Proportion of males with lower fertility spermatozoa estimated from heterospermic insemination

Longer and faster sperm exhibit better fertilization success in Japanese quail

In birds, sperm storage tubules (SST) located in the utero-vaginal junction are thought to be a site of sperm selection; however, the exact mechanism of sperm selection is poorly understood. Here, we investigated sperm entry into the SST and subsequent fertilization success under a competitive situation created by artificial insemination of a sperm mixture obtained from 2 males. We employed 2 quail strains, a wild-type and a dominant black (DB) type, as this allows easy assessment of paternity by feather coloration. We found paternity of embryos was biased toward DB males when a sperm mix with similar sperm numbers from the 2 males strains was artificially inseminated into females. Our novel sperm staining method with 2 different fluorescent dyes showed that the DB-biased fertilization was because of the better ability of DB sperm to enter the SST. Moreover, we found that DB sperm had a longer flagellum and midpiece. These characteristics probably allow sperm to swim faster in a high viscosity medium, which may be a similar environment to the lumen of the female reproductive tract. Our results indicated that sperm competition occurs to win a place in the SST and that filling the SST with their own spermatozoa is a critical step to achieve better fertilization success for the male Japanese quail.

Making the most of sperm activation responses: experiments with boar spermatozoa and bicarbonate

Attempting to extract useful and reliable information about semen quality and its fertility potential remains a difficult exercise, partly because the sperm heterogeneity within samples often renders simple statistical analyses rather meaningless. In fact, a mean and standard deviation may reflect neither the very fast swimming activities of the most active cells nor the slow and sluggish activities of others. Herein we propose that the information value within semen samples can be maximised if current knowledge about sperm activation mechanisms is exploited before undertaking the measurements. We explain, using boar semen as an example, that estimating and defining relative sperm subpopulation sizes, after activation by bicarbonate, provides a means of quantifying sperm quality. Although such estimates may indeed be related to in vivo fertility, the general approach also suggests potential new avenues that could be exploited for the elaboration of novel in vitro tests for the characterisation of toxic environmental chemicals and, indeed, to reduce the number of animals used in such testing programs.

In vitro competitive binding index using fluorochrome-labelled spermatozoa for predicting bull fertility

This work evaluated if an in vitro test, with the combined power of the statistical evaluation of spermatozoa and zona pellucida (ZP) competitive binding ability and a rapid method for accessory sperm counts, could predict the bull fertility. Ten Holstein Friesian bulls of known field fertility (five of high and five of low fertility) were selected. An in vitro heterospermic insemination approach, based on differential staining, was tested on 45 possible pairs of bulls (two batches per bull). Motility and quality (abnormalities and membrane status) seminal characteristics and estimated relative conception rates (ERCR) highlighted only one association between membrane integrity and ERCR (p = 0.007). Differences in ZP binding allowed us to rank bulls into two categories based on low and high binding ability. For eight bulls, this classification reflected the ERCR. Differences between batches were reported for two bulls, in which the effect of heterospermic insemination (the number of sperm binding to ZP from different bulls not in a 1:1 ratio) showed a significant bull-related effect (p < 0.001) in the first batch and no effect (p > 0.05) in the second batch for both bulls. Reduction of the number of oocytes per assay from 25 to 5 had no effect (p > 0.5) on the bulls’ ranking. Our results suggest that in vitro competitive binding is a promising approach for estimating bull fertility and support concepts for further implementation, e.g. drastic reduction of oocyte number in a single pair assay and larger scale testing for batches.

Relationships among lipid peroxidation, glutathione peroxidase, superoxide dismutase, sperm parameters, and competitive index in dairy bulls

