The male effect stimulus positively increased the ovarian and reproductive seasonality in Criollo goats irrespective of a controlled photoperiodic regime

Abstract

Present study evaluated the presence of a sexually active male buck upon the onset of reproductive activity and estrous cycle progression in Criollo goats exposed to a 6-month long controlled photoperiod in a range of 13.4–10.6 light-hours per day. Mexican-native (Criollo) goats (n=10) were randomly assigned into 2 groups: (1) goats exposed to a male buck (n=5); (2) goats not exposed to a male buck (n=5). Blood samples were taken weekly to quantify serum-progesterone levels through radioimmunoanalysis. Male exposure increased luteal activity and estrous cycle progression reflected as a higher number of days in luteal activity (44±9.05 vs. 32.3±20.6); a reduced number of days in anestrous (4.0±4.8 vs. 51.9±28) and a greater number of luteal phases (15.7±4.4 vs. 11.3±8.7) without compromising serum progesterone levels (6.8±0.8 vs. 7.3±0.5). In conclusion, presence of a sexually active male induced a greater ovarian activity in Criollo goats, shortening seasonal anestrous irrespective of the controlled photoperiodic regime.

Keywords:

• male effect
• goats
• ovarian activity
• progesterone
• photoperiod

Introduction

A global world demands an increased goat production and implementation of reproductive technologies (Aréchiga and Rincón 1998; Aréchiga et al. 2008;). Criollo goats display reproductive seasonality, even in subtropical regions such as Mexico, as demonstrated by evaluating reproductive tracts (Valencia et al. 1986, 1990), measuring serum progesterone levels in non pregnant goats (Escobar et al. 1997) or by evaluating reproductive activity patterns (Chemineau et al. 2004). During seasonal anestrous, male bucks have shown a reproductive activity and a reduced sexual stimulus. The ‘male effect’ is a valuable technique for inducing a synchronised fertile ovulation during seasonal and post-partum anoestrous both in goats and sheep (Restall 1992; Walkden-Brown et al. 1999; Gelez and Fabre-Nys 2004; Scaramuzzi and Martin 2008). Photoperiodic treatments have proved to be successful by increasing sexual activity in goats under subtropical latitudes (Delgadillo et al. 2002, 2003, 2004b) as well as in Criollo bucks exposed to alternating light–dark photoperiodic cycles (16 h light: 8 h dark); either with or without melatonin treatment (Delgadillo et al. 1995, 2001, 2002, 2004a, 2006). A combination of photoperiod and male effect has been proposed to regulate goat reproductive seasonality (Delgadillo et al. 2003, 2004, 2006, 2009). In fact, sexually active males exposed to prepuberal (Amoah and Bryant 1984; Mellado et al. 2000) and adult females goats synchronised reproductive activity under either lactational or seasonal anestrous (Véliz et al. 2002, 2006a, 2006b; Pellicer-Rubio et al. 2007). A high proportion of goats exposed to a sexually active male showed estrus behaviour 2 or 3 days after joining with the buck (Chemineau 1983, 1987) and ovulated in response to a male by increases in both GnRH and LH secretion (Chemineau et al. 1986a, 1986b, 2006). However, it has been emphasised that male ‘novelty’ could be more important than male isolation (Delgadillo et al. 2009). Male presence has also induced reproductive activity in melatonin-implanted Mediterranean female goats causing a small retardation in the reactivation of reproductive activity during the natural breeding season (Zarazaga et al. 2009). Also, it has been observed a 2–3 months interval from summer solstice (21 June) to ovarian activity resumption in goats exposed to either natural photoperiod or controlled cycles of artificial photoperiod 6–12 months long (Escobar et al. 1997). Thus, caprine might expend two to three months to develop refractoriness. Therefore, ‘male effect’ and photoperiod may interact synergistically and/or antagonistically, but the precise nature of these interactions and their significance to reproductive outcomes are still not well understood (Scaramuzzi and Martin 2008).

