Genetics of fresh and frozen-thawed semen traits and their relationship with growth rate in rabbits

Se utilizarán eyaculados procedentes de machos de la línea R (línea de conejos seleccionada por velocidad de crecimiento durante el periodo de engorde)alojados en diferentes centros de inseminación artificial. Una vez recuperados los eyaculados se procederá a su valoración y una muestra de todos ellos será crioconservada. La calidad seminal será de nuevo valorada tras el proceso de congelación. Junto con los anàlisis seminales se utilizarán los datos de crecimiento y pedigree de los machos y de todos los animales de la línea R desde su fundación para estimar por un lado los parámetros genéticos de las variables relacionadas con la producción y calidad de dosis seminales en fresco y tras un proceso de crioconservación y la correlación genética existente entre las variables seminales anteriormente citadas y la velocidad de crecimiento. A su vez se estimará mediante un modelo recursivo la relación entre las variables seminales en fresco y tras la descongelación.The general aim of this thesis was to study the genetic determinism for some traits related to artificial insemination (AI) dose production of fresh and frozen-thawed semen, in order to explore the interest and limitation of different strategies for their genetic improvement in a paternal line of rabbits selected for growth rate during the fattening period (28-63 days). In chapter 1, genetic parameters of sperm production traits are estimated as well as the genetic relationship with daily gain (DG). The heritabilities (h2) of the semen traits were 0.13±0.05, 0.08±0.04 and 0.07±0.03 for ejaculate volume (V), sperm concentration (CN) and sperm production (PROD) per ejaculate, respectively. A favourable and moderate genetic correlation was observed between V and DG (0.36±0.34). From this chapter it may be concluded that if a seminal trait is to be included as a selection objective, a useful one could be sperm production, as it is a trait in which both volume and concentration are included. Moreover, there is currently no evidence to suggest that selection for DG in rabbits will affect sperm production adversely. The aim of chapter 2 was to explore the genetic determinism of some sperm quality traits and their genetic relation with the selection criteria of the paternal rabbit line. The heritabilities (h2) of semen quality traits commonly evaluated in a classic spermiogram were 0.18, 0.19 and 0.12 for NAR (%, percentage of sperm with intact acrosome), ANR (%, percentage of sperm abnormalities) and MOT (%, percentage of total motile sperm cells) respectively. We also estimated the h2 of some motion CASA parameters 0.09, 0.11, 0.10, 0.11, 0.11 and 0.11 for VAP (µm/s; average path velocity), VSL (µm/s; straight-line velocity), VCL (µm/s; curvilinear velocity), LIN (%, linearity index), ALH (µm; amplitude of the lateral head displacement), STR (%, straightness). Genetic correlations between DG and semen traits showed a high HPD95% (interval of highest density of 95%). However there is some consistent evidence of the negativity of the genetic correlations of DG with NAR and MOT (-0.40 and -0.53, respectively). Chapter 3 aims to determine the repeatability and heritability of sperm head characteristics: width (W, ¿m), area (A, ¿m2),length (L, ¿m) and perimeter (P, ¿m), and explore the relationships between them and with the selection objective (DG). The results obtained showed that sperm head dimensions are heritable (ranged between 0.2 and 0.29). The genetic correlations between sperm traits were always high and positive (between 0.72 and 0.90), with the exception of L-W genetic correlation, which was moderate. Regarding the genetic correlations between DG and sperm head characteristics, the resulting means ranged from -0.09 for L-DG to -0.43 for W-DG, showing consistent evidence of the negativity of the genetic correlations. The environmental and male effects that could have an influence on sperm freezability are studied in Chapter 4. Six different traits were evaluated: sperm concentration (CONC, 106spermatozoa/mL), acrosome integrity in fresh (NAR, %) and frozen-thawed semen (Nar-FT, %), sperm motility in fresh (MOT, %) and frozen-thawed semen (Mot-FT, %) and the percentage of viable sperm in frozen-thawed semen (Live-FT, %). In addition, two synthetic traits were computed: the relative reduction of acrosome integrity (Rnar, %) and relative reduction of motility (Rmot, %) after the freezing-thawing process. A multiple-trait recursive model was used to analyse the relationships between the semen traits considered. For the fixed effects studied, the season had the highest impact on post-thaw semen characteristics. Results of the analysis of recursive coefficients showed that fresh semen concentration and motility influence the future freezability of the semen. All traits studied presented moderate repeatabilities, ranging from 0.11 to 0.38. These results provide conclusive evidence that sperm freezability in rabbits could be heritable. Regarding male correlations, there were large positive male correlations between fresh traits (rm=0.77-0.57), as well as between direct frozen-thawed traits (rm=0.72-1). Male effects on fresh and direct frozen-thawed traits were generally positively correlated. This correlation was moderate to high for MOT with all frozen-thawed traits (rm=0.41-0.74) and for Mot-FT and all fresh traits (rm=0.5-0.74); these results suggest that these traits could be genetically related. The final chapter of this thesis focused on estimating the heritability of semen freezability traits and estimating the genetic correlation between frozen-thawed sperm traits and the growth rate in a paternal rabbit line. Estimated heritabilities showed that frozen-thawed semen traits are heritable (ranged between 0.08 and 0.15). In the case of Live-FT, the estimated heritability is the highest and suggests the possibility of effective selection. After the study of genetic correlations, it seems that DG was negatively correlated with sperm freezability, but due to the high HPD95% no further conclusions could be drawn. More data should be included in order to obtain better accuracy for the estimates of these genetic correlations. If the results obtained in the present study were confirmed, it would imply that selection for DG could alter sperm cell membranes or seminal plasma composition, both components related to sperm cryoresistance.Lavara García, R. (2013). Genetics of fresh and frozen-thawed semen traits and their relationship with growth rate in rabbits [Tesis doctoral no publicada]. Universitat Politècnica de València. https://doi.org/10.4995/Thesis/10251/31657TESI

