Sperm chromatin structure and sperm morphology: their association with fertility in AI-dairy Ayrshire sires.

Prognostic relations between sperm variables and sire fertility are yet elusive. A retrospective analysis of sperm morphology and chromatin stability (studied using sperm chromatin structure assay [SCSA]) and their relation to fertility after AI (as proportions of 60 days of nonreturn to estrous [NRR], corrected NRR, or calving rate) was studied with preselected frozen semen doses from a group (N = 43) of AI-sires of the Finnish Ayrshire breed composed of 50% subfertile bulls (<55% NRR) and 50% fertile sires (>55% NRR). Fertility, indicated by all three parameters, correlated significantly only with the percentage of morphologically normal spermatozoa, a variable which negatively correlated with the percentage of DNA fragmentation at the time of SCSA, thus confirming the value of always having high numbers of morphologically normal spermatozoa in AI-doses. Proportions of major sperm defects also related to fertility but only when considering corrected NRR, not with calving rate, indicating that proportions of normal spermatozoa, a value surpassing differences between sperm laboratory screening methods, might be valuable and could be easily made routine by the industry. Though SCSA as a method is being contested for DNA- and chromatin analyses in the light of epigenetic changes, a particular parameter, the High Green fluorescence, showed the highest values for sperm doses collected from bulls having meiotic problems and containing a high proportion of diploid spermatozoa (approximately 20%) and also in bulls having a reciprocal chromosomal translocation, thus suggesting such a parameter might be useable to discriminate which bulls ought to be studied in more detail, including cytogenetic analyses.

Diploid spermatozoa caused by failure of the second meiotic division in a bull.

An artificial insemination bull (Bos taurus) exhibiting 23% macrocephalic spermatozoa in the ejaculate was investigated. Spermatozoa with a projected head area of > or = 52 microm(2) were considered macrocephalic. Diploidy was assumed from the measurement of sperm head area and proved by flow cytometry, which was used to sort the sperm into haploid and diploid fractions. Fluorescence in situ hybridization was used to detect the sex chromosomes with an X-Y probe set. Diploid spermatozoa most likely originate from a defective second meiotic division (M2 diploids), as only 0.7% XY-bearing spermatozoa (M1 diploids) were detected in the spermatozoa of the flow cytometric diploid sort. The painting probes generated a single X or Y spot for both unsorted semen and diploid sorted spermatozoa. This indicates a close proximity of the nonpartitioned sister chromatids in the spermatozoa. The BC1.2 probe, which labels BTAYp13-12, was used to clarify the presence of the two chromatids in the singular signal of the simultaneously hybridized Y-painting probe. In scoring more than 1000 randomly sampled spermatozoa hybridized with the BC1.2 probe, 32% showed the YY diploid signal and 18% the Y signal. The sperm diploidy in this bull was caused by an incomplete partitioning of sister chromatids during the second meiotic division (M2) associated with a failure in nuclear cleavage.

Morphometric evaluations of testicular tissues from azoospermic boars in Finnish Yorkshire and Landrace breeds.

In 1996-2005, ejaculates of 2048 boars were collected. All boars were intended for use in artificial insemination or natural breeding and had two descended testes. Azoospermia was present in 16 of the 1097 Yorkshire boars (1.5%) and in 2 of the 951 Landrace boars (0.2%). The two most frequent diagnoses of azoospermia were arrested spermatogenesis at the pachytene spermatocyte stage (n=8) and segmental aplasia of the Wolffian ducts (n=7). Morphometric evaluations of testicular tissues of azoospermic boars were performed using an image analyzer. The morphometric evaluations revealed decreased portions and diameter of seminiferous tubule in tissue slides from the studied azoospermic boars compared with normal boars. The use of an image analyzer for morphometric evaluations of testicular tissues proved to be a good tool to characterize findings in testicular slides of azoospermic boars.

Infertile boars with knobbed and immotile short-tail sperm defects in the Finnish Yorkshire breed.

In the period 1996-2006 two specific sperm defects, the knobbed acrosome (KA) defect and the immotile short-tail sperm (ISTS) defect, showed a strong negative association with fertility in Finnish breeding boars. In this study, we examined the incidence of these two sperm defects in two pig breeds, their effects on fertility and their associations with sperm morphology and testicular histology. Semen samples from 2048 (1097 Yorkshire, 951 Landrace) boars were collected. None of the Landrace boars revealed either the KA defect or the ISTS defect. Of the Yorkshire boars, 0.8% were afflicted with the KA defect and 7.6% with the ISTS defect. Boars diagnosed with the ISTS defect produced no litters. Fertility data were available from two artificially inseminated (AI) boars and six farm breeding boars affected with the KA defect. Breeding boars with 45-81% knobbed spermatozoa (n = 6) did not produce any litters out of 71 sows bred. AI boars with 25-30% knobbed spermatozoa had a poor non-return rate (on average 47% compared with 85% for normal control boars) and produced small litters, on average 2.5 piglets less than other boars of the same breed. Morphometry of testicular tissue and distribution of different cells in the seminiferous tubules were examined in nine boars. Boars with the KA defect had a smaller diameter of the seminiferous tubules (p < 0.05) and a lower number of Sertoli cells (p < 0.05) than controls. ISTS boars, in turn, had a significantly lower number of elongated spermatids (p < 0.05), and they also produced on average only 12% of the spermatozoa of normal boars. The ISTS defect is a manifestation of an autosomal recessive disease caused by an insertion in the KPL2 gene in porcine chromosome 16. Although we tried to map the KA defect, its aetiology remains unclear.