Purpose of present research was to test the hypothesis that a daily exposure of female goats to a sexually active male buck prolongs their estrus and ovulatory activity, reducing length of anestrous season. A male buck became sexually active by exposure to alternated photoperiodic monthly treatments (16 h light:8 h dark; and vice versa; Delgadillo et al. 2001, 2004a, 2004b, 2006). Present work intended to evaluate the effect of presence of a sexually active male on ovarian luteal activity and reproductive seasonality of Criollo goats exposed to a controlled photoperiod and feeding regime at the subtropical Northern-Central Mexico (23° NL).

Materials and methods

Location, animals and treatments

The study was carried out at the University of Zacatecas located in north-central Mexico at 23°00′ North latitude and 102°44′ West longitude and 2150 m above the sea level. The experiment include Criollo goats, (n=10) from a subtropical region located in arid and semiarid areas of Mexico (Zacatecas State). These non-pregnant goats had an average body weight of 39±4.5 kg. and were exposed to a sexually active male buck by alternated monthly photoperiodic treatments of 8 h light:16 h dark and vice versa (Delgadillo et al. 1993, 1995, 2001, 2003).

Animals were located in controlled-photoperiodic chambers (i.e. controlling light-hours per day) to provide 350 lux directly over goat eyes (height). All goats were exposed to 90-day alternating pattern of artificial long (13.4L/10.6D) for the entire study during a period of 2 years [six photoperiodic cycles: ascending (n=3); and descending (n=3) cycles]. Main purpose was to simulate occurrence of two consecutive natural photoperiods during a year, and to evaluate the effect of a specific photoperiod upon reproductive function of goats.

Experimental design

Criollo goats (n=10) were randomly assigned to two groups: Goats non-exposed to presence of a sexually active male buck (Control group, n=5) and goats exposed to a sexually active male buck (Treated group, n=5). Both groups were exposed to a 6-month long controlled artificial photoperiods. Thus, annual variations in light-hours per day were included in a 6-month long controlled artificial photoperiod in order to obtain two photoperiodic cycles within a year and to evaluate variations in response to the presence or absence of a sexually active male buck.

The buck was also exposed to monthly alternated long-short photoperiodic (light–dark) treatments [long: 16 h light/8 h dark; and short:8 h light/16 h dark] as previously reported by Delgadillo et al. (1995). The sexually active buck was introduced to the treated group (goats exposed to a male buck) wearing a harness, beginning at the second photoperiodic cycle and remained with the goats throughout the day for 8–10 h depending upon the photoperiodic treatment received. Control goats were kept permanently without a male presence.

Blood sample collection

Blood samples were collected twice a week to determine progesterone levels (P4). Samples were obtained by jugular venipunction using Vacutainer® tubes and then centrifuged (1500×g, 15 min, 4°C). Blood serum was separated and stored at –20°C until a radioimmunoanalysis assay was performed. Samples with progesterone levels above 1 ng/mL of blood serum were considered as evidence of an active corpus luteum and therefore of a previous ovulation occurrence.

Progesterone radioimmunoassay

Progesterone levels were determined by a solid phase radioimmunoassay (Coat-A-Count, Los Angeles, CA). Assay sensitivity was 0.01 ng/mL and intra- and inter-analyses variation coefficients were 6.7% and 10.6%, respectively. Samples with progesterone levels above 1 ng/mL of blood serum, was considered as evidence of corpus luteum presence and previous ovulation occurrence.

Statistical analyses

Statistical analyses were performed using GLM procedure of SAS (2000). A Tukey test was performed in order to determine mean differences.

Results and discussion

Presence of a sexually active male buck promoted a reduced anestrous season in Criollo goats as well as a greater number of days showing luteal activity, and therefore, a greater number of luteal phases with a trend for higher progesterone levels during a descending artificial photoperiodic cycle as naturally occur during the winter solstice (Table 1; Figure 1).

