The parturition-relevant hormone profile in hyper-prolific sows under different housing conditions

Abstract

Objective

Aim was to characterize birth-relevant hormone profiles of reproductively productive hybrid sows in the peripartum period. It was examined whether there are deviations in the hormone profile depending on the birth process (eutocia:dystocia) and the type of housing (box stall BS vs. farrowing pen FP vs. group housing GH).

Materials and methods

A total of 40 healthy, heavily pregnant hybrid sows (German Landrace x Large White) with a gestation number≥ 2 were available. The distribution between the housing types was: BS n=18, FP n=15, GH n=7. All births occurred after the biologically completed gestation period. Blood samples were taken via indwelling catheters (113th day ante partum to 4th day post partum). Progesterone (P4), oestradiol (E2), prostaglandin F2α and its metabolites (PGFM), relaxin, oxytocin, cortisol, adrenaline and noradrenaline were determined.

Results

The ratio of eutocia:dystocia was 15:25. Dystocia occurred regardless of type of housing. The only reason for dystocia was a weak labor (>60 min). The litter size was 17.73± 3.85 piglets. Differences in the hormone profiles between eutocia and dystocia were as follows: P4 tended to be higher in dystocia p=0.0776; oxytocin higher in eutocia (not significant), 12.5% of sows permanently with hypoxytocinemia; cortisol p=0.0503; noradrenaline p=0.0098. The type of housing had the following influence on the hormone profile: P4 p=0.046; E2 p=0.0009; PGFM p=0.0108; relaxin p=0.0022; noradrenaline p=0.0078.

Conclusions and clinical relevance

The parturition-relevant hormones are related to the parturition and to the type of housing during birth. The hormone profiles obtained could be of use in the discussion about the animal welfare-oriented housing system in the peripartum phase in pigs. The proportion of sows of the hyperproliferative line studied with permanent hypoxytocinaemia in stage II of parturition is remarkable. The ratio of eutocia:dystocia is unevenly distributed. Dystocia occurred regardless of the type of housing.

Zusammenfassung

Gegenstand und Ziel

Zweck dieser Untersuchungen war es, geburtsrelevante Hormonprofile von reproduktiv leistungsstarken Hybridsauen in der peripartalen Periode zu charakterisieren. Es wurde überprüft, ob Abweichungen im Hormonprofil in Abhängigkeit vom Geburtsverlauf (Eutokie vs. Dystokie) und von der Haltungsform (Kastenstand KST vs. Bewegungsbucht BWB vs. Gruppenhaltung G) bestehen.

Material und Methoden

Die Untersuchung fand unter Feldbedingungen statt. Zur Verfügung standen 40 gesunde, hochgravide Hybridsauen (Deutsche Landrasse x Large White) mit der Gestationsziffer≥2. Die Verteilung auf die Haltungsformen war: KST n=18, BWB n=15, G n=7. Alle Geburten traten nach biologisch beendeter Gestationszeit ein. Die Blutentnahmen erfolgten über Dauerkatheter (113. Tag ante partum bis 4. Tag post partum). Progesteron (P4), Östradiol (E2), Prostaglandin F2α (PGF_2α) und seine Metaboliten (PGFM), Relaxin, Oxytocin, Cortisol, Adrenalin und Noradrenalin wurden untersucht.

Ergebnisse

Das Verhältnis Eutokie:Dystokie betrug 15:25. Dystokien traten unabhängig von der Haltungsfom auf. Einziger Grund für einen dystokischen Verlauf war eine Wehenschwäche (> 60 min). Die Wurfgröße lag bei 17,73±3,85 Ferkeln. Abweichungen im Hormonprofil bestanden zwischen Eutokie und Dystokie wie folgt: P4 tendenziell höher bei Dystokie p=0,0776; Oxytocin höhere Werte bei Eutokie (nicht signifikant), 12,5% der Sauen dauerhaft mit Hypoxytocinämie; Cortisol p=0,0503; Noradrenalin p=0,0098. Die Haltungsform hatte folgenden Einfluss auf das Hormonprofil: P4 p=0,046; E2 p=0,0009; PGFM p=0,0108; Relaxin p=0,0022; Noradrenalin p=0,0078.

