The normal state of hematological parameters in mammals at the beginning of ontogenesis is rightfully considered to be functionally very significant for the development of early ontogenesis in them. Hemostasis is considered to be very significant for vital functions and vulnerable blood systems. Its condition affects trophism due to the effect on the state of microcirculation, which is very important at the beginning of ontogenesis. In the neonatal phase, calves and piglets develop the formation of hemostasis and therefore, during these periods it can be easily disrupted. The appearance of hemostatic dysfunctions in the body of young animals, despite its importance, is still very poorly studied. This circumstance was the motivation for the study of the activity of the hemostatic system in calves and piglets that were born physically weakened. It was found that immediately after birth in weakened calves and piglets, there are physiologically unfavorable changes in platelet activity, vascular hemostasis and blood coagulation. This provides them with the appearance of excessive platelet activity and blood clotting with a significant weakening of vascular hemostasis. All these disorders lead to negative changes in their internal organs and create their serious dysfunctions. The development of disorders in the mechanisms of hemostasis in physically weakened calves and piglets during the neonatal phase is a serious mechanism for weakening their adaptation to the environment and slowing the growth and development of animals.