Influence of PMSG antiserum on serum progesterone and estrous cycles of PMSG-treated grlts

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1 Influence of PMSG antiserum on serum progesterone and estrous cycles of PMSG-treated grlts Kirkwood, R. N. and Thacker, P. A Influence of PMSG antiserum on serum progesterone and estrous cycles of PMSG-treated gilts. Can. J. Anim. Sci. 72: Forty-seven prepubertal gilts ( kg) received an injection of 750 IU PMSG to stimulate ovarian activity. After 96 h, 23 gilts received an injection of an anti-pmsg serum. Blood samples were obtained at the time of PMSG injection(day0)and at2,4,6, il, I8,25 and32d. Therewasnoeffectof treatmentonserumestradiol concentrations or on the occurrence ofnormal estrous cycles. However, luteal phase serum progesterone concentrations were higher (P<0.01) in gilts receiving the anti-pmsg. Key words: PMSG, antiserum, gilts, ovulation Kirkwood, R. N. et Thacker, P. A Influence d'un antisdrum du PMSG sur la teneur sdrique en progest6rone et sur le cycle oestrien de cochettes traitdes au PMSG. Can. J. Anim. Sci. 72: Quarante-sept jeunes truies pr6pubbres d'un poids moyen de 88,4 + 0,9 kg ont requ une injection de 730 UI de PMSG pour stimuler I'activit6 ovarienne. Quatre-vingt-seize heures plus tard, 23 des truies recevaient une injection d'un antiserum du PMSG. Des preldvements sanguins ont dte eflectuds au momenl de l'injection de PMSG four 0l er aux jours ll. 18. )5 er 32. L'antis6rum n'a pas eu d'effet sur les concentrations s6riques en estradiol ni sur la frdquence des cycles ovariens normaux. Cependant, les concentrations s6riques en progest6rone dans la phase lut6ale 6taient plus 6lev6es (P<0,01) chez les truies traitdes ir I'antis6rum. The injection of exogenous gonadotrophins into prepubertal gilts is consistently associated with the occurrence of a behavioral estrus and ovulation (Paterson 1982). However, pregnancy rates and subsequent litter size are often compromised if a gilt is inseminated at an induced estrus (Paterson 1982). To obviate potential fertility problems, it is usually recommended that induced silts not be mated until a subsequent, naturally-occurring estrus. However, gilts frequently fail to exhibit normal estrous cycles following a hormonally induced estrus (e.g., Burnett et al. 1988). A possible factor contributing to the reduction in reproductive performance of gonadotrophin-stimulated gilts is an altered steroid profile during the period ofestrus and ovulation. A prolonged period of elevated estradiol has been observed in cattle followins superovulatory doses of pregnant marei serum gonadotrophin (PMSG; R.J. Mapletoft, unpublished data), indicating that follicular Can. J. Anim. Sci. 72: (Mar. 1992) Mots cl6s: PMSG. antis6rum. cochette. ovulation growth continued beyond the induced estrus. Such an altered pattern of follicular growth may be a consequence of the long half-life of PMSG, allowing the recruitment of more follicles both during, and following, the anticipated follicular phase (Kirkwood et al. l99l; G. R. Foxcroft, unpublished data). Such a prolonged elevated estradiol profile may interfere with normal ova and sperm transport, and thus fertilization, since these factors are under steroid control (Hunter 1982). Futhermore, embryo development may also be compromised by inappropriately high estradiol concentrations, since uterine motility and secretory patterns are influenced by steroid hormone concentrations (Knight et al. 1913; Hunter 1982). It has recently been observed that the administration of an anti-pmsg serum, following a PMSG-induced superovulation in beef heifers, returned selum estradiol profiles to the levels observed in control animals (Mapletoft, unpublished data) and decreased the number of unovulated larse tt3

