Male reproductive condition is the limiting factor of efficiency in the male effect during seasonal anestrus in female goats

The effect of flushing and stimulus of estrogenized does on reproductive performance of anovulatory-range goats

This study was conducted to determine whether flushing or the stimulus of estrogenized goats is necessary to achieve a high reproductive response in anestrous goats on rangeland. Does were feed-supplemented on rangeland (flushed, n = 20). Other group was exposed to estrogenized does during the mating period (stimulated, n = 20). A third group was both supplemented and stimulated (stimulated-flushed, n = 20) and other group grazed on rangeland only (control, n = 18). More goats in the stimulated and stimulated-flushed groups showed estrus during the first 5 days of joining (45% and 60%, respectively) than the control and flushed groups (11% and 5%, respectively; P < 0.05). Flushing did not improve prolificacy and reduced (P < 0.05) kidding rates (40% and 35% for the flushed and stimulated-flushed groups, respectively) compared to 67% and 55% for the control and stimulated groups, respectively. This experiment demonstrates potential shortcomings of use of flushing in range goats with inadequate nutrition during gestation.

Artificial long-day photoperiod in the subtropics increases milk production in goats giving birth in late autumn

Two experiments were conducted to determine whether exposure to a photoperiod of artificial long days in autumn increased milk yield in subtropical goats milked once (Exp. I) or twice daily (Exp. II). In Exp. I, starting at d 10 of lactation, 1 group of does was kept under naturally decreasing photoperiod (DD1X; n = 8), whereas the other group was submitted to an artificial photoperiod of long days (LD1X; n = 8; 16 h light:8 h darkness). The kids were weaned 28 d after parturition, and dams were manually milked once daily. Milk yield and milk components (fat, protein, and lactose) were assessed up to 140 d of lactation. From d 0 to 28 of lactation (suckling phase), mean daily milk yield did not differ between DD1X and LD1X goats (2.3 ± 0.2 kg vs. 2.4 ± 0.2 kg; P = 0.717). However, between d 29 and 84 (early milking phase), mean daily milk yield was greater in LD1X does than in DD1X does (2.6 ± 0.1 kg vs. 2.1 ± 0.1 kg; P = 0.001). Finally, between d 85 and 140 (late milking phase), mean daily milk yield was greater in LD1X goats than in DD1X goats (P ≤ 0.05) only during the first 2 wk. In Exp. II, one group of goats was exposed to a photoperiod of naturally decreasing days (DD2X; n = 8) and another group was submitted to an artificial photoperiod of long days (LD2X; n = 7). In both groups, kids were weaned on d 28 of lactation and the dams were manually milked twice daily. During the nursing phase, mean daily milk yield did not differ between the DD2X and LD2X groups (2.5 ± 0.3 kg vs. 2.6 ± 0.2 kg; P = 0.767). In the early milking phase, mean daily milk yield was greater in LD2X than in DD2X goats (3.3 ± 0.2 kg vs. 2.8 ± 0.2 kg; P = 0.022), whereas during the late milking phase, milk yield did not differ between the 2 groups (P = 0.946). In both experiments, milk composition was not significantly influenced by exposure to long-day photoperiod. We conclude that, in subtropical female goats that start lactation in late autumn, exposure to an artificial long-day photoperiod stimulates milk yield, even if goats are milked once daily. In addition, combining exposure to long days with twice-daily milking will increase further milk yield in such goats without affecting milk components.

