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Stimulation of estrous behavior in grazing female goats by continuous or discontinuous exposure to males^1,2

R. Rivas-Muñoz^*, G. Fitz-Rodríguez^*, P. Poindron, B. Malpaux and J. A. Delgadillo^*,3

^* Centro de Investigación en Reproducción Caprina, Universidad Autónoma Agraria Antonio Narro, Periférico Raúl López Sánchez y Carretera a Santa Fe, C.P. 27054, Torreón, Coahuila, México; and and Physiologie de la Reproduction et des Comportements, UMR 6175 INRA-CNRS-Université de Tours-Haras Nationaux, IFR 135, 37380 Nouzilly, France

	Abstract

Top Abstract INTRODUCTION MATERIALS AND METHODS RESULTS DISCUSSION LITERATURE CITED

 
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.

Key Words: anestrous female • estrous activity • male effect • management system • photoperiod

	INTRODUCTION

Top Abstract INTRODUCTION MATERIALS AND METHODS RESULTS DISCUSSION LITERATURE CITED

 
Induction of synchronous estrous behavior and ovulation in anovulatory females after introduction of a ram or buck is called the male effect (Chemineau, 1987; Ungerfeld et al., 2004). Generally, when utilizing the male effect, animals are kept in confined conditions, allowing continuous contact between sexes, a factor considered to be critical for the sexual response of the females exposed to males (Signoret, 1990; Walkden-Brown et al., 1993). Physical contact between sexes must be maintained for several days and be continuous to induce estrous behavior and ovulation in most females (Oldham and Pearce, 1983). When males are removed too early, LH secretion in the females decreases immediately, thus not allowing ovulation to occur (Pearce and Oldham, 1988; Signoret, 1990).

These conditions are not always possible under range conditions, where animals graze about 8 h/d without supplemental feed and remain in pens only at night. Under grazing conditions, estrous behavior and fertility of females exposed to males is low compared with that observed in confined conditions (Hulet et al., 1986; Mellado et al., 1994; Atti et al., 2004). Another critical factor for success of the male effect is use of sexually active males (Fitzgerald and Stellflug, 1991). Bucks treated with long days can stimulate ovulation and estrous behavior in female goats raised in confined conditions, whereas control males cannot (Flores et al., 2000).

Therefore, to optimize the use of the male effect under grazing conditions, the aims of this study were to determine if males exposed to long days can stimulate estrous activity of female goats maintained under grazing conditions and whether the continuous presence of the males is necessary to stimulate estrous activity in anestrous female goats.

	MATERIALS AND METHODS

Top Abstract INTRODUCTION MATERIALS AND METHODS RESULTS DISCUSSION LITERATURE CITED

 
The procedures used in these experiments were in accordance with the Guide for the Care and Use of Agricultural Animals in Agricultural Research and Teaching (FASS, 1999).

The experiments were performed using Mexican goats (Capra hircus) from the Laguna region in the State of Coahuila, Mexico (latitude, 26°23' N and longitude, 104°47' W). The area is characterized by a dry climate, with an average annual rainfall of 27 cm (16 to 50 cm). The rainy season lasts from June to September, with a high interyear variability. Mean annual maximum and minimum temperatures are 36.6°C between May and August and 5.7°C between December and January, respectively.

Goats from the Laguna region were derived from the Spanish Granadina, Murciana, and Malagueña breeds, with repeated crosses with Alpine, Saanen, and Anglo-Nubian breeds. Females are generally anestrus from March to August, and bucks are in sexual rest from January to April (Delgadillo et al., 1999; Delgadillo-Sánchez et al., 2003). Female goats are used to produce milk and meat and are generally allowed to graze from 0900 to 1800 without supplemental feed. At night, does remain in outdoor pens.

Experiment 1
The aim of this study was to determine if males exposed to long days can stimulate estrus in seasonally anestrous female goats maintained under grazing conditions.

