| dc.description.abstracteng | Summary
Estrous cycle control is a widely used reproductive biotechnology for controlled breeding of small ruminants. Besides serving the purpose of synchronizing estrus, so that breeding takes place at a particular time, it serves as basis for associated biotechnologies such as fixed-time artificial insemination, superovulation and embryo transfer.
The first of three studies addresses a comparison of various estrous cycle control protocols and the effect of season in the northern temperate zone on the superovulatory response in Boer goats. Forty-eight pluriparous Boer goat does from our own breeding flock were used in this study. Four groups of 12 does each were treated in February, May, August and November, respectively. Estrus was synchronized by means of progestagen impregnated vaginal pessaries. Half of the does of each group received sponges impregnated with 20 mg fluorogestone acetate (FGA, Cronolone), while the other half received Eazy-Breed CIDRs containing 0.3 mg progesterone. Intravaginal pessaries remained in place for 7 days. Within each subgroup half the does were treated with PGF2α (“Dinoprost”) at pessary insertion, the other half at pessary withdrawal. Beginning 48 h before withdrawal, does were superovulated with six s.c. injection of 4, 4, 2, 2, 2 and 2 Armour Units (AU) of pFSH, supplemented with 40% pLH administered at 12 h intervals. Estrus detection was conducted at 8 h intervalas with the aid of an aproned adult buck and ovarian activity was monitored daily by ultrasonography. Does were mated and 7 days later non-surgical embryo collection was conducted. The type of intravaginal pessary had no effect on the time passing between pessary withdrawal and onset of estrus (sponge: 40.7 h vs. CIDR: 35.2 h), number of ovulations/doe assessed by echographic counting of collapsed large follicles (7.2 vs. 7.6) or corpora lutea (7.1 vs. 9.8), embryo recovery rate (39 % vs. 41 %) and proportion of transferable embryos (66 % vs. 65 %). The effect of PGF2α administration at insertion or at removal of intravaginal pessaries and the effect of season were not significant, except for a shorter interval between pessary removal and onset of estrus in August in comparison to the other months (29.3 vs. 39.4, 40.6 and 42.1 h; P < 0.05). From these results it can be concluded that a short (7 day) treatment with either Cronolone sponges or CIDRs as a part of a superovulation protocol is equally effective in synchronizing estrus. The luteolytic PGF2α treatment may be administered at the beginning or at the end of the progestogen treatment; the latter having the advantage that any corpora lutea present will be receptive. Thus, superovulation and embryo collection may be performed throughout the year, i.e, during and out of the breeding season.
In the second study seasonality in Boer goats in Northern Europe and attempts to overcome it is addressed in three experiments. In the first experiment, estrus activity and serum progesterone concentrations were monitored on sexually matured nulliparous Boer goat crosses. Results indicated that ovarian activity ceased in February/March and was resumed from August onward. In 63.7% of 22 does the first estrus of the season was preceded by one or two ovulations, indicated by an increase in progesterone; in 22.7% first estrus and first ovulation coincided and in the remaining 13.6% the first estrus was not succeeded by formation of a functional corpus luteum. In the second experiment, 31 pluriparous Boer does that weaned between July and September, were randomly allocated to three treatment groups. Does were treated with intravaginal sponges impregnated with 20 mg of the synthetic progestagen fluorogestone acetate (FGA, Intervet, France), either one (Group 1; n=11), seven (Group 2; n=10) or fourteen days after weaning (Group 3; n=10). Sponges were withdrawn after 7 days and simultaneously 250 IU equine chorionic gonadotropin (eCG, Intergonan, Intervet, Unterschleissheim, Germany) was administered i.m. Does were tested for estrus with the aid of an aproned adult buck at 8 h intervals, and on each day of standing estrus they were naturally mated. Pregnancy was diagnosed by transrectal ultrasonography (ALOKA-SSD 500, equipped with transrectal 7.5 MHz linear array transducer) 30 and 45 days after mating. The proportion of does exhibiting estrus was 91%, 100% and 90% for Groups 1, 2 and 3, respectively. The overall average interval from sponge withdrawal to onset of estrus was 33.0 h, ranging from 16 to 72 h, with no significant difference among treatment groups (P>0.05). The overall proportion of pregnant does at 45days after mating was 42%. All of these carried to term (36% treated immediately after weaning, 40% treated one week later and 50% treated two weeks later) and gave birth to, on average, 2.1 kids. In the third experiment, 18 nulliparous does were subjected to the same sponge-eCG protocol described in the second experiment out-of-season between April and mid-June. Does were tested for estrus with the aid of an aproned adult buck at 8 h intervals, and on each day of standing estrus they were naturally mated. Pregnancy was diagnosed 35 days after mating. Serum was analyzed for progesterone content by ELISA. Of 18 does treated, 15 (83%) exhibited estrous symptoms. The mean interval from sponge withdrawal to onset of estrus was of 44.3 (range 16 to 66 ) hours. One doe showed estrus but would not permit intromission. Of the 14 goats mated, only 6 (43%) were diagnosed pregnant and none carried to term. Serum progesterone concentration at insertion and withdrawal of sponges was less than 0.5 ng/ml. Thereafter, progesterone concentration increased to 5.0 ng/ml and 5.4 ng/ml one week after sponge withdrawal in pregnant and non-pregnant does, respectively (P>0.05). Maximum progesterone levels were reached two weeks after sponge withdrawal in both pregnant and non-pregnant does (14.0 and 9.3 respectively; P>0.05). A significant difference in progesterone concentration between pregnant and non-pregnant does was recorded three weeks after sponge withdrawal (13.0 vs. 4.8; P<0.05). From the fourth week after sponge withdrawal onward, in non-pregnant goats mean progesterone levels had declined to basal level (less than 0.5 ng/ml); whilst in pregnant goats only a slight, non-significant decline to 8.0 (SE 2.0) ng/ml was recorded by four weeks and 7.4 (SE 2.0) ng/ml by five weeks after sponge withdrawal. From the present study it may be concluded that in northern Europe Boer goats, albeit to a lesser degree than most dairy breeds, undergo a period of ovarian inactivity, extending approximately from April to August. The stage of ovarian quiescence may be overcome by progestogen-eCG treatment. When mated at induced estrus, close to 50% of weaned does produced, on average, 2.1 kids, whereas none of the young nulliparous does carried to term. To what extent unfavorable environmental factors may have played a role is open to conjunction.