Effect of Blockage of the Ducts of the Vomeronasal Organ on LH Plasma Levels during the "Whitten Effect" in Does

Eighteen mature, nonpregnant, and indigenous South African does were randomly divided into two groups to test if their vomeronasal organs exert an influence on LH plasma levels during a Whitten effect experimental trial. Does in the treatment (VNO ablated) group had their vomeronasal organs rendered nonfunctional by cauterization of the nasoincisive duct under surgical anesthesia. Does in the control group had their nasal civities irrigated with physiological saline under surgical anesthesia. All does were synchronized into oestrus and introduced to bucks one day prior to their expected second oestrus cycle. Successful matings were recorded. Timely blood samples were collected during each of the five days before and five days after buck introduction. Blood plasma concentrations of estradiol and LH were determined by radioimmunoassay. Analysis of variance between groups demonstrated that the does in the VNO ablated group did not demonstrate any interest in mating, did not become pregnant, and did not demonstrate the primary increase in tonic plasma levels of LH that is necessary for ovulation to occur. By contrast, all of the does in the control group demonstrated successful matings, became pregnant, and demonstrated typical primary tonic level increases and preovulation surges in LH. Thus, it was concluded that the vomeronasal organ modulates the primary increase in tonic levels of LH and thus influences ovulation that occurs during the Whitten effect in South African indigenous does.

Four hours of daily contact with sexually active males is sufficient to induce fertile ovulation in anestrous goats

The study was conducted on two consecutive years to determine whether ovulatory activity can be induced in anovulatory goats by exposing them to sexually active bucks for 4, 8, 12 or 16 h per day during 15 consecutive days. In experiment 1, females remained continuously in the experimental pens where they were in contact with males. One group remained isolated from males (controls) and four other groups were exposed to sexually active males for 4, 8, 12 or 16 h per day. In experiment 2, females were taken away to "resting" pens free of male odours between the periods of contact with bucks. They were allocated to 5 groups as in experiment 1. Ovulations were determined by progesterone plasma levels and transrectal ultrasonography. Pregnancy was determined by abdominal ultrasonography. In both experiments, more than 90% of females exposed to the bucks had at least one ovulation during the whole experiment whereas only 11 or 0% (experiments 1 and 2, respectively) did so in the control group (P<0.001). Furthermore, the proportion of females ovulating did not differ among groups depending on duration of contact with bucks (P>0.05). In both experiments, pregnancy rates were not affected by the daily duration of contact with males (P>0.05). To conclude, 4h of daily contact with sexually active males is sufficient to stimulate ovulatory activity in anovulatory goats and this effect is not due to the presence of olfactory cues from the males remaining in the pens.

Male sexual behavior contributes to the maintenance of high LH pulsatility in anestrous female goats

The objective of this study was to determine the importance of male sexual behavior in stimulating LH secretion in anovulatory female goats. Two groups of females (n=10 per group) were each exposed to a buck in sexual rest and submitted to natural daylength. In one group, the buck was awake, whereas in the other group, it was sedated to prevent its sexual behavior. Two other groups of goats (n=10 per group) were exposed to sexually active bucks that had been exposed to 2.5 months of long days. In one group, the buck was awake, and in the other group, it was sedated. LH secretion was determined every 15 min from 4 h before introducing the bucks to 8 h after, then every 15 min again from 20 to 24 h after introducing the bucks. The bucks submitted to natural daylength did not stimulate LH secretion (P>0.05), whether they were sedated or not. In contrast, both the awake and the sedated light-treated bucks induced an increase (P<0.05) of LH pulsatility in the first 4 h following their introduction. However, pulsatility remained elevated until 24 h in the females exposed to the light-treated awake buck, whereas in the group with the light-treated sedated buck, pulsatility diminished (P<0.05) after the first 4 h of stimulation by the buck. In conclusion, the sexual behavior of males contributes to the maintenance of a high LH pulsatility up to 24 h after introduction into a group of anovulatory goats.

The 'male effect' in sheep and goats--revisiting the dogmas

Male-induced ovulation in sheep and goats (the 'male effect'), documented during the period 1940-1960, has long been shrouded in preconceptions concerning how, when and why it worked. These preconceptions became dogmas but recent research is challenging them so, in this review, we have re-visited some major physiological (breed seasonality; characteristics of the response; the nature of the male stimuli) and physical factors (duration of male presence; isolation from male stimuli) that affect the phenomenon. We reject the dogma that ewes must be isolated from males and conclude that male 'novelty' is more important than isolation per se. Similarly, we reject the perception that the neuroendocrine component of the male effect is restricted to anovulatory females. Finally, we re-assess the relative importance of olfactory and non-olfactory signals, and develop a perspective on the way male-induced ovulation fits with preconceptions about pheromonal processes in mammals. Overall, our understanding of the male effect has evolved significantly and it is time to modify or reject our dogmas so this field of research can advance. We can now ask new questions regarding the application of the male effect in industry and develop research so we can fully understand this biological phenomenon.

