Abstract
A study was conducted to evaluate variation in the ratio of X- to Y-bearing sperm of individual ejaculates and to determine any relationship between skewed sex ratio and either routine morphological evaluation or computer assisted sperm analysis (CASA). Semen was collected from bulls weekly for 6 consecutive weeks, sperm DNA was recovered and quantitative, and real-time PCR was used to determine the ratio of X- to Y-bearing sperm in each ejaculate. The overall mean of X-bearing sperm within ejaculates was 54.7% over the 6 weeks of semen collections. The percentages of X-bearing sperm were similar (P > 0.5) across all collections. Between bulls, there were differences (P < 0.05) in the mean percentage of X-bearing sperm. No significant correlations were found between CASA parameters and percentage of X-bearing sperm across bulls, so analysis was done within each bull. Different combinations of CASA and/or morphological parameters were found to correlate with the percentage of X-bearing sperm but the prediction equations were specific for individual bulls and unlikely to be of use across bulls. These results confirm that the ratio of X- to Y-bearing sperm may be skewed in some ejaculates of bull semen. Some sperm parameters measured by CASA or routine morphological evaluation were associated with semen sex ratio.
Highlights
Sex or gender ratio can be defined as the proportion of males to females in a given population
Chandler et al [4] reported that Y-bearing sperm within ejaculates of bull semen varied from 24% to 84%
The present study was conducted to confirm that the ratio of X- to Y-chromosome bearing sperm could be skewed in individual ejaculates of bull semen
Summary
Sex or gender ratio can be defined as the proportion of males to females in a given population. An altered sex ratio might be achieved maternally by facilitating or inhibiting the transport of either X- or Y-bearing sperm through the reproductive tract, preferential selection of sperm at fertilization, or sex-specific death of embryos after fertilization [2]. Chandler et al [5] measured the proportion of Y-bearing sperm in 36 lots (ejaculates) of Holstein semen and correlated the predicted with actual sex ratio of calves born after insemination with the various semen lots. The present study was conducted to confirm that the ratio of X- to Y-chromosome bearing sperm could be skewed in individual ejaculates of bull semen. If CASA motility parameters alone or in combination with morphology could be used to identify ejaculates of semen with skewed sex ratios, it would expand the ability to alter the gender of offspring in cattle
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