Schlussfolgerungen und klinische Relevanz

Die gemessenen, geburtsrelvanten Hormone weisen teilweise Beziehungen zum Geburtsverlauf, teilweise zu den Haltungsbedingungen unter der Geburt auf. Die erstellten Hormonprofile könnten in der Diskussion um die tierwohlgerechte Haltungsform im peripartalen Abschnitt des Reproduktionszyklus beim Schwein von Nutzen sein. Bemerkenswert ist der Anteil an Sauen der untersuchten hyperproliferativen Linie mit einer dauerhaften Hypoxytocinaemie im Stadium II der Geburt. Das Verhältnis Eutokie:Dystokie ist ungleich verteilt. Die Dystokien traten unabhängig von der Haltungsform auf.

Keywords

Birth - dystocia - farrowing crate - farrowing pen - hormone - parturition - prolific sows

Schlüsselwörter

Geburt - Dystokie - Kastenstand - Bewegungsbucht - Hormon - hyperproliferative Sauen

Deceased

Publikationsverlauf

Eingereicht: 13. November 2024

Angenommen: 07. Januar 2025

Artikel online veröffentlicht:
03. März 2025

• References

• 1 Molokwu EC, Wagner WX. Endocrine physiology of the puerperal sow. J Anim Sci 1973; 36: 1158-1163
• 2 Robertson HA, King GJ. Plasma concentrations of progesterone, oestrone, oestradiol-17beta and of oestrone sulphate in the pig at implantation, during pregnancy and at parturition. J Reprod Fertil 1974; 40: 133-141
• 3 Ash RW, Heap RB. Oestrogen, progesterone and corticosteroid concentrations in peripheral plasma of sows during pregnancy, parturition, lactation and after weaning. J Endocrinol 1975; 64: 141-154
• 4 Ellendorff F, Taverne M, Elsaesser F. et al. Endocrinology of parturition in the pig. Anim Reprod Sci 1979; 2: 323-334
• 5 Gooneratne A, Hartmann PE, McCauley I. et al. Control of parturition in the sow using progesterone and prostaglandin. Aust J Biol Sci 1979; 32: 587-595
• 6 Taverne MA, Naaktgeboren C, Elsaesser F. et al. Myometrial electrical activity and plasma concentrations of progesterone, estrogens and oxytocin during late pregnancy and parturition in the miniature pig. Biol Reprod 1979; 21: 1125-1134
• 7 Kunavongkrit A, Kindahl H, Einarsson S. et al. Clinical and endocrinological studies in primiparous zero-weaned sows. 1. Clinical and morphological findings with special reference to the effect of PGF2 alpha treatment. Zentralbl Veterinarmed A 1983; 30: 607-615
• 8 Kunavongkrit A, Kindahl H, Madej A. Clinical and endocrinological studies in primiparous zero-weaned sows. 2. Hormonal patterns of normal cycling sows after zero-weaning. Zentralbl Veterinarmed A 1983; 30: 616-624
• 9 Willcox DL, Arthur PG, Hartmann PE. et al. Perinatal changes in plasma oestradiol-17 beta, cortisol and progesterone and the initiation of lactation in sows. Aust J Biol Sci 1983; 36: 173-181
• 10 Kertiles LP, Anderson LL. Effect of relaxin on cervical dilatation, parturition and lactation in the pig. Biol Reprod 1979; 21: 57-68
• 11 Dusza L, Krzymowska H. Plasma prolactin levels in sows during pregnancy, parturition and early lactation. J Reprod Fertil 1981; 61: 131-134
• 12 Wathes DC, King GJ, Porter DG. et al. Relationship between pre-partum relaxin concentrations and farrowing intervals in the pig. J Reprod Fertil 1989; 87: 383-390
• 13 Widowski TM, Curtis SE, Dziuk PJ. et al. Behavioral and endocrine responses of sows to prostaglandin F2 alpha and cloprostenol. Biol Reprod 1990; 43: 290-297
