Major Components in Limiting Litter Size

The litter size is an important trait in prolific species such as rabbits and pigs. However, selection on litter size has had limited success in these species because of its low heritability and sex-limited expression. The litter size is a complex physiological trait in prolific species, affected by several components that are expressed sequentially, for example, ovulation, fertilization, embryo development, and fetal survival. The selection for ovulation rate or/and prenatal survival has been proposed to improve litter size indirectly. However, these alternative methods have not reached the expected response rate. Implantation is also a critical point in successful gestation, one-third to one-half of prenatal mortality occurring during peri-implantation. The uterus must provide an adequate microenviroment for the growth and development of embryo and for receptivity to implantation. There are multitudes of cellular events involved in crosstalk between embryo and maternal uterus during peri-implantation. A better understanding of molecular mechanisms affecting the implantation process could help to propose new strategies for litter size improvement in prolific species

The Genetic Improvement in Meat Rabbits

Rabbits are raised for many different purposes, such as breeding stock for meat, wool and fur, as an educational and experimental animal model, and as pets and show animals. However, this species is main used for meat production. France, Italy and Spain have an important role in the increase of world rabbit meat production through the development of selection programs in this species. Genetic improvement programs have based on development of maternal lines to improve prolificacy and paternal lines to improve growth rate, but the alternative development of multi-purpose lines for litter size and growth traits will be discussed. In this chapter, the variance components of these traits, the response to selection and the main commercial available lines will be reviewed. Universities and public research centers have played a leading role in the development of these lines and in the diffusion of this genetic material through a pyramid scheme from selection nuclei to farmers. Recently, others functional traits are emerging successfully as selection criteria in breeding programs such as ovulation rate, prenatal survival, longevity, feed efficiency, meat quality, uniformity in production, and resistance to digestive disorders

Relationship between Prenatal Characteristics and Body Condition and Endocrine Profile in Rabbits

[EN] Litter size is an essential trait in rabbit production, and it depends on ovulation rate and embryonic and foetal survival. The period between 8 and 18 d of gestation is critical for foetal survival, as the placenta controls foetal nutrition during this period. Ovulation rate and foetal survival at 12 d of gestation are affected by body condition and metabolic and hormonal profile. Higher foetal survival is related to a higher number of vessels arriving at the implantation site, and may be due to higher available space for the foetus. This study evaluated the relationship between prenatal characteristics and body condition and endocrine profile. A total of 25 non-lactating multiparous females were used. Body condition, measured as body weight and perirenal fat thickness, non-esterified fatty acids (NEFA), leptin, progesterone and 17 beta-estradiol were recorded at mating and 12 d of gestation. Ovulation rate, number of foetuses, ovary and foetal weight, length and weight of uterine horn, available space per foetus and maternal and foetal placental morphometry were recorded at 12 d of gestation. Ovulation rate showed a positive linear relationship with number of foetuses, ovary weight and NEFA. A negative linear relationship between ovulation rate and perirenal fat thickness and leptin was obtained. Ovulation rate was maximum when body weight and 17 beta-estradiol were 4.4 kg and 22.7 pg/mL, respectively. Foetal weight showed a positive relationship with perirenal fat thickness and a negative relationship with leptin. An increase in progesterone and NEFA concentration was related to a positive linear increase in number of foetuses and in uterine horn weight. Space available per foetus was affected both by the number of vessels that reach the implantation site and by position of the foetus in the uterine horn. In conclusion, body condition during mating and early gestation should be maintained within an optimal range to ensure the best prenatal characteristics. While 17 beta-estradiol, NEFA and leptin affected the ovulation rate, progesterone and NEFA affected foetal development. The number of vessels that reach the implantation site determines early foetal survival.This research was funded by Generalitat Valenciana, grant number GVPRE/2008/145.García, M.; Muelas, R.; Argente, M.; Peiró Barber, RM. (2021). Relationship between Prenatal Characteristics and Body Condition and Endocrine Profile in Rabbits. Animals. 11(1):1-13. https://doi.org/10.3390/ani11010095S11311

