Equine chorionic gonadotrophin and porcine luteinizing hormone to shorten and synchronize the wean-to-breed interval among parity-one and parity-two sows

Utilisation de la gonadotrophine chorionique équine et de l’hormone lutéinisante porcine pour raccourcir et synchroniser l’intervalle sevrage-saillie chez les truies de première et deuxième parité

Utilización de gonadotropina coriónica equina y hormona luteinizante porcina para acortar y sincronizar el intervalo de destete a servicio entre hembras de paridad uno y paridad dos

Kristina Bennett-Steward, DVM; Jeff Aramini, DVM, MSc, PhD; Christine Pelland; Robert Friendship, DVM, MSc, Diplomate ABVP

KBS: Bioniche Animal Health, PO Box 1570, Belleville, Ontario, Canada. JA,CP, RF: Department of Population Medicine, Ontario Veterinary College, University of Guelph, Guelph, Ontario, Canada. Corresponding author: Dr Kristina Bennett-Steward, 35 Sunrise Drive, Belleville, ON, Canada K8N 4Z7; Tel: 613-962-8232; E-mail: kbennettsteward@aol.com. Dr Bennett-Steward was employed by Bioniche Animal Health at the time when the study was conducted.

Cite as: Bennet-Steward K, Aramini J, Pelland C, et al. Equine chorionic gonadotrophin and porcine luteinizing hormone to shorten and synchronize the wean-to-breed interval among parity-one and parity-two sows. J Swine Health Prod. 2008;16(4):182–187.
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Keywords: swine, equine chorionic gonadotropin, porcine luteinizing hormone, ovulation synchronization, wean-to-breed interval
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Received: February 19, 2007
Accepted: February 5, 2008

The overall productivity of a commercial swine farm is affected by the wean-to-breed-interval (WBI).¹ If the WBI is variable or longer than average, it may be a barrier to achieving consistent breeding targets, especially for producers employing batch farrowing or all-in, all-out management systems. Variation in the WBI also affects the weaning age of pigs.

Various pharmacological intervention strategies exist to induce ovarian development and estrus behaviour in weaned sows,^2,3 including altrenogest early in the post-weaning period of the primiparous sow,⁴ and equine chorionic gonadotropin (eCG) plus human chorionic gonadotropin (hCG) in primiparous and multiparous sows.^5,6 Although estrus behavior may be effectively synchronized, the timing of ovulation is not more predictable in sows treated with eCG plus hCG than in untreated sows, because the time of ovulation relative to the onset of estrus is still dependent upon the wean-to-estrus interval.⁵ This observation may limit the use of altrenogest and eCG plus hCG in timed-breeding programs, in which sows are bred at their optimal time of insemination, 24 to 4 hours before ovulation.⁶ The timing of ovulation can be predicted when porcine luteinizing hormone (pLH) is incorporated into an ovulation induction protocol.⁷ Among sows treated with eCG at weaning and with or without pLH 80 hours later, 90% to 100% ovulated within 36 to 38 hours after pLH treatment, while only 20% to 40% ovulated during that time when treated with eCG alone.⁷

The objectives of this study were to determine the efficacy of an estrus and ovulation synchronization protocol on WBI, farrowing rates, and litter sizes in parity-one and parity-two sows.

Materials and methods

This study involved eleven farms from across Canada (Alberta, Manitoba, Ontario, and Quebec) that were selected by eight veterinarians who considered the selected farms to have good production results, knowledgeable staff, excellent record-keeping practices, and animal care practices that gave due regard to the welfare of the animals.

Parity-one and parity-two sows were assigned to two groups (control and treatment) on the basis of the results of a coin toss at the time of weaning. Treated sows were given 600 IU eCG (Pregnecol 5000; Bioniche Animal Health, Belleville, Ontario, Canada) by IM injection at weaning, followed by 5 mg pLH (Lutropin-V; Bioniche Animal Health) IM at the first observed sign of estrus. Farm staff administered all doses of gonadotrophins. Sows assigned to the control group remained untreated. On all farms, estrus detection was facilitated by twice-daily boar exposure for 20 minutes, beginning 24 hours after weaning. Treated sows were inseminated twice at fixed times after pLH administration, first at 12 hours and then at 32 hours. Control sows were inseminated at 12 then 32 hours after the onset of standing estrus. All sows were artificially inseminated with insemination doses formulated to contain a minimum of 3 × 10⁹ sperm per dose.

