Synchronization of oestrus in goats: dose effect of progestagen
J.P.C. Greyling
*, M. van der Nest
Department of Animal Science, University of the Free State, P.O. Box 339, Bloemfontein 9300, South Africa
Abstract
A trial was conducted to test the ef®ciency of different doses of intravaginal progestagen in the synchronization of different goat breeds, in the breeding season. Sixty Multiparous Boer and 60 Indigenous feral does were allocated to three treatment groups. The groups consisted of a control group (natural oestrus) (n20/breed); 60 mg MAP sponge groups inserted for 14 days plus 300 IU PMSG at sponge withdrawal (n20/breed) and halved 60 mg MAP (30 mg) sponges inserted for 14 days plus 300 IU PMSG at withdrawal (n20/breed). The time from sponge withdrawal to oestrus was not signi®cantly different in the treatment groups (whole and halved sponges), irrespective of breed. The duration of the oestrous period was signi®cantly (p<0.01) shorter in the control group (29.314.9 h versus 28.015.7 h for the Indigenous and Boer goats, respectively), compared to the induced period for the 60 mg (31.114.7 and 31.515.9 h) or 30 mg (40.022.0 h versus 34.321.7 h) for
the Boer and Indigenous goats, respectively. No signi®cant difference in pregnancy rate following AI was recorded (mean 74.2%). The mean serum progesterone concentration for the observation period varied between 0.01 and 6.19 ng/ml for Indigenous and 0.01 and 9.05 ng/ml for Boer goat does. No signi®cant correlation was recorded between the does pregnant and serum progesterone levels. Mean serum LH concentration of the 60 mg MAP groups (0.590.22 ng/ml) was signi®cantly (p<0.05) lower than the control (0.840.66 ng/ml) and the halved sponge (1.90.49 ng/ml) groups. Dose of progestagen played no role in the ef®ciency of synchronization, regardless of the breed. The mean pregnancy rate achieved, is acceptable following ®xed-time AI in both breeds and at both doses progestagen.#2000 Elsevier Science B.V. All rights reserved.
Keywords:Goats; Synchronization; Dose progestagen; Pregnancy rate
1. Introduction
Modifying the ovarian cycle of mammals has been based on the hypothesis that maximum fertility poten-tial depends upon a ®nely balanced endocrine relation-ship. Any manipulative measure that is aimed at controlling the time of oestrus and ovulation must maintain this balance if optimal fertility is to be achieved.
Of the many factors leading to a depression in fertility, perhaps the most important is the dose level of synthetic progestagen and method of preparation of the drug used. So for example, the amount of steroid actually released from the sponge and the uniformity of the release over the treatment period is more important than the dose impregnated. Studies show that low dose levels of progestagen result in poor synchrony of the subsequent oestrus (Allison and Robinson, 1970; Robinson, 1976). Allison and Robin-son (1970) found a signi®cant linear increase in incidence of oestrus with an increase in the dose of progestagen. Faure et al. (1983), however, found *Corresponding author. Tel.:27-51-401-2210;
fax:27-51-448-0692.
E-mail address: [email protected] (J.P.C. Greyling)
optimal fertility in sheep with lower doses of proges-tagen by halving the intravaginal sponges (MAP) from 60 mg to30 mg. Detrimental effects on sperm trans-port and survival have been retrans-ported following treat-ment with progestagen impregnated sponges. This impairment of the transport and survival of sperm in the female genital tract is associated with an endo-crine response rather than the physical effect of the sponges (Quinlivan and Robinson, 1967; Hawk, 1971).
There is a disturbed temporal relationship between the onset of oestrus and gonadotrophin release in controlled oestrus and ovulation (Gordon, 1975). Where AI is performed after oestrus synchronization, the time of insemination is determined relative to the completion of treatment. It is thus possible that females fail to become pregnant, because this asyn-chrony between oestrus and ovulation results in an inappropriate time of insemination in relation to ovu-lation (Cumming et al., 1973). This trial was thus performed to test the ef®ciency of different doses of intravaginal progestagen in the synchronization of two goat breeds (Boer and Indigenous or Feral goats), in the natural breeding season.
