Experimental demonstration that mammalian oocytes are not selective towards X- or Y-bearing sperm

Maternal hepatitis B status and Sex at birth: A cross-sectional study in a Ghanaian population

Maternal carrier status of hepatitis B has been associated with excess sons while maternal immunity to it has been associated with excess daughters at birth. However, the proportion of males at birth (sex ratio) is relatively low in Sub-Saharan Africa despite the relatively high prevalence of hepatitis B. However, no known study has tested this hypothesis in the Ghanaian population; hence the aim of the study. The study was cross-sectional between January and September 2023 at the Tamale Central Maternal and Child Health unit. The study involved 380 mothers of whom mothers with daughters (MD) were 145 (38.2 %) while the rest were mothers with sons (MS). The mothers were aged between 18 and 43 years and were sampled within one week of delivery to singleton births. Maternal venous blood samples were collected and tested for hepatitis B surface antigen (HBsAg), surface antibody (HBsAb), envelop antigen (HBeAg) envelope antibody (HBeAb) and core antibody (HBcAb) using immunochromatographic technique and total testosterone (TT), using ELISA. There was no significant difference in the serum total testosterone level between MD and MS (0.32 ± 0.13 vs 0.32 ± 0.27, P = 0.991). Moreover, while the mothers were seropositive for HBsAg (10.5 %), HBsAb (35.5 %), HBeAg (0.0 %), HBeAb (5.3 %) and HBcAb (11.8 %), there was no significant association between sex at birth and maternal hepatitis B status for HBsAg (ꭓ2: 0.531, P = 0.472), HBsAb (ꭓ2: 2.655, P = 0.140), HBeAb (ꭓ2: 0.251, P = 0.633) and HBcAb (ꭓ2: 0.101, P = 1.000). Maternal hepatitis B status may not be associated with the offspring sex at birth in the studied population from Ghana.

Polyunsaturated fatty acids influence offspring sex ratio in cows

Dietary polyunsaturated fatty acids (PUFAs) can influence fertility in farm animals. Some evidence in mice and sheep have suggested that PUFAs may influence offspring sex ratio, which may have significant value for cattle production. To test this hypothesis, three groups of Holstein cows were supplemented with either 0%, 3% or 5% protected fat (PF) in the form of calcium salt of fatty acids (rich in omega-6) from 14–21 days pre-partum until conception. Proven-fertile frozen semen from the same ejaculate was used for insemination. Calf sex recorded at birth was 8/19 (42.1%) male offspring in the control group, increasing to 14/20 (70%, P > 0.05) and 17/20 (85%, P < 0.05) in 3% and 5% PF, respectively. To test if this effect was caused by a direct influence on the oocyte, we supplemented bovine cumulus oocyte complexes during in vitro maturation with either omega-3 alpha-linolenic acid (ALA), omega-6 linoleic acid (LA) or trans-10, cis-12 conjugated linoleic acid (CLA). Sex ratio of the produced transferable embryos was determined using PCR of SRY gene. Similar to the in vivo results, sex ratio was skewed to the male side in the embryos derived from LA- and CLA-treated oocytes (79% and 71%) compared to control and ALA-treated oocytes (44% and 54%, respectively). These results indicate that both dietary and in vitro supplementation of omega-6 PUFAs can skew the sex ratio towards the male side in cattle. Further experiments are required to confirm this effect on a larger scale and to study the mechanisms of action that might be involved.

Can mammalian mothers influence the sex of their offspring peri-conceptually?

Although controversial, growing evidence from evolutionary biology suggests that the mammalian mother may have a role in influencing the sex of her offspring. However, there is competing information on the molecular mechanisms by which such influence could be manifested. The new initiatives are based on hypotheses from evolutionary biology: the 'good condition' hypothesis, which suggests that post conception, higher levels of maternal glucose may differentially promote the development of male embryos; and the 'maternal dominance' hypothesis, which proposes that before conception, higher follicular testosterone may influence the development of the ovum so that it emerges already adapted to receive an X- or a Y-chromosome-bearing spermatozoon. Now, it seems these hypothesised mechanisms could be operating in synchrony, each complementing and reinforcing the other. On the other hand, there are continuing problems in identifying a precise sequence of mechanisms as evidenced from research in sperm-sorting. Research on high-fat diets and the sex ratio in polytocous species may indicate important differences in proximate mechanisms for sex allocation between polytocous and monotocous mammals.