Sperm membranes contain high concentrations of polyunsaturated fatty acids that are highly susceptible to oxidative damage that interferes with fertilization ability. The objective of this study was to determine associations among lipid peroxidation (thiobarbituric-acid-reactive substance concentration), antioxidant enzymatic activities in frozen spermatozoa, and competitive indices. Semen from multiple ejaculates collected in succession from each bull (four Holstein and four Jersey) was pooled. Heterospermic doses (20x10(6)sperm/0.5mL straw) were made to obtain 16 Holstein/Jersey combinations (equal number of sperm from each bull). Cows were inseminated on observed or synchronized estrus. The sire of calves (N=460) was determined; based on the number of calves sired, a competitive index was obtained for each bull. Prior to preparation of the heterospermic doses, a sub-sample of semen from each bull was taken, processed, frozen, and stored concurrent with heterospermic samples. After thawing, these homospermic samples were assessed for lipid peroxidation, superoxide dismutase (SOD) activity, glutathione peroxidase (GPx) activity, DNA fragmentation index (DFI), plasma membrane integrity (PMI), and total progressive motility (assessed by CASA). Sperm lipid peroxidation and the competitive index were negatively correlated (r=-0.78; P<0.05), the DFI and sperm lipid peroxidation were positively correlated (r=0.86; P<0.001), and there were negative correlations (P<0.05) for sperm lipid peroxidation and both PMI and total progressive motility (r=-0.78 and -0.83, respectively). There was neither significant association between SOD activity and competitive index, nor between GPx activity and competitive index. In conclusion, bulls with lower sperm lipid peroxidation had higher chances of siring calves; this was attributed to the deleterious effects of lipid peroxidation on sperm plasma membrane integrity and sperm DNA, which may reduce sperm fertilizing potential.

Breed differences in competitive indices of Holstein and Jersey bulls and their association with sperm DNA fragmentation index and plasma membrane integrity

The objective was to evaluate the relationship of a competitive index (CI) determined by heterospermic performance and post-thaw semen quality of the same stored ejaculates. Semen from multiple ejaculates collected in succession from each bull (four Holstein and four Jersey) was pooled. Heterospermic doses (20x10(6)/straw) were made to obtain all possible Holstein-Jersey combinations (16 two-bull combinations) and contained 20x10(6) sperm/mL/bull. Cows at two University dairy farms were inseminated on observed or synchronized estrus. The sire of calves (N=460) were determined and a CI was determined for each bull (based on the number of calves sired). Prior to preparation of the heterospermic doses, a sub-sample of semen from each bull was taken, processed, frozen, and stored concurrently with heterospermic samples. Post-thaw semen samples (homospermic) from each bull were assessed for: sperm morphology, acrosome integrity, sperm motility parameters assessed by computer assisted sperm analysis (CASA), flow cytometry analysis of DNA Fragmentation Index (DFI), and Plasma Membrane Integrity (PMI). Heterospermic performance of Holstein bulls was superior to that of Jersey bulls. The DFI was negatively correlated to CI (r=-0.87; P<0.001), whereas the PMI (r=0.87; P<0.001) and total progressive motility (r=0.74; P<0.05) assessed by CASA were positively correlated to CI. In multivariate regression models, the DFI and PMI accounted for 87% variance in competitive index. In conclusion, bulls with less DFI and higher PMI had higher probabilities of siring calves.

Is quality assurance in semen analysis still really necessary? A spermatologist's viewpoint

In a provocative article to this Journal, Anne Jecquier, an eminent andrologist who, more than 20 years ago, was a prime mover in suggesting the need for quality assurance (QA) in andrology laboratories, has now proposed that the QA schemes may no longer be needed. Here I reply to that proposition, largely by agreeing that, since the QA schemes have brought about higher technical standards in laboratories, Anne Jecquier's assertion is possibly true. However, vigilance is still needed in discriminating between unproductive investment of time and energy in the refinement of tests that may offer little information about fertility, and maintaining technical standards such that where necessary they provide the requisite information. Thus, although it may not matter in practice whether a sperm concentration is estimated as 100 or 200 x 10(6)/ml, distinguishing between 25 and 100 x 10(6)/ml would probably influence a clinician's treatment decisions. Anne Jecquier also suggested that sperm function tests have limited predictive value in terms of fertility assessment. While I agree that this is largely true at present, I also argue that these tests are probably not developed to their full potential. I am optimistic that tests to distinguish and quantify the population of fertilization-competent sperm within an ejaculate will eventually become available.

