A protein produced by cells after they have been exposed to a virus. Interferon prevents the virus from reproducing within the infected cells and can also induce resistance to the virus in other cells.
Calves can be ready for weaning by 3 to 4 weeks of age; however, in Penn State studies calves weaned at 3 weeks required extra attention. The increased time and labor required to get these calves eating starter suggest that waiting until 4 weeks of age would be prudent.
1 During years of drought and poor feed supply, calves should be weaned early (about 6 months), to allow the cow to recover before the onset of winter.  It is important that the cow should recover and that the secretory tissue be restored before the next calf is born.