2 r74 CANADIAN JOURNAL OF ANIMAL SCIENCE follicles. The decrease in the number of unovulated follicles was associated with an increase in ovulation rate. These data suggest that, in cattle, the ability to attenuate the trophic activity of PMSG following a normal period of follicular development may improve reproductive performance. Similarly, an improved ovarian response to PMSG has been observed in sheep treated with an anti-pmsg serum (Jabbour and Evans 1991). Therefore, an experiment was undertaken to examine the hypothesis that an injection of an anti-pmsg serum, following a period of gonadotrophinstimulated follicular development, would improve the cyclic estrous behavior of gilts. During December, 47 Yorkshire x Landrace prepubertal gilts were selected at 88.4 * 0.9 kg body weight. During the experiment, gilts were fed ad libitum a wheat-barleysoybean meal diet formulated to provide 13 MJ DE kg-r and 16% crude protein. At selection, all gilts received an intramuscular injection of 750 IU PMSG (Folligon, Intervet Canada, Guelph, ON). A blood sampie was obtained by jugular venipuncture from each gilt at the time of PMSG injection (day 0) and then at 2,4,6,11, 18,25 and 32 d. Blood samples were centrifuged after 6 h and the until required for serum stored at -20"C hormone assay. At 4 d after PMSG injection, 23 gilts received an intravenous injection of an antiserum to PMSG (Neutra-PMSG, Intervet Canada, Guelph, ON). Control gilts did not receive an injection. Blood samples collected 0, 2, 4 and 6 d were assayed for concentrations of estradiol in a single assay using a commercial kit (Intermedico, Markham, ON). Parallelism between inhibition curves with standards and various dilutions of a control semm was demonstrated. Recovery ofestradiol added to control serum and intra-assay coefficient of variation (CV) were 92 and 7.3%, respectively. All samples were assayed for progesterone, to confirm a prepubertal condition prior to PMSG injection and to monitor cyclic ovarian activity, using a commercial kit (Intermedico, Markham, ON) as described previously (Van Lunen et al. 1989). The samples were processed in a single assay with an intra-assay CY of 4.3%. Gilts were slaughtered 33 to 35 days after PMSG injection and their ovaries recovered to determine the incidence of normal estrous cycles and ovulation rate. Ovarian activity was classified as being a normal cycle when progesterone was high (>5 ng ml-') on days 11 and 18, low ((2 ng ml-') at day 25, and high again at day 32.In addition, the ovaries needed to have both corpora albicantia and corpora lutea. A prolonged cycle was considered to have occurred when serum progesterone was high on days 1 I through 25 but low at 32 days. The ovaries of these gilts exhibited corpora albicantia but no corpora lutea. Non-cyclic gilts had high progesterone on days 1 1 and I 8 but low thereafter. Again, only corpora albicantia were evident. Non-responding gilts had uniformly low progesterone and no corpora albicantia or corpora lutea. Treatment effects on serum hormone concentrations were investigated by repeated measure analysis of variance using the Number Cruncher Statistical System (NCSS 1987; N. J. Hintze, Kaysville. Utah). Mean hormone concentrations at specific times and mean numbers of corpora lutea were compared using Students' / test (NCSS 1987). The influence of the anti-pmsg on the incidence of normal estrous cycles was examined by Fisher's exact test (NCSS 1987). Overall, 74% of grlts ovulated in response to PMSG injection. The ovulatory response to PMSG has been shown to vary between herds, but the ovulatory response observed in this study is typical of the gilts in our herd and was not influenced by treatment. In those gilts responding to PMSG, the incidence of normal estrous cycles was high and not affected by anti-pmsg (Table l). Similarly, the incidence of prolonged cycles or a failure to cycle were low and not affected by treatment. A high incidence of normal estrous cycles. following a gonadotrophin-induced ovulation-contrasts with the results of previous workeri (e.g., Paterson and Lindsey 1981)' However, as mentioned earlier, the gilt response to gonadotrophic stimulation is variable and unpredictable.