Identification of functional mutations associated with environmental variance of litter size in rabbits

[EN] Background Environmental variance (V-E) is partly under genetic control and has recently been proposed as a measure of resilience. Unravelling the genetic background of the V-E of complex traits could help to improve resilience of livestock and stabilize their production across farming systems. The objective of this study was to identify genes and functional mutations associated with variation in V-E of litter size (LS) in rabbits. To achieve this, we combined the results of a genome-wide association study (GWAS) and a whole-genome sequencing (WGS) analysis using data from two divergently selected rabbit lines for high and low V-E of LS. These lines differ in terms of biomarkers of immune response and mortality. Moreover, rabbits with a lower V-E of LS were found to be more resilient to infections than animals with a higher V-E of LS. Results By using two GWAS approaches (single-marker regression and Bayesian multiple-marker regression), we identified four genomic regions associated with V-E of LS, on chromosomes 3, 7, 10, and 14. We detected 38 genes in the associated genomic regions and, using WGS, we identified 129 variants in the splicing, UTR, and coding (missense and frameshift effects) regions of 16 of these 38 genes. These genes were related to the immune system, the development of sensory structures, and stress responses. All of these variants (except one) segregated in one of the rabbit lines and were absent (n = 91) or fixed in the other one (n = 37). The fixed variants were in the HDAC9, ITGB8, MIS18A, ENSOCUG00000021276 and URB1 genes. We also identified a 1-bp deletion in the 3 ' UTR region of the HUNK gene that was fixed in the low V-E line and absent in the high V-E line. Conclusions This is the first study that combines GWAS and WGS analyses to study the genetic basis of V-E. 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Selection for environmental variance of litter size in rabbits involves genes in pathways controlling animal resilience

[EN] Background Environmental variance (V-E) is partially under genetic control, which means that the V-E of individuals that share the same environment can differ because they have different genotypes. Previously, a divergent selection experiment for V-E of litter size (LS) during 13 generations in rabbit yielded a successful response and revealed differences in resilience between the divergent lines. The aim of the current study was to identify signatures of selection in these divergent lines to better understand the molecular mechanisms and pathways that control V-E of LS and animal resilience. Three methods (F-ST, ROH and varLD) were used to identify signatures of selection in a set of 473 genotypes from these rabbit lines (377) and a base population (96). A whole-genome sequencing (WGS) analysis was performed on 54 animals to detect genes with functional mutations. Results By combining signatures of selection and WGS data, we detected 373 genes with functional mutations in their transcription units, among which 111 had functions related to the immune system, stress response, reproduction and embryo development, and/or carbohydrate and lipid metabolism. The genes TTC23L, FBXL20, GHDC, ENSOCUG00000031631, SLC18A1, CD300LG, MC2R, and ENSOCUG00000006264 were particularly relevant, since each one carried a functional mutation that was fixed in one of the rabbit lines and absent in the other line. In the 3MODIFIER LETTER PRIMEUTR region of the MC2R and ENSOCUG00000006264 genes, we detected a novel insertion/deletion (INDEL) variant. Conclusions Our findings provide further evidence in favour of V-E as a measure of animal resilience. Signatures of selection were identified for V-E of LS in genes that have a functional mutation in their transcription units and are mostly implicated in the immune response and stress response pathways. However, the real implications of these genes for V-E and animal resilience will need to be assessed through functional analyses.We are grateful to CEGEN-PRB3-ISCIII for their genotyping service, supported by Grant No PT17/0019 of the PE I+D+i 2013-2016, funded by ISCIII and ERDF. Cristina Casto-Rebollo acknowledges a FPU17/01196 scholarship from the Spanish Ministry of Science, Innovation and Universities. This study was supported by Projects AGL2014-5592, C2-1-P and C2-2-P, and AGL2017-86083, C2-1-P and C2-2-P, funded by the Spanish Ministerio de Ciencia e Innovacion (MIC)-Agencia Estatal de Investigacion (AEI) and the European Regional Development Fund (FEDER).Casto-Rebollo, C.; Argente, MJ.; García, ML.; Blasco Mateu, A.; Ibáñez-Escriche, N. (2021). Selection for environmental variance of litter size in rabbits involves genes in pathways controlling animal resilience. Genetics Selection Evolution. 53(1). https://doi.org/10.1186/s12711-021-00653-y53