Study of failures in a rabbit line selected for growth rate

[EN] Selection for growth rate is negatively related with reproductive fitness. The aim of this work was to analyse the causes of fertility failure in rabbit does selected for growth rate and characterised for reproductive deficiencies (line R). In the experiment, 82 does were divided into 2 groups: naturally mated (NM) and artificially inseminated (AI), to relate luteinizing hormone (LH) concentration with ovulation induction and pregnancy rate by laparoscopic determination. Additionally, in 38 of these females ovulation rate and metabolites determination (leptin, NEFA, BOHB and glucose) were analysed and perirenal fat thickness measurement and live body weight (LBW) determined. The results showed that all ovulated does (both NM and AI) presented higher concentrations of LH than non-ovulated females. In addition, non-ovulated females showed high levels of leptin and BOHB, as well as LBW. Females from line R have an inherit reduced fertility due to ovulation failure as a consequence of a reduction in LH release, which could be explained by a heavier body weight and higher leptin concentrations.This work was supported by the Spanish Research Project AGL2011-30170-C02-01 (CICYT). Carmen Naturil-Alfonso was supported by a research grant from the Education Ministry of the Valencian Regional Government (programme VALi+d. ACIF/2013/296). English text version was revised by N. Macowan English Language Service.Naturil Alfonso, C.; Lavara García, R.; Millán, P.; Rebollar, P.; Vicente Antón, JS.; Marco Jiménez, F. (2016). Study of failures in a rabbit line selected for growth rate. World Rabbit Science. 24(1):47-53. https://doi.org/10.4995/wrs.2016.4016SWORD475324

