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Oestrous synchronization is an effective management tool to control reproduction in goats, both for artificial insemination and multiple ovulation and embryo transfer programs (Leboeuf, et al., 1998; Wildeus, 2000; Whitley and Jackson, 2004; Chao, et al., 2008). Procedures aimed at manipulating the oestrous cycle in different ruminant breeds involve either shortening the luteal phase using luteolytic doses of prostaglandin F2α (PGF2α) or through extending the follicular phase with exogenous progesterone or progestagens (Kusina, et al., 2000; Wildeus, 2000; Lopez-Sebastian, et al., 2007).
PGF2α or its analogue based synchronization protocols are only applicable during the breeding season in cyclic goats with corpus luteum. The most widely practiced method of oestrous synchronization is progesterone or progestagens based protocols (Husein, et al., 2007; Lopez-Sebastian, et al., 2007; Menchaca, et al., 2007; Letelier, et al., 2009). Progesterone impregnated intravaginal products used in goats include controlled internal drug-releasing device (CIDR), Fluorogestone acetate (FGA) and methyl acetoxyl progesterone (MAP) (Wildeus, 2000). Reduced dose levels of FGA Letelier, et al. (2009) or MAP Greyling, and Van der Nest, (2000) does not affect the efficiency of synchronization in goats.
Oestrous synchronization methods using either progesterone or prostaglandin were suggested to be more effective when gonadotrophin co-treatments were used (Oliveira, et al., 2001; Pierson, et al., 2001; Husein, et al., 2007). Equine chorionic gonadotrophin (eCG) and follicle stimulating hormone (FSH) are the most often used gonadotrophin in oestrous synchronization protocols (Bearden, 2004; Gordon, 2004). High level of oestrus synchronization has been reported when eCG was incorporated into the synchronization protocol in sheep and goats in and out of the breeding season (Regueiro, et al., 1999; Zarkawi, et al., 1999; Al-Merestani, et al., 2003; Amarantidis, et al., 2004; Husein, et al., 2007). FSH was similarly reported to be effective in synchronization of oestrus (Gonzalez-Bulnes, et al., 2000).
(Ozawa, et al., 2005) suggested that heat stress during follicular recruitment suppresses subsequent growth to ovulation, accompanied by decreased LH receptor level and oestradiol synthesis activity in the follicles. According to Silanikove, et al. (2000), the complexities of the factors associated with thermal heat exchange in ruminants suggests that physical measurements of environmental temperature though useful may be less than satisfactory index of thermal stress, because the impact of environment may be modified by animal behaviour which could differ between specie, breed or individual levels (Silanikove, et al., 2000; Sejian, et al., 2010). Plasma cortisol levels may thus provide valuable information on stress levels associated with production conditions including ambient temperature, and relative humidity.
This study was therefore conducted to study the follicular development, oestrus response, time of onset and duration of oestrus behavior following oestrous synchronization using PGF2α, FGA or their combinations with exogenous eCG or FSH in non-seasonally poly-estrous, peri-pubertal Boer goats intensively raised under tropical farm conditions.
Estrous synchronization methods using either progesterone or prostaglandin were suggested to be more effective when gonadotrophin co-treatments were used (Oliveira, et al., 2001; Pierson, et al., 2001; Gonzalez-Bulnes, et al., 2005; Husein, et al., 2007; Menchaca, et al., 2007). This study found a 100% and 73% oestrus response in the PGF2α+eCG and PGF2α+FSH synchronized groups respectively. Amarantidis et al. (2004) reported 100% oestrus response in FGA or FGA+PGF2α synchronized indigenous Greek goats with and without PMSG (eCG). (Regueiro, et al. (1999) similarly obtained 100% oestrus response in Saanen, Nubian goats and their crosses synchronized with MAP, with or without 500IU eCG. Zarkawi et al. (1999) also induced 100% oestrus response outside the breeding season in Damascus goats synchronized with MAP plus injection of eCG at the time of sponge removal. Motlomelo et al. (2003) also reported a slightly lower (96.7%) oestrus response in FGA+PMSG synchronized goats. Dogan et al., (2005) suggested 85.7 and 94.4% in FGA+PMSG+PGF2α and FGA+PMSG synchronized Anatolian black does respectively.