• 14 Meunier-Salaün MC, Gort F, Prunier A. et al. Behavioural patterns and progesterone, cortisol and prolactin levels around parturition in European (Large-White) and Chinese (Meishan) sows. Applied Animal Behaviour Science 1991; 31: 43-59
• 15 Castrén H, Algers B, de Passillé A-M. et al. Preparturient variation in progesterone, prolactin, oxytocin and somatostatin in relation to nest building in sows. Appl Anim Behav Sci 1993; 38: 91-102
• 16 Gilbert CL, Goode JA, McGrath TJ. Pulsatile secretion of oxytocin during parturition in the pig: temporal relationship with fetal expulsion. J Physiol 1994; 475: 129-137
• 17 Lawrence AB, Petherick JC, McLean KA. et al. The effect of environment on behaviour, plasma cortisol and prolactin in parturient sows. Appl Anim Behav Sci 1994; 39: 313-330
• 18 Boulton MI, McGrath TJ, Goode JA. et al. Changes in content of mRNA encoding oxytocin in the pig uterus during the oestrous cycle, pregnancy, at parturition and in lactational anoestrus. J Reprod Fertil 1996; 108: 219-227
• 19 Jarvis S, Lawrence AB, McLean KA. et al. The effect of environment on plasma cortisol and beta-endorphin in the parturient pig and the involvement of endogenous opioids. Anim Reprod Sci 1998; 52: 139-151
• 20 Osterlundh I, Holst H, Magnusson U. Hormonal and immunological changes in blood and mammary secretion in the sow at parturition. Theriogenology 1998; 50: 465-477
• 21 Damm B, Bildsøe M, Gilbert C. et al. The effects of confinement on periparturient behaviour and circulating prolactin, prostaglandin F2α and oxytocin in gilts with access to a variety of nest materials. Appl Anim Behav Sci 2002; 76: 135-156
• 22 Devillers N, Farmer C, Mounier A-M. et al. Hormones, IgG and lactose changes around parturition in plasma, and colostrum or saliva of multiparous sows. Reprod Nutr Dev 2004; 44: 381-396
• 23 Malmkvist J, Damgaard BM, Pedersen LJ. et al. Effects of thermal environment on hypothalamic-pituitary-adrenal axis hormones, oxytocin, and behavioral activity in periparturient sows. J Anim Sci 2009; 87: 2796-2805
• 24 Yun J, Björkman S, Pöytäkangas M. et al. The effects of ovarian biopsy and blood sampling methods on salivary cortisol and behaviour in sows. Res Vet Sci 2017; 114: 80-85
• 25 Phillips CE, Farmer C, Anderson JE. et al. Preweaning mortality in group-housed lactating sows: hormonal differences between high risk and low risk sows. J Anim Sci 2014; 92: 2603-2611
• 26 Chang J, Frandsen S, D'Annibale-Tolhurst M. et al. Prostaglandin (PTG) E and F receptors in the porcine corpus luteum; effect of tumor necrosis factor-α. Anim Reprod Sci 2018; 195: 139-148
• 27 Ison SH, Jarvis S, Hall SA. et al. Periparturient Behavior and Physiology: Further Insight Into the Farrowing Process for Primiparous and Multiparous Sows. Front Vet Sci 2018; 5: 122
• 28 Kaiser M, Jacobsen S, Andersen PH. et al. Hormonal and metabolic indicators before and after farrowing in sows affected with postpartum dysgalactia syndrome. BMC Vet Res 2018; 14: 334
• 29 Roelofs S, Godding L, de Haan JR. et al. Effects of parity and litter size on cortisol measures in commercially housed sows and their offspring. Physiol Behav 2019; 201: 83-90
• 30 Quiniou N, Dagorn J, Gaudré D. Variation of piglets’ birth weight and consequences on subsequent performance. Livest Prod Sci 2002; 78: 63-70
• 31 Rutherford KM, Baxter EM, D’Eath RB. et al. The welfare implications of large litter size in the domestic pig I: biological factors. Animal Welfare 2013; 22: 199-218
