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a Centro de Neurobiología, Universidad Nacional Autónoma de México, AP 1-1141, Juriquilla, Querétaro, México
b Departamento de Ciencias Médico Veterinarias, Universidad Autónoma Agraria Antonio Narro, Carretera a Santa Fe y Periférico, Torreón, Coahuila, México
c INRA, Neuroendocrinologie Sexuelle, PRMD, 37380 Nouzilly, France
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ABSTRACT |
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 TOP ABSTRACT INTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONREFERENCES |
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INTRODUCTION |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONREFERENCES |
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A major limitation of the male effect to induce reproductive activity in the female is that this effect is weak when teasing is performed during seasonal anestrus, especially in breeds of sheep or goats that are strongly seasonal. Thus, in breeds exhibiting only a moderate seasonality such as the Merino sheep or Creole goats of Guadeloupe Island, male introduction induces an ovulatory response throughout the year [7, 11]. However, in more seasonal breeds, the male effect is limited to the onset of the normal breeding season [10, 12]. The failure of teasing outside this limited period may be due to the inability of the female to respond during anestrus, resulting from refractoriness of the female to the male stimulus. Alternatively, it may be due to inadequate stimulation from the male. Indeed, male behavioral and physiological activity tends to decrease during the period of female anestrus in both sheep [13, 14] and goats [15–17]. It is well established in these species that physical contact and/or high sexual activity in males enhances the female response to teasing [8, 18–22]. Also, the emission of olfactory cues from the male may be reduced during sexual rest. The present study was performed to test the hypothesis that the inefficiency of the male effect during seasonal anestrus in goats is due to poor stimulating ability of the male. We studied whether sexual activity can be induced in seasonally breeding Mexican Creole goats [23] during seasonal anestrus by exposing them to bucks previously brought into reproductive activity by a treatment with long days and melatonin implants.
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MATERIALS AND METHODS |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONREFERENCES |
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Two experiments were carried out in 2 consecutive years. In the first year, the experiment was on two farms 4 km apart to avoid any risk of interaction between the experimental and control groups. In the second year, the experiment was repeated using a single flock divided into two groups to verify that the difference of response between the control and the experimental group observed during the first year was not due to some unknown difference in the responsiveness of the two flocks. The males used in this study were part of a homogeneous group of Creole adult males of the Laguna region in the State of Coahuila, Mexico (26°N) [17]. They were kept outdoors, and fed alfalfa ad libitum and 300 g of commercial concentrate food with 14% protein (Generaleche; Ralston-Purina, St. Louis, MO), with free access to mineral blocks and water. The females were maintained under an extensive management system before the beginning of the study. All females had given birth in December 1997 and December 1998, and were milked manually once daily during the study. One month before the introduction of males, the females were kept in 7 x 10-m shaded pens with 8–10 females in each, and fed alfalfa ad libitum and 200 g of concentrate food with 14% protein (Generaleche, Purina). They had free access to mineral blocks and water.
Experiment 1
Males Four males (sexually inactive-SI; n = 4) were exposed to natural photoperiodic variations (13 h 41 min of light at the summer solstice and 10 h 19 min of light at the winter solstice) throughout the study. The other group of males (sexually active-SA; n = 4) was subjected to a treatment of long days (16L:8D) from 1 November 1997 to 15 January 1998. On 16 January 1998, each male received 2 s.c. implants containing 18 mg of melatonin each (Regulin-Mélovine, Sanofi SNA, Libourne, France). At this time, the light treatment was stopped, and the males were exposed to the natural day length until the end of the study. This treatment has been shown previously to induce sexual activity in males during the period of sexual rest [24].
Females Multiparous Mexican Creole goats (n = 88) belonging to 2 different flocks (flock 1 and 2) located 4 km apart and with similar characteristics of husbandry were involved in the experiment. On 25 February 1998 and 5 March 1998, plasma progesterone concentrations in blood samples were measured by RIA, a procedure that allows cyclic females to be distinguished from anovulatory ones [25]. Eleven does in flock 1 and 3 does in flock 2 showed ovarian activity, and therefore were removed from the experiment. As a consequence, 34 and 40 females were exposed to males in flocks 1 and 2, respectively. On the day of teasing (Day 1), another blood sample was collected from each doe to check that no other females had initiated ovarian activity.