2. Material and methods
The two breeds (Boer and Indigenous;n60/breed) were randomly divided into three equal treatment groups of 20 does per breed per treatment. Oestrous cycles of all animals were synchronized in different treatment regimes, using intravaginal progestagen sponges impregnated with medroxy acetate progester-one (MAP), (Repromap, Upjohn) as follows: Treat-ment 1 (Control group): 20 Boer does and 20 Indigenous does were synchronized a cycle earlier (for practical reasons) by inserting 60 mg MAP sponges for 14 days, followed by an intramuscular injection of 300 IU PMSG (Fostim, Upjohn, South Africa) at sponge withdrawal. All observations were taken at the subsequent (second) natural oestrous cycle. Treatment 2: twenty Boer does and 20 Indigen-ous does were synchronized using 60 mg MAP sponges inserted intravaginally for 14 days, plus 300 IU PMSG administered intramuscularly at sponge withdrawal. Treatment 3: twenty Boer does and 20 Indigenous does were treated with 30 mg MAP
sponges (halved 60 mg MAP sponges), followed by a 300 IU PMSG intramuscular injection at sponge withdrawal.
Following sponge withdrawal in all treatments, does were tested for oestrus at 8 h intervals using vasectomized bucks. Oestrus was monitored up to the end of the induced oestrous period, or for a total observation period of 120 h following the cessation of treatment. Cervical AI was performed at a ®xed time (48 and 60 h following sponge withdrawal) in the treated groups, and 12 and 24 h after the onset of oestrus in the control groups. Fresh undiluted Boer buck semen (0.05 ml) was used for insemination in both the Boer and Indigenous does. Two months after AI, all animals were diagnosed for pregnancy by laparoscopy.
Concurrent with detection of oestrus after synchro-nization treatment, blood (10 ml) was collected via jugular veni puncture from ®ve animals randomly selected from each treatment group. Serum was recov-ered and stored at ÿ208C until assayed for serum progesterone and LH concentration. Serum progester-one concentrations were determined using the Coat-A-Count solid-phase RIA kit, as validated by Greyling et al. (1994) in goats (sensitivity of 0.01 ng/ml). The inter and intra-assay coef®cients of variation were 8.9 and 15.1%, respectively. Serum LH levels were deter-mined according to the RIA double-antibody techni-que of Miller and Aehnelt (1977) for ovine. Puri®ed ovine LH was radio-iodinated by a modi®cation of the method of Hunter and Greenwood (1962).
All data was analysed in Latin square design by analysis of variance. To determine which groups performed the best, the smallest signi®cant difference was calculated and compared. Thew2-test was used to compare reproductive responses between groups (Sne-decor and Cochran, 1980).
3. Results
two treatments (whole or halved sponges). As ex-pected, the time to oestrus was however, noticeably longer for untreated (control) animals in both Boer and Indigenous does (76.042.4 and 104.050.5 h, respectively), compared to the treated groups (53.2 27.5 and 43.124.7 h for Boer does and 50.726.3 and 44.624.8 h for Indigenous does in the 60 and 30 mg MAP treatments, respectively).
Between breeds there was no signi®cant difference in the duration of the oestrous period. However, within breeds the control groups had a signi®cantly (p<0.01) shorter duration of the natural oestrous period (29.314.9 h versus 28.015.7 h for Indigen-ous and Boer goats, respectively), compared to the induced periods for either the 60 mg (31.1 14.7 h for Boer does and 31.515.0 h for Indigenous does) or the 30 mg (40.022.0 h versus 34.321.7 h for Boer and Indigenous does) MAP sponge treated groups.
The mean pregnancy rate following AI for all animals in this study was 74.2%, with 12 animals not showing any oestrous response, but diagnosed
pregnant two months after AI. There was no signi®-cant difference in the pregnancy rates between breeds or treatments (Table 1).