Males.
Twenty adult male goats were used. Bucks were 2 to 4 yr old at the beginning of the study. Males were divided into 2 groups, according to BW, testicular weight, BCS, and male odor (see below for methodology) and kept in 2 outdoor pens (1 pen/group) from November 1 to March 28, when they were introduced into the groups of females. Control males (sexually inactive; n = 10) were exposed to natural photoperiod (13 h 41 min of light at the summer solstice and 10 h 19 min of light at the winter solstice) throughout the study. Treated males (sexually active; n = 10) were submitted to 16 h of light/d from November 1 to January 15. Artificial light was provided from 0600 to 0800 and from 1800 to 2200. The light intensity was at least 300 lx positioned laterally to the eyes of the animals. On January 16, the light treatment was stopped, and males were exposed only to the natural photoperiod until April 12. This treatment stimulates testosterone secretion, ano-genital sniffing, nudging, and mounts during the sexual rest (Delgadillo et al., 2002; Véliz et al., 2006). Males were fed alfalfa hay (18% CP, DM basis) ad libitum and 300 g/d of commercial concentrate (14% CP; 1.7 Mcal/kg; DM basis) per buck, with free access to mineral blocks and water during the outdoor photoperiod treatment.

Females.
Eighty multiparous, anovulatory female goats selected from a larger flock were used in this experiment. In these females, progesterone concentrations had been determined by RIA for plasma obtained from blood collected on March 2, 11, and 28 to verify the absence of ovarian activity until introduction of the males (Terqui and Thimonier, 1974). Does had given birth between August 1 and November 30, and kids were weaned between 20 and 30 d of age. All females were hand-milked daily during the experiment and isolated from any male from December 15 until March 28, when exposure to males was implemented. All female goats were allowed to graze for 8 h/d before the study.

On March 15, half of the females (n = 40) were maintained under grazing conditions; the other half (n = 40) was kept in confinement (open pens; 10 x 10 m). Allocation of animals between these conditions was done by BCS and milk production. On March 26, animals in both management conditions were further divided into 2 halves, by BCS and milk production, to constitute the experimental groups (n = 20/group). Before exposure of does to the males, 1 doe in the confined group was eliminated due to sanitary problems. The 2 confined groups were kept in 2 shaded pens (4 x 5 m). The 2 grazed groups were kept during the night in 2 pens (4 x 5 m). The distance between 2 groups was at least 200 m.

Does in confined conditions were fed alfalfa hay (18% CP, DM basis) ad libitum and 200 g of commercial concentrate (14% CP; 1.7 Mcal/kg; DM basis), with free access to water and mineral blocks. Grazing females were kept on natural pasture from 0900 to 1800 without supplemental feed. At night, does remained in the pens. The natural vegetation consisted mainly of shrubs (Pro-sopis glandulosa, Acacia farneciana, Atriplex acantocarpa, Agave scabra, and Mimosa biuncifera), herbaceous plants (Heliantus ciliaris, Salsola kali, and Solanum elaeagnilolium), and grasses (Sorghum halepense, Chloris virgata, Setaria verticillata, Eragrostis pectinacea, Bouteloua curtipendula, Aristida purpurea, and Bouteloua barbata).

Male Effect.
On March 28 at 1800 (d 0), females in confined and grazing conditions were exposed to randomly selected control or light-treated bucks (n = 2/group). Males remained with the females for 15 d.

Measurements.
Body and testicular weights were measured every 2 wk throughout the experiment. Testicular weight was determined by comparative palpation with an orchidometer (Oldham et al., 1978). Body condition score and male odor were determined weekly. Male odor and BCS were determined according to Walkden-Brown et al. (1993, 1997). Measurements were performed by the same operator. Sexual behavior of the bucks was observed from 0730 to 0900 and from 1800 to 1930 during the first 5 d after their introduction to females. Trained observers followed the bucks individually and recorded the following behaviors: self-urination, flehmen, ano-genital sniffing, nudging, mounting attempts, and mounts (with or without vaginal intromission; Gonzalez et al., 1988; Véliz et al., 2004). For females, estrous behavior was checked twice daily (0800 and 1800) throughout the experiment (Chemineau et al., 1992).

Experiment 2
The aim of this study was to determine if the continuous presence of males exposed to long days is necessary to stimulate estrous behavior in seasonally anestrous female goats maintained under grazing conditions.

Males.
Six adult male goats were submitted to the same photoperiod treatment as in Exp. 1 to induce their sexual activity during the nonbreeding season (Delgadillo et al., 2002). Bucks were 3 to 5 yr old at the beginning of the study.

