Abstract
BackgroundArtificial insemination is widely used in many cattle breeding programs. Semen samples of breeding bulls are collected and closely examined immediately after collection at artificial insemination centers. Only ejaculates without anomalous findings are retained for artificial insemination. Although morphological aberrations of the spermatozoa are a frequent reason for discarding ejaculates, the genetic determinants underlying poor semen quality are scarcely understood.ResultsA tail stump sperm defect was observed in three bulls of the Swedish Red cattle breed. The spermatozoa of affected bulls were immotile because of severely disorganized tails indicating disturbed spermatogenesis. We genotyped three affected bulls and 18 unaffected male half-sibs at 46,035 SNPs and performed homozygosity mapping to map the fertility disorder to an 8.42 Mb interval on bovine chromosome 13. The analysis of whole-genome re-sequencing data of an affected bull and 300 unaffected animals from eleven cattle breeds other than Swedish Red revealed a 1 bp deletion (Chr13: 24,301,425 bp, ss1815612719) in the eleventh exon of the armadillo repeat containing 3-encoding gene (ARMC3) that was compatible with the supposed recessive mode of inheritance. The deletion is expected to alter the reading frame and to induce premature translation termination (p.A451fs26). The mutated protein is shortened by 401 amino acids (46 %) and lacks domains that are likely essential for normal protein function.ConclusionsWe report the phenotypic and genetic characterization of a sterilizing tail stump sperm defect in the Swedish Red cattle breed. Exploiting high-density genotypes and massive re-sequencing data enabled us to identify the most likely causal mutation for the fertility disorder in bovine ARMC3. Our results provide the basis for monitoring the mutated variant in the Swedish Red cattle population and for the early identification of infertile animals.Electronic supplementary materialThe online version of this article (doi:10.1186/s12863-016-0356-7) contains supplementary material, which is available to authorized users.
Highlights
Artificial insemination is widely used in many cattle breeding programs
Histological sections of the testicles revealed a lack of full-length sperm tails in the luminal part of the tubuli seminiferi indicating disturbed spermatogenesis (Fig. 1c-d)
We consider the frameshift in armadillo repeat containing 3-encoding gene (ARMC3) as the most likely causal mutation because it is predicted to result in a protein that lacks 401 amino acids
Summary
Artificial insemination is widely used in many cattle breeding programs. Semen samples of breeding bulls are collected and closely examined immediately after collection at artificial insemination centers. Artificial insemination (AI) is widely used instead of natural mating in many cattle breeding populations. Ejaculates of breeding bulls are collected once or twice a week and closely examined immediately after semen collection at highly specialized AI centers. Diagnoses of insufficient semen quality involve the absence of spermatozoa, low sperm concentration, reduced motility or viability and morphological aberrations of spermatozoa [2]. Morphological aberrations of the sperm tail compromise sperm motility and impair fertilization. Such aberrations are collectively referred to as multiple morphological abnormalities of the flagella (MMAF, [3]).
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