The mean serum progesterone concentrations dur-ing the observation period varied between 0.01 and 6.19 ng/ml for the Indigenous does and 0.01 and 9.05 ng/ml for the Boer goat does. There was no signi®cant difference between the mean serum pro-gesterone levels for the Boer and Indigenous does (1.210.44 and 1.410.45 ng/ml, respectively) as shown in Fig. 1. Regarding the correlation between the serum progesterone levels and the percentage does diagnosed as pregnant at 2 months after AI, there was no signi®cance (r0.08 for Boer goat andr0.27 for Indigenous goats).
There was also no signi®cant difference between the mean serum LH concentration of the Boer and Indigenous does (2.690.39 and 2.450.47 ng/ml, respectively) as shown in Fig. 2. The mean serum LH concentration of the 60 mg MAP sponge treated (Treatment 2) groups differed signi®cantly (p<0.05) from the control and the 30 mg MAP sponge Table 1
The oestrous response, time to oestrus, duration of the induced oestrous period and pregnancy rates in Boer and Indigenous does following treatment with whole and halved MAP sponges (meanSE)
Indigenous Boer
Control 60 mg Halved 60 mg Control 60 mg Halved 60 mg
N 20 20 20 20 20 20
Oestrous response (%) ± 15 (75) 14 (70) ± 17 (85) 13 (65)
Sponge withdrawal to oestrus (h) 104.050.5 50.726.3 44.624.8 76.042.4 53.227.5 43.124.7 Duration of oestrus (h) 29.3a14.9 31.5b15.0 34.3b21.7 28.0a15.7 31.1b14.7 40.0b22.0 No animals pregnant (%) 15 (75) 13 (65) 13 (70) 16 (80) 16 (80) 16 (80)
a,bDifferent letters in each column differ signi®cantly (p<0.05).
Table 2
The distribution of the oestrous response at different time intervals in Boer and Indigenous does following treatment with whole and halved MAP sponges
Treatment n Time intervals (h)
0±24 25±48 49±72 73±96 97±120
Boer 60 mg MAP 20 0 10 (50%) 3 (15%) 2 (10%) 0
halved or30 mg MAP 20 1 (5%) 11 (55%) 1 (5%) 1 (5%) 0
Total 40 1 (2.5%) 21 (52.5%) 4 (10%) 3 (7.5%) 0
Indigenous 60 mg MAP 20 1 (5%) 8 (40%) 3 (15%) 1 (5%) 0
halved or30 mg MAP 20 0 9 (45%) 7 (35%) 2 (10%) 1 (5%)
treated groups (Treatment 3). The serum LH level for Treatment 2 was lower than that of treatments 1 and 3 (0.590.22 ng/ml versus 0.840.66 and 1.90 0.49 ng/ml, respectively).
4. Discussion
Despite initial reports of high fertility following synchronization using synthetic progestagens such as Fig. 1. Mean serum progesterone concentration (ng/ml) during treatment and during the induced oestrous period for all Boer and Indigenous does after synchronization with MAP sponges (both doses).
medroxy acetate progesterone (MAP), subsequent work has shown conception rates to be lower than in the natural cycle (Minoia and Taranto, 1975). Some of the factors that lead to the depression in fertility include levels and methods of preparation of the drug used (Haresign, 1978). The results in the present study indicate that intravaginal sponges impregnated with MAP (irrespective of dose) were ef®cient oestrous synchronization agents (mean response of 73.5%). It is evident that the dose of progestagen in the sponge played no signi®cant role in the effectiveness of synchronization of oestrus in the does. The minimum dose of progestagen in the half-sponge was suf®cient to effectively synchronize oestrus. This is in accor-dance with Greyling et al. (1994), who found no differences in oestrous response for different doses of progestagens. No studies have however been direc-ted at comparing Boer and Indigenous goats in their oestrous response. No signi®cant differences for all three treatment groups was observed in this study. The dose of progestagen was suf®cient, regardless of the breed.