Females.
Fifty-two multiparous anovulatory goats selected from a larger flock were used in this experiment. As in Exp. 1, these females were selected on the basis of ovarian inactivity, which was verified by plasma progesterone assay from blood samples taken on March 17, 26, and April 4 (Terqui and Thimonier, 1974). Does had given birth between August 1 and November 30, and kids were weaned at about 25 d of age. All females were hand-milked once daily during the experiment and isolated from any males from December 15 to March 30. All female goats were maintained under grazing conditions during the study. On March 31, females were divided into 2 groups (n = 26) balanced for BCS and milk production. From March 31 onward, both groups grazed separately in open range from 0900 to 1700. At night, the goats were penned in 2 pens. Goats received 1.5 kg of alfalfa hay (18% CP, DM basis) and 500 g of a commercial concentrate with 14% CP (1.7 Mcal/kg of BW, DM basis) and had free access to mineral blocks and water during the entire study.

Male Effect.
On April 4 at 1700 (d 0), females were exposed to randomly selected, long day-treated bucks (n = 3/group). Animals in 1 group grazed together in open range and remained constantly in contact with the males (continuous group). In the other group, males remained in the shaded pen during the day whereas females grazed in open range; bucks were therefore exposed to females only for 16 h daily from 1700 to 0900. This was the discontinuous group. Bucks remained with the females for 18 d.

Measurements and Definitions.
Sexual behavior of bucks was observed from 0800 to 0900 during the first 3 d after their introduction to the females, as described for Exp. 1. Trained observers followed the bucks individually and recorded the following behaviors: self-urination, flehmen, ano-genital sniffing, nudging, mounting attempts, and mounts (Gonzalez et al., 1988; Véliz et al., 2004). For the females, estrous behavior was checked twice daily at 0800 and 1800 throughout the experiment (Walkden-Brown et al., 1993). The interval between introduction of the males and the onset of estrous behavior was recorded. Estrous cycle duration is the number of days between 2 consecutive estrus. Duration of a short estrous cycle is <17 d (Chemineau et al., 1992). Fertility (number of does kidding/number of does exposed to males) and prolificacy (number of kids born/number of does giving birth) were recorded at parturition after the experiment.

Statistical Analyses
The statistical design used in these experiments was completely randomized, with a 2 x 2 factorial arrangement of treatments. Animals were divided into 2 (males) or 4 (females) groups, which then served as the experimental units for allocations to treatments. In Exp. 1, variables concerning males (BW, testicular weight, BCS, male odor) were analyzed by a 2-way ANOVA, with repeated measurements to test effects of photoperiod treatment and time, followed by t-test or Mann Whitney test (males odor) for 2 x 2 comparisons. Differences in the number of male sexual behaviors recorded were analyzed using ². The proportion of females exhibiting estrus on each day, the cumulative percentage of females exhibiting estrus, the proportion of does exhibiting short estrous cycles, and fertility were compared by ². The interval between introduction of the males and onset of the estrous behavior was analyzed by a 2-way ANOVA to test the effects of photoperiod treatment of bucks and management, followed by t-test. The duration of the short estrous cycles and the prolificacy were analyzed using t-test. In Exp. 2, the effect of discontinuous exposure to males was tested by a 1-way ANOVA. Analyses were computed using Systat 10 (Evanston, IL).

	RESULTS

Top Abstract INTRODUCTION MATERIALS AND METHODS RESULTS DISCUSSION LITERATURE CITED

 
Experiment 1
Body Weight.
Mean BW of males (Figure 1A) increased throughout the experiment (effect of time, P < 0.001) and these changes differed between males exposed to long days and control bucks (group x time interaction, P = 0.046). However, a comparison of groups at individual time points did not reveal differences in BW (P > 0.05).

View larger version (12K): [in this window] [in a new window]   Figure 1. Temporal measures (mean ± SEM) of (A) BW, (B) BCS, (C) testicular weight, and (D) male odor score in 2 groups of male goats from subtropical Mexico subjected to natural changes in day length (sexually unprepared males, ; n = 10) or to artificial long days (16 h of light/d) between November 1 and January 15 (sexually prepared males, •; n = 10). Body and testicular weights were measured twice each month, whereas BCS and male odor were determined weekly. For all variables, there was a group x time interaction (P < 0.05). Time point differences are indicated by *P < 0.05 and **P < 0.01.