Parity of female goats does not influence their estrous and ovulatory responses to the male effect

The objective of the present study was to determine whether parity is a factor that influences the estrous and ovulatory responses of female goats when they are stimulated by males that show increased sexual activity. To stimulate sexual activity, four adult male goats were subjected to photoperiodic treatment for 2.5 months comprising long days, with the treatment commencing on 1 November. On 14 April at 1,900 h, a group of multiparous females (n=21) and a group of 16 months-old nulliparous females (n=19) were exposed to four bucks (two per group) for 15 days. Throughout the study period, the estrous behavior of these female goats was detected twice on a daily basis. Ovulations of the female goats were determined by ecography on days 7 and 18 after exposure to males. The sexual behavior of males was recorded twice every day from 0800 to 0900 h and from 1730 to 1,830 h during the first 4 days after introduction in the pen of females. The total cumulative proportion of multiparous females that had ovulations (100%) and displayed estrous behavior (100%) during the 15 days of exposure to males did not differ (P>0.05) from that of nulliparous females (100% and 95%, respectively). The interval between introduction of males and onset of estrous behavior did not differ (P>0.05) between multiparous (1.9+/-0.1 days) and nulliparous (1.7+/-0.2 days) females. The proportion of females displaying a short estrous cycle was greater (P<0.05) in multiparous (13/21, 62%) than in nulliparous (5/19, 26%) females. Duration of these shorter than typical estrous cycles did not differ (P>0.05) between groups (multiparous: 5.2+/-0.3 days, nulliparous: 4.5+/-0.1 days). The number of anogenital sniffings was greater (P<0.001) in males exposed to nulliparous than in those exposed to multiparous females. In contrast, the number of mounting attempts was greater (P<0.01) in males that were introduced to multiparous than in those that were introduced to nulliparous does. The number of flehmen, nudging, self-marking with urine, and mounts was not different (P>0.05) between males that were in contact with multiparous and nulliparous females. These results indicate that regardless of parity, female goats respond to male introduction if they are stimulated by males that were previously exposed to artificial long days to increase their sexual behavior.

Stimulation of estrous behavior in grazing female goats by continuous or discontinuous exposure to males1,2

Two experiments were conducted during the anestrous period to determine: (1) whether males rendered sexually active by exposure to artificial long days stimulate estrous activity of female goats under grazed conditions (Exp. 1); and (2) whether continuous presence of the buck is necessary to stimulate this estrous activity (Exp. 2). In Exp. 1, 2 groups of females (n = 20/group), one in confinement and another under grazing conditions, were exposed to 4 bucks subjected to natural photoperiod (2 males/group). Two other groups of females (n = 20/group), in confinement or grazing, were exposed to 4 males treated with artificial long days (2 males/group). All groups were exposed to males for 15 d. The percentage of does detected in estrus during these 15 d was greater (P < 0.001) in the 2 groups exposed to males sexually prepared by long days (confined, 95%; grazed, 90%) than in groups exposed to males in natural photoperiod (confined, 15%; grazed, 45%). Does in Exp. 2 were allowed to graze and were exposed continuously (n = 26) or discontinuously (from 1700 to 0900; n = 26) for 18 d to males that had been stimulated to enter the breeding season by exposure to long days. The proportion of does that displayed estrous behavior in 18 d did not differ (P = 0.55) between groups (96.2 and 92.3% for continuous and discontinuous groups, respectively). The results indicate that anestrous goats managed under grazing conditions can be stimulated to express estrus by joining with males previously exposed to artificial long days. Continuous presence of the male is not necessary for this male effect.