Oestrus behaviour in FGA synchronized goats alone or in combination with PGF2α was reported to be frequently approach 100% (Romano, et al., 1996; Freitas, et al., 1997; Ahmed, et al., 1998; Zarkawi, et al., 1999; Amarantidis, et al., 2004; Romano, et al., 2004). The oestrus response observed in this study in PGF2α+FGA+eCG, FGA+PGF2α+eCG and FGA+eCG synchronized goats were significantly higher than response observed in PGF2α+FGA+FSH, FGA+PGF2α+FSH and FGA+FSH synchronized groups.
The proportion of ewes in oestrus was similar in FSH and eCG synchronized ewes (90 and 92.5% respectively) at middle of the breeding season (Boscos, et al., 2002). (Boscos, et al., 2002) compared eCG and FSH use in progestagen-gonadotrophin treatment for oestrus synchronization in sheep and found that at the beginning of the breeding season, a single 5 or 10IU FSH treatment at the end of progestagen appeared to be superior in inducing first oestrus and during the mid breeding season, FSH was equally as effective as eCG.
Romano, et al. (2004) suggested that oestrus onset occurred 32.9±9.7 hours in intravaginal FGA pessary synchronized goats given PGF2α at removal. Motlomelo et al. (2003) also reported 30.9±0.40 hours time to oestrus from cessation of treatment in FGA+PMSG synchronized goats during the breeding season. Dogan et al., (2005) suggested mean time to oestrus onset as 18.0±1.9 and 22.9±1.6 in FGA+PMSG+PGF2α and FGA+PMSG synchronized Anatolian black does respectively.
The mean ± SD of oestrus duration was not significantly different between FGA (43.8 ± 13.8) MAP and CIDR synchronized goats (Montlomelo, et al., 2002; Romano, et al., 2004). The mean oestrus onset and duration CIDR synchronized and control goats were suggested to be 30.4±3.6, 32.5±4.5 and 31.5±5.5, 40.6±6.7 (Menchaca, et al., 2007). Other reported mean time to oestrus onset includes 25±1.56, Pierson, et al. (2001), 52.3±14.3, Ahmed, et al. (1998) and 49.7±15.7 (Fonseca, et al., 2005).
The onset and length of oestrus were not significantly different from each other in goats synchronized with FGA+PMSG and FGA alone (Romano, et al., 1996; Amarantidis, et al., 2004; Romano, et al., 2004). (Amarantidis, et al., 2004) however reported that onset and duration of oestrus were higher in PGF2α synchronized or in short term (5 days FGA treatment) FGA+PMSG or FGA alone synchronization methods (59.5 ± 4.2, 36.9 ± 5.9, 39.5 ± 4.3) respectively. They also found no differences in the onset of oestrus whether PMSG was used in the short term FGA treatment or not. The same observations were made for the duration of oestrus i.e. (50.6 ± 4.7, 33.1 ± 4.4, 34.6 ± 7.0) respectively (Amarantidis, et al., 2004). Time to onset of oestrus with FGA was found to be 30.9±0.4 h and the length of induced oestrus periods was 33.33+13.4 hours compared to FGA and MAP sponges (Montlomelo, et al., 2002). There were however no significant differences in the oestrus duration (Montlomelo, et al., 2002).
