Elsevier

Theriogenology

Volume 96, 1 July 2017, Pages 111-117
Theriogenology

Seasonal infertility in gilts and sows: Aetiology, clinical implications and treatments

https://doi.org/10.1016/j.theriogenology.2017.04.004Get rights and content

Abstract

In gilts and sows, the summer-autumn period often is characterized by reduced fertility. Heat stress and long photoperiods during the warm season can cause a reduction in feed intake and an imbalance of the hypothalamic-hypophysial-ovarian axis. The increased variability in the interval between oestrus onset and ovulation results in an increased number of poorly timed inseminations. The altered endocrine activity compromises follicular and corpora luteal development, reduces oocyte quality and increases embryo mortality. This paper reviews current knowledge on the metabolic and endocrine mechanisms associated with seasonal infertility in gilts and sows and describes some pharmacological approaches that can be utilized to counter this infertility.

Introduction

In swine, summer and early autumn are the periods when reproductive variables consistently show their lowest values. This period is often referred to as summer infertility or, more appropriately, as seasonal infertility since effects can be apparent outside of the summer months [1], [2], [3], [4]. Manifestations of seasonal infertility include delayed puberty [3], [5], [6], prolonged or irregular weaning to oestrus intervals [4], [7], [8], [9], reduced farrowing rates [2], [4], [10], [11], [12], [13], anoestrus and reduced litter sizes [1], [14].

Seasonal infertility can be attributed to various factors but is primarily associated with seasonally high environmental temperatures negatively impacting lactation nutrient intakes [1], [2], [15], [16]. However, an influence of photoperiod on seasonal infertility is suggested by a 5 year study in France showing consistent seasonal infertility apparently independent of annual environmental temperatures [17]. These latter authors documented that in each year 25% of French herds had pregnancy rate reductions of at least 7.1% during the seasonal infertility period even when environmental temperatures were not particularly high. Similarly, Peltoniemi et al. [3] describe seasonal infertility in Finland where barn temperatures did not exceed 25 °C, suggesting photoperiod was more important than environmental temperatures. Reduced feed intakes may also interact with photoperiod as feed restriction resulted in higher circulating melatonin in pigs under a long photoperiod (ie. summer) but not under a short photoperiod [2]. Generally, seasonal infertility is expressed more often in gilts and primiparous sows than in older sows [18], [19], likely because these younger animals have innately smaller appetites and are still growing to their mature size.

Various management protocols can be implemented to counteract seasonal infertility including the control of temperature, humidity and, if possible, photoperiod. However, where these approaches are not feasible or not sufficiently effective, the utilization of exogenous hormones can be considered to stimulate follicular development, oestrus, ovulation, and to help to maintain pregnancy. The aim of this review is to discuss factors mediating seasonal infertility and to present some hormonal protocols to combat the infertility in female swine.

Section snippets

Endocrinology of seasonal infertility

The underlying cause of seasonal infertility of sows is unclear but is likely multifactorial and involves effects on ovarian follicular and/or corpora luteal function, presumably driven by alterations in gonadotrophic stimulation, resulting in some sows being more sensitive to changes in their environment. The trigger(s) for seasonal infertility in these sensitive sows is variously suggested to be low lactation nutrient intake consequent to elevated temperatures and the longer photoperiods of

Puberty onset

Temperature and photoperiod during warm seasons are two environmental factors that can potentially delay puberty onset [2], [16], [36], [37]. However, while there is clear evidence that elevated temperatures influence age at puberty, the effect of photoperiod is contentious. There are reports showing a benefit from an increased photoperiod on age at puberty [37], [38], [39] but these effects have not been observed in other studies [6], [40] and in a tropical country such as Thailand, delayed

Hormonal treatment to counteract seasonal infertility

As described above, several factors are involved in the mechanism causing seasonal infertility in swine; heat stress and/or photoperiod are involved but the effects of photoperiod are often masked by the presence of heat stress. Heat stress can influence the secretion of hormones including cortisol [67], [68] and prolactin [69], [70], and can reduce feed intakes with problems for the energy balance of the animal. One consequence could be that during the summer season the activity of the

Conclusion

Fig. 1 summarizes the main effects of heat stress and photoperiod on hormonal and metabolic mechanism that may impact sow fertility during the hot summer season with some hormonal treatments that can be utilized to counteract these effects. During summer, heat stress and photoperiod can alter the development of follicles and the quality of corpora lutea, oocytes and embryos, with deleterious effects on pregnancy rate and total piglets born. Seasonal infertility in swine includes delayed

References (109)

  • R. Iida et al.

    Interactions between climatic and production factors on returns of female pigs to service during summer in Japanese commercial breeding herds

    Theriogenology

    (2013)
  • P. Tummaruk

    Effects of season, outdoor climate and photo period on age at first observed estrus in Landrace × Yorkshire crossbred gilts in Thailand

    Livest Sci

    (2012)
  • F. De Rensis et al.

    Control of oestrus and ovulation: fertility to timed insemination of gilts and sows

    Theriogenology

    (2016)
  • B.A. Belstra et al.

    Factors affecting temporal relationships between estrus and ovulation in commercial sow farms

    Anim Reprod Sci

    (2004)
  • A.J. Vargas et al.

    Reproductive performance of swine females re-serviced after return to estrus or abortion

    Anim Reprod Sci

    (2009)
  • E. Poleze et al.

