Ovulation and LH secretion in the goat after intravaginal progestagen sponge\p=n-\PMSGtreatment A. J. Ritar, W. M. C. Maxwell and S. Salamon Department of Animal Husbandry, University of Sydney, New South Wales 2006, Australia

Summary. The time and rate of ovulation, and preovulatory release of LH were examined in Angora goats after treatment with progestagen-impregnated intravaginal sponges with or without PMSG during the anoestrous and breeding seasons. The administration of PMSG was necessary to stimulate a satisfactory ovulatory response in lactating and non-lactating females, and in the anoestrous and breeding seasons. Increasing doses of PMSG increased the ovulation rate in non-lactating goats and advanced the time of ovulation in lactating and non-lactating females. The advancement of time of ovulation and of the preovulatory LH surge was most pronounced when PMSG was administered 48 h before rather than at sponge removal.

Introduction

Knowledge of the time, rate and synchrony of ovulation during the induced oestrus is important to ensure that mating or artificial insemination is conducted at a time which will result in maximum fertility. There are studies on these characteristics in relation to induced oestrus in sheep (Cognié, Mariana & Thimonier, 1970; Smith, 1977; Evans & Robinson, 1980a), but no information is available for goats. We have therefore examined the time and rate of ovulation, and the preovulatory release of luteinizing hormone (LH) in female goats after progestagen sponge-PMSG treatment during the anoestrous and breeding seasons. A preliminary report has been presented elsewhere (Ritar, Salamon & Maxwell, 1981).

Materials and Methods

Mature feral and crossbred Angora goats were treated with intravaginal sponges containing 45 mg flugestone acetate (Chronogest: Intervet (Australia), Pty Ltd, Sydney) for 16-18 days. PMSG (Gravamed, Beresford Laboratories, Melbourne) was administered as a single intramuscular injection 48 h before ( —48 h) or at (0 h) sponge removal. The animals were grazed on good quality pastures before and during the period of sponge insertion, and were allocated randomly to PMSG treatment groups. After sponge removal, the ovaries of each animal were examined 4 times by laparoscopy for recent ovulation(s) and corpora lutea. The ovulation rate was determined at the final examination 85 h after sponge removal.

Experiment 1. This experiment (2x3 factorial, = 9, = 54) was conducted in the anoestrous season (December) using non-lactating and lactating feral goats. Animals received no PMSG or were injected with 400 or 800 i.u. PMSG at sponge removal. Progeny from the non-lactating

* Present address: CSIRO Division of Animal Production, Private Mail Bag, Wembley, Western Australia 6014, Australia. t Present address: Animal Breeding and Research Institute, Katanning, Western Australia 6317, Australia. Downloaded from Bioscientifica.com at 09/26/2021 12:30:10PM via free access females had been weaned 12 weeks before laparoscopy and the lactating females had given birth 12 weeks before laparoscopy. Experiment 2. Non-lactating goats were used in the anoestrous season (December; crossbred Angora) and in the breeding season (April; feral). Animals received either no PMSG (control group) or were injected with 200, 400 or 600 i.u. PMSG at 0 or —48 h. In the anoestrous season, blood was collected from 3 control animals and 6 animals in each PMSG treatment group at hourly intervals from 31 to 43 h after sponge removal. In the breeding season, blood was collected from 5 control animals and 10 animals in each PMSG treatment group at 2-h intervals for 12 h starting at 21 and 31 h after sponge removal for females receiving PMSG at 48 h and 0 h respectively. Blood — was collected from the jugular vein into heparinized vacutainers, centrifuged and the plasma stored at 20°C until assay. All samples from each animal were examined in a single assay. — LH estimation. LH concentrations in plasma samples were determined in duplicate by a solid- phase single-antibody radioimmunoassay (Evans & Robinson, 1980b). Ovine LH was used as the reference standard (NIH-LH-S22; National Hormone and Pituitary Programme, NIH, Baltimore, MA, U.S.A.) and as the iodinated tracer (NIH-LER-1374A). The rabbit antiserum (UWA-3B) to ovine LH showed cross-reactivity with NIH-FSH-S12 (0-9%), NIH-GSH-S8 (4-6%), NIH-P-S12 (0-2%), NIH-TSH-S8 (9-4%) and NIH-GH-S11 (1-3%). Three pooled samples containing 0-69 + 0-03,2-16 ± 0T5and 12-35 ± 0-30 ng/ml were included in each of the 14 assays: the coefficients of variation within assays were 9-1%, 6-8% and 14-2% and between assays were 16-7, 9-6 and 9-1% respectively. The assay sensitivity (twice the s.d. of the error in the zero standard) was 0-3 ng LH/ml. Preliminary studies revealed that there was no significant non-parallelism of the inhibition curves of serial dilutions of plasma samples from several goats with the ovine LH curve. The preovulatory LH surge was assumed to have occurred when the LH concentrations rose above and returned below 5 ng/ml (Evans & Robinson, 1980b). Analysis of data. Data for the rate of ovulation were examined by analysis of variance. Treatment effects on the number of females that had ovulated at laparoscopy were analysed by 2 tests. Overall contingency tables are not presented because some cells did not contain sufficient animals for the distribution to be regarded as 2. Females receiving no PMSG (control) were not included in the statistical analyses. Due to the lack of sufficient data in Exp. 2, the relationships between the LH responses and the dose of PMSG and time of injection could not be examined statistically. However, the differences between means for the time of peak of LH surge, the LH peak level and the rate of ovulation for the animals involved were examined by t test.

