Field Trials with Living Virus Vaccine for Newcastle Disease

•*- tests with the attenuated strain of Newcastle disease virus propagated in duck embryos (1), a series of trials was undertaken to determine the behavior of the vaccine under field conditions. Trials were carried out on four different farms in the Delaware-Maryland broiler area and 4 to 5-week old flocks were chosen for vaccination. The first group was vaccinated on February 9th and the 21-day observation period of the fourth flock was completed on April 13, 1948. The vaccine employed in these trials was prepared from the 12th duck-em-bryo passage of the MK-107 strain. This lot of vaccine, designated B, differed from lot A (1) in the following respect: The harvested and homogenized fluid-tissue suspension was frozen and dried in vacuo in the bulk state. The dry residue was pulverized in a ball mill and the resulting powder screened through a #60 mesh screen. Twenty-five milligram quantities of the dry powder were delivered into glass ampoules which were then exhausted in a vacuum chamber and flushed with dry nitrogen gas. The ampoules were sealed under nitrogen at atmospheric pressure. The contents of one ampoule, when reconstituted in 2 cc of 40 percent glycerol-saline, had a chick embryo LDBo titer of 10-4-5. All field vaccinations were performed by wing-web puncture as previously de-scribed (1). Prior to vaccination blood samples were taken from a small num-ber of representative birds in each flock, or portion of the flock if the birds were housed in more than one separate unit. In each test-flock a group of non-vac-cinated control birds was left. Where possible this control group was the pen next to the fee'droom since birds in this location were usually exposed to a maxi-mum of traffic to and from the vaccinated pens