Inflammatory correlated response in two lines of rabbit selected divergently for litter size environmental variability

[EN] Animal welfare is a priority objective for the livestock industry. Litter size environmental variability has been related to environmental sensitivity. A divergent selection experiment for environmental variance of litter size variance was carried out successfully in rabbits over thirteen generations. The low line showed a lower inflammatory response and susceptibility to infectious disorders than the high line. In conclusion, the decrease of environmental sensitivity seems to increase the adaptation of the animal to the environment, and thus, its welfare.This research was supported by Projects AGL2017-86083, C2-1-P and C2-2-P, funded by Ministerio de Ciencia e Innovacion (MIC)-Agencia Estatal de Investigacion (AEI) and el Fondo Europeo de Desarrollo Regional (FEDER) "Una manera de hacer Europa" and Project AICO/2019/169 funded by Valencia Regional Government.Beloumi, D.; Blasco Mateu, A.; Muelas, R.; Santacreu Jerez, MA.; García, MDLL.; Argente, M. (2020). 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Correlated Response to Selection for Litter Size Residual Variability in Rabbits' Body Condition

[EN] Selection for decreasing litter size residual variance has been proposed as an indirect way to select for resilience. Resilience has been directly related to welfare. A good body condition and efficient body fat mobilization have been associated with an optimal level of animal welfare. Two rabbit lines have been divergently selected for litter size residual variability. The low line selected for decreasing litter size variance more efficiently managed the body fat from mating to weaning in the second productive cycle in females compared to the high line, which could be related to the lower culling rate reported previously in the low line. Therefore, body condition can be used as a useful biomarker of resilience. A divergent selection experiment for residual variance of litter size at birth was carried out in rabbits during twelve generations. Residual variance of litter size was estimated as the within-doe variance of litter size after pre-correction for year and season as well as parity and lactation status effects. The aim of this work was to study the correlated response to selection for litter size residual variability in body condition from mating to weaning. Body condition is related directly to an animal's fat deposits. Perirenal fat is the main fat deposit in rabbits. Individual body weight (IBW) and perirenal fat thickness (PFT) were used to measure body condition at second mating, delivery, 10 days after delivery, and weaning. Litter size of the first three parities was analyzed. Both lines decreased body condition between mating to delivery; however, the decrease in body condition at delivery was lower in the low line, despite this line having higher litter size at birth (+0.54 kits, p = 0.93). The increment of body condition between delivery and early lactation was slightly higher in the low line. On the other hand, body condition affected success of females' receptivity and fertility at the third mating, e.g., receptive females showed a higher IBW and PFT than unreceptive ones (+129 g and +0.28 mm, respectively), and fertile females had a higher IBW and PFT than unfertile ones (+82 g and +0.28 mm, respectively). In conclusion, the does selected for reducing litter size variability showed a better deal with situations of high-energy demand, such as delivery and lactation, than those selected for increasing litter size variability, which would agree with the better health and welfare condition in the low line.This research was supported by Project AGL2017-86083-C2-2-P, funding by Ministerio de Ciencia e Innovacion (MIC)-Agencia Estatal de Investigacion (AEI) and el Fondo Europeo de Desarrollo Regional (FEDER).Agea, I.; García, MDLL.; Blasco Mateu, A.; Massanyi, P.; Capcarová, M.; Argente, M. (2020). Correlated Response to Selection for Litter Size Residual Variability in Rabbits' Body Condition. Animals. 10(12):1-8. https://doi.org/10.3390/ani10122447S181012Colditz, I. G., & Hine, B. C. (2016). Resilience in farm animals: biology, management, breeding and implications for animal welfare. Animal Production Science, 56(12), 1961. doi:10.1071/an15297Berghof, T. V. L., Poppe, M., & Mulder, H. A. (2019). Opportunities to Improve Resilience in Animal Breeding Programs. Frontiers in Genetics, 9. doi:10.3389/fgene.2018.00692Schröder, U. J., & Staufenbiel, R. (2006). Invited Review: Methods to Determine Body Fat Reserves in the Dairy Cow with Special Regard to Ultrasonographic Measurement of Backfat Thickness. Journal of Dairy Science, 89(1), 1-14. doi:10.3168/jds.s0022-0302(06)72064-1Maes, D. G. D., Janssens, G. P. J., Delputte, P., Lammertyn, A., & de Kruif, A. (2004). Back fat