Subfertile Animals Research Articles

The predictive value of semen analysis in the evaluation of stallion fertility.

Pregnancy rates in managed horse populations depend on the innate fertility of the mares and stallions involved and on the quality of breeding management. Of course, because a single stallion usually mates many mares, stallion fertility is a critical factor in the overall success of a breeding program. Unfortunately, accurate evaluation of stallion fertility per se requires a large number of normal mares to be mated and is necessarily retrospective. Rather, the ideal is to predict fertility in advance of the stallion's breeding career, and this is currently attempted by way of a thorough physical examination and a routine analysis of semen quality. However, while such a 'breeding soundness examination' identifies stallions that clearly lack the capacity for adequate fertility, it is of limited use for predicting the level of fertility and fails to identify some seriously sub-fertile animals. Similarly, while various sperm function tests (e.g., sperm head morphometry, the hypoosmotic swelling test, glass wool-sephadex filtration, progesterone receptor exposure) have been shown to correlate fairly well with fertility in the field, most examine only a single or a narrow range of the attributes that a sperm must possess if it is to fertilize an oocyte in vivo, and are thus more useful for identifying specific causes of sub-fertility than for predicting the level of fertility. On the other hand, combining the results of the various sperm function tests does improve the reliability of fertility estimation and current research is therefore concentrated on identifying a range of tests that covers as many important sperm attributes as possible but that can be performed rapidly and cheaply. In this respect, flow-cytometry has proven to be an ideal tool because it allows the objective, rapid and simultaneous analysis of a number of properties in a large number of sperm. Moreover, stains are available for an increasing range of sperm characteristics including viability, capacitation and acrosome status, mitochondrial activity and chromatin integrity. Flow-cytometric analysis of sperm with appropriate probes thus offers considerable promise for the prediction of stallion fertility.

Repeat breeding in dairy heifers: follicular dynamics and estrous cycle characteristics in relation to sexual hormone patterns

Repeat breeding occurs at an incidence of 10% in the Swedish dairy cow population. Evidence is available for a hormonal asynchrony around estrus in repeat-breeder heifers (RBH). This asynchrony seems to be the underlying cause for a series of dysfunctions such as prolonged standing estrus and delayed ovulation, leading to fertilization failure. For further determinations of repeat-breeder estrous cycle characteristics, seven strictly selected RBH and six virgin heifers (VH) were studied during 3–7 consecutive cycles, with particular attention paid to the estrous period. Follicular dynamics were studied by ultrasonography and related to estrous behavior and pattern of sexual hormones (progesterone, estradiol-17β, and LH) in peripheral circulation. Mean group data were compared and a classification model was designed. The most prominent findings for RBH were prolonged duration of estrus, delayed LH peak, prolonged lifespan of the preovulatory follicle, and a late postovulatory rise in plasma progesterone. There was also a strong tendency for peri-ovulatory suprabasal progesterone levels in RBH. It is suspected that these deviations cause changes in the microenvironment of the preovulatory follicle, negatively affecting the final maturation of the oocyte. The heterogeneity of the RBH group underlines the multifactorial cause of the repeat-breeder syndrome. The VH formed a homogenous group with data varying within physiological limits. A classification model based on three characteristic variables managed to identify 81% of the VH and 79% of the RBH correctly. Results from this study propose that some heifers have general, consistent problems in synchronizing estrous events, displayed as varying symptoms in the course of consecutive estrous cycles. These subfertile animals could be classified as repeat-breeders.

Capacitation dependent lipid rearrangements in the plasma membrane of equine sperm

In general, fertility in breeding stallions is lower and more variable than in the other farm animal species, primarily because selection is based on pedigree, looks and/or athletic performance, with little consideration of fertility or fertility potential. Moreover, because the average stallion breeds only a limited number of mares per year and in-field fertility is influenced significantly by non-stallion factors such as management and mare fertility, meaningful fertility data are hard to come-by. Unfortunately, generating usable figures would involve impractically high costs, time and numbers of mares. Instead, a breeding soundness examination (BSE), based on assessments of sperm number, motility and morphological normality and of mating ability, is often carried out with the ostensible aim of identifying animals with the “potential for good fertility”. In fact, the BSE generally succeeds only in ruling out those stallions with a very clear reason for sub-fertility, and still fails to identify some seriously sub-fertile animals. Thus, the routine BSE has very limited use as a predictor of subsequent fertility. This paper reviews assays developed for identifying capacitated, acrosome-reacted and DNA-damaged sperm, and assesses their utility for improving our ability to predict a stallion's fertility prior to the onset of his breeding career.