• 32 Baxter EM, Rutherford KM, D’Eath RB. et al. The welfare implications of large litter size in the domestic pig II: management factors. Animal Welfare 2013; 22: 219-238
• 33 Berchieri-Ronchi CB, Kim SW, Zhao Y. et al. Oxidative stress status of highly prolific sows during gestation and lactation. Animal 2011; 5: 1774-1779
• 34 Muns R, Malmkvist J, Larsen MLV. et al. High environmental temperature around farrowing induced heat stress in crated sows. J Anim Sci 2016; 94: 377-384
• 35 Kemp B, Da Silva CLA, Soede NM. Recent advances in pig reproduction: Focus on impact of genetic selection for female fertility. Reprod Domest Anim 2018; 53: 28-36
• 36 Blim S, Lehn D, Scheu T. et al. Evaluation of the electrolyte status in hyperprolific sows on the farrowing process under different housing conditions. Theriogenology 2022; 193: 37-46
• 37 Dumniem N, Boonprakob R, Parsons TD. et al. Pen Versus Crate: A Comparative Study on the Effects of Different Farrowing Systems on Farrowing Performance, Colostrum Yield and Piglet Preweaning Mortality in Sows under Tropical Conditions. Animals (Basel) 2023; 13
• 38 Liu X, Schwarz T, Murawski M. et al. Measurements of circulating progesterone and estrone sulfate concentrations as a diagnostic and prognostic tool in porcine pregnancy revisited. Domest Anim Endocrinol 2020; 71: 106402
• 39 Forsling ML, Taverne MA, Parvizi N. et al. Plasma oxytocin and steroid concentrations during late pregnancy, parturition and lactation in the miniature pig. J Endocrinol 1979; 82: 61-69
• 40 Guthrie HD, Meckley PE, Young EP. et al. Effect of altrenogest and Lutalyse on parturition control, plasma progesterone, unconjugated estrogen and 13,14-dihydro-15-keto-prostaglandin F2 alpha in sows. J Anim Sci 1987; 65: 203-211
• 41 Csapo A. Progesterone block. Am J Anat 1956; 98: 273-291
• 42 Anderson LL. Reproductive Biology of Pigs. Ames (Iowa): Iowa State University; 2009.
• 43 Damm BI, Lisborg L, Vestergaard KS. et al. Nest-building, behavioural disturbances and heart rate in farrowing sows kept in crates and Schmid pens. Livest Prod Sci 2003; 80: 175-187
• 44 Lawrence AB, Petherick JC, McLean K. et al. Naloxone prevents interruption of parturition and increases plasma oxytocin following environmental disturbance in parturient sows. Physiol Behav 1992; 52: 917-923
• 45 Jarvis S, Lawrence AB, McLean KA. et al. The effect of opioid antagonism and environmental restriction on plasma oxytocin and vasopressin concentrations in parturient gilts. J Endocrinol 2000; 166: 39-44
• 46 Algers B, Uvnäs-Moberg K. Maternal behavior in pigs. Horm Behav 2007; 52: 78-85
• 47 Algers B, Blokhius HJ, Broom DM. et al. Animal health and welfare aspects of different housing and husbandry systems for adult breeding boars, pregnant, farrowing sows and unweaned piglets – Scientific Opinion of the Panel on Animal Health and Welfare. EFSA Journal 2007; 5: 572
• 48 Yun J, Swan K-M, Oliviero C. et al. Effects of prepartum housing environment on abnormal behaviour, the farrowing process, and interactions with circulating oxytocin in sows. Appl Anim Behav Sci 2015; 162: 20-25
• 49 Peltoniemi O, Björkman S, Oliviero C. Parturition effects on reproductive health in the gilt and sow. Reprod Domest Anim 2016; 51: 36-47
• 50 de Rensis F, Saleri R, Tummaruk P. et al. Prostaglandin F2α and control of reproduction in female swine: a review. Theriogenology 2012; 77: 1-11
