this study aimed to investigate the effect of different concentration of zinc nano-complex on bull spermatozoa quality and pregnancy outcome after freeze-thawing process. ejaculates were collected from four holstein bulls, twice a week during four weeks. semen samples diluted with bioxcell extender containing zero (control), 10-6, 10-5, 10-4, 10-3 and 10-2 m of zinc nano-complex. the samples we...