Step1OK=Passive decline <line> of maternal antibodies.&&Step1A=All chicks do not have <line> the same level <line> of maternal antibodies <line> at day old. <line> Some have a level <line> above average.& &Step1B=Some have a level <line> below average.&&Step2Hyper=Limit of vaccine take of an <line> Intermediate Plus vaccine: 500 .&&Step2Class=Limit of vaccine take <line> of an Intermediate vaccine: 250.&&Step3Hyper=Vaccination must ideally <line> be performed when the maternal antibody level <line> reaches a value of 500.&&Step3Class=Vaccination must ideally <line> be performed when <line> the maternal antibody level <line> reaches a value of 250.&&Step3B=For security reasons, <line> to be sure to vaccinate <line> birds with low or high <line> maternal antibody levels, <line> vaccination must be performed <line> -3 days and %2b3 days <line> from the calculated theoretical <line> vaccination date.&&Step4precFirst=Choosing too early <line> a vaccination date will lead <line> to the vaccine virus being <line> neutralized by maternal <line> antibodies from the first vaccination. <line> Nevertheless, the second vaccination will be effective <line> and result in an increase <line> in antibodies that will protect <line> birds against infection by <line> a wild Gumboro virus.&&Step4precScd=Choosing too early a vaccination date will lead to the vaccine virus being neutralized by maternal antibodies. The vaccine will not be able to induce the production of antibodies. The maternal antibody level will decline below the limit of protection against the wild virus. The antibody production will be low or null, birds will not be properly protected against a wild Gumboro virus.&&Step4Norm=The vaccine will induce <line> the production of antibodies <line> that will protect birds against <line> infection by a wild Gumboro virus.&&Step4Tard=Choosing too late <line> a vaccination date <line> will result in a decrease <line> in antibody levels below <line> the minimum limit of protection; <line> then the vaccine will raise <line> the antibody level again <line> and protect the birds. <line> As long as the maternal <line> antibody level is below the limit <line> of protection against a natural infection, birds are receptive <line> to the wild virus.&&Step5OK=Double vaccination provides an optimal vaccine take in a heterogeneous flock.&