Male effect Before teasing, females were not allowed contact with males for 45 days, and bucks were kept on another experimental farm 15 km from both flocks. Males were exposed to females on 15 March 1998 at 0800 h. In flock 1, females were allocated to 1 of 4 pens (8 or 9/pen), and 4 SI males were introduced (1 in each pen); this constituted the SI-treated group. In flock 2, females were allocated to 1 of 4 pens (10/pen), and 4 SA males were introduced; this constituted the SA-treated group. In both groups, the males remained with the females until the end of the study (20 April 1998). The SA males were introduced into flock 2, which had shown the lower spontaneous ovulatory activity (percentage of cyclic females on 25 February 1998 and 5 March 1998), i.e., where the response potential of the females was lower.
Experiment 2
The difference between groups observed in the first experiment could have been caused by a difference of responsiveness between flocks. Therefore, the following year, the study was performed at the same time of year with only the females of flock 1. As in experiment 1, cyclic females (n = 12), as determined by plasma progesterone concentrations, were eliminated before the introduction of males. For this study, 66 anovular multiparous Creole goats were divided in 2 groups of 33 females each. The animals of both groups were penned in small yards with 1 male per 11 does in each yard (in total, 3 males for 33 females in each group). In this second experiment, only estrous behavior was recorded during 35 days to assess the response to teasing. Otherwise, photoperiodic and melatonin treatment of the males, recording of behavior, and other procedures were identical to those of experiment 1.
Measurements
Males In both experiments, during the first 5 days following the introduction of the males, sexual behavior of the bucks was observed for 2 h, from 0800 to 1000 h. The same person observed each buck and recorded the following characteristics; ano-genital sniffing, nudging, mount intention movements, and mounts (with and without ejaculation).
Females Blood samples were obtained daily from Day 2 to Day 10 and every 2 days from Day 11 to Day 35 after introduction of the males to assess ovarian activity by measuring the plasma concentrations of progesterone. Concentrations of progesterone were measured by a quantitative assay slightly modified from that described by Saumande et al. [26]. Sensitivity of the assay was 0.1 ng/ml of plasma, and intra- and interassay coefficients of variation were 9.5% and 14.8%, respectively. This assay allowed the assessment of the quality of luteal phases induced by the male introduction (i.e., short cycles). All blood samples were collected by jugular venipuncture in tubes containing EDTA, and centrifuged immediately at 2500 x g for 20 min; plasma was stored at -15°C. Females with progesterone levels above 0.5 ng/ml were considered to have ovulated [27]. Goats were considered pregnant when they displayed a continuous elevation of progesterone levels in blood samples obtained between Days 11 and 35. Fertility was measured as the percentage of pregnant females.
In both experiments, estrous behavior was monitored using bucks painted on the chest with colored grease that was replaced twice daily (0800 and 1800 h) from 15 March to 20 April of 1998 and 1999.
Statistical Analyses
Between-group differences in male sexual behavior were analyzed by comparing the frequencies of the behaviors observed in each group with a random repartition, using Fisher's exact probability tests. In the females, the proportions showing estrous and ovarian activity were compared by Fisher's exact probability test.
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RESULTS |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONREFERENCES |
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Sexual behavior of bucks The sexual behavior observed during the first 5 days after the males were introduced differed significantly between the 2 groups of 4 males joined with females (Fig. 1). The males treated with long days and melatonin were more active. Of 272 instances of ano-genital sniffing observed in the males of both groups, 215 were performed by SA males (versus 136, in the case of a random repartition; P < 0.001). Of 492 instances of nudging observed, 485 were observed in the SA group (P < 0.001). Of 27 mount intention movements, 26 were performed by SA bucks (P < 0.001). Finally, all observed mounts (26) were performed by SA males (P < 0.001).
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Response of females to male effect: ovarian and estrous activity During the study, only 2 does in contact with SI males showed an ovulation, without associated estrous behavior, between Days 5 and 7 after male introduction, as detected by progesterone assay. No further ovarian or behavioral activity was observed during the remainder of the study. In contrast, all females (40 of 40) exposed to SA males ovulated and showed at least one estrous behavior during the first 11 days following male introduction (P < 0.001 versus SI-treated). Between Days 1 and 6, 26 SA-exposed goats ovulated and displayed estrus, and 6 other goats ovulated without estrus. Among these 32 females, 4 did not show any other ovulation or estrus and became pregnant; the first cycle of the 28 others was of short duration, and therefore they showed another ovulation accompanied with estrus between Days 7 and 11. The 8 goats that had not ovulated between Days 1 and 6 did so between Days 7 and 11, and these ovulations were associated with estrous behavior. After Day 12, no ovulation or estrous behavior was recorded (Fig. 2). In does that showed an early response (Days 1–6), the interval between introduction of the males and onset of estrous behavior was 3.5 ± 0.2 days. In does that responded later (Days 7–11), this interval was 9.1 ± 0.4 days. Overall, 38 of 40 females stimulated with treated bucks were diagnosed as pregnant at 35 days, according to progesterone assay (versus 0 in the SI-treated group: P < 0.001).
