Climate change and male animal reproduction: effects of heat stress and season

L’objectiu general d’aquesta tesi doctoral ha estat estudiar l’impacte que pot tenir el canvi climatic, provocant situacions d’estres termic, i l’estacionalitat climatica sobre la reproduccio animal, en concret sobre la qualitat espermatica, utilitzant un model experimental (conill) i un model d’una especie de gran interes ramader (bovi). L’objectiu del primer capitol va ser avaluar l’efecte d’un model d’estres termic in vivo de cicles circadians d’estiu continus amb periodes de recuperacio sobre la qualitat espermatica, la fertilitat, la prolificitat i en la concentracio d’hormones d’estres utilitzant el conill com model. La fiabilitat del model es va demostrar mitjancant l’increment de metabolits de cortisol fecal en animals sotmesos a estres termic. L’exposicio d’animals a l’estres termic in vivo va comportar la disminucio del percentatge d’espermatozoides viables, i l’augment de la proporcio d’alteracions acrosomiques i d’espermatozoides sense cua. Tot i que es van observar efectes negatius en alguns parametres de qualitat espermatica, la fertilitat i la prolificitat no es van veure negativament afectades. Per tant, es suggeri la hipotesi d’un possible desenvolupament de tolerancia o d’adaptacio dels animals a l’estres termic. En el capitol 2a es va desenvolupar un metode fluorometric vital (resazurin reduction test, RRT) per tal d’avaluar l’activitat metabolica dels espermatozoides de conill. Els resultats van mostrar una correlacio positiva entre l’activitat metabolica a traves del RRT i la proporcio d’espermatozoides viables, i una correlacio negativa entre l’activitat metabolica i la presencia d’espermatozoides amb anomalies acrosomiques. El RRT es per tant un metode prometedor per a l’avaluacio indirecta de la viabilitat i els parametres morfologics. En el capitol 2b es va avaluar l’impacte d’un model d’estres termic in vitro en la qualitat espermatica del conill. A mes, es va determinar els possibles efectes d’estacionalitat climatica en la tolerancia termica de l’esperma. Les mostres espermatiques recollides en estacions calides i fredes van ser exposades a temperatures escrotals (32,5oC), corporals (37oC) o d’hipertermia (42oC). Nomes l’exposicio de les mostres espermatiques a temperatures d’hipertermia va comportar la reduccio dels valors mitjans de motilitat total, activitat metabolica, i velocitat curvilinia i mitjana. L’activitat metabolica tambe va ser influenciada per la interaccio entre l’estres termica i l’estacio climatica. Per tant, es pot extrapolar que en condicions in vivo, la presencia d’espermatozoides en uters i oviductes de femelles en estat d’hipertermia podria comprometre la posterior fertilitat. En el capitol 3 es van avaluar els possibles efectes climatics en la qualitat espermatica de toros estabulats al nord d’Espanya. Les mostres seminals recollides a la primavera van mostrar valors cinematics (motilitat total i progressiva, velocitat mitjana i velocitat rectilinia), percentatges d’espermatozoides viables, proporcio d’espermatozoides viables amb acrosoma no reaccionat, i proporcio d’espermatozoides vius no productors de superoxid o peroxid d’hidrogen mes elevats que les mostres recollides en les altres estacions climatiques estudiades. Aquests resultats poden ser indicatius d’una millor qualitat espermatica en les mostres recollides a la primavera comparat amb les mostres recollides en altres estacions climatiques. L’objectiu del capitol 4 va ser estudiar l’efecte de l’estacionalitat en la capacitat fecundant dels espermatozoides bovins i el seu posterior desenvolupament embrionari in vitro. Oocits bovins van ser madurats i fecundats in vitro amb espermatozoides de toro recollits en diferents estacions climatiques. Dels parametres estudiats, nomes la taxa de divisio embrionaria mostrava una tendencia cap a la significacio entre estacions. Les mostres espermatiques recollides a la primavera van mostrar desenvolupaments embrionaris mes rapids. S’hauran de realitzar mes estudis per tal de verificar aquest resultats preliminars. The general purpose of this doctoral thesis has been to study the impact of climate changes, such as heat stress, and season on sperm quality using an experimental model (rabbit) and a livestock model (bovine). The aim of the first chapter was to evaluate the effect of an in vivo heat stress model of continuous summer circadian cycles with periods of recovery on sperm quality, fertility, prolificacy and concentrations of stress hormones in rabbits. The reliability of the model was demonstrated by the higher values of faecal cortisol metabolites of the animals exposed to heat stress. The exposure to the in vivo heat stress decreased the percentage of viable spermatozoa, and increased the proportion of acrosome abnormalities and tailless spermatozoa. Although negative effects were observed in some sperm quality parameters, fertility and prolificacy were not adversely affected. A hypothesis of development of stress tolerance or species adaptation to stress is suggested. In Chapter 2a, a vital fluorometric method (resazurin reduction test; RRT) for evaluating metabolic activity of rabbit sperm cells was developed. A positive correlation between metabolic activity through RRT and the proportion of viable spermatozoa, and a negative correlation between metabolic activity and sperm cells with acrosomic abnormalities were observed. RRT is a promising method for a dual indirect assessment of viability and morphological parameters. Chapter 2b evaluated the impact of an in vitro heat stress model on rabbit sperm quality and to determine possible seasonal effects on sperm heat tolerance. Sperm samples collected both in the warm and the cold seasons were exposed to scrotal (32.5oC), body (37oC) or hyperthermic (42oC) temperatures for 3 hours. Only the exposure to hyperthermic conditions decreased the average values of total motility, metabolic activity, and curvilinear and mean velocity. Metabolic activity was also influenced by the interaction of heat stress and season. Thus, extrapolating to in vivo conditions, the presence of sperm cells in a hyperthermic uterus or oviduct could compromise fertility. In Chapter 3, the possible effects of climate factors on sperm quality of bulls housed in northern Spain were evaluated. Samples collected in spring showed higher average kinematic values (total and progressive motility, average path velocity and straight line velocity), proportion of viable spermatozoa and proportion of viable spermatozoa with non-reacted acrosome, and proportion of live spermatozoa not producing superoxide or hydrogen peroxide when compared to ejaculates from the same bull obtained in winter and summer. These results may be indicative of better sperm quality in samples collected in spring than samples collected in other seasons. The aim of chapter 4 was to study the effects of season on the fertilizing ability of bovine spermatozoa and subsequent embryo development in vitro. Bovine oocytes were matured and fertilized in vitro with sperm cells from ejaculates collected in different seasons. From the studied parameters, only embryo development rates showed a trend towards significance among seasons. Semen samples collected in spring results in embryos that developed at a faster rate. Further studies should be performed in order to verify these preliminary interesting results.