In agreement with this study, Dogan, et al. (2005) similarly found no significant differences in mean time to onset, and duration of oestrus between FGA+PMSG+PGF2α, FGA+PMSG, MAP+PMSG+PGF2α, MAP+PMSG synchronized groups. The percentage oestrus response, time to onset and duration of the induced oestrus following injection of PGF2α either at the time of sponge insertion or at the time of sponge removal were not significantly different. However, FGA+eCG alone resulted in the same percentage oestrus response, advanced time to onset and shorter duration of the induced oestrus compared with FGA+eCG group additionally injected with PGF2α at sponge removal or insertion. The results agree with the findings of Amarantidis et al. (2004) who suggested that priming with FGA before the administration of PGF2α influenced not only the onset, but also the duration of the induced estrous period. They further suggested that the mean estrous period was short in the FGA/PGF2α treatment (33.9±5.8h) and even shorter in long-term FGA-treatment (30.5±4.5h), when compared to the double PGF2α injection treatment (50.6±4.7h).
The PGF2α+FSH, PGF2α+FGA+FSH, FGA+PGF2α+FSH and FGA+FSH synchronized groups (groups which FSH were co-administered) were observed to have smaller percentage oestrus response, shorter time to onset of oestrus and shorter duration of the induced oestrus compared with groups injected with eCG suggesting that a single injection of FSH is not as effective as a single injection of eCG in oestrous synchronization. This does not agree with (Boscos, et al., 2002) who compared eCG and FSH use in progestagen-gonadotrophin treatment for oestrus synchronization in sheep. Boscos et al. (2002) found that at the beginning of the breeding season, a single 5 or 10IU FSH treatment at the end of progestagen treatment appeared to be superior in inducing first oestrus and during the mid breeding season, FSH was equally as effective as eCG. The differences in the observed responses to eCG and FSH may be due to the long and short half life of 6 Days (eCG) and 3.4 hours (FSH) respectively.
FSH was however shown to be superior to eCG when multiple doses are given for superovulation and embryo recovery in goats (Rosnina et al., 1992). According to Riesenberg et al. (2001), ultrasonic screening of goats shows that not only eCG but also hMG and pFSH given as a single application appears to provide a sufficient stimulus to achieve a satisfactory superovulatory response. Superovulatory response was observed in some goats in this study which might suggest differential sensitivity of the ovaries of goats to eCG
Differences in the dynamics of growth and functionality of preovulatory follicles in response to method of oestrous synchronization in goats have been reported (Fernandez-Moro, et al., 2008). The total numbers of follicles observed in PGF2α+FSH, PGF2α+FGA+FSH, FGA+PGF2α+FSH and FGA+FSH synchronized groups were higher than the number of follicles observed in the PGF2α+FGA+eCG, FGA+PGF2α+eCG and FGA+eCG synchronized groups. The higher follicle number observed in the FSH groups suggests better stimulation of ovarian follicular development compared to eCG. This finding is supported by the reported superiority of FSH over eCG given as multiple application for superovulation and embryo recovery in goats (Rosnina et al., 1992; Riesenberg et al., 2001). According to Riesenberg et al. (2001), ultrasonic screening of goats' shows that both eCG (1250IU) and FSH (17mg) given as a single application appears to provide a sufficient stimulus to achieve a satisfactory superovulatory response. The dose levels used were however larger than those used in this study (300IU) and 4mg respectively but superovulatory response was still observed in 2 goats both synchronized with PGF2α+FGA+eCG in this study which might suggest differential sensitivity of the ovaries of goats to eCG.
Large persistent follicles occur as a result of low systemic progesterone concentrations that were reported to occur towards the end of intravaginal insert frequently resulting in abnormal follicular development or large persistent follicles (Menchaca et al., 2007).
Gonzalez-Bulnes, et al. (2004) suggested that oestrous synchronization with PGF2α result in dominant follicles of mid-luteal phase with higher maximum diameter and longer permanence that could be related to low progesterone levels found in the cloprostenol-treated goats. Low LH pulse resulting from these low progesterone levels were associated in number, size and permanence of the largest follicles (Rubianes, and Menchaca 2003; Gonzalez-Bulnes, et al., 2004).