Fertility assessment through heterospermic insemination of flow-sorted sperm in cattle

The ability to assess fertility of bovine sperm accurately and rapidly would be very useful for research and applications to the cattle industry. Sperm motility and other in vitro tests of sperm normality are only partially correlated with fertility, and lengthy breeding trials are expensive and time consuming. Heterospermic insemination by mixing sperm from more than one male provides an in vivo method to assess relative fertility among bulls that can be economical and rapid. Sperm that had been flow-sorted and cryopreserved from four groups of four bulls were inseminated in all combinations of three bulls within groups into nonsuperovulated heifers or superovulated heifers. Embryos were collected nonsurgically between d 13.5 and 20 following estrus and evaluated for paternity by genotyping. Following determination of paternity, a heterospermic index was created for each bull using a maximum likelihood function. These indices ranged from 0.22 +/- 0.15 to 2.43 +/- 0.43 (mean = 1.00, with a higher value indicative of greater fertility). In all four groups, either the high- or low-fertility bull was identified (P < 0.05) using a total of 25 to 36 genotypable embryos from nonsuperovulated heifers. The heterospermic rankings of bulls were similar for single and superovulated heifers for one group of bulls, but dissimilar for a second group. Heterospermic insemination followed by genotyping of embryos proved to be efficacious for rapidly ranking fertility of flow-sorted sperm from bulls when females were not superovulated, but results were less clear when females were superovulated.

Fertility estimation: a review of past experience and future prospects

Fertility has many components and stages which require that males and females be functionally capable of carrying out all critical stages if each generational reproductive cycle is to be completed. To accomplish this, the male must produce and ejaculate normal fertile sperm. The female must produce, store and ovulate normal fertilizable oocytes. Furthermore, the female must provide a reproductive system compatible with sperm transport, capacitation, and fertilization of the oocytes, embryo and fetal development, and finally birth of healthy young. Reproductive success or failure at several of these points can be estimated quantitatively on a population basis, and in a few situations on an individual basis. It is important that fertility estimates be determined accurately and with precision to be most useful to researchers and managers of animal enterprises. Many studies have underestimated the biological relationship of fertility to other traits because the estimates lacked precision. Many in vitro manipulations of sperm in artificial insemination, of gametes in various assisted reproductive technologies, and of embryos in embryo transfer are utilized in animal breeding programs. Accurate estimation of reproductive efficiency of these in vitro procedures also is important. Conditions surrounding different sets of fertility estimates almost certainly will be different. These conditions should be described as precisely as possible, and appropriate controls included in all experiments. When possible, experiments should be replicated over time and place to determine the repeatability of the various criteria used to estimate fertility and reproductive efficiency. Advances in genomic information and molecular biology should facilitate characterizing more fully inherent potential fertility of animals at birth. In vitro tests will improve, and automated techniques will facilitate making multiple determinations possible on a large scale. Reliability of fertility estimates will increase, with the potential for enhanced animal reproductive performance through more accurate selection, genetic engineering, and enlightened animal care. Simultaneously, it is important to recognize that prediction of future fertility is more hazardous than estimating fertility, as a completely new set of circumstances may occur which are not predictable. Because fertility estimation may be applied under a myriad of conditions, principles and factors affecting fertility will be emphasized in this review as being more useful than a compilation of numerical examples.

Do sire-dam interactions contribute significantly to fertility comparisons in heterospermic insemination trials

The percentage of offspring sired after heterospermic insemination of equal numbers of spermatozoa is believed to be a very sensitive measure of relative in vivo fertility of the inseminated samples. The objective of these trials was to evaluate whether there was a detectable male-female interaction in the fertilizing ability of spermatozoa. If there was such an interaction, we reasoned that the paternity of offspring from individual females in a heterospermic trial the second year would be similar to the paternity of offspring in the same individual females the first year if the same ejaculates were used. Five groups of ewes were inseminated with different combinations of semen (a single Merino ejaculate from one of five rams randomly paired with five different pools of Suffolk semen) in a heterospermic trial. Those ewes conceiving the first year were inseminated in a second breeding season with the same combination of semen used previously. The percentage of lambs sired by each ejaculate/pool of ejaculates was calculated for all lambs born from all ewes inseminated with each semen combination. These percentages would be the expected ratios of Merino-sired:Suffolk-sired lambs if there is no male-female interaction. Ewes in each group were divided into two subgroups: those conceiving only Merino-sired lambs the first year and those conceiving at least one Suffolk-sired lamb the first year. The ratio of Merino-sired lambs:Suffolk-sired lambs did not differ in either subgroup from those expected if there was no male-female interaction. These results are consistent with the absence of a male-female interaction in relative fertilizing ability of spermatozoa.