measurements in sows from three commercial pig herds: relationship with reproductive efficiency and correlation with visual body condition scores. Livestock Production Science, 91(1-2), 57-67. doi:10.1016/j.livprodsci.2004.06.015Pascual, J. J., Castella, F., Cervera, C., Blas, E., & Fernández-Carmona, J. (2000). The use of ultrasound measurement of perirenal fat thickness to estimate changes in body condition of young female rabbits. Animal Science, 70(3), 435-442. doi:10.1017/s135772980005178xBarletta, R. V., Maturana Filho, M., Carvalho, P. D., Del Valle, T. A., Netto, A. S., Rennó, F. P., … Wiltbank, M. C. (2017). Association of changes among body condition score during the transition period with NEFA and BHBA concentrations, milk production, fertility, and health of Holstein cows. Theriogenology, 104, 30-36. doi:10.1016/j.theriogenology.2017.07.030Van Staaveren, N., Doyle, B., Manzanilla, E. G., Calderón Díaz, J. A., Hanlon, A., & Boyle, L. A. (2017). Validation of carcass lesions as indicators for on-farm health and welfare of pigs. Journal of Animal Science, 95(4), 1528. doi:10.2527/jas2016.1180Sánchez, J. P., de la Fuente, L. F., & Rosell, J. M. (2012). Health and body condition of lactating females on rabbit farms1. Journal of Animal Science, 90(7), 2353-2361. doi:10.2527/jas.2011-4065Mulder, H. A., & Rashidi, H. (2017). Selection on resilience improves disease resistance and tolerance to infections. Journal of Animal Science, 95(8), 3346. doi:10.2527/jas2017.1479Argente, M. J., García, M. L., Zbyňovská, K., Petruška, P., Capcarová, M., & Blasco, A. (2019). Correlated response to selection for litter size environmental variability in rabbits’ resilience. Animal, 13(10), 2348-2355. doi:10.1017/s1751731119000302Blasco, A., Martínez-Álvaro, M., García, M.-L., Ibáñez-Escriche, N., & Argente, M.-J. (2017). Selection for environmental variance of litter size in rabbits. Genetics Selection Evolution, 49(1). doi:10.1186/s12711-017-0323-4Beloumi, D., Blasco, A., Muelas, R., Santacreu, M. A., García, M. de la L., & Argente, M.-J. (2020). Inflammatory Correlated Response in Two Lines of Rabbit Selected Divergently for Litter Size Environmental Variability. Animals, 10(9), 1540. doi:10.3390/ani10091540García, M. L., Blasco, A., García, M. E., & Argente, M. J. (2019). Correlated response in body condition and energy mobilisation in rabbits selected for litter size variability. Animal, 13(4), 784-789. doi:10.1017/s1751731118002203Pascual J.J., Blanco J., Piquer O., & Quevedo F. Cervera C. (2010). Ultrasound measurements of perirenal fat thickness to estimate the body condition of reproducing rabbit does in different physiological states. World Rabbit Science, 12(1). doi:10.4995/wrs.2004.584Iung, L. H. de S., Carvalheiro, R., Neves, H. H. de R., & Mulder, H. A. (2019). Genetics and genomics of uniformity and resilience in livestock and aquaculture species: A review. Journal of Animal Breeding and Genetics, 137(3), 263-280. doi:10.1111/jbg.12454Agea, I., García, M.-L., Blasco, A., & Argente, M.-J. (2019). Litter Survival Differences between Divergently Selected Lines for Environmental Sensitivity in Rabbits. Animals, 9(9), 603. doi:10.3390/ani9090603Fortun-Lamothe, L. (2006). Energy balance and reproductive performance in rabbit does. Animal Reproduction Science, 93(1-2), 1-15. doi:10.1016/j.anireprosci.2005.06.009Feugier, A., & Fortun-Lamothe, L. (2006). Extensive reproductive rhythm and early weaning improve body condition and fertility of rabbit does. Animal Research, 55(5), 459-470. doi:10.1051/animres:2006025Theilgaard, P., Baselga, M., Blas, E., Friggens, N. C., Cervera, C., & Pascual, J. J. (2009). Differences in productive robustness in rabbits selected for reproductive longevity or litter size. Animal, 3(5), 637-646. doi:10.1017/s1751731109003838Theilgaard, P., Sánchez, J. P., Pascual, J. J., Friggens, N. C., & Baselga, M. (2006). Effect of body fatness and selection for prolificacy on survival of rabbit does assessed using a cryopreserved control population. Livestock Science, 103(1-2), 65-73. doi:10.1016/j.livsci.2006.01.007Arias-Álvarez, M., García-García, R. M., Rebollar, P. G., Revuelta, L., Millán, P., & Lorenzo, P. L. (2009). Influence of metabolic status on oocyte quality and follicular characteristics at different postpartum periods in primiparous rabbit does. Theriogenology, 72(5), 612-623. doi:10.1016/j.theriogenology.2009.04.017Castellini, C. (2007). Reproductive activity and welfare of rabbit does. Italian Journal of Animal Science, 6(sup1), 743-747. doi:10.4081/ijas.2007.1s.743Castellini, C., Dal Bosco, A., Arias-Álvarez, M., Lorenzo, P. L., Cardinali, R., & Rebollar, P. G. (2010). 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Identification of differentially expressed genes in the oviduct of two rabbit lines divergently selected for uterine capacity using suppression subtractive hybridization

