Structure of sperm cell subpopulations in the bull frozen semen influences in vitro fertility

Abstract

Sperm morphometric subpopulations and hetero morphism in Bos taurus indicus bull semen and their influence on in vitro fertilization were investigated. Area, center of mass and width obtained on 200 digitized cells/animal (n=9) were used to determine the subpopulations. The analysis of Ward’s grouping with Euclidean distance was used to determine the subpopulations, and number of subpopulations was defined according to the behavior of distance level and similarity. Fertility was evaluated by Pro-Nuclei Formation Rate (PFR) after In Vitro Fertilization (IVF). Sperm hetero morphism in one hundred cells considered to be morphologically normal was assessed by Harmonic Fourier Descriptors and Principal Component Analysis (PCA). Four subpopulations (SP1 to SP4) were determined, exhibiting asymmetrical distribution. SP4 was composed by 43.0% of the cells that showed the greatest area (39.3 ± 1.8 µm2), while SP1 (35.3±2.4 µm2), SP2 (35.9 ± 2.5 µm2), and SP3 (36.9 ± 3.0 µm2) presented similar distribution (21.0%; 17.5%; 18.5%; respectively). A negative correlation (r= -0.86; P=0.01) was observed between the SP4 and PFR. Hetero morphism rate did not influence PFR. In conclusion, semen of Bos taurus indicus bulls exhibited morphological heterogeneous structure and cells exhibiting large head area presented lower capacity of IVF.