IBD and ND in new layer flock especially in pullets

In my experience, during the rearing period of layer flock, most farmers faced problems with IBD and ND (resp.form/visceral form) at 20 to 30 days of age. Sometimes along with coccidiosis or colibacillosis. Mortality varies from 20 to 30%. Lost uniformity, less feed intake ,due to lake of knowledge, debeaking was done with less body weight. Lately, the flock performance was not satisfactory.

Could veterinarians please help me with any suggestion?