Highly synchronous and fertile reproductive activity induced by the male effect during deep anoestrus in lactating goats subjected to treatment with artificially long days followed by a natural photoperiod

The response to the male effect was studied in two flocks of Saanen and three of Alpine goats during deep anoestrus in three consecutive years. Males and females were subjected to artificially long days for about 3 months (between December 4 and April 1) followed by a natural photoperiod. Bucks joined goats 42-63 days after the end of the long days treatment (between April 20 and June 3) and fertilisation was ensured by natural mating. In experiment 1 (n=248), female goats were treated or untreated with melatonin at the end of the long days treatment and treated or untreated for 11 days with fluorogestone acetate (FGA) before teasing. The males received melatonin implants. In experiment 2 (n=337), the factor studied was the association or non-association of the 11-day FGA treatment. Neither males nor females received melatonin implants. In experiment 3 (n=180), goats were treated for 11 days with FGA or with natural progesterone (CIDR). Neither males nor females received melatonin implants. In experiment 1, among the non-cycling goats (n=218), 99% ovulated and 81% kidded at 161+/-8 days after joining. Ninety-two percent of FGA-treated goats displayed an LH surge at 65+/-11h after teasing. Melatonin treatment did not affect any parameter but FGA advanced the kidding date. In experiment 2, 94% of the goats ovulated and 87% kidded. A major peak of conception was observed on days 3 and 8 after joining in FGA-treated and untreated goats, respectively. Among the FGA-treated goats, 83% displayed an LH surge. Over all flocks, most of the LH surges occurred over a 24-36 h interval, but the surge was initiated at different times in different flocks (36, 48 or 60 h after joining). FGA treatment did not influence the results, except for advancement of births of about 5 days. Differences among flocks were highly significant. In experiment 3, 94% of the goats displayed the LH surge, 93% ovulated and 68% kidded. Significant differences were found among flocks, but not between the FGA and CIDR groups. Bucks marked 85% of the goats 24-72 h after joining. The time interval between the detection of marked goats and detection of the LH surge depended on the time of marking (r=-0.62; p<0.05). In conclusion, treatment of both males and females goats with artificially long days followed by a natural photoperiod is very effective in inducing highly synchronous and fertile reproductive activity via the male effect in the middle of seasonal anoestrus.

Seasonality of plasma testosterone in males of four Mediterranean goat breeds and in three different climatic conditions

The aims of the present work were to evaluate if a seasonality of plasma testosterone concentrations exists in Mediterranean male goats and it may be affected by climatic conditions. Testosterone concentrations were determined throughout 1 year in blood samples collected weekly from 24 males of 4 Mediterranean goat breeds (Ionica, Garganica, Maltese and Red Syrian), fed a constant diet, maintained without interactions with does and reared in 3 farms with different climates, in Italy. Plasma testosterone concentrations were affected by season (P<0.0001), being higher during summer (8.33+/-0.35 ng/mL) than during autumn (6.81+/-0.26 ng/mL), which were in turn higher than in winter (1.55+/-0.08 ng/mL) and spring (2.04+/-0.15 ng/mL). An effect of breed was recorded (P<0.001), Ionica bucks having the highest plasma testosterone means, Red Syrian and Maltese the lowest. The onset of the reproductive season was similar among the breeds. Ionica bucks had a later offset than Red Syrian and Maltese and a longer reproductive season than Maltese bucks (P<0.05). No effect of farm nor interaction breed x farm was recorded. Single sporadic peaks of plasma testosterone were recorded in many bucks, outside the main reproductive season, especially during spring. In conclusion the bucks of all the four breeds displayed a clear seasonality of plasma testosterone, with very low levels from January to May and high levels from July to November; hormone levels and pattern of seasonality were affected by breed and not by climate.

