X-Y aneuploidy rate in sperm of two "minor" breeds of cattle (Bos taurus) by using dual color fluorescent in situ hybridization (FISH).

The present study reports on the frequency of X-Y aneuploidy in the sperm population of two minor cattle breeds reared in Italy, namely Modicana and Agerolese, which are listed in the "Anagraphic Register of autochthonous cattle populations with limited distribution". More than 50 000 sperm nuclei from 11 subjects (5 and 6, respectively for each breed) have been analyzed by the fluorescent in situ hybridization with the Xcen and Y-chromosome specific painting probes. The fraction of X- and Y-bearing sperm was close to the 1:1 ratio in the Modicana breed, whereas in the Agerolese the Y-fraction was significantly higher (P < 0.002) compared to the X-counterpart. The mean rates of X-Y aneuploidy were 0.510 and 0.466%, respectively, in the two breeds; no significant differences were found among individual bulls within each breed. Average frequencies of disomic and diploid sperm were 0.425 and 0.085% in the former and 0.380 and 0.086% in the latter. In both breeds, (a) disomy was significantly more frequent than diploidy (P < 0.01), (b) YY disomy was significantly (P < 0.001) more frequent than XY or XX; (c) MI errors (XY disomy) were significantly (P < 0.01) less represented than MII (XX + YY disomy). Compared to the dairy (Italian Friesian and Brown) and meat (Podolian and Maremmana) breeds previously analyzed, the "minor" breeds investigated in the present study showed a significantly (P < 0.002) higher rate of X-Y aneuploidy (0.486 vs. 0.159 and 0.190%, respectively). Considering all the breeds analyzed -so far- and assuming no significant interchromosomal effect, the baseline level of aneuploidy in the sperm population of the species Bos taurus was estimated as 5.19%. Establishing the baseline level of aneuploidy in the sperm population of the various livestock species/breeds engaged in animal production could reveal useful for monitoring future trends of their reproductive health, especially in relation to management errors and/or environmental hazards.