Testicular Weight.
Testicular weight (Figure 1C) was influenced by the group x time interaction (P < 0.001). However, a comparison of groups at individual time points did not reveal differences in testicular weight (P > 0.05).

Male Odor.
The intensity of male odor (Figure 1D) varied during the study (effect of time, P < 0.001), and these changes were modified by photoperiod treatment (group x time interaction, P < 0.05). Odor of males exposed to long days was stronger (P < 0.05) than that of control bucks in March when bucks were under natural photoperiod.

Male Sexual Behavior.
The number of all sexual behaviors during d 0 to 5 of exposure to does was greater (P < 0.05) in males exposed to long days than in control bucks. More than 75% of all behaviors observed were recorded in males exposed to long days (40/47 self urination, 244/334 flehmen, 1,082/1,449 ano-genital sniffing, 1,485/1,941 nudging, 97/113 mounting attempts, and 50/58 mounts).

Response of Females to Male Effect.
The daily and cumulative percentages of does displaying estrous behavior are shown in Figure 2. The total cumulative proportion of does that exhibited estrus in the 15 d of buck exposure was greater (P < 0.001) for does exposed to photoperiod treated males (93%) than for those exposed to control bucks (30%; Figure 2C, 2D). There was no difference (P = 0.579) in the total daily proportion of females showing estrus during the 15-d period between females maintained in confined (95%, 18/19) or grazed (90%, 18/20) conditions and exposed to males treated with long days. However, the cumulative percentages of females in estrus were greater in confined females on d 2, 3, and 7 of exposure to males (P < 0.05). In contrast, the proportion of females showing estrus when exposed to control bucks was less (P = 0.038) in confined goats (15%, 3/20) than in those under grazing conditions (45%, 9/20). There was an effect of preparation of bucks by photoperiod on latency to first estrous behavior (P = 0.011) and an interaction between preparation of bucks and management conditions (P = 0.044). For females displaying estrus following exposure to males treated with long days, this interval was shorter (P = 0.045) in females under confinement (2.5 ± 0.4 d) than those in grazing females (4.3 ± 0.7 d). In contrast, this interval was similar (P = 0.87) in females exposed to control bucks in confined (6.5 ± 0.5 d) or grazing conditions (6.3 ± 0.9 d). The proportion of females exposed to long day-treated males that displayed a short estrous cycle did not differ (P = 0.75) between does in confined (58%, 11/20) or grazing conditions (50%, 10/20; Figure 2A). Furthermore, the duration of the short estrous cycles was similar (P = 0.68) in confined (5.4 ± 0.2 d) and grazing groups (5.6 ± 0.4 d). Only 1 female exposed to control males displayed a short estrous cycle (estrous behavior on d 3 and again on d 6 after male introduction, duration of 3.3 d; Figure 2B).

View larger version (14K): [in this window] [in a new window]   Figure 2. Left panel: Daily percentage of female goats exhibiting estrus (A) when maintained in confined (n = 19, •) or grazed (n = 20, ) management and exposed to male goats rendered sexually active by treatment with long days (2 males/group), and (B) when maintained in confined (n = 20, ) or grazed (n = 20, ) management and exposed to control males (2 males/group). Right panel: Cumulative percentage of goats exhibiting estrus (C) when females are maintained in confined (n = 19, •) or grazed (n = 20, ) management after exposure to male goats rendered sexually active by treatment with long days (2 males/group), and (D) when females are maintained in confined (n = 20, ) or grazed (n = 20, ) management and exposed to control males (2 males/group). Data for daily estrous behavior included short and normal estrous cycles. Control bucks: bucks exposed to natural photoperiod. Treated bucks: bucks subjected to 2.5 mo of artificial long days (16 h of light/d) between November 1 and January 15. Day 0 is the day on which the bucks were placed with the does. *Time point differences are indicated by P < 0.05. There was a significant interaction between the type of bucks used for teasing and management on the latency of females to first estrus after introduction of the bucks (P = 0.044).

