Identification of genomic regions associated with total and progressive sperm motility in Italian Holstein bulls.

Sperm motility is directly related to the ability of sperm to move through the female reproductive tract to reach the ovum. Sperm motility is a complex trait that is influenced by environmental and genetic factors and is associated with male fertility, oocyte penetration rate, and reproductive success of cattle. In this study we carried out a GWAS in Italian Holstein bulls to identify candidate regions and genes associated with variations in progressive and total motility (PM and TM, respectively). After quality control, the final data set consisted of 5,960 records from 949 bulls having semen collected in 10 artificial insemination stations and genotyped at 412,737 SNPs (call rate >95%; minor allele frequency >5%). (Co)variance components were estimated using single trait mixed models, and associations between SNPs and phenotypes were assessed using a genomic BLUP approach. Ten windows that explained the greatest percentage of genetic variance were located on Bos taurus autosomes 1, 2, 4, 6, 7, 23, and 26 for TM and Bos taurus autosomes 1, 2, 4, 6, 8, 16, 23, and 26 for PM. A total of 150 genes for TM and 72 genes for PM were identified within these genomic regions. Gene Ontology enrichment analyses identified significant Gene Ontology terms involved with energy homeostasis, membrane functions, sperm-egg interactions, protection against oxidative stress, olfactory receptors, and immune system. There was significant enrichment of quantitative trait loci for fertility, calving ease, immune response, feed intake, and carcass weight within the candidate windows. These results contribute to understanding the architecture of the genetic control of sperm motility and may aid in the development of strategies to identify subfertile bulls and improve reproductive success.

Comparison between primary sex ratio in spermatozoa of bulls and secondary sex ratio in the deriving offspring.

The objectives of the present work were to compare the primary sex ratio in sperm with the secondary sex ratio recorded in the offspring produced by artificial insemination (AI) with the same sperm and assess whether the primary sex ratio is influenced by sperm survival and motility after thawing. Calving data of 98 Holstein Friesian bulls used in AI were collected during 4 years, and commercial semen of the same bulls was analyzed immediately after thawing and after swim-up using a real-time polymerase chain reaction method developed and validated in our laboratory. Calving data relative to single bulls did not reveal any significant deviation between genders from the theoretical 1:1 for none of the bulls, being the mean values of male and female calves born 52.1 ± 2.80% and 47.9 ± 2.71%, respectively. Thereafter, calving events of bulls were classified and analyzed according to four classes of years: 2009 (n = 13,261), 2010 (n = 21,551), 2011 (n = 24,218), and 2012 (n = 41,726), and seasons categorized as winter, spring, summer, and fall. When data aggregated per years were analyzed, the difference between the two sexes was significant (P < 0.005) in favor of the male gender, whereas no influence of the season was evidenced. Real-time polymerase chain reaction did not evidence any difference between the mean values of frequency of Y chromosome-bearing sperm detected in three sperm batches of the same bulls analyzed immediately after thawing (51.1 ± 2.1), nor a difference with respect to the theoretical 1:1 ratio was reported after sperm analysis of one batch of sperm of the bulls analyzed after swim-up and immediately after thawing (50.1 ± 2.1 and 49.8 ± 1.8, respectively). The results are consistent with the observation of the farmers who often report a skewed sex ratio of the calves being born with AI in favor of the male gender. However, we have not evidenced differences in the primary sex ratio with respect to the theoretical 1:1 ratio both at thawing and after swim-up, thus demonstrating that the freezing procedure itself does not impact selectively on the survival of the X or Y chromosome-bearing sperm. Therefore, we hypothesize that the difference between genders observed after AI is more likely due to the events occurring after fertilization, which can comprise an impaired function of the X- or Y-bearing sperm with consequences on embryo development or a maternal influence.

High-resolution melt analysis does not reveal mutagenic risk in sexed sperm and in vitro-derived bovine embryos.

