Report on the Agricultural Experiment Stations, 1953 Page: 15
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LIVESTOCK PRODUCTION AFFECTED BY ANIMAL DISEASES 15
absent. Mortality as a rule is negligible but may reach 1 or 2 percent
in the younger flocks.
Field tests indicate that this method of vaccination provides satisfactory
protection. Nebulization (spraying) of B1 vaccine (Blacksburg
strain) has been found by a number of stations to be satisfactory
as a method of vaccination against Newcastle disease. The immunity
thus produced was as good as when the vaccine was dropped into the
eye or nostril. By this method, the Virginia station has found that
100 day-old chicks can be easily vaccinated every 3 minutes by one
individual and only about one-half as much vaccine is required.
Reports of breaks and the isolation of virulent Newcastle disease
virus following vaccination by the intranasal route with B1 vaccine
suggested to the Texas station that there is need of further exposure
to the B1 virus at a time when parental immunity would not interfere.
The difficulty of catching the chicks when they are 4 to 5 weeks of
age prompted the use of the virus in the drinking water. One group
which received the vaccine in the drinking water at 44 and 50 days
of age showed 100-percent protection when challenged.
The New Hampshire station has shown that a combination of its
low-virulence strain of infectious bronchitis with B1 Newcastle virus
into a single vaccine is effective for immunizing chicks against both
diseases. These findings and those of the Virginia station are in
agreement. However, the duration of resistance is still unknown.
The Virginia station, by tagging the virus in the vaccine with radioactive
isotopes, has been able to determine its location in the bird's
body after nebulization. Such tagged virus was detected in the
trachea, lungs, and air sacs of the birds.
Breeding for resistance to Newcastle disease has been carried out
by the Delaware and Oklahoma stations. From six selected families
of pedigreed New Hampshires at the Delaware station, matings were
made between those showing high and low resistance in the first generation
for production of the second generation. These were challenged
with the California strain of Newcastle disease virus. Using
daily mortality as a criterion for measurements of differences, a significant
difference was observed between the males used in one of the
crosses. The differences observed indicate that there may be an
inherent mechanism that causes some families to die faster than others
when challenged with Newcastle disease virus.
As a part of a study on the physiology of avian reproduction, selection
has been made by the Maryland station to produce two strains of
chickens differing in their response to thiouracil. A significant result
thus far is a marked difference between the two lines in their resistance
to Newcastle disease. This is additional evidence that Newcastle
disease may be partially controlled through breeding.
The serious consequences of infectious bronchitis outbreaks in laying
flocks have stimulated interest among poultrymen and veterinarians
in immunization of replacement pullets. Some hens affected
by the disease go out of production and come back slowly, and the
interior and exterior quality of their eggs is impaired permanently.
Other flocks may never come back into production, even though they
look like good laying birds. The Rhode Island station has been carry
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United States. Office of Experiment Stations. Report on the Agricultural Experiment Stations, 1953, book, 1953; Washington D.C.. (digital.library.unt.edu/ark:/67531/metadc5989/m1/17/: accessed June 26, 2017), University of North Texas Libraries, Digital Library, digital.library.unt.edu; crediting UNT Libraries Government Documents Department.