Ovarian hormone patterns and subfertility in dairy cows

AbstractDecreasing levels of fertility of dairy cows are occurring, associated with increased average annual milk yields, increased herd size and a decreased labour investment per animal. To-date, there has been no positive genetic selection in the UK for improved female fertility due to the lack of reliable recording of fertility traits. Selection is further limited by the low heritabilities of traditional fertility measures, which are subject to environmental influences and management decisions and biological restraints such as age and sex. Assessment of the hormone patterns of fertile cows and determination of the atypical patterns exhibited by subfertile animals provides an objective method of identifying the causes and assessing the impact of subfertility and for the development of remedial treatment strategies. This knowledge can then be used to identify potential physiological parameters associated with high fertility which, in future, may be used for sire breeding value estimations to select for more fertile offspring. Regular assessment of the progesterone concentrations in milk provides a non invasive method of determining progesterone patterns. The results of two studies of milk progesterone levels in cows taken between 1975/82 and 1995/98 involving over 3200 lactations have been analysed and compared. They indicate a major increase over this period in the proportion of animals showing atypical milk progesterone patterns before mating from 32 to 44% (P<0.001) associated with less animals inseminated, delays to conception and lower conception rates. There was a significant decrease (P<0.01) over this period in animals calving to first postpartum insemination from 57% to less than 40% a decrease of approximately l%per annum. This may indicate an increase in the level of early embryo mortality. An early post ovulatory progesterone rise to adequate luteal phase levels has been shown essential for normal embryo development with low post ovulatory levels occurring in some cows resulting in lower calving rates. Milk progesterone analysis provides a robust and reliable method of measuring progesterone patterns for identifying subfertile animals, for targeting remedial treatments to improve fertility and for investigations into heritable fertility parameters for future selection programmes.

Discriminant analysis indicates a single sperm protein (SP22) is predictive of fertility following exposure to epididymal toxicants.

In a previous study, we found that ethane dimethanesulphonate (EDS) compromised the fertilizing ability of proximal cauda epididymal sperm from the rat within 4 days of exposure, an effect that persisted in castrated, testosterone (T)-implanted animals, establishing direct action on the epididymis. This EDS-induced reduction in fertilizing ability was highly correlated with a quantitative decrease in specific sperm protein. Here we sought to determine whether the fertility of proximal cauda epididymal sperm recovered from animals exposed to a variety of male reproductive toxicants could be predicted by assessing quantitative changes in specific sperm protein(s), or whether more common endpoints (e.g., sperm motility, sperm morphology, serum and epididymal tissue T, cauda epididymal sperm reserves) also are required to predict fertility. Intact adult male rats were dosed with EDS (25 or 50 mg/kg), chloroethylmethanesulphonate (CEMS; 12.5 or 18.75 mg/kg), or epichlorohydrin (EPI; 3 or 6 mg/kg) daily for 4 days. Castrated, T-implanted rats were dosed with hydroxyflutamide (HFLUT; 12.5 or 25 mg/kg) daily for 5 days. On day 5, proximal cauda epididymal sperm were inseminated in utero into receptive, cervically stimulated adult females, and on day 9, fertility (implants/corpora lutea) was assessed. Fertility-was decreased by the higher dose of each toxicant (P < 0.05) and also by the lower dose of EPI and HFLUT. Likewise, an acidic 22 kDa sperm protein (SP22) was decreased quantitatively (P < 0.05) in silver-stained two-dimensional gels by the higher dose of each toxicant as well as by the lower dose of EPI and HFLUT. Although sperm motility and serum T were altered by specific exposures, these endpoints were not useful in predicting fertility. In contrast, SP22 was highly correlated (P < 0.0001; r2 = 0.83) with fertility. Indeed, the amount of SP22 correctly predicted 90% and 94% of the fertile (> 50% fertility) and subfertile (< 50 fertility) animals, respectively, when discriminant analysis was performed. Thus, the amount of SP22 in a cauda epididymal sperm sample may be a useful predictor of fertility in toxicant-treated animals.

The DNA content of spermatozoa from different strains of mice.

Certain morphological characters of mammalian spermatozoa have been shown to have a high heritability (Beatty, 1970). Sperm dimensions may be altered by genetic selection (Woolley, 1970). In addition to the biological action ofthe genes, the actual mass of the DNA and proteins, which constitute the major components of the head, may affect the sperm phenotype. Unlike genetically active cells in which nuclear size is governed, to a certain extent, by metabolic factors, the sperm genome is condensed, homogeneous and inactive. It might therefore be expected that head size would be influenced both by the quantity of DNA present and by the way it is condensed. Thus diploid spermatozoa have enlarged heads (Beatty & Fechheimer, 1972), whereas spermatozoa with abnormally small heads might have a lower Feulgen\p=m-\DNAcontent than morphologically normal members of the same ejaculate (Gledhill, 1970). The size differences described in the latter studies probably reflect alterations in sperm chromatin structure affecting the availability of Feulgen-reactive sites. When the DNA contents of small and normal spermatozoa were compared by ultraviolet (u.v.) absorption methods, no significant differences were observed (Gledhill, 1970). There are also many instances in the literature of variations in Feulgen\p=m- and u.v.-DNA contents in morphologically normal spermatozoa of fertile and subfertile animals (Leuchtenberger, Leuchtenberger, Schrader & Weir, 1956; Leidl & Stolla, 1969; Gledhill, 1970), although no actual measurements of sperm head dimensions were recorded in some of these studies. Expected variations in the DNA content, as in Xand Y-bearing spermatozoa can be detected chemically but not morphologically (Beatty, 1970; Evans, 1972). In an attempt to clarify the relationship between genome and head size, Feulgen-DNA measurements were made in strains of mice in which variations in morphology have been reported (Beatty & Sharma, 1960). Four inbred strains were studied : A, JBT, CBA and C57. The spermatozoa of these strains are known to differ from each other in the size and shape of the head and midpiece. If head area alone is considered, A > CBA > JBT > C57, but the only significant differences are those involving C57 (see Table 1). Two males from each strain, aged between 9 and 11 weeks, were used. Spermatozoa from the ductus deferens were dispersed in a small volume of saline and smeared on glass slides. Each slide (A series) bore a total of eight * Present address: The Department of Zoology, Australian National University, Canberra, A.C.T., Australia. t Agricultural Research Council Unit of Animal Genetics.