Ovulation induction protocol using equine chorionic gonadotropin and porcine luteinizing hormone in the weaned sow

Protocolo de inducción de la ovulación utilizando gonadotropina coriónica equina y hormona luteinizante porcina en cerdas destetadas

Protocole d’induction de l’ovulation utilisant la gonadotrophine chorionique équine et l’hormone lutéinisante porcine chez la truie sevrée

Kristina Bennett-Steward, DVM; Glen Cassar, DVM, PhD; Claire Plante, DVM, PhD, Diplomate ACT; Robert M. Friendship, DVM, MSc, Diplomate ABVP; Louisa Zak, PhD

KBS, LZ: Bioniche Animal Health, Belleville, Ontario, Canada. GC, RMF: Department of Population Medicine, Ontario Veterinary College, University of Guelph, Guelph, Ontario, Canada. CP: Genesafe Technologies Ltd, Guelph, Ontario. Dr Bennett-Steward was a consultant to Bioniche Animal Health while this study was being conducted. Dr Zak became a Bioniche Animal Health consultant after the study had been conducted, and contributed to data analysis and manuscript preparation. Corresponding author: Dr Kristina Bennett-Steward, Veterinary Technical Services, Bioniche Animal Health, PO Box 1570, Belleville, ON K8N 5J2; Tel: 800-265-5464; E-mail: Kristina.Bennett-Steward@Bioniche.com.

Cite as: Bennett-Steward K, Cassar G, Plante C, et al. Ovulation induction protocol using equine chorionic gonadotropin and porcine luteinizing hormone in the weaned sow. J Swine Health Prod. 2007;15(4):194–197.
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Keywords: swine, equine chorionic gonadotrophin, porcine luteinizing hormone, ovulation, ultrasound
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Received: May 17, 2006
Accepted: December 8, 2006

Artificial insemination is the predominant method of breeding in the swine industry.¹ Optimal fertilization rates are achieved when insemination occurs within a period of 4 to 24 hours before ovulation. However, timing of ovulation is often difficult to predict accurately when it is based on the first observed behavioural estrus post weaning,² which depends upon the estrus-detection protocol utilized,³ wean-to-estrus interval, and duration of estrus.

The best estimate of the time from onset of estrus to ovulation is based on the knowledge that for most weaned sows, ovulation occurs two-thirds of the way through estrus.⁴

Hormones administered at weaning, eg, equine chorionic gonadotropin (eCG)⁵ or eCG in combination with human chorionic gonadotropin (hCG),⁶ are effective in reducing the wean-to-estrus interval, and more treated sows exhibit estrus behavior than naturally cyclic sows. However, even with eCG or eCG-hCG treatment, the time of ovulation cannot be accurately predicted in relation to the onset of estrus.^7,8

Sequential administration of exogenous hormones, eg, eCG followed by porcine luteinizing hormone (pLH), induce ovulation.^9,10 A commonly used protocol includes administration of 600 IU eCG at weaning, followed up to 80 hours later by 5.0 mg of pLH, which induces ovulation approximately 40 hours later.⁹ Using this protocol, the optimal timing of insemination¹¹ (ie, within 24 hours of ovulation) can be accurately predicted. The objective of this field trial was to determine the lowest efficacious dose of pLH to induce a predictable ovulatory response in weaned sows.

Materials and methods

A dose-titration study was conducted to establish the lowest effective dose of pLH (Lutropin-V; Bioniche Animal Health Canada Inc, Belleville, Ontario, Canada) necessary to predictably induce ovulation in mixed-parity sows. The trial was conducted on a 650-sow farrow-to-grower commercial unit and performed using two replicates of 30 sows each, conducted in August 2004 and January-February 2005. Treatment groups were equally represented in each replicate. The animals were cared for and managed with due regard for their welfare.

The study included 60 mixed-parity sows (parity range 1 to 17) weaned 21 to 28 days after farrowing (average lactation length 26 days). Sows were assigned alternately in order of weaning to five treatment groups (Table 1). All sows received 600 IU eCG (Pregnecol 5000; Bioniche Animal Health Canada Inc) IM in the neck at weaning, followed 80 hours later by an IM injection of either saline (Control) or pLH. The approximate time of ovulation was determined using realtime transrectal ultrasound (RTU) (5mHz linear probe; Falco Vet 100 ultrasound machine, Pie Medical, Maastricht, Holland), performed 8 hours before and 16 hours post pLH injection, then at 8-hour intervals until ovulation was confirmed, ie, less than four follicles > 6.5 mm in diameter remaining on the ovaries.⁷ On this commercial farm, as is usual practice, estrus detection was enhanced by once-a-day boar contact in front of the stalls.

Treatment effect on time to ovulation after pLH administration (pLH-to-ovulation interval) was analysed using the General Linear Model procedure of SAS (SAS Institute Inc, Cary, North Carolina). In the event of a significant treatment effect, differences among treatment means were determined using probability for differences of the least squared means (SAS, PROC PDIFF). Chi-squared analysis (SAS, PROC CATMOD) was used to determine the differences among treatment groups in the number of sows ovulating 24 to 40 hours after pLH or saline injection. Bartlett’s test was used to determine the homogeneity of variance, ie, to measure the dispersion associated with pLH-to-ovulation interval. A 5% significance level was applied for all analyses.

