Provide a long answer for the given question:
Suggest some preventive measures for the diseases of poultry birds.
a. Poultry birds are vulnerable to diseases caused by ___________, and nutritional deficiencies.
b. The poultry farm and its surroundings must be kept clean and hygienic through regular maintenance.
c. Proper and timely disposal of poultry waste, such as excreta and feathers, is not essential for maintaining hygiene.
d. Farm spaces must be cleaned and dried before applying disinfectants like phenolic compounds through aerosols, sprays, or fumigation.
e. It is not advisable to strictly adhere to a fixed poultry vaccination schedule to prevent diseases.