Conference Lecture: Influence of stress on estrus, gametes and early embryo development in the sow S. Einarsson a, * , Y. Brandt a , H. Rodriguez-Martinez a , A. Madej b a Department of Clinical Sciences, Division of Reproduction, Faculty of Veterinary Medicine and Animal Science, Swedish University of Agricultural Sciences, P.O. Box 7054, SE-75007 Uppsala, Sweden b Department of Anatomy, Physiology and Biochemistry, Faculty of Veterinary Medicine and Animal Science, Swedish University of Agricultural Sciences, Uppsala, Sweden Abstract Systems with loose-housed sows have become common. Regrouping, which is commonly done after weaning and may coincide with many important reproductive events, causes stressful situations with elevated blood cortisol concentrations. Depending on group size, approximately 2–7 d are required for a new group of sows to become relatively stable. In a series of studies, the social stress after regrouping was simulated with repeated adrenocorticotrophic hormone (ACTH) treatments for approximately 48 h. Sows were allocated into control and experimental groups, fitted with jugular catheters, and blood samples were collected every 2 or 4 h. Follicular development and ovulation were monitored by transrectal ultrasonography every 4 h. Simulated stress during pro- estrus prolonged estrus and disturbed the follicular growth and ovulation. Giving ACTH during estrus elevated concentrations of cortisol and progesterone, and changed the intraluminal environment, including exaggerated amounts of mucus in the UTJ and isthmus. Although ACTH had no effect on the time of ovulation (relative to onset of standing estrus), or on embryo development, fewer oocytes/embryos were retrieved from the ACTH group than from the control group (51% vs. 81%, P < 0.05), and there was a tendency towards faster embryo transportation to the uterus. Short-term fasting after ovulation had an unfavourable effect on sperm numbers in UTJ/isthmus, cleavage rate of fertilized ova, as well as ova transport through the isthmic part of the oviduct. Treatment with ACTH after ovulation reduced numbers of spermatozoa at the zona pellucida and retarded cleavage rate of fertilized ova. Therefore, the timing of stress seemed to be an important factor regarding effects on reproductive events. # 2008 Elsevier Inc. All rights reserved. Keywords: Stress; Estrus; Gametes; Early embryo development 1. Introduction Stress can be defined as the biological response to an event that the individual perceives as a threat to its homeostasis [1]. Perception of stressful stimuli leads, e.g. to activation of the hypothalamic–hypophyseal–adreno- cortical system, which in turn results in the release of a variety of peptides, principally corticotrophin releasing hormone (CRH) and vasopressin from the hypothalamus [2]. It is well known that CRH stimulates the hypophysis to secrete adrenocorticotrophic hormone (ACTH) and other proopiomelanocortin (POMC) derived peptides, e.g. beta-endorphin, and that ACTH acts on the adrenal glands and causes secretion of glucocorticoid hormones, e.g. cortisol. Furthermore, ACTH causes the release of other hormones from the adrenal glands, e.g. progester- one and possibly inhibin a [3]. Management procedures in modern pig production include a number of events which might act as stressors. www.theriojournal.com Available online at www.sciencedirect.com Theriogenology 70 (2008) 1197–1201 * Corresponding author. Tel.: +46 18 671000; fax: +46 18 673545. E-mail address: Stig.Einarsson@kv.slu.se (S. Einarsson). 0093-691X/$ – see front matter # 2008 Elsevier Inc. All rights reserved. doi:10.1016/j.theriogenology.2008.06.015