FarmersJoint.com

When is the right time to give gumboro vaccine to chicks?
Ans:

Gumboro Vaccine for broilers:
1. Intermediate plus (Nobilis Gumboro 228E): From 12 days
2. Intermediate vaccine (Nobilis Gumboro D78): From 18 days.

For layers:
1. Intermediate plus (Nobilis Gumboro 228E): From 18 days
2. Intermediate vaccine (Nobilis Gumboro D78): From 28 days.

A chicken is protected within 5-7 days of successful vaccination. 2 vaccination is required with a 5-7 days interval. Give the vaccine 5-7 days before the expected time of Gumboro break out. Eg:
My broilers had a spike in mortality due to Gumboro at 21 days of age. At what age should I vaccinate the next flock?

Ans: 21 day old – (5 or 7 days) = 14 or 16 day old, so vaccinate at this age with intermediate plus vaccine. Give first vaccination at 12 days of age, second at 17.

Que: My layers had a spike in mortality due to Gumboro at 35 days of age. At what age should I vaccinate the next flock?

Ans: 35-(5 or 7) = 28-30 days. Intermediate vaccines are effective in layer. First vaccination at 21, second at 28.

Never give gumboro intermediate plus before 10 days of age in broilers and 15 in layers and breeder pullets so as to avoid damage to the bursa of fabricius.

Source: Gumboro.com/questions

You fail to list out an important info from the source. Here is it:

"Commercial broiler or layer chicks originating from parent birds vaccinated with an inactivated gumboro vaccine generally have maternal antibody titers in the range of 1,000 to 8,000 ELISA units. Based on this assumption we can predict that for:"

Unfortunately, some hatcheries in Nigeria will fail to meet this standard from time to time and if you follow this vaccination plan, a lot of your birds will die. I escaped such experience by doing day old chick (DOC) screening. The result showed that my chicks have low resistance to gumboro and newcastle disease. So I have to start gumboro vaccine on day 5 (I actually gave them on day 6), followed the next day by immucox, day 8: lasota. Day 15: Gumboro again, day 17 lasota, mareks day 25, gumboro @day 29, lasota day 31 etc. So it is better to go for DOC screening for a better vaccination plan and antibiotic sensitivity test.