3 KIRKWOOD AND THACKER ANTI-PMSG AND REPRODUCTION IN GILTS - r't5 Table 1. The effect of anti-pmsg on the ovarian response of gilts to gonadotrophin Number of gilts Normal cycles Prolonged cycles Non-cyclic Non-response Ovulation ratey Serum progesterone (ng ml-l)* Day 0 Day 4 Day ll Day 18 Day 25 Day 32 Control 1/ 1.7 (71)z 6 (2s) t I 4.1a 45.', c "Data in parentheses are percentage. vovulation rate at the second estrus. determined at slaushter. xlncludes only those gilts exhibiting normal estrous cycies. a-d Means followed by different letters differ (a,b P<0.051' c,d P<0.01). Serum concentrations of estradiol were similar in both groups of gilts and there was no evidence of a prolonged production of estradiol. Serum estradiol levels increased from a basal level of pg ml-] to a peak of pg ml-', which occurred at d after PMSG injection. Serum estradiol concentrations approached basal levels by 24 h after their peak. From these data, it is concluded that gonadotrophin stimulation of ovarian activity did not result in prolonged follicular activity. The absence of an altered steroid profile is reflecting the high incidence of normal estrous cyclic activity in our gilts. Although the treatment of gilts with anti- PMSG had no effect on the incidence of norrnal estrous cycles, it did result in a marked increase in serum progesterone concentrations during the luteal phase of those gilts exhibiting normal estrous cycles (Table 1). The cause of this effect is unknown. However, it is reasonable to suggest that the treatment with anti-pmsg either resulted in an increased ovulation rate or improved corpora lutea function (or both). Since the gilts were allowed to cycle, it was not possible to investigate either of these possibilities. The serum progesterone concentrations following the second estrus were not affected by treatment Anti-PMSG LJ ls (6s) 6 (26) lb d at the first estrus (Table 1). Similarly, the ovulation rate at the second estrus was not different between treatments (Table 1). We conclude that the sequential administration of PMSG and anti-pmsg results in an elevation of luteal phase serum progesterone concentrations. However, the etiology of this effect, and its consequences for swine performance, requires further investigation. The expert technical assistance of Ms. B. A. Guedo is gratefully acknowledged. Financial support for this study was provided by the Province of Saskatchewan Agriculture Development Fund. Burnett, P. J., Walker, N. and Kilpatrick, D. J The effect of age and growth traits on puberty and reproductive performance in the gilt. Anim. Prod. 46: Hunter, R. H. F Interrelationships between spermatozoa, the female reproductive tract and the egg investments. Pages in D. J. A. Cole and G. R. Foxcroft, eds. Control of pig reproduction. Butterworths, London, U.K. Jabbour, H. N. and Evans, G Ovarian and endocrine responses of merino ewes following treatment with PMSG and GnRH or PMSG antiserum. Anim. Reorod. Sci. 24: 259 2'70. Kirkwood, R. N., Thacker, P. A. and Chaplin, R. K The influence of exogenous gonadotrophins and cloprostenol on ovulation in gilts. Can. Vet. J. 32:

4 r'16 CANADIAN JOURNAL OF ANIMAL SCIENCE Knight, J. W., Bazer, F. W. and Wallace' H. D Hormonal regulation of porcine uterine protein secretion. J. Anim. Sci.36: Paterson, A. M The controlled induction of puberty. Pages ind.l. A. Cole and G. R. Foxcroft, eds. Control of pig reproduction. Butterworths, London, U.K. Paterson, A. M. and Lindsey, D. R Induction ofpuberty in gilts. 2, The effect ofboars on maintenance of cyclic activity in gilts induced to ovulate with PMSG and HCG. Anim. Prod. 32: Van Lunen, T. A., Kirkwood, R. N. and Thacker, P. A The influence ofallyl trenbolone on the occurrence of normal estrous cycles following a gonadotrophin-induced ovulation in prepubertal gilts. Can. J. Anim. Sci.69: R. N. Kirkwood and P. A. Thacker Department of Animal and Pouhry Science, University of Saskatchewan, Saskatoon, Saskatchewan, Canada S7N 0W0. Received 18 June l99l accepted 7 Nov

5 This article has been cited by: 1. R. N. Kirkwood, N. M. Soede, G. W. Dyck, P. A. Thacker The effect of immunoneutralization of PMSG at a gonadotropin-induced oestrus on the duration of ovulation and reproductive performance of sows. Animal Science 61:02, [Crossref] 2. R. N. Kirkwood, A. J. Peacock, T. A. Van Lunen, P. A. Thacker The effect of immunoneutralization of PMSG near a gonadotropin-induced oestrus on the reproductive performance of gilts. Animal Science 58:03, [Crossref]