Abstract
Crossbreeding of indigenous cattle (Bos indicus) with improved (Bos taurus) breeds gained momentum and economic relevance in several countries to increase milk production. While production performance of the crossbred offspring is high due to hybrid vigor, they suffer from a high incidence of reproductive problems. Specifically, the crossbred males suffer from serious forms of subfertility/infertility, which can have a significant effect because semen from a single male is used to breed several thousand females. During the last two decades, attempts have been made to understand the probable reasons for infertility in crossbred bulls. Published evidence indicates that testicular cytology indices, hormonal concentrations, sperm phenotypic characteristics and seminal plasma composition were altered in crossbred compared to purebred males. A few recent studies compared crossbred bull semen with purebred bull semen using genomics, transcriptomics, proteomics and metabolomics; molecules potentially associated with subfertility/infertility in crossbred bulls were identified. Nevertheless, the precise reason behind the poor quality of semen and high incidence of sub-fertility/infertility in crossbred bulls are not yet well defined. To identify the underlying etiology for infertility in crossbred bulls, a thorough understanding of the magnitude of the problem and an overview of the prior art is needed; however, such systematically reviewed information is not available. Therefore, the primary focus of this review is to compile and analyze earlier findings on crossbred bull fertility/infertility. In addition, the differences between purebred and crossbred males in terms of testicular composition, sperm phenotypic characteristics, molecular composition, environmental influence and other details are described; future prospects for research on crossbred males are also outlined.
Highlights
150 million rural households (750 million people) around the world are engaged in milk production, mainly in developing countries (FAO et al, 2018)
Few studies used high throughput techniques for assessment of transcriptomic, proteomic and metabolomic differences between semen of high- and low-fertile bulls and identified potential molecules for fertility prediction (Peddinti et al, 2008; D’Amours et al, 2010; Card et al, 2013, 2017; Prakash et al, 2021). While these approaches offer a great scope for prediction of bull fertility, reported variations in sperm molecules among different breeds (Aslam et al, 2015) indicate that fertility associated semen molecules might vary with breed, which in turn demand identification of breed specific fertility markers. Despite these fertility problems, crossbreeding is commonly adopted to improve the milk productivity of indicine and nondescript cattle; the reason for the higher incidence of subfertility or poor semen quality in crossbred bulls compared to purebred bulls is not fully understood
These studies indicate that the testicular environment is altered in crossbred bulls compared to purebred bulls
Summary
150 million rural households (750 million people) around the world are engaged in milk production, mainly in developing countries (FAO et al, 2018). The male progeny born via crossbreeding of a Bos taurus male with Bos indicus female, not sterile, show increased incidences of sub-fertility and/or infertility compared to their parents (Thippeswamy et al, 2014). While these approaches offer a great scope for prediction of bull fertility, reported variations in sperm molecules among different breeds (Aslam et al, 2015) indicate that fertility associated semen molecules might vary with breed, which in turn demand identification of breed specific fertility markers Despite these fertility problems, crossbreeding is commonly adopted to improve the milk productivity of indicine and nondescript cattle; the reason for the higher incidence of subfertility or poor semen quality in crossbred bulls compared to purebred bulls is not fully understood. The differences between purebred and crossbred males in terms of testicular composition, sperm phenotypic characteristics, molecular composition, environmental influence, and other details are described and future prospects for research on crossbred males are outlined
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