Figure 1.  Effect of presence of a sexually active male buck on number of Criollo goats showing estrous cycles under a controlled photoperiod.

Table 1. Effect of a sexually active male presence stimulus on luteal activity, estrous cycle succession and serum progesterone concentrations of Criollo goats under a controlled photoperiodic regime.

	Sexually active male buck presence^a	Sexually active male buck absence
Days of luteal activity (d)	44.0±9.05	32.3±20.6
Anestrous period (d)^b	4.0±4.8	51.9±28
Number of luteal phases	15.7±4.4	11.3±8.7
Mean serum progesterone levels	6.8±0.8	7.3±0.5^c
^aStatistical significant difference (p<0.05).
^bSerum progesterone levels <1 ng/ml were considered as absence of corpora lutea and ovarian activity.
^cNon-statistically significant.

When the sexually active male buck was introduced these effects remain longer despite the occurrence of ascending artificial photoperiodic cycles (summer solstice), which supposed to be periods of reproductive inactivity. A greater number of goats remained cycling while a greater estrous-cycle progression was observed (Table 1; Figures 1 and 2).

Figure 2.  Effect of presence of a sexually active male buck on luteal activity as determined by serum progesterone levels of goats exposed to controlled photoperiodic cycles.

Criollo goats exposed to the presence of a sexually active male buck presented a greater luteal activity (Table 1; Figures 1 and 2), as well as a greater estrous cycles progression than goats not exposed to a male buck (Figures 1 and 2). Such reproductive behaviour was evident due to a higher number of days in luteal activity (44±9.05 vs. 32.3±20.6), a reduced number of days in anestrous (4.0±4.8 vs. 51.9±28), a reduced progesterone secretion (6.8±0.8 vs. 7.3±0.5); as well as a greater number of luteal phases (15.7±4.4 vs. 11.3±8.7); (p<0.05) (Table 1; Figures 1 and 2).

Control goats not exposed to males showed reproductive activity only during the influence of winter-solstice artificial-photoperiodic cycles (decreased photoperiod with low light-hours during the day). In contrast, goats exposed to the presence of a sexually active male buck showed reproductive activity practically during the whole experimental period, irrespective of the influence of a prolonged or a reduced artificial photoperiod (summer or winter solstice photoperiod, respectively).

Therefore, presence of a sexually active male induced a greater reproductive (ovarian and/or luteal) activity of goats compared to goats not exposed to the presence of a male. Such reproductive activity was measured by a greater number of estrous cycles, and a greater estrous cycle progression, even during periods of reduced reproductive activity such as an increased photoperiod.

Such effect could be a synergic effect on reproductive activity of Criollo goats, which seems to have developed timely dependent environmental adaptative mechanisms to better sort out environmental challenges (Meza-Herrera et al. 2006, 2007a, 2007b).

Artificial photoperiodic cycles (6-month long) were implemented to simulate two natural photoperiods in a year, through alternating ascendant and descendant photoperiodic cycles (Escobar et al. 1997). Range of light-hours per day used for present study was 13.4 and 10.6 h light/dark and was determined based on previous studies using goats in the same location, observing a photoperiodic-dependent influence on the ovarian activity of these Criollo goats (Escobar et al. 1997).

A descending artificial photoperiod obtained in controlled-environmental chambers is able to stimulate reproductive function in Criollo goats. However, during the reproductive season there was not continuity in the estrous cycle progression. Introduction and presence of a sexually active male buck increase reproductive activity stimuli on goats. Male introduction during a summer-solstice artificial photoperiod generated ovarian activity in an average interval of 12.4 days. Similar results were observed in sheep (Martin et al. 1986) and goats under natural (Chemineau 1987), and artificially controlled (Chemineau et al. 1986b) photoperiods.

