Development of an in vitro index to characterize fertilizing capacity of boar ejaculates

The aim of this research was the selection of spermatozoa parameters related to boar fertility performance and their combination into an in vitro index. A first set (data set 1) of 36 Pietrain boars with 138 ejaculates from two seasons with 5083 single-sire inseminations from 34 farms was used to determine correlations between in vitro sperm quality parameters and fertility performance. 2970 ejaculates representing a second set (data set 2) served calculation of seasonal and age effects on semen quality. Morphological spermatozoa parameters were estimated manually with a phase contrast microscope on the day of semen collection, whereas mitochondrial activity and viability were analyzed by double-staining with rhodamine123/propidium iodide on day 2 of semen storage using flow cytometry. Sperm motility was tested on day 7 by thermoresistance (TRT) after 30min (TRT1) and 300min (TRT2) incubation at 38̊C using computer-assisted semen analysis (CASA). Correlations revealed four independent sperm quality parameters qualifying as relevant predictors of boar fertility: (i) percentage of spermatozoa with proximal cytoplasmic droplets, (ii) percentage of spermatozoa with active mitochondria, (iii) beat cross frequency of progressively motile spermatozoa in TRT1, and (iv) oscillation measure of the actual path of progressively motile spermatozoa in TRT2. There were no significant effects of sperm concentration, ejaculate volume, and total number of sperm cells per ejaculate on litter size (LS) and on pregnancy rate (PR). Our findings suggest the usefulness of sperm quality parameters based on adjusted range of methods and enable the construction of an in vitro index as a means to predicting boar fertility.