Results Experiment 1 Of the animals that were not treated with PMSG (control), only one lactating female ovulated (Table 1). The lactational status of animals within PMSG treatment did not influence the number of females with ovulation(s) at different times of laparoscopy. However, more animals responded to 800 than 400 i.u. PMSG by 56 h ( < 0-10), 61 h ( < 0-05) and 66 h ( < 010) after sponge removal. The number of females which had ovulated up to the final examination (85 h) was similar for the two doses of PMSG. The analysis of variance showed that there was an interaction between the lactational status of animals and dose of PMSG on ovulation rate (P < 0-05).

Experiment 2 The data on ovulatory response are presented in Table 2. When sponge withdrawal was not accompanied by PMSG treatment ovulation occurred in only 3 animals in the anoestrous season

Downloaded from Bioscientifica.com at 09/26/2021 12:30:10PM via free access Table 1. Ovulatory response of non-lactating ( = 9) and lactating ( = 9) females after progestagen sponge-PMSG treatment in the anoestrous season No. of females with ovulation(s) Dose of Lactational after sponge removal at: Ovulation rate PMSG status of at 85 h (i.u.) females 56 h 61 h 66 h 85 h (mean + s.e.m.) 0 (control) Non-lactating 0 0 0 0 Lactating 1 1 I 1 400 Non-lactating 1 2 5 8 2-33 + 0-44 Lactating 3 4 6 9 400 + 0-50 Total and mean 4(22) 6(33) 11 (61) 17 (94) 3-17 + 0-38 800 Non-lactating 4 7 9 3-11+0-73 Lactating 5 6 2-33 + 0-41 Total and mean 9 (50) 13 (72) 16 (89) 17 (94) 2-72 + 0-42

Values in parentheses are percentages of PMSG-treated females that ovulated.

Table 2. Ovulatory response of non-lactating females after progestagen sponge-PMSG treatment in the anoestrous and breeding seasons when PMSG was injected at sponge removal (0 h, = 10) or 48 h before sponge removal ( —48 h, = 10) No. of females with ovulation(s) after Time of Dose of sponge removal at: Ovulation PMSG PMSG rate at 85 h Season injection (i-u.) 46 h 51 h 56 h 61 h 66 h 85 h (mean + s.e.m.) Anoestrous 0 (control) 1 2 3 3 0-4 + 0-22 (December) 200 3 4 6 9 1-5 + 0-22 0 h 400 2 6 7 9 1-8 + 0-25 600 6 9 9 10 2-5 + 0-27 Total and mean 11(37) 19 (63) 22 (73) 28 (93) 1-9 + 0-16

200 7 9 9 10 2-0 ± 0-21 -48 h 400 6 8 9 10 2-2 + 0-33 600 8 10 10 10 3-4 + 0-65 Total and mean 21 (70) 27 (90) 28 (93) 30 (100) 2-5 + 0-27 Breeding 0 (control) 0 1 01 (April) 200 3 9 2-1+0-43 0 h 400 5 9 2-1+0-43 600 7 9 3-3 + 0-67 Total and mean (17) 15 (50) 23 (77) 27 (90) 2-5 + 0-31

200 2 4 6 1-1+0-35 -48 h 400 5 6 8 2-5 + 0-52 600 3 6 8 8 2-6 + 0-70 Total and mean 10 (33) 16 (53) 22 (73) 22 (73) 2-1+0-33

Values in parentheses are percentages of PMSG-treated females that ovulated. and 1 animal in the breeding season. A higher proportion of PMSG-treated animals had ovulated at 56 h ( < 0-01), 61 h ( < 0-05) and 66 h ( < 0-05) after sponge removal when PMSG was injected at —48 h than at 0 h. The number of animals that had ovulated by 85 h after sponge removal was indistinguishable for both time of PMSG injection and for the dose of PMSG (Table 2). In the light of the data on the time of ovulation obtained in the anoestrous season, the animals treated with PMSG at 48 h in the breeding season were examined at earlier times in relation to —