The objectives of the present work were to verify whether simultaneous exposure to Hoechst 33342 and UV irradiation during sorting by flow cytometry may induce gene point mutations in bovine sperm and to assess whether the dye incorporated in the sperm may imply a mutagenic effect during the embryonic development. To this aim, high-resolution melt analysis (HRMA) was used to discriminate variations of single nucleotides in sexed vs. non-sexed control samples. Three batches of sorted and non-sorted commercial semen of seven bulls (42 samples) were subjected to HRMA. A set of 139 genes located on all the chromosomes was selected, and 407 regions of the genome covering a total of 83 907 bases were analyzed. Thereafter, sperm of one sexed and one non-sexed batch of each bull was used in in vitro fertilization, and the derived embryos were analyzed (n = 560). One hundred and thirty-three regions of the bovine genome, located in 40 genes, were screened for a total coverage of 23 397 bases. The comparison between the frequencies of variations, with respect to the sequences deposited, observed in the sexed and non-sexed sperm (843 vs. 770) and embryos (246 vs. 212) showed no significant differences (P > 0.05), as measured by chi-square tests. It can be concluded that staining with Hoechst 33342 and exposure to UV during sorting does not lead to significant changes in the frequencies of variants in the commercial sexed semen and in embryos produced in vitro with the same treated sperm.

Minimum number of spermatozoa per dose in Mediterranean Italian buffalo (Bubalus bubalis) using sexed frozen semen and conventional artificial insemination.

In buffaloes, AI with sexed semen is not fully optimized, and the procedure has only been performed using the approach currently in use for cattle. The objective of the present work was to compare the pregnancy rates in Mediterranean Italian buffalo cows inseminated with sexed frozen-thawed semen at 2, 4, 6, and 8 million sperm per dose, using the Ovsynch protocol and conventional AI at a fixed time. Fresh ejaculates from three buffalo bulls were processed according to Beltsville sperm sorting technology, and packaged in 0.25-mL straws with two total concentrations of 2 and 4 million live sorted sperm per straw. After thawing, semen was evaluated for total motility, forward motility, average path velocity, membrane and DNA integrity, and membrane fluidity. Sorting efficiency was estimated using a real time polymerase chain reaction method developed and validated in our laboratory. The artificial inseminations were conducted during the breeding season on 849 Italian Mediterranean buffalo heifers and cows distributed in 13 farms in northern and central Italy. No significant difference in quality parameters was reported between nonsexed and sexed straws produced with 2 and 4 million sperm. Lower pregnancy rate (P < 0.001) was reported when inseminating doses of sexed semen at 2 million were used (53/170; 31.2%), with respect to conventional nonsexed (78/142; 54.9%), and sexed doses at 4, 6, and 8 million spermatozoa (102/205, 49.8%; 84/175, 48.0%; and 74/157, 47.1%, respectively). No differences were evident using conventional doses and sexed semen with sperm numbers equal or higher than 4 million per dose. Pregnancies were not affected by the sire; 39/82 (47.6%), 120/270 (44.4%), and 151/355 (42.5%), respectively, for the three bulls. Variability in pregnancy rates observed in different herds was not significant. Furthermore, no significant difference was reported between pregnancies obtained with sexed semen in heifers and multiparous, respectively, 179/407 (44.0%) and 131/300 (43.7%). The results of the present work indicate that in Mediterranean Italian buffalo the dose of 4 million represents an optimal compromise when using sexed semen with conventional technologies of insemination, together with estrus synchronization, and the minimum number of spermatozoa per dose. In addition, the real time polymerase chain reaction method was optimized and is now available for estimating sorting efficiency in buffalo.

Comparison of three PCR-based methods to detect a Piedmontese cattle point mutation in the Myostatin gene.

Despite many recent advances in single nucleotide polymorphism (SNP) genotyping technologies, there is still the need for methodologies with a reasonable throughput. In this study, we compared three PCR-based methods for SNP detection: (1) a conventional PCR-based allele detection system with fluorescent genotyping technology, (2) a SNaPshot methodology by single nucleotide primer extension and, (3) a real-time PCR-based method by allele-specific minor groove-binder probes. These three methodologies were used to analyze 104 meat samples of a particular Italian cattle breed known for producing excellent quality meat and for a characteristic increased development of muscle mass, caused by a point mutation (C313Y) in the Myostatin gene. The analysis revealed 98 samples to be homozygous (mh/mh) and five to be heterozygous (mh/+) for the mutation whereas one sample resulted to be homozygous for the wild type (+/+). The results obtained with the three different assays were consistent. Overall, all three methodologies proved to be efficient for allelic discrimination studies; however, real-time PCR was faster and allowed to genotype up to 96 samples in a single step, minimizing the number of steps required for samples manipulation.