• 51 Mueller A, Maltaris T, Siemer J. et al. Uterine contractility in response to different prostaglandins: results from extracorporeally perfused non-pregnant swine uteri. Hum Reprod 2006; 21: 2000-2005
• 52 Le Cozler Y, Beaumal V, Neil M. et al. Changes in the concentrations of glucose, non-esterified fatty acids, urea, insulin, cortisol and some mineral elements in the plasma of the primiparous sow before, during and after induced parturition. Reprod Nutr Dev 1999; 39: 161-169
• 53 Schiffner R, Rodríguez-González GL, Rakers F. et al. Effects of Late Gestational Fetal Exposure to Dexamethasone Administration on the Postnatal Hypothalamus-Pituitary-Adrenal Axis Response to Hypoglycemia in Pigs. Int J Mol Sci 2017; 18
• 54 Edwards PD, Boonstra R. Glucocorticoids and CBG during pregnancy in mammals: diversity, pattern, and function. Gen Comp Endocrinol 2018; 259: 122-130
• 55 Hales J, Moustsen VA, Devreese AM. et al. Comparable farrowing progress in confined and loose housed hyper-prolific sows. Livest Sci 2015; 171: 64-72
• 56 Björkman S, Oliviero C, Rajala-Schultz PJ. et al. The effect of litter size, parity and farrowing duration on placenta expulsion and retention in sows. Theriogenology 2017; 92: 36-44
• 57 Björkman S, Oliviero C, Kauffold J. et al. Prolonged parturition and impaired placenta expulsion increase the risk of postpartum metritis and delay uterine involution in sows. Theriogenology 2018; 106: 87-92
• 58 Thorsen CK, Schild S-LA, Rangstrup-Christensen L. et al. The effect of farrowing duration on maternal behavior of hyperprolific sows in organic outdoor production. Livest Sci 2017; 204: 92-97
• 59 Langendijk P, Plush K. Parturition and Its Relationship with Stillbirths and Asphyxiated Piglets. Animals (Basel) 2019; 9
• 60 Peltoniemi O, Oliviero C, Yun J. et al. Management practices to optimize the parturition process in the hyperprolific sow. J Anim Sci 2020; 98: S96-S106
• 61 Vongsariyavanich S, Sundaraketu P, Sakulsirajit R. et al. Effect of carbetocin administration during the mid-period of parturition on farrowing duration, newborn piglet characteristics, colostrum yield and milk yield in hyperprolific sows. Theriogenology 2021; 172: 150-159
• 62 Adi YK, Boonprakob R, Kirkwood RN. et al. Factors Associated with Farrowing Duration in Hyperprolific Sows in a Free Farrowing System under Tropical Conditions. Animals (Basel) 2022; 12
• 63 Oliviero C, Heinonen M, Valros A. et al. Environmental and sow-related factors affecting the duration of farrowing. Anim Reprod Sci 2010; 119: 85-91
• 64 Zhang X, Li C, Hao Y. et al. Effects of Different Farrowing Environments on the Behavior of Sows and Piglets. Animals (Basel) 2020; 10
• 65 Ward SA, Kirkwood RN, Plush KJ. Are Larger Litters a Concern for Piglet Survival or an Effectively Manageable Trait?. Animals (Basel) 2020; 10
• 66 Schild S-LA, Foldager L, Rangstrup-Christensen L. et al. Characteristics of Piglets Born by Two Highly Prolific Sow Hybrids. Front Vet Sci 2020; 7: 355
• 67 van de Wiel DF, Eikelenboom G. Verbessertes Verfahren zur Dauer-Katheterisierung von Schwinen. Dtsch Tierarztl Wochenschr 1977; 84: 12-16
• 68 Hultsch KH, Ellendorff F. Ein neues Verfahren zur Blutentnahme beim Schwein. (Kurzmitteilung). Dtsch Tierarztl Wochenschr 1979; 89: 313-314
• 69 Brüssow K-P, Bergfeld J, Parchow G. Über mehrjährige Erfahrungen zur Blutgewinnung durch intravenöse Dauerkatheter beim Schwein. Monatshefte für Veterinärmedizin 1981; 36: 300-303