Importance of the signals provided by the buck for the success of the male effect in goats

Under temperate and subtropical latitudes, ewes and goats display a reproductive seasonal pattern and their sexual activity during the anestrous period can be stimulated and synchronized by the introduction of males in the group, which is called the "male effect". The response of females to the male effect in the middle of the anestrous season is weak or absent. This failure may be due to the inability of the female to respond to males, as a result of a refractoriness of the female to the male stimulus. But, it may also be due to a low quality stimulus provided by the male which is, as the females, in seasonal rest. We tested this latter hypothesis in seasonally inactive goats kept under subtropical conditions by comparing the use of males with their sexual behavior stimulated or not by photoperiodic treatments. Treated males were able to induce estrous activity of females during the whole anestrus season. We have also determined that previous separation of the males and continuous contact during teasing are not absolute requisites when active bucks are used. While odor from the male and its sexual behavior play a primary role in inducing ovulation, vocalizations appear to facilitate the display of the does' estrous. It remains to be determined to which extent these conclusions apply under temperate latitudes and with more seasonal breeds.

Inactivation of the olfactory amygdala prevents the endocrine response to male odour in anoestrus ewes

Our aim was to study the role of the olfactory amygdala (medial and cortical nuclei) and the ventromedial nucleus of the hypothalamus (VMN) in the ability of the male odour or live males to induce a release of luteinizing hormone in anoestrus ewes. To achieve this, we temporarily blocked the activity of these structures by localized retrodialysis administration of the anaesthetic lidocaine. The effect of ram odour on the secretion of luteinizing hormone was completely blocked by inactivation of the cortical nucleus of the amygdala. In contrast, inactivation of part of the accessory olfactory system (the medial nucleus of the amygdala or the VMN) had no effect. In the presence of the male, lidocaine never impaired the endocrine response of the ewes. These results show that modulation of reproduction by the sexual partner even through pheromonal cues does not occur via the direct circuit of the accessory system. On the contrary, the cortical nucleus of the amygdala is absolutely necessary for the treatment of and/or the response to the male olfactory signal but this structure can be bypassed when other sensory cues are available.

Overview of the response of anoestrous ewes to the ram effect

The present review summarises knowledge of the reproductive response of anoestrous ewes to the introduction of rams – in other words, the ram effect. The ovarian and endocrine response, the factors that determine whether ewes will respond or not (associated with both the stimulus and the receptivity of the ewes) and some aspects of practical management are discussed. Information on the use of the ram effect to stimulate post-partum, prepubertal and cyclic ewes is also given. New insights are provided on ovarian response patterns, including recently collected information on luteal responses. The existence of delayed ovulation (5–7 days after the introduction of the rams) followed by luteal phases of normal or short length, luteal cysts and luteinised follicles is reported after scanning the ovaries with ultrasound. Endocrine parameters for depth of anoestrus, such as LH pulsatility and FSH concentrations, and how the concentrations of these hormones should be considered are discussed. Particular attention is paid to the observation of spontaneous, higher LH pulsatility and higher FSH concentrations in anoestrous ewes that respond to rams with luteal phases than in those that fail to respond. The use of progestogen priming and single progestogen administration and the possible advantages for synchronisation of oestrus are also discussed. Other factors that should be considered before the ram effect is applied, such as the strength of the stimulus and some practical considerations, are also included.

Management of photoperiod to control caprine reproduction in the subtropics

Reproductive seasonality is observed in some breeds originating from or adapted to subtropical latitudes. In ‘photoperiodic flexible breeds’, such as Australian cashmere goats, the annual breeding season can be manipulated through nutrition, whereas in ‘photoperiodic rigid breeds’, such as Creole goats from subtropical Mexico, sexual activity can be controlled by altering the photoperiod. In males from the latter breed, artificial long days, whether or not accompanied by the administration of melatonin, stimulate sexual activity during the non-breeding season. These treated males are able to induce the sexual activity of anoestrous females through the male effect under intensive or extensive conditions. Photoperiodic treatments and the male effect can be easily integrated into different breeding management systems in subtropical latitudes.