Food availability, although not considered a critical or main regulating factor, becomes also a modulating factor on reproductive function of Criollo goats (Urrutia-Morales et al. 2009). Nevertheless, other authors have found an increase in reproductive activity and pregnancy rates by implementing a ‘male effect’ stimulus (De Santiago-Miramontes et al. 2009; Fitz-Rodríguez et al. 2009). In present experiment, goats were kept under same feeding and controlled photoperiod regime.

Thus, presence of a sexually active male buck allow to positively increase reproductive function of native goats independently of the photoperiodic treatment, as it has been previously reported by Malpaux et al. (1997) and Delgadillo et al. (2002). Such effect seems to be independent of the male–female proportion (Carrillo et al. 2007) as well as continuity or discontinuity of the ‘male effect’ treatment (Rivas-Muñoz et al. 2007). Although, recently, it has been more associated with ‘novelty’ of the male (Delgadillo et al. 2009).

Sexual activity induction in male bucks has been previously reported using different treatments. One treatment, is based on alternate photoperiodic treatments (2-month long; 16 h light/8 h dark) reported by Delgadillo and Chemineau (1992) in northern Mexico (26°23′N latitude; 104°47′W longitude). Delgadillo et al. (1993) also reported sexual activation by controlled photoperiod and melatonin treatment in male bucks (Chemineau et al. 1999; Flores et al. 2000). For present trial, the male buck received a monthly alternated photoperiodic treatment of 16 h light/8 h dark in order to prevent seasonal changes on the hypothalamic-hypophyseal-gonadal axis, and improved testicular weight and semen production (Delgadillo et al. 1995).

Male introduction stimulate estrous cycle progression preventing or reducing seasonal anestrous. On this respect, 5 days after male introduction into seasonal annovulatory goats, increased ovulation rate within a 2–3 days peak (Chemineau 1983). The male effect stimulus of a sexually active male buck increased luteal activity (44±9.1 vs. 32.3±20.6 days), reduced anestrous (4.0±4.8 vs. 51.9±28 days) and there were no differences on serum levels of progesterone (6.8±0.8 vs. 7.3±0.5), however, there was a clear difference on the number of luteal phases observed (15.7 vs. 11.3). In our study, luteal phases increased as determined by the progesterone secretion patterns demonstrating a better estrous cycle progression, an increased number of estrous cycles as well as a better reproductive outcome; all of these irrespective of the photoperiodic regime.

Male buck remained 8–10 h per day interacting with goats depending upon the photoperiodic treatment, promoting a constant ovarian activity. Also, it has been observed a 2–3 months interval from summer solstice (21 June) to ovarian activity resumption in goats exposed to either natural photoperiod or controlled cycles of artificial photoperiod 6–12 months long (Escobar et al. 1997). The last suggests that goats might expend 2–3 months to develop refractoriness. Male presence, have also induced reproductive activity in melatonin-implanted Mediterranean female goats causing a small retardation in the reactivation of reproductive activity during the natural breeding season (Zarazaga et al. 2009).

An artificially controlled photoperiodic treatment to be used in all goats seems complicated and impractical. However, a real alternative could be to expose the male buck into a photoperiodic treatment (16 h light/8 h dark), since the male only requires a single controlled environmental chamber. Such management practices represent a real alternative for goats under extensive production systems. The last, in order to control both the breeding and kidding seasons to the most profitable and optimal time of the year as required by most goat producers.

Conclusion

The presence of a sexually active male buck increased ovarian activity, estrous cycling activity and estrous cycle progression of Criollo goats under subtropical conditions, despite the influence of an increased controlled-photoperiod.

Implications

A controlled-photoperiodic treatment on male bucks might result in an alternative to schedule breeding seasons at selected time-windows by introducing a sexually active male buck exposed to alternate periods of 16 h light:8 h dark. Such reproductive technology and management require minimal infrastructure and equipment in goat extensive production systems typical of arid and semi-arid regions of the world.

Acknowledgements

Research was partially supported by a SIVILLA-CONACYT Grant No. 1998401010-4 and a SAGARPA-CONACYT Grant.