Which among the following is a incorrect statement ?

In human female implantation occurs almost 7 to 10 days after fertilization. In birds and mammals internal fertilisation takes place . Colostrum contains several antibodies . Polyspermy in mammals is prevented by chemical changes in egg surface .

Polyspermy in mammals is prevented by chemical changes in egg surface .

In mammals, polyspermy is not prevented by chemical changes. Once the sperm attaches to the zona pellucida layer of the ovum, it brings about physiological changes in the ovum's membrane and blocks the entry of other sperms.