This is the accepted version of the following article: Ballester, M.; Castelló, A.; Peiró Barber, RM.; Argente, M. J.;Santacreu Jerez, MA.; Folch, J. M. (2013). Identification of differentially expressed genes in the oviduct of two rabbit lines divergently selected for uterine capacity using suppression subtractive hybridization. Animal Genetics. 44:296-304. doi:10.1111/AGE.12005. , which has been published in final form at http://dx.doi.org/10.1111/age.12005.[EN] Suppressive subtractive hybridization libraries from oviduct at 62h post-mating of two lines of rabbits divergently selected for uterine capacity were generated to identify differentially expressed genes. A total of 438 singletons and 126 contigs were obtained by cluster assembly and sequence alignment of 704 expressed sequence tags (ESTs), of which 54% showed homology to known proteins of the non-redundant NCBI databases. Differential screening by dot blot validated 71 ESTs, of which 47 showed similarity to known genes. Transcripts of genes were functionally annotated in the molecular function and the biological process gene ontology categories using the blast2go software and were assigned to reproductive developmental process, immune response, amino acid metabolism and degradation, response to stress and apoptosis terms. Finally, three interesting genes, PGR, HSD17B4 and ERO1L, were identified as overexpressed in the low line using RT-qPCR. Our study provides a list of candidate genes that can be useful to understanding the molecular mechanisms underlying the phenotypic differences observed in early embryo survival and development traits.We would like to thank Henry Cardona Cadavid for help in the sequencing. This study was funded with project AGL2005-07624-C03.Ballester Devis, M.; Castelló Farre, A.; Peiró Barber, RM.; Argente, MJ.; Santacreu Jerez, MA.; Folch, JM. (2013). Identification of differentially expressed genes in the oviduct of two rabbit lines divergently selected for uterine capacity using suppression subtractive hybridization. Animal Genetics. 44:296-304. https://doi.org/10.1111/AGE.12005S2963044