Data recorded for sows included farm, parity, treatment group, previous lactation length, weaning date, date of breeding, actual farrowing date, and subsequent litter size (total and born alive). Any sow that had a recorded lactation length of ≤ 10 days or ≥ 30 days was not included in the analysis.

Descriptive analyses were performed and the effects of treatment and parity (controlling for farm and previous lactation length) on the WBI and litter size (total and born alive) were analyzed using linear mixed effect models (PROC MIXED, SAS 9.1.3; SAS Institute, Inc, Cary, North Carolina). To improve normality of the WBI response, a log10 transformation was used. Furthermore, for the WBI and litter-size outcomes, sows not bred by 21 days were excluded from analyses, as inclusion of these data might skew the results, and these sows were not in the main population of interest. The effects of treatment and parity (controlling for farm and previous lactation length) on farrowing rate and on the proportions of sows bred by 5, 7, and 10 days after weaning were assessed using logistic regression (GLIMMIX macro, SAS 9.1.3; SAS Institute, Inc). Adjusted farrowing rate was defined as number of sows farrowed divided by number of sows bred by 21 days, excluding sows that were culled for any reason. For all analyses, treatment, parity, and previous lactation length were modeled as fixed effects, and farm was considered a random effect. The interaction between treatment effect and parity was considered throughout. A P value of < .05 was considered statistically significant. Model assumptions were assessed by examining residuals for normality and homogeneity.

Results

In total, 2372 sows were involved in the study: 1172 control sows and 1200 treated sows (49% parity one and 51% parity two). Parity values were missing for nine sows (five treated and four controls), which were excluded from calculations that were based on parity. Of the 2302 sows bred, 2219 (96.4%) were bred by 21 days. The distributions of WBI for parity-one and parity-two sows are presented in Figure 1. The effect of treatment on the WBI, controlling for previous lactation length and random farm effects, are described in Table 1. Wean-to-breed interval was shorter for treated sows than for controls. Because of a significant treatment-parity interaction effect (P < .05), results are presented separately for each parity. Although the difference in the least squares (LS) means for WBI (ie, controlling for farm and previous lactation length) was more pronounced for parity-one sows (0.84 days) than for parity-two sows (0.36 days), the effects were significant for both parity groups (Table 1). Furthermore, as demonstrated in Figure 1 and confirmed by examining the variances of the model residuals, treatment was associated with less variation in WBI. Among parity-one sows, the log-transformed WBI variance estimate among treated sows (0.014) was approximately 50% of that of control sows (0.030). The effect of treatment on the WBI was also assessed by examining the proportions of sows bred by 5, 7, and 10 days (while controlling for lactation and farm effects). Results are provided in Table 2. Treatment was associated with significantly more parity-one sows bred by 5 days (difference approximately 20%), 7 days (difference approximately 10%), and 10 days (difference approximately 7%). Treatment was also associated with significantly more parity-two sows bred by 5 days (5%).

Adjusted farrowing rates and litter sizes (total and live births) for all treatment-parity groups were consistently high (Table 3). Although adjusted farrowing rates and litter sizes were significantly associated with parity, after controlling for previous lactation length and random farm effects, treatment had no significant effect on these production parameters.

Discussion

The production parameter with the greatest influence on the number of pigs weaned per female per year and per lifetime is the number of nonproductive sow days, defined as the number of days when a breeding female is neither gestating nor lactating.⁸ The most common factors contributing to nonproductive sow days are reproductive failure⁹ and the length of time from weaning to rebreeding¹⁰ in sows of all parities, but especially in those of lower parities.¹¹ This study demonstrated that in good production farms, an estrus synchronization protocol employing eCG, followed by ovulation induction with pLH, can reduce both WBI and variability of the WBI, without impacting farrowing rates and litter size, with the treatment effect most pronounced among parity-one sows.