Response of Females to Male Effect.
The daily and cumulative percentages of females that displayed estrous behavior did not differ (P = 0.55) between continuous (96.2%, 25/26) and discontinuous groups (92.3%, 24/26; Figure 3). Mean interval between introduction of males and onset of estrous behavior was not different (P = 0.15) between groups (continuous: 3.9 ± 0.6 d, discontinuous: 2.8 ± 0.4 d). There was no difference (P = 0.09) in the proportion of females displaying short estrous cycles from continuous (30.8%, 8/26) and discontinuous (53.9%, 14/26) groups. In addition, duration of these short estrous cycles was similar (P = 0.65) between groups (continuous: 5.4 ± 0.3 d, discontinuous: 5.2 ± 0.2 d).

View larger version (14K): [in this window] [in a new window]   Figure 3. (A) Daily and (B) cumulative percentage of female goats that displayed estrous behavior after continuous (24 h/d; ) or discontinuous (16 h/d; •) exposure to sexually prepared male goats for 18 d. Males were subjected to 2.5 mo of artificial long days (16 h of light/d) between November 1 and January 15. Day 0 is day on which the bucks were placed with the does.

	DISCUSSION

Top Abstract INTRODUCTION MATERIALS AND METHODS RESULTS DISCUSSION LITERATURE CITED

 
These studies demonstrate that male goats that have been treated with artificial long days can stimulate estrous and ovulatory activities of seasonally anovulatory goats even without confinement between sexes. Furthermore, our results show that continuous presence of bucks is not necessary to stimulate reproductive activity in such goats. The fact that bucks kept under natural photoperiod were unable to stimulate reproductive activity as efficiently as bucks treated with long days could be due to the lower emission of pheromones and display of sexual behavior by these control males, as reported previously (Chemineau et al., 1986; Delgadillo et al., 2004). Nonetheless, the fact that control bucks were able to induce some reproductive activity in grazed females, as also reported by Mellado et al. (1996), suggests that, under grazing conditions, some unknown factors can facilitate the response of females to the male effect.

Small pens were postulated to increase physical contact between sexes, thereby enhancing response of females to male exposure (Walkden-Brown et al., 1993; Restall et al., 1995). Nonetheless, when bucks exposed to long days were used, the effect of confinement appeared only marginal because it was only limited to the first week of stimulation by bucks. Furthermore, when control bucks were used, reproductive response of females was greater under grazing conditions. These data are consistent with those reported by Rosa et al. (2003) who showed that the response of ewes exposed to the ram effect did not differ between females managed in a low (12 ewes/ha) or high (84 ewes/ha) stocking rate. As a whole, preparation of bucks with artificial photoperiod is clearly more important than confinement for the quality of the response.

As for duration of daily exposure to males, results of Exp. 2 showed that continuous presence of males is not necessary to stimulate estrous behavior in females, if bucks exposed to long days are used. This contrasts with reports in ewes indicating that continuous presence of males is necessary to stimulate sexual activity of females (Signoret et al., 1982). In addition, our results indicate that reducing contact with males to 16 h/d does not impair fertility and prolificacy. However, the current study does not provide insight into the minimum time of daily contact required between sexes to obtain a high percentage of females ovulating in response to the male effect. Whether the duration of exposure to males can be reduced to less than 16 h/d remains to be verified, especially when considering that in ewes, only 20% of females ovulated after 8 h of exposure to rams (Signoret et al., 1982). It will be interesting to assess this point to optimize use of the buck effect under grazing conditions.

The present results have practical implications concerning reproductive management of goats. First, males treated with long days stimulate a high proportion of does exposed to the male effect in grazed as well as in confined management. Availability of sexually active males allows producers to manipulate the annual breeding season according to consumer demands, without the restraint of also keeping females in confinement for teasing. Second, the fact that continuous presence of males is not necessary to stimulate reproductive activity of females gives the opportunity to use the male effect according to the necessities of each producer. For example, males can be kept in pens to rest during the day, whereas females go to the rangelands. In summary, this is an easy and inexpensive way to initiate caprine reproduction. In addition, the demonstration that continuous presence of male goats is not a prerequisite to stimulate this reproductive activity allows flexibility in use of males to induce estrus in female goats. Additional studies are needed to determine if sexually prepared bucks can stimulate sexual activity in anestrous females of other breeds and in other environmental conditions and geographical zones.