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Experiment 2
Sexual behavior of bucks When the study was performed with females of a single flock, the sexual behavior displayed by the males was similar to that observed in experiment 1. The sexual behavior of SA males was higher that of SI males (Fig. 3). Of 489 instances of ano-genital sniffing observed, 404 were performed by SA bucks (P < 0.001). Of 993 cases of nudging recorded for males of both groups, 970 were observed in the SA group (P < 0.0001). All mount intention movements and mounts were performed by SA males (65 and 58, respectively; P < 0.001).
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Response of females to male effect One doe in contact with SI males showed estrous behavior on Day 10 after the males were introduced. In contrast, 81.8% (27 of 33) of the does in contact with SA males showed estrous behavior between Day 3 and Day 14 after the beginning of teasing (Fig. 4). Twenty-one of 33 females (63.6%) showed estrous behavior between Days 2 and 6. Nineteen of these 21 does showed a short estrous cycle and displayed estrus a second time between Day 7 and Day 14. The other 2 does showed a normal cycle. Twenty-six of 33 females showed estrous behavior between Days 7 and 14. After Day 14, no estrous behavior was recorded. The interval between the introduction of the males and the onset of estrus was 3.7 ± 0.2 days for the does that showed an early response (< 6 days) and 8.7 ± 0.3 days for the others.
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DISCUSSION |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONREFERENCES |
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Of the females in contact with SI males, only 2 does ovulated, and none showed estrous behavior during the whole study in experiment 1; only one doe displayed estrous behavior in experiment 2. This absence of response of the females to teasing could appear different from results previously reported in ewes [4] and goats [10]. According to these reports, the introduction of males without previous treatment into a group of anovulatory females after at least 3 wk of complete separation induced sexual activity in anovulatory females. However, these results were obtained just before the spontaneous onset of the sexual season, when the females are about to initiate breeding activity. In our case, the study was performed during the period of seasonal anestrus, which could explain why teasing with control males was not effective. Indeed, previous reports indicate that the response of does to male introduction depends on the depth of anestrus, as assessed by the number of females that ovulate spontaneously before male introduction [10]. In experiment 1, 14 of the 88 does sampled showed ovarian activity and were eliminated from the study before male introduction. In experiment 2, 15 of 78 were cyclic, which indicates that in both experiments, the majority of the females were anovulatory.
One could speculate that the ability to respond to males in experiment 1 may have been lower in the SI-treated group because of some uncontrolled variation in that flock, such as health condition, or differences in genetic background between flocks. However, this seems unlikely for at least three reasons. First, animals were on the same feeding plan for 1 mo before teasing, and there was no apparent difference between these groups. Second, the SI males were introduced to the flock with the larger proportion of cycling goats before male introduction, suggesting that, if anything, the response potential of this flock may have been higher than in the goats exposed to SA males. Third, and most importantly, the results obtained in two different flocks in the first study were confirmed in the second study, in which both SI-treated and SA-treated groups came from the same flock and were maintained under the same conditions. In this latter case, females of the same flock that had not responded the previous year showed a full response with SA bucks, and again no response with control bucks.
Our results are consistent with other reports of studies conducted at the same latitude as northern Mexico, that the introduction of males, either intact or castrated and treated with testosterone during anestrus, was not effective in inducing sexual activity in anovulatory goats [28]. In our study, in experiment 1, the females in contact with SA males showed sexual activity within 11 days after teasing. After a few days in contact with males, all does showed ovarian activity and estrous behavior. The ovarian and estrous activities were divided in two periods, with a high percentage of does showing two ovulatory and estrous cycles. In the second study, in which only estrous behavior was recorded, 81.8% (27 of 33) of does showed such behavior between Day 2 and Day 14. The physiological response of the females teased with SA males was similar to that reported in anovulatory females goats after male introduction without previous treatment, but at times when the maximum response to teasing can be expected [8, 10, 29].