Effect of environmental variance-based resilience selection on the gut metabolome of rabbits

Background Gut metabolites are key actors in host-microbiota crosstalk with efect on health. The study of the gut metabolome is an emerging topic in livestock, which can help understand its efect on key traits such as animal resilience and welfare. Animal resilience has now become a major trait of interest because of the high demand for more sustainable production. Composition of the gut microbiome can reveal mechanisms that underlie animal resil ience because of its infuence on host immunity. Environmental variance (VE), specifcally the residual variance, is one measure of resilience. The aim of this study was to identify gut metabolites that underlie diferences in the resilience potential of animals originating from a divergent selection for VE of litter size (LS). We performed an untargeted gut metabolome analysis in two divergent rabbit populations for low (n=13) and high (n=13) VE of LS. Partial least square-discriminant analysis was undertaken, and Bayesian statistics were computed to determine dissimilarities in the gut metabolites between these two rabbit populations. Results We identifed 15 metabolites that discriminate rabbits from the divergent populations with a prediction performance of 99.2% and 90.4% for the resilient and non-resilient populations, respectively. These metabolites were suggested to be biomarkers of animal resilience as they were the most reliable. Among these, fve that derived from the microbiota metabolism (3-(4-hydroxyphenyl)lactate, 5-aminovalerate, and equol, N6-acetyllysine, and serine), were suggested to be indicators of dissimilarities in the microbiome composition between the rabbit populations. The abundances of acylcarnitines and metabolites derived from the phenylalanine, tyrosine, and tryptophan metabo lism were low in the resilient population and these pathways can, therefore impact the infammatory response and health status of animals. Conclusions This is the frst study to identify gut metabolites that could act as potential resilience biomarkers. The results support diferences in resilience between the two studied rabbit populations that were generated by selec tion for VE of LS. Furthermore, selection for VE of LS modifed the gut metabolome, which could be another factor that modulates animal resilience. Further studies are needed to determine the causal role of these metabolites in health and diseas

Evaluación de la calidad seminal y la longevidad de líneas de conejos gestionadas en un centro de inseminación / Semen quality and longevity of maternal and paternal rabbit lines in an artificial insemination center

El objetivo de este trabajo es la comparación de la calidad seminal y la longevidad de 4 líneas genéticas en un centro de inseminación artificial (CIA). Para ello, se evaluaron un total de 50.993 muestras de semen de 688 machos. Las líneas maternales A y L son seleccionadas por tamaño de camada al destete. Las líneas paternales R y C son seleccionadas por velocidad de crecimiento postdestete. Se registró el volumen del eyaculado y la motilidad en una escala de 0 a 5. También se evaluó la edad de eliminación o muerte de los machos en el centro de inseminación artificial. Los análisis estadísticos se realizaron con metodología bayesiana. La línea paternal C presentó mayor volumen de semen y motilidad (1,24 ml y 3,69) que la línea R (1,07 ml y 3,55) y las líneas maternales (A, 0,92 ml y 3,33; L, 1,01 ml y 3,62) siendo la diferencia relevante (Pr = 1,00). La longevidad de los machos es superior en las líneas maternas (25 y 20 meses para la línea A y L, respectivamente) que en las líneas paternas (16 y 14 meses para la línea C y R, respectivamente), siendo relevante la diferencia entre la línea A y las líneas paternas (Pr = 1,00). En conclusión, la línea paterna C presentó los mejores parámetros de calidad espermática y las líneas maternas son más longevas en los CIA que las líneas paternas debido al mayor intervalo generacional