The average WBI was approximately 1 day shorter in treated than in control parity-one sows, and approximately 0.3 day shorter in treated than in control parity-two sows. In addition, the overall breeding period was shorter in treated sows, especially among parity-one sows. Larger proportions of treated sows were bred by 5, 7, and 10 days, and the variability in the WBI was lower among treated sows. It is reported that the administration of eCG decreases the wean-to-estrus interval;^12,13 however, not all sows respond equally. As demonstrated in our study, parity-one sows were more likely than parity-two sows to respond to exogenous eCG.

Stimulation of behavioral estrus after weaning and having more sows bred by 7 days has been achieved by others through use of eCG and hCG.² However the endogenous hormone profiles associated with treating weaned sows with eCG plus hCG¹³ or eCG alone¹⁴ are similar to those observed naturally, in that the duration of estrus behavior is inversely proportional to the wean-to-estrus interval.¹⁵ This observation has been confirmed by ultrasound examination of the ovaries,³ and suggests that even when exogenous gonadotrophins are used, insemination protocols still need to consider the wean-to-estrus interval to ensure that spermatozoa are deposited within the female tract 24 to 4 hours before ovulation.⁴

The additional step of using exogenous pLH in this study’s protocol was an attempt to induce ovulation 36 to 38 hours after pLH administration, independent of the wean-to-estrus interval or duration of estrus.^5-7,16 Knowing when ovulation will occur minimizes unnecessary inseminations and associated labor costs.¹⁷ Furthermore, ovulation synchronization allows for development of an insemination program to optimize the time of insemination relative to the time of pLH injection. Maximal oocyte fertilization rates can be achieved⁴ and the number of inseminations per sow can be tailored to one⁵ or two⁶ without compromising farrowing rates or litter sizes. In this study, farrowing rates and litter sizes were not affected by the ovulation-synchronization and timed-insemination program. These data suggest that a combination of eCG and pLH may be helpful in minimizing the labor devoted to rebreeding weaned sows.

A major advantage of this protocol is that both estrus and ovulation are synchronized. Labor can be directed to optimal times of estrus detection based around the time of pLH administration, and semen usage can be standardized to two (or perhaps one) inseminations per sow, without having any detrimental effect on production parameters. Results of this study suggest that this treatment protocol can improve breeding synchronization (especially among first-parity sows), and the majority of sows can be bred by day 5 after weaning.

Implications

• Under the conditions of this study, administration of exogenous eCG and pLH with subsequent timed double insemination shortens the WBI in weaned parity-one and parity-two sows.

• Use of this estrus- and ovulation-synchronization protocol could allow for more predictable crate utilization and narrow the range in gestational age of sows in the farrowing room.

Acknowledgement

The authors would like to thank the following swine practitioners for their contribution to this project: Dr Robert Bilodeau, St Lambert de Lauzon, Quebec; Dr Francois Cardinal, Consultants Avi-Pork, Drummondville, Quebec; Drs Brad Chappell and Greg Meunch, Sheridan, Hueser, and Provis, Winnipeg, Manitoba; Dr John Hancock, Picton Animal Hospital, Picton, Ontario; Dr Brent Jones, MacDougald and Jones, Stratford, Ontario; Dr Frank Marshall, Marshall Swine Health Services, Camrose, Alberta

References

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13. Lucia T Jr, Correa MN, Deschamps JC, Peruzzo IA, Matheus JEM, Aleixo JAG. Influence of equine gonadotropin on weaning to estrus interval and estrus duration in early weaned primiparous female swine. J Anim Sci. 1999;77:3163–3167.

14. Johnson RK, Neilson MK, Casey DS. Response in ovulation rate, embryonal survival and litter traits in swine to 14 generations of selection to increase litter size. J Anim Sci. 1999;77:541–557.

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*16. Viana CHC, Candini PH, Gama RD, Carbone SA, Santos ICC, Viana WL, Barnabe RC. Evaluation of a synchronization of ovulation protocol in cyclic sows. Proc 17th IPVS. Ames, Iowa. 2002;678.

17. Ruiz-Flores A, Johnson RK. Direct and correlated responses to two-stage selection for ovulation rate and number of fully formed pigs at birth in swine. J Anim Sci. 2001;79:2286–2297.

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