ESTIMACIÓN DE LOS PARÁMETROS GENÉTICOS DE PRODUCCIÓN Y CALIDAD SEMINAL EN UNA LÍNEA PATERNAL DE CONEJOS

Se estimaron los componentes de varianza-covarianza de las variables producción, calidad, motilidad y morfometría espermática en una línea paternal de conejos. Las heredabilidades de la morfometría y morfología espermática fueron intermedias. Las correlaciones genéticas fueron desfavorables con el criterio de selección, a excepción del volumen.Lavara García, R. (2009). ESTIMACIÓN DE LOS PARÁMETROS GENÉTICOS DE PRODUCCIÓN Y CALIDAD SEMINAL EN UNA LÍNEA PATERNAL DE CONEJOS. http://hdl.handle.net/10251/12908Archivo delegad

Genetic variation in head morphometry of rabbit sperm

The aim of this study was to determine the repeatability and heritability of sperm head characteristics: width (W, mu m), area (A, mu m2), length (L, mu m), and perimeter (P, mu m), and to explore the relationships between them and with the selection objective in a rabbit paternal line selected for daily weight gain (DG, g/day) between 28 and 63 days of age. Six sets of three-trait analyses were performed involving 12,908 DG records, with 1795 ejaculates corresponding to 283 males and 14,700 animals in pedigree file. The results obtained showed that sperm head dimensions are heritable (ranged between 0.2 and 0.29). The genetic correlations between sperm traits were always high and positive (between 0.72 and 0.90), with the exception of L-W genetic correlation, which was moderate. Regarding the genetic correlations between DG and sperm head characteristics, the resulting means ranged from -0.09 for L-DG to -0.43 for W-DG, showing a consistent evidence of the negativity of the genetic correlations. Further studies should be focused on the relationship between sperm head morphometry and different semen or ejaculate characteristics and also between sperm head morphometry and field fertility and prolificacy. Published by Elsevier Inc.Lavara García, R.; Vicente Antón, JS.; Baselga Izquierdo, M. (2013). Genetic variation in head morphometry of rabbit sperm. Theriogenology. 80(4):313-318. doi:10.1016/j.theriogenology.2013.04.015S31331880

Does storage time in LN2 influence survival and pregnancy outcome of vitrified rabbit embryos?

Vitrification is one of the most widely used techniques for embryo cryopreservation. The aim of this work was to study the effect of storage time in liquid nitrogen on vitrified rabbit embryos. A total of 1467 vitrified rabbit embryos were transferred into 174 females. The embryos had been maintained in liquid nitrogen during 3 different periods, A) 15 years (32 transfers, 280 embryos). A generalized linear model was used to determine the effect of period on pregnancy and birth rates. A Bayesian approach was applied to analyze the survival rate of the vitrified embryos. In all analyses the number of transferred embryos was included as covariate. It was observed that neither the period of storage nor the number of transferred embryos affected pregnancy rate, and all periods presented similar pregnancy rates (0.85 0.04; 0.86 0.05; 0.78 0.07 for A, B and C). Fertility at birth was affected by the number of transferred embryos, but non-significant differences between periods were detected (0.77 0.04, 0.75 0.07; 0.69 0.08 for A, B and C). Also, the posterior means (highest posterior density intervals at 95%) of embryo survival at birth from pregnant females were similar between the different periods (47 [41 53]; 47 [38 56]; 42 [31 54]; for A, B and C). Results obtained in the present experiment point out that vitrified embryos could be stored in liquid nitrogen during at least fifteen years, achieving good pregnancy rate, fertility and survival at birth. © 2011 Elsevier Inc.This study was supported by the Generalitat Valenciana research program (Prometeo 2009/125) and Spanish Research Project (CICYT AGL2008-03274). Raquel Lavara was supported by a research grant from Spanish Ministry of Education (MEC, FPU AP2007-03755).Lavara García, R.; Baselga Izquierdo, M.; Vicente Antón, JS. (2011). Does storage time in LN2 influence survival and pregnancy outcome of vitrified rabbit embryos?. Theriogenology. 76(4):652-657. https://doi.org/10.1016/j.theriogenology.2011.03.018S65265776