The ineffectiveness of SI males in inducing sexual activity during anestrus suggests that females respond to teasing during anestrus only when sexually active males are introduced. In the two experiments, the males treated with 2.5 mo of long days and melatonin showed an intense behavioral activity. Moreover, when put in contact with females, these males showed a dramatically greater number of instances of ano-genital sniffing and nudging, mount intention movements, and mounting than the control bucks, at least during the first 5 days of teasing. The presence of estrous females may then have elicited some self-reinforcing of stimulation between males and does [30] and/or female-to-female stimulation [31]. On the other hand, it must be noted that in the SI-treated group of experiment 2, no significant response to teasing was observed, despite the fact that 1 goat displayed estrous behavior. This suggests that the social reinforcement of the response due to the presence of 1 estrous female or to a female effect can hardly account for the major effects observed in the SA-treated group. Therefore, the high level of sexual behavior of SA males was probably at least partly responsible in itself for the high response of the females to teasing, whereas the low level of sexual behavior of the SI bucks was not sufficient to induce a response in the females. This is consistent with the various studies in goats and in sheep indicating that behavioral activity can be sufficient to elicit some response to teasing [21–32]. On the other hand, it is clear that cues not assessed in our study, such as the emission of pheromones or vocalizations of the bucks, were also likely to be stronger in the SA males than in the controls. It is well established that olfactory cues also stimulate ovulation in anovular goats [18, 20, 33], and it cannot be ruled out at this stage that a more intense production of pheromones in response to the photoperiodic and melatonin treatment was partly responsible for the good response to teasing in the SA group. Further studies, for instance with anosmic females, will be necessary to determine the relative importance of sexual activity, emission of pheromones, and vocalizations in causing the different responses to SA and SI males.
In the first experiment, 65% of the females in contact with SA males showed a short ovarian cycle after the first induced ovulation. This is similar to the case in previous studies [7, 8], in which a high incidence of short luteal phases due to low and transient progesterone plasma secretion by the corpus luteum was reported [10]. The presence of short ovulatory cycles in goats at the beginning of the breeding season [34, 35], or after the introduction of a buck into a group of anestrous does is well known [7, 20]. In females that responded to the presence of males, more does exhibited estrus at the second ovulation. This is consistent with a previous report showing that a large number of females show estrous behavior at the second ovulation [10]. In our study, the conception rate at the first buck-induced estrus was lower than at the second induced estrus (10% versus 95%, respectively). This very low conception rate is similar to that reported by Thimonier et al. [36], and probably was due to the altered hormonal balance that usually follows the first buck-induced ovulation. The luteal failure probably did not allow the establishment of pregnancy, whereas the establishment of normal ovarian function at the second ovulation supported a conception rate equivalent to that obtained during the natural breeding season.
Our study provides unequivocal evidence that the male effect is an effective method for inducing synchronous cyclic reproductive activity during seasonal anestrus, but only if fully sexually active bucks are used. The failure of the male effect during anestrus in goats, at least under subtropical latitudes, is not due to the existence of some total physiological or sensory refractoriness by the female to the stimulation of the male. Rather, it appears that the stimulus provided by the male at this time of year is insufficient. Whether this is also true under higher latitudes with more seasonal breeds of sheep and goats remains to be investigated. Taken together with the fact that in other situations the response also depends on the depth of anestrus in the female, our results indicate that the efficiency of teasing depends on an interaction between the response threshold of the female at a given time and the stimulating capacity of the male. While our results point to a likely role of male sexual behavior as the triggering cue of female response, more studies are needed to investigate the possible role of other sensory cues, especially pheromone synthesis and emission, given the multisensory nature of the male effect.
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ACKNOWLEDGMENTS |
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FOOTNOTES |
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1 This work was supported by CONACyT-SIREYES (Grant 970401020) and the International Foundation of Science (Grant B/2071-3F). J.A.F. was supported by a CONACyT scholarship for doctoral studies. Collaboration between French and Mexican scientists was made possible by the French-Mexican exchange program SEP-CONACyT-ANUIES-ECOS (Grant M95-B05). 
2 Correspondence: J.A. Delgadillo, Departamento de Ciencias Médico Veterinarias, Universidad Autónoma Agraria Antonio Narro, Carretera a Santa Fe y Periférico, Apartado Postal 940, Torreón, Coahuila, México. FAX: 52 17 33 12 10; delgadil{at}ul.uaaan.mx
Accepted: December 31, 1999.
Received: September 17, 1999.
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONREFERENCES |
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