Intrafollicular testosterone concentration and sex ratio in individually cultured bovine embryos

Recent studies have suggested a relationship between bovine follicular fluid testosterone concentration and the likelihood of the oocyte being fertilised by an X- or Y-bearing spermatozoon; however, this theory has been challenged. To further test this hypothesis, follicles were dissected from the ovaries of slaughtered heifers, measured and carefully ruptured. The cumulus–oocyte complex (COC) was removed and the follicular fluid collected and testosterone concentration determined by radioimmunoassay. COCs were matured, fertilised and cultured in an individually identifiable manner; all cleaved embryos (2- to 4-cell stage, n = 164) had their sex determined by PCR. Testosterone concentrations were positively skewed. There was no significant difference between follicular fluid testosterone concentrations in male and female embryos (mean ± s.e.m. 51.5 ± 5.59 and 49.5 ± 7.42 ng mL–1, respectively). Linear, quadratic and cubic logistical regression showed that follicular testosterone concentration could not reliably predict the sex of the embryo with odds ratios of 1.001, 1.013 and 1.066, repectively, and coefficient of determination (R2) values of 0.0003, 0.0126 and 0.0567, respectively. Follicular size and testosterone concentration were not related (R2 = 0.087). Finally, follicular size had no influence on embryo sex determination (P = 0.70). In conclusion, under the conditions of the present study, the likelihood of an oocyte being fertilised by an X- or Y-bearing spermatozoon was not affected by the size of the follicle from which it was derived, nor by the testosterone concentration in the follicular fluid.

Applications and interpretation of computer-assisted sperm analyses and sperm sorting methods in assisted breeding and comparative research

Theoretical and practical knowledge of sperm function is an essential requirement in almost every aspect of modern reproductive technology, if the overarching objective is the eventual production of live offspring. Artificial insemination (AI) techniques depend on the availability of high quality semen, whether fresh, diluted and stored, or frozen. Assessing such semen for quality and the likelihood of fertility is therefore also important, as much time, resources and effort can easily be wasted by using poor samples. Some semen technologies are aimed not at quality assessment, but at attempting to skew the breeding outcomes. Sex preselection by separating the male- and female-bearing spermatozoa using flow cytometry is now practised routinely in the agricultural industry, but speculatively it may eventually be possible to use other genetic markers besides the sex chromosomes. A moment's reflection shows that although sex-biasing flow cytometry technology is well developed and generally fulfils its purpose if presorting of sperm quality is adequate, other technologies aimed specifically at semen assessment are also sophisticated but provide inadequate data that say little about fertility. This is especially true of instrumentation for objective sperm motility assessment. Here we aim to examine this technological paradox and suggest that although the sperm assessment equipment might be sophisticated, the shortcomings probably lie largely with inappropriate objectives and data interpretation. We also aim to review the potential value and use of sperm sexing technology for non-domestic species, arguing in this case that the limitations also lie less with the technology itself than with the applications envisaged. Finally, the potential application of a sorting method directed at motility rather than sperm DNA content is discussed.

Scrotal heat stress effects on sperm viability, sperm DNA integrity, and the offspring sex ratio in mice

Evidence exists to suggest detrimental effects of heat stress on male fertility. This study was designed to assess the effects of scrotal heat stress on mature and developing sperm in a mouse model. After receiving shock heat treatment (42 degrees C for 30 min), mature spermatozoa were recovered from the epididymis hours (6) or Days (7, 14, 21, 28, 60) later, to determine the variables: number of spermatozoa, sperm viability, motility and progressive motility, sperm DNA integrity as established by the TUNEL method, embryo implantation rate, and sex ratio of the fetuses conceived using the heat-exposed spermatozoa. Our results indicate that transient mild heat treatment does not affect in the same way the different types of male germ cells. Spermatocytes present within the testis at the time of heat stress resulted into a lower concentration of spermatozoa with reduced viability and low motility. Even though, DNA integrity of spermatozoa resulting from spermatocytes was also compromised by heat stress, the higher degree of DNA damage was found among spermatozoa resulting from spermatids present within the testis at the time of heat stress. At last, heat shock effect on spermatozoa present in the epididymis at the time of thermal stress resulted into a sex ratio distortion. These findings point to a higher sensitivity of spermatocytes to heat exposure and also suggest a different response of X and Y chromosome-bearing spermatozoa to heat stress that warrants further investigation.