Researchers have reported the onset of oestrus within 18±96 h following progestagen withdrawal (Alacam et al., 1985; Goswami et al., 1987). In this trial, animals demonstrated oestrus within 24±120 h after treatment and this supports the ®ndings of Ishwar and Pandey (1990), Walker et al. (1989) and Greyling et al. (1997) who reported mean times to oestrus of 93.7, 69 and 30.5 h, respectively. The time from sponge withdrawal to the onset of oestrus was not signi®cantly different between either the breeds or the treatment regimes. Thus, dose of progestagen exerted no effect on the response time. The use of halved MAP sponges tended to induce oestrus sooner, when com-pared to animals treated with whole sponges. The reason for the delayed time to oestrus of the 60 mg MAP sponges can possibly be attributed to more residual progesterone being available to the animal. This is in agreement with Faure et al. (1983) and Greyling et al. (1997). This variation in the time of oestrus and ovulation is likely to affect the ef®ciency of ®xed-time AI. The duration of the oestrous period of the control groups was shorter than that of the treated groups, but are in line with the results of Boshoff (1980) and Fuenmayor et al. (1973).
There are con¯icting reports on the fertility (con-ception rates) when progesterone and/or
gonadotro-phin is administered to synchronize oestrus (Van der Westhuysen, 1979). Baumgartner et al. (1974) re-ported a decline in fertility, possibly due to detrimental effects of synchronization on sperm transport and survival in the female reproductive tract (Pearce and Robinson, 1985). Other studies report improved fertility (Bongso et al., 1982; Beeze and Pappd, 1984). There was no signi®cant difference in the conception rate between breeds or treatments in this study. The overall pregnancy rates observed in this study were acceptable (70 and 80% for the Indigenous and Boer goats, respectively) and in line with those obtained by Faure et al. (1983) and Greyling et al. (1994).
Twelve animals did not show any overt signs of oestrus, but were diagnosed pregnant two months after AI. This would imply a 10% incidence of silent heats occurred in all animals. It can be suggested, that these `silent' heats may be related to inadequate endogenous progesterone (Allison and Robinson, 1970).
The mean serum progesterone concentrations dur-ing the observation period followdur-ing intravaginal sponge treatment remained relatively low for all groups, varying between 0.01 and 9.05 ng/ml with a mean serum progesterone concentration of 0.38 and 0.04 ng/ml at the onset of oestrus for all Boer and Indigenous goats, respectively. This is in agreement with reports by Thorburn and Schneider (1972) and Greyling et al. (1994). Pearce and Robinson (1985) recorded the decline in plasma levels of progesterone following sponge withdrawal to be more rapid than in normal luteolysis. The negative feedback of exogen-ous progestagens could possibly also be more effec-tive than the endogenous progesterone.
Intravaginal sponges, whether being halved or whole, effectively synchronized oestrus in both Boer and Indigenous does. Although the dose of progesta-gen impregnated in the 60 mg MAP sponges could be in excess for the synchronization of goats, no signi®-cant detrimental effects on reproductive performances were observed. It appears that the reduction of the exogenous progestagen used, holds no real advantage in the ef®ciency of synchronization or economic practices. No signi®cant difference in the serum pro-gesterone concentration was recorded. However, the mean serum LH concentration of the 60 mg MAP treated animals tended to be signi®cantly lower than that of the halved MAP and control animals which could be related to a greater relative feedback mechan-ism by the higher progestagen dose. In conclusion, it can be said that intravaginal progestagen sponge synchronization achieved acceptable high conception rates in both breeds and at both doses and is acceptable as a reproductive management tool in both the smaller Indigenous (mean body weight 24.74.8 kg) and larger (mean body weight 54.76.8 kg) Boer goat does. Halved MAP sponges were as ef®cient as whole 60 mg MAP intravaginal sponges in the ef®ciency of synchronization.
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