	Footnotes

 
¹ This work was supported in part by the ANUIES, SEP, CONA-CyT-ECOS exchange program between Mexico and France (M02-A04).

² The authors are grateful to Rogelio Muñoz and Gonzalo Zárate for providing the female goats necessary for these studies; to Dolores López for her excellent and kind secretarial assistance. Raymundo Rivas-Muñoz (grateful to Instituto Tecnológico de Torreón-DGEST) and Gonzalo Fitz-Rodríguez were supported by a CONACyT scholarship during their doctoral studies.

³ Corresponding author: joaldesa{at}yahoo.com

Received for publication February 28, 2006. Accepted for publication October 26, 2006.

	LITERATURE CITED

Top Abstract INTRODUCTION MATERIALS AND METHODS RESULTS DISCUSSION LITERATURE CITED

 


Atti, N., F. Bocquier, and G. Khaldi. 2004. Performance of the fat-tailed barbarine sheep in its environment: Adaptive capacity to alternation of underfeeding and re-feeding periods. A review. Anim. Res. 53:165–176.[CrossRef]

Chemineau, P. 1987. Possibilities for using bucks to stimulate ovarian and oestrous cycles in anovulatory goats. A review. Livest. Prod. Sci. 17:137–147.

Chemineau, P., A. Daveau, F. Maurice, and J. A. Delgadillo. 1992. Seasonality of estrus and ovulation in not modified by subjecting female alpine goats to a tropical photoperiod. Small Rumin. Res. 8:299–312.[CrossRef]

Chemineau, P., F. Levy, and J. Thimonier. 1986. Effects of anosmia on LH secretion, ovulation and oestrous behaviour induced by males in the anovular creole goat. Anim. Reprod. Sci. 10:125–132.[CrossRef]

Delgadillo, J. A., G. A. Canedo, P. Chemineau, D. Guillaume, and B. Malpaux. 1999. Evidence for an annual reproductive rhythm independent of food availability in male creole goats in subtropical northern México. Theriogenology 52:727–737.[CrossRef][Medline]

Delgadillo, J. A., G. Fitz-Rodríguez, G. Duarte, F. G. Véliz, E. Carrillo, J. A. Flores, J. Vielma, H. Hernandez, and B. Malpaux. 2004. Management of photoperiod to control caprine reproduction in the subtropics. Reprod. Fertil. Dev. 16:471–478.[CrossRef][Medline]

Delgadillo, J. A., J. A. Flores, F. G. Véliz, H. F. Hernández, G. Duarte, J. Vielma, P. Poindron, P. Chemineau, and B. Malpaux. 2002. Induction of sexual activity in lactating anovulatory female goats using male goats treated only with artificially long days. J. Anim. Sci. 80:2780–2786.[Abstract/Free Full Text]

Delgadillo-Sánchez, J. A., J. A. Flores, F. G. Véliz, G. Duarte, J. Vielma, P. Poindron, and B. Malpaux. 2003. Control de la reproducción de los caprinos del subtrópico mexicano utilizando tratamientos fotoperiódicos y efecto macho. Vet. Méx. 34:69–79.

FASS. 1999. Guide for the Care and Use of Agricultural Animals in Agricultural Research and Teaching. Fed. Anim. Sci. Soc., Savoy, IL.

Fitzgerald, J. A., and J. N. Stellflug. 1991. Effects of melatonin on seasonal changes in reproduction of rams. J. Anim. Sci. 69:264–275.[Abstract]

Flores, J. A., F. G. Véliz, J. A. Pérez-Villanueva, G. Martínez de la Escalera, P. Chemineau, P. Poindron, B. Malpaux, and J. A. Delgadillo. 2000. Male reproductive condition is the limiting factor of efficiency in the male effect during seasonal anestrus in female goats. Biol. Reprod. 62:1409–1414.[Abstract/Free Full Text]

