Increasing the reproductive efficiency of pig breeding through the application of advanced techniques for sperm chromatin analysis and selection by colloid

Sow_and_five_pigletsThe efficacy and reliability of early sire selection is critical in the highly competitive pig industry. Subfertile boars have a substantial impact in the expenses of genetics and artificial insemination (AI) companies, and on the overall performance of swine farms. Attempts to to predict not only the quality of the ejaculate but also the productive life span of the boar (as “unproductive” days because of bad sperm quality) have been unsuccessful up to now. The analysis of sperm chromatin status has drawn attention because of its relationship with fertility and for being a parameter often fixed for a given male. However, most studies have aimed at testing sperm DNA fragmentation (SDF), apparently with little potential for boar semen.

Our main hypothesis is that the advanced analysis of the sperm chromatin could allow us to improve the reproductive efficiency of the pig industry, and that colloid selection could modify the chromatin status pattern in a favourable manner. We want to go beyond the classical SDF and include information on chromatin structure. Moreover, we want to use fast methods for sperm evaluation, based in flow cytometry, to comply with the needs of the pig industry of quick and repeatable evaluation of the samples. These techniques allow to study DNA fragmentation, chromatin compaction, protamination, protamin condensation, base oxidation and presence and modification of histones. We are combining this data with statistics allowing to consider all this information as a whole and not as separate variables, and to combine it with data provided by our partner in this proposal, Topigs-Norsvin (one of the largest and most innovative genetics and AI companies worldwide).

The general objectives are therefore:

DNA-damage1. Characterizing the sperm chromatin in an ample number of boar semen AI doses, refrigerated and frozen and from animals bred in different systems and environments, using fast and reliable techniques (therefore, with potential for practical use), investigating the association of these techniques both with sperm quality, with fertility and with environmental and internal variables.

2. Selecting the most efficient methodology to identify subfertile males or suboptimal AI doses as early as possible by studying one or more aspects of the sperm chromatin, in a broader perspective than traditionally considered.

3. Using these techniques to evaluate the ability of sperm selection by using colloids to modify the pattern of sperm subpopulations as defined by chromatin status; thus, providing information about this technique as an effective method to select a population of spermatozoa with optimized chromatin structure from problematic semen samples.

This proposal has a practical approach to solve a very relevant problem for the pig industry. In addition, we are partnering with SERIDA (Asturias) to include an autochtonous breed with extensive rearing, and with Chulalongkorn University (Thailand) to include animals reared in tropical conditions. This enables us to extend the reach of this research beyond industrial breeding in temperate countries. We also have arranged a collaboration with CalPoly (USA) for testing the new analyses in a novel pig model for obesity/diabetes, testing it as a model for the effects of these diseases on male reproduction, and adding interdisciplinarity to the proposal and allowing to increase the project output.