5Kellokumpv et al. Effect of low zinc on the uptake of human chorionic gonadotropin(HcG)in rates testis and tesosterone respondse in vivo. Biol reprod, 1981,24: 298.
6Piper E T, et al. Influence of copper and zinc supplementation on mineral status growth and reproductive performance of heifers. J Animal Science, 1982, 53: 319.