Gonzalez, R., P. Poindron, and J. P. Signoret. 1988. Temporal variation in LH and testosterone responses of rams after the introduction of oestrous females during the breeding season. J. Reprod. Fertil. 83:201–208.[Abstract/Free Full Text]

Hulet, C. V., W. L. Shupe, T. Ross, and T. Richards. 1986. Effects of nutritional enviroment and ram effect on breeding season in range sheep. Theriogenology 25:317–323.[CrossRef][Medline]

Mellado, M., L. Cantú, and J. E. Suárez. 1996. Effects of body condition, length of breeding period, buck: Doe ratio, and month of breeding on kidding rates in goats under extensive conditions in arid zones of México. Small Rumin. Res. 23:29–35.[CrossRef]

Mellado, M., A. Vera, and H. Loera. 1994. Reproductive performance of crossbred goats in good or poor body condition exposed to bucks before breeding. Small Rumin. Res. 14:45–48.[CrossRef]

Oldham, C. M., N. R. Adams, P. B. Gherardi, D. R. Lindsay, and B. Mackintosh. 1978. The influence of level of feed intake on sperm-production capacity of testicular tissue in the ram. Aust. J. Agric. Res. 29:173–179.[CrossRef]

Oldham, C. M., and D. T. Pearce. 1983. Mechanism of the ram effect. Proc. Aust. Soc. Reprod. Biol. 15:72.

Pearce, G. P., and C. M. Oldham. 1988. Importance of non-olfactory ram stimuli in mediating ram-induced ovulation in the ewe. J. Reprod. Fertil. 84:333–339.[Abstract/Free Full Text]

Restall, B. J., H. Restall, and S. W. Walkden-Brown. 1995. The induction of ovulation in anovulatory goats by oestrous females. Anim. Reprod. Sci. 40:299–303.[CrossRef]

Rosa, H. J. D., C. C. Silva, and M. J. Bryant. 2003. The effect of paddock size on the response of seasonal anoestrous ewes to the ram effect. Small Rumin. Res. 48:233–237.[CrossRef]

Signoret, J. P. 1990. The influence of the ram effect on the breeding activity of ewes and its underlying physiology. Pages 59–70 in C. M. Oldham, G. B. Martin, and I. W. Purvis, editors. Reproductive physiology of merino sheep: Conceptus and Consequences. University of Western Australia, Perth.

Signoret, J. P., W. J. Fulkerson, and D. R. Lindsay. 1982. Effectiveness of testosterone-treated wethers and ewes as teasers. Appl. Anim. Ethol. 9:37–45.[CrossRef]

Terqui, M., and J. Thimonier. 1974. Nouvelle méthode radio-immuno-logique rapide pour l’estimation du niveau de progestérone plasmatique. Application pour le diagnostic précoce de la gestation chez la brebis et la chèvre. C.R. Acad. Sci. Paris. D279:1109–1112.

Ungerfeld, R., M. Forsberg, and E. Rubianes. 2004. Overview of the response of anoestrous ewes to the ram effect. Reprod. Fertil. Dev. 16:479–490.[CrossRef][Medline]

Véliz, F. G., P. Poindron, B. Malpaux, and J. A. Delgadillo. 2006. Maintaining contact with bucks does not induce refractoriness to the male effect in seasonally anestrous female goats. Anim. Reprod. Sci. 92:300–309.[CrossRef][Medline]

Véliz, F. G., L. I. Vélez, J. A. Flores, G. Duarte, P. Poindron, B. Malpaux, and J. A. Delgadillo. 2004. La presencia del macho en un grupo de cabras anestricas no impide su respuesta estral a la introducción de un nuevo macho. Vet. Méx. 35:169–178.

Walkden-Brown, S. W., B. Restall, and Henniawati. 1993. The male effect in the Australian cashmere goat. 3. Enhancement with buck nutrition and use of oestrous females. Anim. Reprod. Sci. 32:69–84.[CrossRef]

Walkden-Brown, S. W., B. J. Restall, R. J. Scaramuzzi, G. B. Martin, and M. A. Blackberry. 1997. Seasonality in male Australian cashmere goats: Long term effects of castration and testosterone or oestradiol treatment on changes in LH, FSH, and prolactin concentrations, and body growth. Small Rumin. Res. 26:239–252.[CrossRef]

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