Downloaded from Bioscientifica.com at 09/26/2021 12:30:10PM via free access sponge removal than the animals treated with PMSG at 0 h. Of females injected at 0 h, 50% had ovulated by 61 h whereas of females injected at —48 h 53% had ovulated by 51 h. The dose and the time of administration (0 or —48 h) of PMSG did not influence the number of females that had ovulated by 85 h. There was a linear relationship between the dose of PMSG and the rate of ovulation ( < 0-01 in anoestrus and < 0-05 in breeding season). The ovulation rate was higher after injection of PMSG at —48 h than at 0 h in the anoestrous (P < 0-05) but not in the breeding season. There was no interaction between the dose of PMSG and the time of injection on the rate ofovulation in either season. The dose of PMSG had no effect on the time of peak of LH surge and LH peak level. Hence data for doses of PMSG within time of PMSG injection were pooled and are presented in Table 3. LH surges were detected for 10 and 17 females treated with PMSG in the anoestrous and breeding season respectively and all of these animals subsequently ovulated by 85 h. One animal in the control group (breeding season) exhibited an LH surge and ovulated. Females that did not ovulate or had 'late' ovulations (between 66 and 85 h) did not exhibit LH surges during the blood sampling period.

Table 3. Time of LH surge, peak LH value and ovulation rate after progestagen sponge-PMSG treatment

Time of peak of Time of No. of LH surge after LH peak PMSG females with sponge removal cone. Ovulation Season injection LH surges (h) (ng/ml) rate

Anoestrous Oh 4 37-25 + 0-85 4200 + 8-20 2-00 + 0-41 (December) -48 h 6 34-00 + 1-15 60-11 + 7-32 2-33 + 0-21 Breeding Oh 10 38-50 + 0-90 54-29 + 5-58 3-70 + 0-63 (April) -48 h 7 27-71+0-78** 48-59 + 4-78 2-29 + 0-29

Values are mean + s.e.m. ** < 0001 compared with 0 h value.

The LH peak levels were not significantly different for times of PMSG injection within time of year. The mean peak of the LH surge occurred 3-25 h ( < 0T0)and 10-79h(P < 0-001) earlier for females injected at —48 h than at 0 h in the anoestrous and breeding seasons respectively.

Discussion

The injection of PMSG in conjunction with progestagen-sponge treatment has been shown to eliminate partly the variability in the ovulatory response and ensure that the majority of female goats ovulate whether they are treated in the breeding season (Dhindsa, Hoversland & Metcalfe, 1971 ; Pretorius & Van der Westhuysen, 1971) or in the anoestrous season (Van der Westhuysen, 1979). In the present experiments, very few animals responded to progestagen sponge treatment without supplementation of PMSG in the anoestrous or the breeding season. The ovulatory activity was equally well stimulated in non-lactating and lactating females after PMSG injection. Increasing the dose of PMSG injected at sponge removal advanced the time of ovulation, but this effect was small compared to the much earlier ovulation following PMSG injection at —48 h than at 0 h. In the latter case, some 73% of females had ovulated by 56 h after sponge removal. LH surges were not detected in females that did not ovulate, whereas all females that had LH surges subsequently ovulated. Of the 8 females which did not receive PMSG and were

Downloaded from Bioscientifica.com at 09/26/2021 12:30:10PM via free access blood sampled, only 1 had an LH surge and only this animal subsequently ovulated. LH peaks appeared to precede ovulation by about 18-28 h which is an interval similar to that found in the ewe in which it is regarded as relatively constant (Cumming et al, 1973; Quirke, Hanrahan & Gosling, 1981). Bindon, Blanc, Pelletier, Terqui & Thimonier (1979) reported that in the ewe the interval between treatment with luteolytic prostaglandin and the LH peak was significantly correlated with the ovulation rate. In the present study the time of peak of LH surge in relation to time of PMSG injection appeared to have no effect on the ovulation rate. Further, LH peak levels ranging from < 30 to > 80 ng/ml plasma were recorded (data not shown) but were unrelated to the time or rate of ovulation. When PMSG was injected at —48 h the peak of the LH surge occurred later in the anoestrous than in the breeding season, but this was most probably due to the different blood sampling schedule (31-43 h compared to 21-33 h, respectively, after sponge removal). Regarding the time of insemination, it appears that for females receiving PMSG at 48 h — artificial insemination should be carried out earlier than for females treated at 0 h. However, for animals treated with PMSG at 0 or 48 h in the breeding season there is no difference in fertility — after insemination at 48 or 55 h (Ritar & Salamon, 1983) and 40 or 48 h (A. J. Ritar & S. Salamon, unpublished) after sponge removal. It therefore appears that the time of PMSG injection does not critically influence the relationship between the time of ovulation, time of insemination and subsequent fertility. Further, administration of a dose of PMSG above 400 i.u. was not warranted in terms of the time and rate of ovulation.

We thank Mr J. Mclntyre, Murray Flats, Goulburn, NSW., and Mr. S. Holt, Riverina Artificial Breeders, Albury, NSW., for generous provision of experimental animals and facilities; Professor D. R. Lindsay, University of Western Australia, Perth, for the LH antiserum; and Intervet (Australia) Pty Ltd, Sydney, NSW., for the Chronogest sponges. A.J.R. was the recipient of a University of Sydney Post-graduate Research Studentship.

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