Gene expression in the in vitro-produced preimplantation bovine embryos.

Recent studies have demonstrated the relevance of a gene expression profile as a clinically important key feature determining embryo quality during the in vitro preimplantation period. Although the oocyte origin can play a crucial role in blastocyst yield, the postfertilization culture period has a profound effect in determining the blastocyst quality with particular regard to the relative abundance of many developmentally and clinically important candidate genes. During the preimplantation period, the embryo undergoes several morphogenetic developmental events including oocyte maturation, minor and major forms of embryonic genome activation and transition of transcription from maternal to embryonic control. The effect of an altered gene expression pattern on the in vitro-produced bovine embryos, particularly when cultured under suboptimal conditions, was reflected by the occurrence of clinically important phenomena like apoptosis and the large offspring syndrome. This review attempts to focus on the morphogenetic embryo development and gene expression profile in the in vitro-produced bovine embryos, with special emphasis on the different parameters that may alter gene expression pattern during the critical period of in vitro culture. The effect of the in vitro system, as reflected by some clinically important phenomena like apoptosis, is also discussed.

Sex ratio determination in bovine semen: a new approach by quantitative real time PCR.

Sex preselection of livestock offspring in cattle represents, nowadays, a big potential for genetic improvement and market demand satisfaction. Sperm sorting by flow cytometer provides a powerful tool for artificial insemination and production of predefined sexed embryos but, an accurate verification of the yield of sperm separation remains essential for a field application of this technique or for improvement and validation of other related semen sexing technologies. In this work a new method for the determination of the proportion of X- and Y-bearing spermatozoa in bovine semen sample was developed by real time PCR. Two sets of primers and internal TaqMan probes were designed on specific X- and Y-chromosome genes. To allow a direct quantification, a standard reference was established using two plasmid cDNA clones (ratio 1:1) for the specific gene targets. The method was validated by a series of accuracy, repeatability and reproducibility assays and by testing two sets of sorted and unsorted semen samples. A high degree of accuracy (98.9%), repeatability (CV=2.58%) and reproducibility (CV=2.57%) was shown. The results of X- and Y-sorted semen samples analysed by real time PCR and by flow cytometric reanalysis showed no significant difference (P>0.05). The evaluation of X-chromosome bearing sperms content in unsorted samples showed an average of 51.11+/-0.56% for ejaculates and 50.17+/-0.58% for the commercial semen. This new method for quantification of the sexual chromosome content in spermatozoa demonstrated to be rapid and reliable, providing a valid support to the sperm sexing technologies.

Comparative FISH-mapping of the survival of motor neuron gene (SMN) in domestic bovids.

A comparative fluorescence in situ mapping of the SMN gene was performed on R-banded chromosome preparations of cattle (Bos taurus, BTA, 2n = 60), river buffalo (Bubalus bubalis, BBU, 2n = 50), sheep (Ovis aries, OAR, 2n = 54) and goat (Capra hircus, CHI, 2n = 60), as well as on those of a calf from Piedmont breed affected by arthrogryposis. SMN was located on BTA20q13.1, OAR16q13.1, CHI20q13.1 and BBU19q13. These chromosomes and chromosome bands are believed to be homeologous, confirming the high degree of chromosome homeologies among bovids. The position of SMN was refined in cattle, compared to the two previous localizations, while it is a new gene assignment in the other three bovids. A comparative fiber-FISH performed on extended chromatin of both normal cattle and calf affected by arthrogryposis revealed more extended FITC signals in the calf, compared to the normal cattle (control), suggesting a possible duplication of the SMN gene in the calf affected by arthrogryposis. .