Induction of sexual activity in lactating anovulatory female goats using male goats treated only with artificially long days

Two experiments were conducted to determine the response of Creole male goats treated with long days and melatonin implants, and the response of the anovulatory does to male effect using males treated only with artificially long days. All animals were allocated to open sheds. In Exp. 1, one group of males was under natural photoperiod (CG; n = 7); the second group was submitted to 2.5 mo of long days followed by the insertion of two s.c. melatonin implants (LD+MEL; n = 7); the third group was subjected only to 2.5 mo of long days (LD; n = 7). Testicular weight was measured every 2 wk. Plasma testosterone concentrations were determined weekly. A treatment x time interaction was detected (P < 0.001) for testicular weight and plasma testosterone concentration. In the LD+MEL and LD groups, testicular size and plasma testosterone levels varied in a similar way, but differed from those observed in CG (P < 0.001). In this latter group, testicular weight displayed seasonal variations and peaked in June, whereas in treated groups this peak occurred in March. In CG, testosterone varied in a seasonal manner and plasma concentrations increased in June and remained elevated throughout the study. In experimental groups, testosterone increased in February and peaked in March. In Exp. 2, one group of males was left under natural photoperiod (CG, n = 5) and the other one was submitted to 2.5 mo of artificially long days (LD, n = 4). On March 16, two control and two treated males were put in contact with 20 and 19 females, respectively. Sexual behavior of the bucks was observed during the 5 d following male introduction. Progesterone assays and estrous behavior were used to determine ovarian and behavioral responses of the females to teasing. The anogenital sniffing, nudging, and mount instances registered in LD-treated males were greater than those observed in CG (P < 0.05). Of the does exposed to CG, none ovulated and only two of 20 females displayed estrous behavior. All does in contact with LD-treated males ovulated and showed at least one estrous behavior during the 15 d following joining (P < 0.001). These results indicate that the sexual activity of male goats from subtropical latitudes can be induced using only artificially long days. In addition, males treated in this way are capable of stimulating sexual activity in anovulatory females by the male effect.

Male effect in seasonally anovulatory lactating goats depends on the presence of sexually active bucks, but not estrous females

A study was conducted in subtropical northern Mexico (26 degrees N) to determine whether the presence of estrous females can improve the response of seasonally anovulatory goats to the introduction of bucks in the group. The induction of estrous activity was studied in three groups of anovulatory lactating goats during seasonal anestrus. These females were of the Mexican Creole breed. In the control group (sexually inactive (SI), n = 20), two control (SI) bucks exposed to normal seasonal daylength variations were used. In the second group (SI + E, n = 20 + 3), two control males were also used, but in addition, three females of the group were in estrus at the time of male introduction. In the third group (sexually active, SA + E, n = 19 + 4), anovulatory females were exposed to two bucks made sexually active by exposure to 2.5 months of long days (16L:8D) followed by two subcutaneous 18 mg melatonin implants, and four estrous females were also present when introducing the bucks. In all groups, males were introduced on 15 March and estrous detection was conducted twice daily for 15 days. The sexual activity of the bucks was observed from 08:00 to 10:00 h during the first five days of exposure to females. More females displayed estrous behavior in the first 15 days following the introduction of the males in the SA + E group (18/19) as compared with the SI or SI + E groups (2/20 and 0/20, respectively; P < 0.001). No difference was observed between the two latter groups. Thirteen females of SA + E group showed a second estrus between days 6 and 11 (short estrous cycle duration: 5.4 +/- 0.4 days). By contrast, in the SI group none showed a second estrus. The sexual behavior of the males in the SA + E group was greater as compared with that of the males in SI and SI + E groups (over 80% of the total sexual activity recorded in the three groups; P < 0.001). By contrast, no differences were found between SI and SI + E males. These results indicate that the presence of estrous females alone at the time of buck introduction is not sufficient to induce an adequate stimulation of seasonally inactive males. The use of sexually active bucks is necessary to induce reproductive activity in anovulatory females, whereas preparation of the bucks with long days followed by melatonin implants allows them to gain such a capacity.