Analysis of reproductive traits in crosses among maternal lines of rabbits

A crossbreeding experiment, between three maternal lines of rabbits, was carried out to estimate the effects of the crosses on reproductive traits. The experiment was designed as a complete diallel cross involving the lines, A, V and H, selected for litter size. A total of 1190 does, distributed between the nine types originating from the diallel cross, and born, reared and bred on the same commercial farm, were controlled. The recorded traits were the total number of young born, the number of born alive and the number of stillborn per litter (3759 records), and the interval between kindlings (2505 records). A repeatability animal model was used first to obtain the REML estimates of the components of variance. This was followed by a generalised least squares analysis and the estimates of the type of doe effects were obtained. Finally the differences among the lines within direct and maternal effects, and the corresponding values of the individual heterosis were estimated. Important differences in the direct effects were found between lines V and A. All the maternal effects were not significant. Favourable heterosis ($4{-}10\%$) was found for prolificacy traits in the crosses of line A with lines V and H, being the heterosis, very dependent on the performance and history of the lines involved.Analyse de caractères de reproduction par le croisement de souches maternelles de lapin. Une expérience de croisements de trois souches maternelles de lapins a été menée pour estimer les effets des croisements sur les caractères de reproduction. L'expérience a été construite sur un schéma diallèle complet des souches A, V et H sélectionnées pour la taille de la portée par le département de Science Animale de l'Université Polytechnique de Valence en Espagne. Au total 1190 lapines nées et élevées dans la même ferme de production et réparties dans les neuf types génétiques ont été contrôlées. Les caractères mesurés ont été le nombre total de lapereaux nés, nés vivants et mort nés (3759 données), et l'intervalle entre portées (2505 données). Un modèle animal avec répétabilité a été utilisé dans un premier temps pour l'estimation des composantes de la variance par REML. Cela a été suivi d'une analyse GLM pour l'estimation des effets de chaque type génétique. Finalement les différences entre souches au regard des effets directs et maternels et les effets d'hétérosis en ont été déduits. Des différences importantes d'effets directs ont été trouvées entre les souches A et V. Tous les effets maternels n'étaient pas significatifs. Une hétérosis favorable ($4{-}10$ %) a été trouvée pour les caractères de prolificité entre les croisements de la souche A avec les souches V et H, cette hétérosis paraissant très dépendante des performances et de l'histoire des souches impliquées

Generation of live offspring from vitrified embryos with synthetic polymers Supercool X-1000 and Supercool Z-1000

[EN] BACKGROUND: Ice growth and recrystallisation are considered important factors in determining vitrification outcomes. Synthetic polymers inhibit ice formation during cooling or warming of the vitrification process. OBJECTIVE: The aim of this study was to assess the effect of adding commercially available synthetic polymers SuperCool X-1000 and SuperCool Z-1000 to vitrification media on in vivo development competence of rabbit embryos. METHODS: Four hundred and thirty morphologically normal embryos recovered at 72 h of gestation were used. The vitrification media contained 20% dimethyl sulphoxide and 20% ethylene glycol, either alone or in combination with 1% of SuperCool X-1000 and 1% SuperCool. RESULT: Our results show that embryos can be successfully vitrified using SuperCool X-1000 and SuperCool Z-1000 and when embryos are transferred, live offspring can be successfully produced. CONCLUSIONS: In conclusion, our results demonstrated that we succeeded for the first time in obtaining live offspring after vitrification of embryos using SuperCool X-1000 and SuperCool Z-1000 polymers.This work was supported by the Spanish Research Project AGL2011-30170-C02-01 and by funds from the Generalitat Valenciana Research Programme (Prometeo 2009⁄125). Estrella Jiménez was supported by a research grant from the Education Ministry of the Valencian Regional Government (programme VALi+d. ACIF/2010/262).Marco Jiménez, F.; Jiménez Trigos, ME.; Lavara García, R.; Vicente Antón, JS. (2014). Generation of live offspring from vitrified embryos with synthetic polymers Supercool X-1000 and Supercool Z-1000. Cryo Letters. 35(4):286-292. http://hdl.handle.net/10251/65518S28629235