Portuguese to English Science Livestock / Animal Husbandry cattle immunology

Could some learned person confirm my understnading of the above phrase which is a research on administering Selium (Se) to calves, in orde rto improve their immune system etc?
The full context follows:-

Segundo van Ryssen et al. (1989), uma vez que os microrganismos mostraram alterar as formas de Se no rúmen, iniciaram-se vários estudos ""