Results

The mean pLH-to-ovulation interval differed among treatment groups (P < .001). Mean pLH-to-ovulation interval was shorter in sows administered the combination of eCG and 1.25, 2.5, or 5.0 mg pLH than in sows treated with eCG and saline only (Table 1). The mean pLH-to-ovulation interval in sows treated with 2.5 mg pLH was shorter than that in sows treated with 1.25 mg pLH (Table 1), but did not differ from that in sows treated with 5.0 mg pLH (Table 1).

There was a significant effect of treatment (P < .01) on the number of sows ovulating within 24 to 40 hours after pLH or saline injection. Fewer control sows (two of 15; 13%; P < .01) and more sows treated with 2.5 mg pLH (17 of 21; 81%; P < .05) or 5.0 mg pLH (four of five; 80%; P < .01) also ovulated in this period (Table 2). The standard deviations for the pLH-to-ovulation interval tended to differ among treatments (Table 1).

Discussion

In this study, the wean-to-ovulation interval was shorter in sows treated with 1.25 mg to 5.0 mg of pLH than in control sows. These observations are in agreement with results of other studies in which the time interval from pLH administration to ovulation was shortened as the dose of pLH was increased up to 2.5 mg pLH,¹² or when weaned sows given eCG at weaning followed 80 hours later by 5.0 mg pLH were compared to sows given only eCG at weaning.¹³

Although we and others^10,12,14-16 found that the pLH-to-ovulation interval was shorter when 1.25, 2.5, or 5.0 mg pLH was administered after eCG given at weaning, the average pLH-to-ovulation interval was still within the physiological time frame observed in weaned sows ovulating after an endogenous LH surge, following a 14-day or 24-day lactation period.¹⁷ This suggests that the ovulation-induction protocol used in this study allows follicles to ovulate within a period that is not dissimilar to that for ovulation after an endogenous LH surge.

Other studies have shown that the timing of ovulation can be made more predictable and that variation in the timing of ovulation can be significantly reduced in sows treated with 2.5 or 5.0 mg of pLH.^10,12,14-16 Although we did not observe a significant increase in the homogeneity of the pLH-to-ovulation interval in this study, we did find that more sows ovulated within 24 to 40 hours after administration of 2.5 or 5.0 mg pLH, compared to sows given 1.25 mg or no pLH, which suggests a more precise timing of ovulation in response to pLH.

Together, these findings show that the time from pLH administration to ovulation is shorter in sows treated with 1.25, 2.5, or 5.0 mg pLH, and more sows given 2.5 or 5.0 mg pLH ovulate within 24 to 40 hours after administration of pLH.

Implications

• 2.5 and 5.0 mg of pLH do not differ in their effect of inducing ovulation in an estrus-synchronization program initiated with 600 IU of eCG at weaning.

• Knowing when the majority of sows will ovulate may enhance reproductive performance and reduce the number of nonproductive sow days by allowing insemination at an optimal time relative to ovulation.

References

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3. Behan JR, Watson PF. The effect of managed boar contact in the post-weaning period on the subsequent fertility and fecundity of sows. Anim Reprod Sci. 2005;88:319–324.

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*9. Candini PH, Zanelli E, Silveira PRS, Moretti AS, Viana CHC, Valentim R. Utilisation of porcine LH on synchronization of ovulation in weaned sows. Proc Braz Cong Swine Vet Pract; 1999.

10. Viana CHC, Candini PH, Gama RD, Carbone SA, Santos ICC, Viana WL, Barnabe RC. Effect of insemination to induced ovulation interval on fertilization rate, embryo viability and number of accessory sperms in sows. Braz J Vet Res Anim Sci. 2006;43:132–138.

11. Nissen AK, Soede NM, Hyttel P, Schmidt M, D’Hoore L. The influence of time of insemination relative to time of ovulation on farrowing frequency and litter size in sows as investigated by ultrasonography. Theriogenology. 1997;47:1571–1582.

*12. Viana CHC, Castricini ESC, Santos ICC. Determination of the minimum porcine LH dose in synchronization of ovulation in sows. Proc ICPR. Amsterdam; 2005.

13. Candini PH, Moretti AS, Silveira PRS, Viana CHC, Santos ICC. Single or double artificial insemination in fixed time in sows with ovulation induced by luteinizing hormone. Braz J Vet Res Anim Sci. 2004;41:124–130.

14. Gama RD, Viana WL, Pinese ME, Rossetto AC, Moretti AS. Different doses of porcine luteinizing hormone in precocious puberty induction in gilts. Reprod Domest Anim. 2005;40:433–435.

15. Cassar G, Kirkwood RN, Poljak Z, Bennett-Steward K, Friendship RM. Effect of single or double insemination on fertility of sows bred at an induced estrus and ovulation. J Swine Health Prod. 2005;13:254–258.

*16. Cassar G, Kirkwood RN, Bennett-Steward K, Friendship RM. Towards fixed time insemination in sows. Proc AASV. Toronto, Ontario, Canada. 2005:353–355.

17. Willis HJ, Zak LJ, Foxcroft GR. Duration of lactation, endocrine and metabolic state, and fertility of primiparous sows. J Anim Sci. 2003;81:2088–2102.

* Non-refereed references.