The maximum follicular diameter observed in this study (6.17±0.75mm) in the control group which were synchronized with a double injection of cloprostenol 11 days apart without gonadotrophin were lower than the maximum diameter of ovulatory follicle in PGF2α synchronized (8.3±0.4mm) and natural (7.2±0.4mm) cycle in Anglo Nubian goats observed by Vazquez, et al. (2010). Simoes et al. (2006) suggested that the maximum diameter of the preovulatory follicle in PGF2α synchronized Serrana goats were (7.1±1.0mm), Gonzalez-Bulnes et al. (2004) suggested 7.8±0.4mm for PGF2α synchronized Murciana-Granadina does. Cueto et al. (2006) suggested the maximum diameter of ovulatory follicles to be 6.1mm in short hair and 6.5mm in PGF2α (double injection, 11 days apart) synchronized long hair Neuquen-Criollo goats which closely agrees with the results of our study.
The largest mean diameters of follicles were observed in PGF2α+eCG (9.08±4.18) and PGF2α+FSH (7.17±1.06) groups respectively compared with FGA synchronized groups. These results were lower than the follicular diameter at ovulation in CIDR+eCG, synchronized Alpine dairy goat and control (CIDR without eCG) groups (10.7±1.7 and 9.9±0.9) respectively (Menchaca, et al., 2007). These differences in oestrus response and follicular development between the peripubertal boer goats observed in this study and previous studies could be as a result of breed, age, body condition or weight influences between the various studies.
Time of ovulation from onset of oestrus in PG/PG/eCG, PG/FGA/eCG, FGA/PG/eCG, FGA/FGA/eCG and control were 44.00±32.8, 36.00±9.80, 21.6±13.14, 24.00±12.00, 11.59±12.37 and 24.00±0.00 respectively. Time to ovulation to oestrus onset in PGF2α synchronized nulliparous Serrana goats were 30.1±1.1 hours (Simoes et al., 2008). Riesenberg et al. (2001) suggested that due to the short half-life of FSH, a strong exogenous stimulus with FSH might only initiate the superovulatory reaction, while the final follicle development is supported by endogenously produced gonadotrophin. This may explain the lack of ovulations observed in the FSH groups though higher numbers of follicles were observed in these goats. Conversely, eCG which has a longer half life resulted in more ovulations. Ovulation rates were shown to be affected by parity Simoes et al. (2008).weight and body condition De Santiago-Miramontes et al. (2009)
Serum cortisol levels assayed in this study were found to be within normal range and not different between the groups studied, suggesting that the goats may not stressed sufficiently to affect the oestrus response or follicular dynamics studied. The use of intravaginal sponges for estrous synchronization of goats was reported to cause an increased level of oxidative stress (Sonmez, et al., 2009).
It was suggested that hyperthermia is deleterious to any form of productivity (Lu, 1989; Silanikove, 2000; Al-Tamimi, 2007., Sejian and Srivastava, 2010). (Sejian and Srivastava, 2010) also reported that plasma cortisol levels in heat stressed goats were significantly higher compared to controls (82.74±2.44 and 18.76±4.33 nmol/L) respectively. Ozawa et al. (2005) suggested that heat stress during follicular recruitment suppresses subsequent growth to ovulation, accompanied by decreased LH receptor level and oestradiol synthesis activity in the follicles. Though the environmental conditions were hot and humid during the period of this study, the goats were kept in well ventilated and shaded pens with unlimited supply of water which ameliorated their stress levels. According to Al-Tamimi, (2007) goats acquire homeothermy following chronic exposure to solar heat via harmonized thermoregulatory mechanisms, e.g. the adjustment of respiratory evaporative cooling and blood redistribution and a subsequent increase in the peripheral blood flow with a modification in feeding and water intake patterns. Al-Tamimi, (2007) further suggested that accessibility of goats to shade during summer is a simple and yet an efficient tool to minimize solar radiation-induced heat stress.