    Consequences of variation in weaning-to-estrus interval in reproductive performance of swine females

    Livest Sci

    (2006)
  • W. Tantasuparuk et al.

    Reproductive performance of purebred landrace and Yorkshire sows in Thailand with special reference to seasonal influence and parity number

    Theriogenology

    (2000)
  • P.J. Hansen et al.

    Adverse impact of heat stress on embryo production: causes and strategies for mitigation

    Theriogenology

    (2001)
  • R. Mauget

    Seasonality of reproduction in the wild boar

  • T.M. Brown-Brandl et al.

    Thermoregulatory profile of a newer genetic line of pigs

    Livest Prod Sci

    (2001)
  • S. Tao et al.

    Heat stress effects during late gestation on dry cows and their calves

    J Dairy Sci

    (2013)
  • J. Seyfang et al.

    Human chorionic gonadotrophin in early gestation induces growth of estrogenic ovarian follicles and improves primiparous sow fertility during summer

    Anim Reprod Sci

    (2016)
  • J.E. Tilton et al.

    Ovarian steroid secretion changes after hCG stimulation in early pregnant pigs

    Theriogenology

    (1989)
  • A.J. Ziecik et al.

    Aberrant effects of altrenogest and exposure to exogenous gonadotropins on follicular cysts appearance in gilts

    Theriogenology

    (2017)
  • F. Martinat-Botte et al.

    Synchronization of oestrus in gilts with altrenogest: effects on ovulation rate and foetal survival

    Anim Reprod Sci

    (1995)
  • F. Koutsotheodoros et al.

    The effects of post-weaning progestagen treatment (Regumate) of early-weaned primiparous sows on subsequent reproductive performance

    Anim Reprod Sci

    (1998)
  • F. Martinat-Botté et al.

    Induction and synchronization of ovulations of nulliparous and multiparous sows with an injection of gonadotropin-releasing hormone agonist (Receptal)

    Theriogenology

    (2010)
  • H. Andersson et al.

    Influence of artificial light regimens on sexual maturation and boar taint in entire male pigs

    Anim Reprod Sci

    (1998)
  • A. Tast et al.

    The photophase light intensity does not affect the scotophase melatonin response in the domestic pig

    Anim Reprod Sci

    (2001)
  • R. Claus et al.

    Influence of light and photoperiodicity on pig prolificacy

    J Reprod Fertil Suppl

    (1985)
  • R.J. Love et al.

    Seasonal effects on fertility in gilts and sows

    J Reprod Fertil Suppl

    (1993)
  • O.A. Peltoniemi et al.

    Seasonal effects on reproduction in the domestic sow in Finland–a herd record study

    Acta Vet Scand

    (1999)
  • B. Flowers et al.

    Effect of elevated ambient temperatures on puberty in gilts

    J Anim Sci

    (1989)
  • J.P. Hurtgen et al.

    Seasonal influence on the fertility of sows and gilts

    JAVMA

    (1980)
  • E. Benjaminsen et al.

    Post weaning oestrus and luteal function in primiparous and pluriparous sows

    Res Vet Sci

    (1981)
  • M. Sterning et al.

    A study on primiparous sows of the ability to show standing oestrus and to ovulate after weaning. Influences of loss of body weight and backfat during lactation and of litter size, litter weight gain and season

    Acta Vet Scand

    (1990)
  • R.L. Edwards et al.

    Reproductive performance of gilts following heat stress prior to breeding and in early gestation

    J Anim Sci

    (1968)
  • I.T. Omtvedt et al.

    Influence of heat stress during early, mid and late pregnancy of gilts

    J Anim Sci

    (1971)
  • J.L. Xue et al.

    Multiple manifestations of season on reproductive performance of commercial swine

    JAVMA

    (1994)
  • K. Wegner et al.

    Effects of temperature and temperature-humidity index on the reproductive performance of sows during summer months under a temperate climate

    Anim Sci J

    (2016)
  • R.J. Love

    Seasonal infertility in pigs

    Vet Rec

    (1981)
  • O.A. Peltoniemi et al.

    Seasonality of reproduction in gilts and sows

    Soc Reprod Fertil Suppl

    (2006)
  • S. Bloemhof et al.

    Effect of daily environmental temperature on farrowing rate and total born in dam line sows

    J Anim Sci

    (2013)
  • A. Prunier et al.

    Effect of light under various ambient temperatures on sow and litter performance

    J Anim Sci

    (1994)
  • R.N. Kirkwood et al.

    The influence of feeding level during lactation on the occurrence and endocrinology of the post weaning estrus

    Can J Anim Sci

    (1987)
  • R.N. Kirkwood et al.

    The influence of feeding level during lactation and gestation on the endocrine status and reproductive performance of second parity sows

    Can J Anim Sci

    (1990)
  • S.K. Baidoo et al.

    Effect of feed intake during lactation and after weaning on sow reproductive performance

    J Anim Sci

    (1992)
  • F.X. Aherne et al.

    Nutrition and sow prolificacy

    J Reprod Fertil Suppl

    (1985)
  • R.N. Kirkwood et al.

    Post weaning plasma levels of LH, prolactin, oestradiol 17β and progesterone in sows following lactations of 10 or 35 days

    J Reprod Fertil

    (1984)
  • H. Clarke et al.

    Comprehensive review on kisspeptin and its role in reproductive disorders

    Endocrinol Metab

    (2015)
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