The purpose of the third study was to determine temporal relationships between estrus, preovulatory LH surge and ovulation in Boer goat does subjected to different regimes for controlling estrus and ovulation. The study was conducted during the breeding season (late August to December) on 28 pluriparous does. Does were randomly allocated to three treatment groups. In Group 1 (n=8), blood samples were drawn daily from day 5 to day 12 of the estrous cycle to be analyzed for progesterone content. As soon as serum progesterone exceeded 5 ng/ml, two injections of dinoprost were administered at 12 h interval. Does were tested for estrus with the aid of an aproned adult buck at 8 h intervals. Ovarian activity was monitored ultrasonographically 24, 72 and 96 hours after the first dinoprost injection. After the first dinoprost injection, blood samples were drawn every 3 hours until 30 hours after the onset of behavioural estrus. Does of Group 2 (n=10) were provided with intravaginal sponges impregnated with 20 mg of the synthetic progestagen flurogestone acetate for a period of 11 days. Forty-eight hours before withdrawal, does received two i.m. injection of 5 mg dinoprost at 7 hour interval. Concurrent with the first dinoprost injection, 200 IU of eCG was administered i.m. Does were tested for estrus with the aid of an aproned adult buck at 8 h intervals. Ovarian activity was monitored 24 and 48 hours after sponge withdrawal. Does of Group 3 (n=10) were subjected to the same treatment as does of Group 2, with the only difference that, 30 h after sponge withdrawal, they received an i.m. injection of 0.004 mg of the GnRH-analog buserelin. In Group 3 ovarian activity in the latter group was not monitored. Blood plasma collected from does in the three treatment groups was analyzed for luteinizing hormome (LH) content by ELISA. Ovulation was assumed to have taken place halfway between the ultrasound measurements before and after collapse of large follicles (Suyadi and Holtz, 2012). All does presented an estrous response irrespective of the treatments applied. Estrus lasted 37.5, 40.8 and 44.8 hours in Groups 1, 2 and 3, respectively (P>0.05). The interval to onset of estrus was significantly longer in Group 1 in comparison to in Groups 2 and 3 (40.3 vs. 23.4 and 26.4; P<0.05). In Group 1, the interval from the first dinoprost injection to the LH peak was significantly longer than the interval observed from sponge withdrawal in Groups 2 and 3 (44.7 vs. 34.5 and 32.0 h; P<0.05). The interval from the onset of estrus to the LH peak was 7.2, 12.8 and 5.6 h for Groups 1, 2 and 3, respectively, being only significantly different between Groups 2 and 3 (P<0.05). Does in Group 3 presented a tightly synchronized LH peak 32.0 h after sponge withdrawal, and 2 h after the administration of buserelin. In Groups 1 and 2, this peak was less synchronous, ranging from 24 to 57 h in Group 1 (after the first dinoprost injection) and 27 to 45 h in Group 2 (after sponge withdrawal). The magnitude of the LH peak was significantly lower in Group 1 as compared to Groups 2 and 3 (46.5, range 19.0-70.0 ng/ml vs. 59.6, range 32.0-96.0 ng/ml and 82.3, range 50-94.0 ng/ml; P<0.05). Based on the echographic monitoring, ovulation occurred 47.9 and 37.5 h after the occurrence of the recorded LH peak in Groups 1 and 2 (P>0.05). From the results obtained in the present study, iy may be concluded that a prostaglandin regime designed to synchronize estrus during the breeding season is equally effective as a progestagen regime. Incorporating GnRH into the sponge-eCG treatment will induce a highly synchronized preovultory LH peak. This can be particularly useful when practicing fixed-time artificial insemination. | de |