable that reduced pregnancy rates in mares bred to subfertile stallions is attributable, in part, to the reduced number of normal spermatozoa that colonize the oviduct. Administration of oxytocin stimulates both uterine and oviductal contractility. The hypothesis that oxytocin may enhance sperm transport to/into the oviducts, and thereby increase pregnancy rates, was tested in 2 trials. For both trials, fertile estrous mares with follicles > or = 35 mm in diameter were inseminated once at 24 h after administration of 1500 to 2000 U hCG. The inseminate dose was limited to 100 million spermatozoa in order to lower pregnancy rates and thus increase the chance of detecting a treatment effect. Pregnancy status was determined by transrectal ultrasound examination 14 to 16 d after insemination. In Trial 1, 49 mares were inseminated with 4 mL extended semen from 1 of 3 stallions (1 fertile and 2 subfertile males). Immediately after insemination, the mares were administered either 20 U oxytocin or 1 mL saline intravenously. In Trial 2, 51 mares were inseminated with 4 mL extended semen from 1 of 4 stallions (1 fertile and 1 subfertile male used in Trial 1, and 2 additional fertile males). Immediately after insemination, and again 30 min later, mares were administered either 5 U oxytocin or 0.25 mL saline intramuscularly. To test for effects of treatment with oxytocin and for the interaction between semen quality and treatment, a generalized linear mixed regression model was used that accounted for the split-plot design (treatment within stallions), the random effect of stallion, the fixed effect of semen quality, the binary outcome of a single breeding trial, and the varying number of trials per stallion/treatment groups. Three treatment protocols or regimens were used: placebo, 5 U oxytocin injected twice intramuscularly, and 20 units oxytocin injected twice intravenously. Semen was classified as high (fertile stallions) or low (subfertile stallions) quality. No interaction between semen quality and treatment was detected (P > 0.10). The pregnancy rate of mares treated with oxytocin immediately after insemination was 30% (15/50) compared with 50% (25/50) for mares treated with saline immediately after breeding. Administration of oxytocin did not affect pregnancy rates (P > 0.10).     

Influence of ejaculation frequency of stallions on characteristics of semen and output of spermatozoa.

Approximately 1 week was required to stabilize the extragonadal sperm reserves in stallions ejaculated daily for 10 weeks. The true daily sperm output of a stallion was equal to the mean daily sperm output of seven ejaculates +/- 1-35 X 10(9) spermatozoa. Mean concentrations of spermatozoa/ml and number of spermatozoa/ejaculate were higher (P less than 0-01) for X1 and X3/week ejaculation frequencies than for a X6/week frequency. Sperm output/week was nearly identical for a X6/week frequency. Sperm output/week was nearly identical for the X3 and X6 frequencies and higher (P less than 0-01) than the X1 frequency. Increase of ejaculation frequency from one to two ejaculates/day twice weekly significantly (P less than 0-01) raised the output of spermatozoa/week. Gel-free semen volume, spermatozoa/ml, and number of spermatozoa/ejaculate were higher (P less than 0-01) in the first, than in the second, ejaculate. Collection of semen on alternate days would be a practical ejaculation frequency for inseminating mares. Two ejaculates collected twice a week would be a practical ejaculation frequency for long-term storage of stallion semen.     

妊娠期腹腔注射多氯联苯对大鼠性行为的影响

将50只同期怀孕的大鼠分为5组,在怀孕第7-18d,每天分别给两组大鼠腹腔注射1．00和20．00mg／kg体重2,2’,4,4’-四氯联苯（PCB47）;分别给另两组注射0．25和1．00mg／kg体重3,3’,4,4’-四氯联苯（PCB77）;对照组注射0．10mL芝麻油。幼鼠出生后第70-91d、97-101d测试F1代雌鼠的接近时间（AL）、爬跨后返回时间（MRL）、插入后返回时间（IRL）、射精后不应期（PER）、脊柱前凸系数（LQ）和雄鼠的爬跨频率（MF）、爬跨等待时间（ML）、插入频率（IF）、插入等待时间（IL）、射精等待时间（EL）、射精后不应期（PEI）、插入率等性行为。结果显示,妊娠期腹腔注射PCB47和PCB77显著降低F1代雌鼠的LQ（对照组为84．4％;PCB47组分别为76．0％、67．8％;PCB77组分别为64．4％、53．3％;P〉0．05）,但对雌鼠的AL、MRL、IRL、PER和雄鼠的MF、ML、IF、IL、EL、PEI和插入率无显著影响（P〉0．05）。