• 70 Niiyama M, Yonemichi H, Harada E. et al. A simple catheterization from the ear vein into the jugular vein for sequential blood sampling from unrestrained pigs. Jpn J Vet Res 1985; 33: 1-9
• 71 Dixon WJ, Brown MB. BMDP statistical software. 1985th ed. Berkeley: University of California Press; 1985
• 72 Egli PT, Schüpbach-Regula G, Nathues H. et al. Influence of the farrowing process and different sow and piglet traits on uterine involution in a free farrowing system. Theriogenology 2022; 182: 1-8
• 73 Trachsel C, Küker S, Nathues H. et al. Influence of different sow traits on the expulsion and characteristics of the placenta in a free farrowing system. Theriogenology 2021; 161: 74-82
• 74 Will KJ, Magoga J, Conti ERde. et al. Relationship between dexamethasone treatment around parturition of primiparous sows and farrowing performance and newborn piglet traits. Theriogenology 2023; 198: 256-263
• 75 Olsson A-C, Botermans J, Englund J-E. Piglet mortality – A parallel comparison between loose-housed and temporarily confined farrowing sows in the same herd. Acta Agriculturae Scandinavica, Section A — Animal Science 2018; 68: 52-62
• 76 Bill R, Carmo LP, Vidondo B. et al. Effect of intramuscular and intravaginal PGE-2 treatment compared to intramuscular oxytocin treatment in eutocic sows on the farrowing performance in a free farrowing system. Theriogenology 2021; 161: 1-7
• 77 Feyera T, Pedersen TF, Krogh U. et al. Impact of sow energy status during farrowing on farrowing kinetics, frequency of stillborn piglets, and farrowing assistance. J Anim Sci 2018; 96: 2320-2331
• 78 Yun J, Han T, Björkman S. et al. Factors affecting piglet mortality during the first 24 h after the onset of parturition in large litters: effects of farrowing housing on behaviour of postpartum sows. Animal 2019; 13: 1045-1053
• 79 Walls A, Hatze B, Lomax S. et al. Defining "Normal" in Pig Parturition. Animals (Basel) 2022; 12
• 80 First NL, Bosc MJ. Proposed mechanisms controlling parturition and the induction of parturition in swine. J Anim Sci 1979; 48: 1407-1421
• 81 Fèvre J. Corticostéroïdes maternels et foetaux chez la Truie en fin de gestation. C R Acad Hebd Seances Acad Sci D 1975; 281: 2009-2012
• 82 Randall GC. Changes in the concentrations of corticosteroids in the blood of fetal pigs and their dams during late gestation and labor. Biol Reprod 1983; 29: 1077-1084
• 83 Young IR. The comparative physiology of parturition in mammals. Front Horm Res 2001; 27: 10-30
• 84 Bazer FW, Johnson GA. Pig blastocyst-uterine interactions. Differentiation 2014; 87: 52-65
• 85 Christiaens I, Zaragoza DB, Guilbert L. et al. Inflammatory processes in preterm and term parturition. J Reprod Immunol 2008; 79: 50-57
• 86 Jarvis S, Lawrence AB, McLean KA. et al. The effect of environment on behavioural activity, ACTH, (β-endorphin and cortisol in pre-farrowing gilts. Animal Science 1997; 65: 465-472
• 87 Foisnet A, Farmer C, David C. et al. Relationships between colostrum production by primiparous sows and sow physiology around parturition. J Anim Sci 2010; 88: 1672-1683
• 88 Nara BS, First NL. Effect of indomethacin and prostaglandin F2 alpha on parturition in swine. J Anim Sci 1981; 52: 1360-1370
• 89 Gilbert CL, Burne THJ, Goode JA. et al. Indomethacin blocks pre-partum nest building behaviour in the pig (Sus scrofa): effects on plasma prostaglandin F metabolite, oxytocin, cortisol and progesterone. J Endocrinol 2002; 172: 507-517
• 90 Oliviero C, Heinonen M, Valros A. et al. Effect of the environment on the physiology of the sow during late pregnancy, farrowing and early lactation. Anim Reprod Sci 2008; 105: 365-377
• 91 Cho S-J, Dlamini BJ, Klindt J. et al. Antiporcine relaxin (antipRLX540) treatment decreases relaxin plasma concentration and disrupts delivery in late pregnant pigs. Anim Reprod Sci 1998; 52: 303-316
• 92 Taverne M, Willemse AH, Dieleman SJ. et al. Plasma prolactin, progesterone and oestradiol-17β concentrations around parturition in the pig. Anim Reprod Sci 1979; 1: 257-263
• 93 Blim SM. Über das Geburtsgeschehen bei Schweinen einer hochproliferativen Linie unter verschiedenen Haltungsbedingungen: Quantifizierung der partusrelevanten Belastung anhand klinischer, stoffwechselbezogener und ethologischer Parameter. Universitätsbibliothek Gießen 2020;
• 94 Husslein P. Hrsg Klinik der Frauenheilkunde und Geburtshilfe. Physiologie und Pathologie der Geburt.
• 95 Ka H, Seo H, Choi Y. et al. Endometrial response to conceptus-derived estrogen and interleukin-1β at the time of implantation in pigs. J Anim Sci Biotechnol 2018; 9: 44
• 96 Lange IG, Hartel A, Meyer HHD. Evolution of oestrogen functions in vertebrates. J Steroid Biochem Mol Biol 2002; 83: 219-226
• 97 Vallet JL, Miles JR, Brown-Brandl TM. et al. Proportion of the litter farrowed, litter size, and progesterone and estradiol effects on piglet birth intervals and stillbirths. Anim Reprod Sci 2010; 119: 68-75
• 98 Sherwood OD. Relaxin's physiological roles and other diverse actions. Endocr Rev 2004; 25: 205-234
• 99 Eldridge-White R, Easter RA, Heaton DM. et al. Hormonal control of the cervix in pregnant gilts. I. Changes in the physical properties of the cervix correlate temporally with elevated serum levels of estrogen and relaxin. Endocrinology 1989; 125: 2996-3003
• 100 Sherwood OD, Nara BS, Welk FA. et al. Relaxin levels in the maternal plasma of pigs before, during, and after parturition and before, during, and after suckling. Biol Reprod 1981; 25: 65-71
• 101 Sherwood OD, Chang CC, Bevier GW. et al. Radioimmunoassay of plasma relaxin levels throughout pregnancy and at parturition in the pig. Endocrinology 1975; 97: 834-837
• 102 Lawrence A, Petherick J, McLean K. et al. The effects of chronic environmental stress on parturition and on oxytocin and vasopressin secretion in the pig. Anim Reprod Sci 1995; 38: 251-264
• 103 Dalin AM, Magnusson U, Häggendal J. et al. The effect of thiopentone-sodium anesthesia and surgery, relocation, grouping, and hydrocortisone treatment on the blood levels of cortisol, corticosteroid-binding globulin, and catecholamines in pigs. J Anim Sci 1993; 71: 1902-1909
• 104 Segal S, Csavoy AN, Datta S. The tocolytic effect of catecholamines in the gravid rat uterus. Anesth Analg 1998; 87: 864-869
• 105 Gladbach C. Untersuchungen über den Einfluss der Gen-Umwelt-Interaktion auf klinische, endokrinologische und metabolische Parameter im Verlauf der Geburt bei einer Schweinerobustrasse (Angler Sattelschwein) und einer modernen reproduktiv leistungsstarken Schweinerass (Deutsche Landrasse) [Dissertation]. VVB LAUFERSWEILER Verlag, Justus-Liebig-Universität Gießen; 2022
• 106 106 Wang C, Han Q, Liu R. et al. Equipping Farrowing Pens with Straw Improves Maternal Behavior and Physiology of Min-Pig Hybrid Sows. Animals (Basel) 2020; 10